NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
High Performance Current
Mode Resonant Controller
with Integrated High-
Voltage Drivers
The NCP1399 is a high performance current mode controller for half
bridge resonant converters. This controller implements 600 V gate
drivers, simplifying layout and reducing external component count. The
built−in Brown−Out input function eases implementation of the
controller in all applications. In applications where a PFC front stage is
needed, the NCP1399 features a dedicated output to drive the PFC
controller. This feature together with dedicated skip mode technique
further improves light load efficiency of the whole application. The
NCP1399 provides a suite of protection features allowing safe operation
in any application. This includes: overload protection, over−current
protection to prevent hard switching cycles, brown−out detection, open
optocoupler detection, automatic dead−time adjust, overvoltage (OVP)
and overtemperature (OTP) protections.
Features
High−Frequency Operation from 20 kHz up to 750 kHz
Current Mode Control Scheme
Automatic Dead−time with Maximum Dead−time Clamp
Dedicated Startup Sequence for Fast Resonant Tank Stabilization
Skip Mode Operation for Improved Light Load Efficiency
Off−mode Operation for Extremely Low No−load Consumption
Latched or Auto−Recovery Overload Protection
Latched or Auto−Recovery Output Short Circuit Protection
Latched Input for Severe Fault Conditions, e.g. OVP or OTP
Out of Resonance Switching Protection
Open Feedback Loop Protection
Precise Brown−Out Protection
PFC Stage Operation Control According to Load Conditions
Startup Current Source with Extremely Low Leakage Current
Dynamic Self−Supply (DSS) Operation in Off−mode or Fault Modes
Pin to Adjacent Pin / Open Pin Fail Safe
These are Pb−Free Devices
Typical Applications
Adapters and Offline Battery Chargers
Flat Panel Display Power Converters
Computing Power Supplies
Industrial and Medical Power Sources
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16
1
SOIC−16 NB
(LESS PINS 2 AND 13)
D SUFFIX
CASE 751DU
MARKING DIAGRAM
16
NCP1399xy
AWLYWWG
1
NCP1399 = Specific Device Code
x = A or B
y = A, B, C, F, G H, I, J and K
A = Assembly Location
WL = Wafer Lot
Y = Year
WW = Work Week
G = Pb−Free Package
PIN CONNECTIONS
HV 1
VBULK/PFCFB 3
SKIP/REM 4
LLCFB 5
LLCCS 6
OVP/OTP 7
PON/OFF 8
16 VBOOT
15 HB
14 MUPPER
12 MLOWER
11 GND
10 VCC
9 PFCMODE
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information on page 10 of
this data sheet.
© Semiconductor Components Industries, LLC, 2016
August, 2016 − Rev. 10
1
Publication Order Number:
NCP1399/D


NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
Figure 1. Typical Application Example without PFC Stage − WLLC Design (Active OFF off−mode)
Figure 2. Typical Application Example with PFC Stage (Active OFF off−mode)
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NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
Figure 3. Typical Application Example with PFC Stage (Active ON off−mode)
PIN FUNCTION DESCRIPTION
Pin No. Pin Name
Function
Pin Description
1
HV
High*voltage startup
Connects to rectified AC line or to bulk capacitor to perform functions of
current source input
Start*up Current Source and Dynamic Self*Supply
2 NC
Not connected
Increases the creepage distance
3 VBULK / Bulk voltage monitoring input Receives divided bulk voltage to perform Brown−out protection.
PFC FB
4
SKIP/REM
Skip threshold adjust / Sets the skip in threshold via a resistor connected to ground – version
Off−mode control input NCP1399Ay. Activates off−mode (or Standby) when pulled−up by external
auxiliary voltage source / deactivates off−mode when pull down by external
off−mode control optocoupler – version NCP1399By.
5 LLC FB
LLC feedback input
Defines operating frequency based on given load conditions. Activates skip
mode operation under light load conditions. Activates off−mode operation for
NCP1399Ay version.
6
LLC CS
LLC current sense input Senses divided resonant capacitor voltage to perform on−time modulation, out
of resonant switching protection, over−current protection and secondary side
short circuit protection.
7
OTP / OVP
Over−temperature and Implements over−temperature and over−voltage protection on single pin.
over−voltage protection input
8 P ON/OFF PFC turn−off FB level adjust Adjusts the FB pin to a level below which the PFC stage operation is disabled.
9
PFC MODE
PFC and external HV
Provides supply voltage for PFC front stage controller and/or enables Vbulk
switch control output
sensing network HV switch.
10 VCC Supplies the controller The controller accepts up to 20 V on VCC pin
11 GND
Analog ground
Common ground connection for adjust components, sensing networks and
DRV outputs.
12
MLOWER
Low side driver output
Drives the lower side MOSFET
13 NC
Not connected
Increases the creepage distance
14 MUPPER High side driver output Drives the higher side MOSFET
15 HB Half*bridge connection Connects to the half*bridge output.
16 VBOOT
Bootstrap pin
The floating VCC supply for the upper stage
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NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
Figure 4. Internal Circuit Architecture
MAXIMUM RATINGS
Rating
Symbol
Value
Unit
HV Startup Current Source HV Pin Voltage (Pin 1)
VBULK/PFC FB Pin Voltage (Pin3)
SKIP/REM Pin Voltage (Pin 4) NCP1399Ay Revision Only
SKIP/REM Pin Voltage (Pin 4) NCP1399By Revision Only
LLC FB Pin Voltage (Pin 5)
LLC CS Pin Voltage (Pin 6)
PFC MODE Pin Output Voltage (Pin 9)
VCC Pin Voltage (Pin 10)
Low Side Driver Output Voltage (Pin 12)
High Side Driver Output Voltage (Pin 14)
VHV
VBULK/PFC FB
VSKIP/REM
VSKIP/REM
VFB
VCS
VPFC MODE
VCC
VDRV_MLOWER
VDRV_MUPPER
−0.3 to 600
−0.3 to 5.5
−0.3 to 5.5
−0.3 to 10
−0.3 to 5.5
−5 to 5
−0.3 to VCC + 0.3
−0.3 to 20
−0.3 to VCC + 0.3
VHB – 0.3 to
VBOOT + 0.3
V
V
V
V
V
V
V
V
V
V
High Side Offset Voltage (Pin 15)
VHB
VBoot −20 to
VBoot +0.3
V
High Side Floating Supply Voltage (Pin 16)
High Side Floating Supply Voltage (Pin 15 and 16)
TJ = −40°C to +125°C
TJ = −55°C to −40°C
Allowable Output Slew Rate on HB Pin (Pin 15)
OVP/OTP Pin Voltage (Pin 7)
P ON/OFF Pin Voltage (Pin 8)
Junction Temperature
Storage Temperature
Thermal Resistance Junction−to−air
Human Body Model ESD Capability per JEDEC JESD22−A114F (except HV Pin – Pin 1)
VBOOT
VBoot–VHB
dV/dtmax
VOVP/OTP
VP ON/OFF
TJ
TSTG
RθJA
−0.3 to 620
−0.3 to 618
−0.3 to 20.0
50
−0.3 to 5.5
−0.3 to 5.5
−55 to 150
−55 to 150
130
4.5
V
V
V/ns
V
V
°C
°C
°C/W
kV
Charged−Device Model ESD Capability per JEDEC JESD22−C101E
− 1 kV
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
1. This device contains latch−up protection and exceeds 100 mA per JEDEC Standard JESD78.
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NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
ELECTRICAL CHARACTERISTICS
(For typical values TJ = 25°C, for min/max values TJ = −40°C to +125°C, VCC = 12 V unless otherwise noted.)
Symbol
Rating
Pin Min Typ Max Unit
HV Startup Current Source
VHV_MIN1
Minimum voltage for current source operation
(VCC = VCC_ON −0.5 V, ISTART2 drops to 95 %)
VHV_MIN2
Minimum voltage for current source operation
(VCC = VCC_ON −0.5 V, ISTART2 drops to 5 mA)
ISTART1
Current flowing out of VCC pin (VCC = 0 V)
ISTART2
Current flowing out of VCC pin (VCC = VCC_ON −0.5 V)
ISTART_OFF
Off−state leakage current (VHV = 500 V, VCC = 15 V)
IHV_OFF−MODE
HV pin current when off−mode operation is active
(VHV = 400 V)
Supply Section
VCC_ON
Turn−on threshold level, VCC going up
VCC_OFF
Minimum operating voltage after turn−on
VCC_RESET
VCC level at which the internal logic gets reset
VCC_INHIBIT
VCC level for ISTART1 to ISTART2 transition
VCC_ON_BLANK Delay to generate DRVs pulses after VCC_ON is reached
ICC_OFF−MODE
Controller supply current in off−mode,
VCC = VCC_ON − 0.2 V (except NCP1399AG)
ICC_SKIP−MODE
Controller supply current in skip−mode, VCC = 15 V
(NCP1399AA, NCP1399BA, NCP1399AC, NCP1399AH,
NCP1399AI, NCP1399AK)
(NCP1399AF, NCP1399AG, NCP1399AJ)
1
1
1, 10
1, 10
1
1
10
10
10
10
10
10, 11
10, 11
− − 60
− − 60
0.2 0.5 0.8
6 9 13
− − 10
−−8
15.3 15.8 16.3
9.0 9.5
10
5.8 6.6 7.2
0.40 0.80 1.25
100 125 150
10 27 40
580 750 900
500 670 820
V
V
mA
mA
mA
mA
V
V
V
V
ms
mA
mA
ICC_LATCH
Controller supply current in latch−off mode,
VCC = VCC_ON − 0.2 V (except NCP1399AI)
10, 11
330 490 600
mA
ICC_AUTOREC
Controller supply current in auto−recovery mode,
VCC = VCC_ON − 0.2 V (except NCP1399AF)
10, 11
300 490 600
mA
ICC_OPERATION
Controller supply current in normal operation,
fsw = 100 kHz, Cload = 1 nF, VCC = 15 V
10, 11 4.0 5.4 7.0 mA
Bootstrap Section
VBOOT_ON
Startup voltage on the floating section (Note 5)
16, 15
8
9 10 V
VBOOT_OFF
Cutoff voltage on the floating section
16, 15 7.2 8.2 9.0
V
IBOOT1
Upper driver consumption, no DRV pulses
16, 15 30 75 130 mA
IBOOT2
Upper driver consumption, Cload = 1 nF between Pins 13 &
15 fsw = 100 kHz, HB connected to GND
16, 15
1.30 1.65 2.00
mA
HB Discharger
IDISCHARGE1
HB sink current capability VHB = 30 V
15 5 − − mA
IDISCHARGE2
HB sink current capability VHB = VHB_MIN
15 1 − − mA
VHB_MIN
HB voltage @ IDISCHARGE changes from 2 to 0 mA
15 − − 10 V
Remote Input – NCP1399By
VREM_ON
Remote pin voltage below which off−mode is deactivated
(VREM going down)
4
1.0 1.5 2.0
V
VREM_OFF
Remote pin voltage above which off−mode is activated
(VREM going up)
4
7.2 8.0 8.8
V
tREM_TIMER
Remote timer duration
4 80 100 120 ms
IREM_LEAK
Remote input leakage current (VREM = 10 V)
4
0.02 1.00
mA
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
2. The NCP1399Ay version has skip adjustable externally.
3. Guaranteed by design.
4. Minimal impedance on P ON/OFF pin is 1 kW
5. Minimal resistance connected in series with bootstrap diode is 3.3 W
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NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
ELECTRICAL CHARACTERISTICS
(For typical values TJ = 25°C, for min/max values TJ = −40°C to +125°C, VCC = 12 V unless otherwise noted.)
Symbol
Rating
Pin Min Typ Max Unit
Remote Input – NCP1399By
RSW_REM
Internal remote pull down switch resistance (VREM = 8 V)
4
Remote Control – NCP1399Ay (i.e. Off−mode is Sensed via FB Pin, except NCP1399AG)
VFB_REM_ON
FB pin voltage above which off−mode is deactivated
(VFB going up)
5
VFB_REM_OFF
FB pin voltage below which off−mode is activated
(VFB going down)
5
IFB_REM_BIAS
Pull−up FB pin bias current during off−mode
5
Driver Outputs
tr Output voltage rise−time @
CL = 1 nF, 10−90% of output signal
12, 14
tf Output voltage fall−time @
CL = 1 nF, 10−90% of output signal
12, 14
ROH
Source resistance
12, 14
ROL Sink resistance
12, 14
IDRVSOURCE
Output high short circuit pulsed current
VDRV = 0 V, PW 10 ms
12, 14
IDRVSINK
Output high short circuit pulsed current
VDRV = VCC, PW 10 ms
12, 14
IHV_LEAK
Leakage current on high voltage pins to GND
14, 15, 16
Dead−time Generation
tDEAD_TIME_MAX Maximum Dead−time value if no dV/dt falling/rising edge is
received
12, 14
3
1.5
0.36
1.0
20
5
4
1
720
2.0
0.40
2.3
45
30
16
5
0.5
1
800
7
2.5
0.44
4.0
80
50
32
11
5
880
kW
V
V
mA
ns
ns
W
W
A
A
mA
ns
NDT_MAX
Number of DT_MAX events to enters IC into fault
12, 14, 16
8
(NCP1399AA, NCP1399BA, NCP1399AH, NCP1399AK)
Number of DT_MAX events to enters IC into fault
12, 14, 16
16
(NCP1399AC, NCP1399AF, NCP1399AG, NCP1399AI,
NCP1399AJ)
dV/dt Detector
PdV/dt_th
Positive slew rate on VBOOT pin above which automatic
dead−time end is generated
16 − 10 − V/ms
NdV/dt_th
Negative slew rate on VBOOT pin above which automatic
dead−time end is generated
16 − 10 − V/ms
PFC MODE Output and P ON/OFF Adjust
VPFC_M_BO
PFC MODE output voltage when VFB < VP ON/OFF
(sink 1 mA current from PFC MODE output)
9
5.75 6.00 6.25
V
VPFC_M_ON
PFC MODE output voltage when VFB > VP ON/OFF
(sink 10 mA current from PFC MODE output)
9
VCC
V
0.4
IPFC_M_LIM
tP ON/OFF_TIMER
IP ON/OFF
P ON/OFFHYST
PFC MODE output current limit (VPFC MODE < 2 V)
Delay to transition PFC MODE from VPFC_M_ON to
VPFC_M_BO after VFB drops below VP ON/OFF
Pull−up current source (Note 4)
P ON/OFF comparator hysteresis – percentage level of P
ON/OFF pin voltage
9
5, 8, 9
8
5, 8, 9
0.7 1.2 1.85 mA
9.4 − 10.9 s
18 20 22 mA
80 100 120 %
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
2. The NCP1399Ay version has skip adjustable externally.
3. Guaranteed by design.
4. Minimal impedance on P ON/OFF pin is 1 kW
5. Minimal resistance connected in series with bootstrap diode is 3.3 W
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High Performance Current Mode Resonant Controller

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NCP1399 Series
ELECTRICAL CHARACTERISTICS
(For typical values TJ = 25°C, for min/max values TJ = −40°C to +125°C, VCC = 12 V unless otherwise noted.)
Symbol
Rating
Pin Min Typ Max Unit
OVP/OTP
VOVP
VOTP
IOTP
OVP threshold voltage (VOVP/OTP going up)
OTP threshold voltage (VOVP/OTP going down)
OTP/OVP pin source current for external NTC –
during normal operation
7
2.35 2.50 2.65
V
7
0.76 0.80 0.84
V
7 90 95 100 mA
IOTP_BOOST
OTP/OVP pin source current for external NTC –
during startup
7
180 190 200
mA
tOVP_FILTER
tOTP_FILTER
tBLANK_OTP
Internal filter for OVP comparator
Internal filter for OTP comparator
Blanking time for OTP input during startup (NCP1399AA,
NCP1399BA, NCP1399AK)
7 32 37 44 ms
7
200 330 500
ms
7 7.3 8.0 8.7 ms
Blanking time for OTP input during startup (NCP1399AC,
NCP1399AF, NCP1399AG, NCP1399AH, NCP1399AI,
NCP1399AJ)
7 14 16 18 ms
VCLAMP_OVP/OTP_1 OVP/OTP pin clamping voltage @ IOVP/OTP = 0 mA
VCLAMP_ OVP/OTP_2 OVP/OTP pin clamping voltage @ IOVP/OTP = 1 mA
Start−up Sequence Parameters
tTON_MAX
Maximum on−time clamp (NCP1399AA, NCP1399BA,
NCP1399AK)
7
1.0 1.2 1.4
V
7
1.8 2.4 3.0
V
12, 14 7.3 7.7 8.4 ms
Maximum on−time clamp (NCP1399AC, NCP1399AG,
NCP1399AI)
12, 14
10.6 11.2 12.1
ms
t1st_MLOWER_TON
Maximum on−time clamp (NCP1399AF, NCP1399AJ)
Maximum on−time clamp (NCP1399AH)
Initial Mlower DRV on−time duration (NCP1399AA,
NCP1399BA, NCP1399AC, NCP1399AG, NCP1399AH,
NCP1399AI, NCP1399AK)
12, 14
12, 14
12
15.2 16.3 17.8
8.8 9.5 10.5
4.7 4.9 5.4
ms
ms
ms
t1st_MLOWER_TON Initial Mlower DRV on−time duration (NCP1399AF,
NCP1399AJ)
12 9.3 10 11 ms
t1st_MUPPER_TON
Initial Mupper DRV on−time duration (NCP1399AA,
NCP1399BA, NCP1399AC, NCP1399AG, NCP1399AH,
NCP1399AI, NCP1399AK)
14
0.72 0.79 0.88
ms
t1st_MUPPER_TON Initial Mupper DRV on−time duration (NCP1399AF,
NCP1399AJ)
14
0.99 1.10 1.21
ms
tSS_INCREMENT On−time period increment during soft−start (NCP1399AA, 12, 14 17 20 22 ns
NCP1399BA, NCP1399AC, NCP1399AG, NCP1399AH,
NCP1399AI, NCP1399AK)
tSS_INCREMENT On−time period increment during soft−start (NCP1399AF, 12, 14 75 80 88 ns
NCP1399AJ)
KSS_INCREMENT
Soft−Start increment division ratio (NCP1399AA,
NCP1399BA, NCP1399AK)
12, 14
4
Soft−Start increment division ratio (NCP1399AC,
NCP1399AF, NCP1399AG, NCP1399AH, Ncp1399AI,
NCP1399AJ)
12, 14
8
tWATCHDOG
Time duration to restart IC if start−up phase is not finished
12, 14
0.45 0.50 0.55
ms
Feedback Section
RFB Internal pull−up resistor on FB pin
5 15 18 25 kW
KFB VFB to internal current set point division ratio
5
1.92 2.00 2.08
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
2. The NCP1399Ay version has skip adjustable externally.
3. Guaranteed by design.
4. Minimal impedance on P ON/OFF pin is 1 kW
5. Minimal resistance connected in series with bootstrap diode is 3.3 W
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High Performance Current Mode Resonant Controller

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NCP1399 Series
ELECTRICAL CHARACTERISTICS
(For typical values TJ = 25°C, for min/max values TJ = −40°C to +125°C, VCC = 12 V unless otherwise noted.)
Symbol
Rating
Pin Min Typ Max Unit
Feedback Section
VFB_REF
Internal voltage reference on the FB pin
5
4.60 4.95 5.30
V
VFB_CLAMP
Internal clamp on FB input of On−time comparator referred
to external FB pin voltage
5
4.4 4.6 4.8
V
VFB_SKIP_IN
Feedback voltage thresholds to enters in skip mode for
NCP1399By version (Note 2)
5
0.44 0.50 0.56
V
VFB_SKIP_HYST
Skip comparator hysteresis (NCP1399AA, NCP1399BA,
NCP1399AC, NCP1399AG, NCP1399AH, NCP1399AK)
5 130 160 200 mV
Skip comparator hysteresis (NCP1399AF, NCP1399AJ)
5 105 140 175
t1st_MLOWER_SKIP
V1st_MUPPER_SKIP
Skip comparator hysteresis (NCP1399AI)
On−time duration of 1st Mlower pulse when FB cross
VFB_SKIP_IN + VFB_SKIP_HYST threshold (NCP1399AA,
NCP1399BA, NCP1399AK)
On−time duration of 1st Mlower pulse when FB cross
VFB_SKIP_IN + VFB_SKIP_HYST threshold (NCP1399AC,
NCP1399AG, NCP1399AI)
On−time duration of 1st Mlower pulse when FB cross
VFB_SKIP_IN + VFB_SKIP_HYST threshold (NCP1399AF,
NCP1399AJ)
On−time duration of 1st Mlower pulse when FB cross
VFB_SKIP_IN + VFB_SKIP_HYST threshold (NCP1399AH)
Internal FB level reduction during 1st Mupper pulse when FB
cross VFB_SKIP_IN + VFB_SKIP_HYST threshold (NCP1399AA,
NCP1399BA, NCP1399AC, NCP1399AG, NCP1399AI,
NCP1399AK) (Note 3)
Internal FB level reduction during 1st Mupper pulse when FB
cross VFB_SKIP_IN + VFB_SKIP_HYST threshold (NCP1399AF,
NCP1399AJ) (Note 3)
Internal FB level reduction during 1st Mupper pulse when FB
cross VFB_SKIP_IN + VFB_SKIP_HYST threshold
(NCP1399AH) (Note 3)
5
5, 12
5, 12
5, 12
5, 12
5, 6, 14
5, 6, 14
5, 6, 14
0 23 50
0.95 1.05 1.15
1.8 1.9 2.1
1.08 1.20 1.32
2.1 2.4 2.7
− 150 −
− 100 −
−0−
ms
ms
ms
ms
mV
mV
mV
Skip Input – NCP1399Ay version
ISKIP
Internal Skip pin current source
4 48 50 52 mA
CSKIP_LOAD_MAX Maximum loading capacitance for skip pin voltage filtering
(Note 3)
4
− − 10 nF
Current Sense Input Section
tpd_CS
On−time comparator delay to Mupper driver turn off
5, 6 − − 250 ns
VFB = 2.5 V, VCS goes up from –2.5 V to 2.5 V with rising
edge of 100 ns
ICS_LEAKAGE
VCS_OFFSET
Current sense input leakage current for VCS = ± 3 V
Current sense input offset voltage (NCP1399AA,
NCP1399BA, NCP1399AC, NCP1399AG, NCP1399AH,
NCP1399AI, NCP1399AK)
6 − − ±1 mA
6 160 200 240 mV
Current sense input offset voltage (NCP1399AF,
NCP1399AJ)
6 110 150 190 mV
tLEB
Leading edge blanking time of the on−time comparator output 5, 6, 14 360 440 540
ns
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
2. The NCP1399Ay version has skip adjustable externally.
3. Guaranteed by design.
4. Minimal impedance on P ON/OFF pin is 1 kW
5. Minimal resistance connected in series with bootstrap diode is 3.3 W
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High Performance Current Mode Resonant Controller

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NCP1399 Series
ELECTRICAL CHARACTERISTICS
(For typical values TJ = 25°C, for min/max values TJ = −40°C to +125°C, VCC = 12 V unless otherwise noted.)
Symbol
Rating
Pin Min Typ Max Unit
Faults and Auto−Recovery Timer
tFB_FAULT_TIMER
FB fault timer duration (NCP1399AA, NCP1399BA,
NCP1399AK)
− 160 200 240 ms
FB fault timer duration (NCP1399AC, NCP1399AF,
NCP1399AG, NCP1399AI, NCP1399AJ)
− 80 100 120 ms
FB fault timer duration (NCP1399AH)
− 240 300 360 ms
NFB_FAULT_COUNTER Number of DRV pulses to confirm FB fault
VFB_FAULT
FB voltage when FB fault is detected
NCS_FAULT_COUNTER Number of CS_fault cmp. pulses to confirm CS fault
VCS_FAULT
CS voltage when CS fault is detected (NCP1399AA,
NCP1399BA, NCP1399AC, NCP1399AF, NCP1399AH,
NCP1399AI, NCP1399AK)
(NCP1399AG)
CS voltage when CS fault is detected (NCP1399AJ)
− 1000 −
5
4.5 4.7 4.9
V
− −5−−
6V
2.5 2.7 2.9
3.2 3.4 3.6
1.85 2.00 2.15
tA−REC_TIMER
Auto−recovery duration, common timer for all fault condition
(NCP1399AA, NCP1399BA, NCP1399AC, NCP1399AG,
NCP1399AH, NCP1399AJ, NCP1399AK)
0.8 1 1.2 s
Auto−recovery duration, common timer for all fault condition
(NCP1399AI)
1.6 1.9 2.4
Brown−Out Protection
VBO Brown−out turn−off threshold
IBO Brown−out hysteresis current, VVBULK/PFC_FB < VBO
VBO_HYST
Brown*Out comparator hysteresis
IBO_BIAS
Brown*Out input bias current
tBO_FILTR
BO filter duration
Ramp Compensation
RCGAIN
Ramp compensation gain (NCP1399AA, NCP1399BA,
NCP1399AC, NCP1399AF NCP1399AG, NCP1399AK)
Ramp compensation gain (NCP1399AI)
Ramp compensation gain (NCP1399AJ)
Ramp compensation gain (NCP1399AH)
3
0.965 1.000 1.035
V
3 4.3 5.0 5.4 mA
3 5 12 25 mV
3 − − 0.05 mA
3 10 20 30 ms
mV/ms
− 58 82 108
82 110 131
92 125 150
107 149 168
tRC_SHIFT
Ramp compensation time shift
Temperature Shutdown Protection
TTSD
Temperature shutdown TJ going up (NCP1399AA,
NCP1399BA, NCP1399AH, NCP1399AK)
− − 0.6 − ms
− 124 −
°C
Temperature shutdown TJ going up (NCP1399AC,
NCP1399AF, NCP1399AG, NCP1399AI, NCP1399AJ)
− 137 −
°C
TTSD_HYST
Temperature shutdown hysteresis
− − 30 − °C
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
2. The NCP1399Ay version has skip adjustable externally.
3. Guaranteed by design.
4. Minimal impedance on P ON/OFF pin is 1 kW
5. Minimal resistance connected in series with bootstrap diode is 3.3 W
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NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
IC Options
Option
FB fault
FB fault
source
NCP1399AA Auto−recovery Timer
NCP1399BA Auto−recovery Timer
NCP1399AC Auto−recovery Timer
NCP1399AF
Latch
Timer
NCP1399AG Auto−recovery Timer
NCP1399AH Auto−recovery Timer
NCP1399AI Auto−recovery Timer
NCP1399AJ Auto−recovery Timer
NCP1399AK Auto−recovery Timer
Cumulative
FB fault
timer/
counter
CS_FAULT
TON_MAX
fault
OVP fault
OTP fault
Dedicated
Soft_start_-
seq
NO
Auto−recovery Auto−recovery
Latch
Auto−recovery
ON
NO
Auto−recovery Auto−recovery
Latch
Auto−recovery
ON
NO Auto−recovery OFF
Latch
Latch
ON
NO
Latch
Latch
Latch
Latch
ON
NO Auto−recovery OFF
Latch
Auto−recovery
ON
NO
Auto−recovery Auto−recovery
Latch
Auto−recovery
ON
NO
Auto−recovery Auto−recovery Auto−recovery Auto−recovery
ON
NO
Auto−recovery Auto−recovery
Latch
Latch
ON
NO
Auto−recovery Auto−recovery
Latch
Auto−recovery
ON
Option
NCP1399AA
NCP1399BA
NCP1399AC
NCP1399AF
NCP1399AG
NCP1399AH
NCP1399AI
NCP1399AJ
NCP1399AK
PFC_MODE Dead time
skip status control
Dead time
fault
OFF−mode
version
ON ZVS or Auto−recovery Active OFF
DT_max
ON ZVS or Auto−recovery Active ON
DT_max
ON ZVS or Auto−recovery Active OFF
DT_max
OFF
ZVS or
DT_max
OFF
Active OFF
OFF
ZVS or Auto−recovery
DT_max
ON
ZVS or
OFF
Active OFF
DT_max
ON
ZVS or
DT_max
Auto−recovery
Active OFF
OFF
ZVS or
DT_max
OFF
Active OFF
OFF
ZVS or
DT_max
Auto−recovery
Active OFF
OFF−mode
status
ON
ON
ON
ON
OFF
ON
ON
ON
ON
BO status
ON
ON
ON
ON
ON
ON
ON
ON
ON
Ramp comp P ON/OFF
status
pull−up
Without ramp
shift
ON
Without ramp
shift
ON
Without ramp
shift
ON
Without ramp
shift
ON
Without ramp
shift
ON
Without ramp
shift
ON
Without ramp
shift
ON
Without ramp
shift
ON
Without ramp
shift
ON
ORDERING INFORMATION
Part Number
Marking
Package
Shipping
NCP1399AADR2G
NCP1399AA
NCP1399BADR2G
NCP1399BA
NCP1399ACDR2G
NCP1399AC
NCP1399AFDR2G
NCP1399AGDR2G
NCP1399AHDR2G
NCP1399AF
NCP1399AG
NCP1399AH
SOIC−16
(Pb−Free)
2500 / Tape & Reel
NCP1399AIDR2G
NCP1399AI
NCP1399AJDR2G
NCP1399AJ
NCP1399AKDR2G
NCP1399AK
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
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High Performance Current Mode Resonant Controller

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NCP1399 Series
TYPICAL CHARACTERISTICS
0.30 1.05
0.25 0.95
0.20 0.85
0.15 0.75
0.10 0.65
0.05 0.55
0 0.45
−55 −25 5 35 65 95 125
−55 −25 5 35 65 95 125
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 5. ISTART_OFF vs. Temperature
Figure 6. VCC_INHIBIT vs. Temperature
0.55
0.54
0.53
0.52
0.51
0.50
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 7. ISTART1 vs. Temperature
125
9.4
9.3
9.2
9.1
9.0
8.9
8.8
8.7
8.6
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 8. ISTART2 vs. Temperature
125
9.45 15.85
9.43 15.80
9.41 15.75
9.39 15.70
9.37
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 9. VCC_OFF vs. Temperature
15.65
125 −55 −25 5 35 65 95
TEMPERATURE (°C)
Figure 10. VCC_ON vs. Temperature
125
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High Performance Current Mode Resonant Controller

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NCP1399 Series
TYPICAL CHARACTERISTICS
6.48 820
6.47
6.46
6.45
6.44
6.43
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 11. VCC_RESET vs. Temperature
125
800
780
760
740
720
700
−55 −25 5 35 65 95 125
TEMPERATURE (°C)
Figure 12. ICC_SKIP−MODE vs. Temperature
485 7.0
465 6.8
445 6.6
425 6.4
405
385
−55 −25 5 35 65 95
TEMPERATURE (°C)
Figure 13. ICC_AUTOREC vs. Temperature
125
6.2
6.0
−55 −25 5 35 65 95 125
TEMPERATURE (°C)
Figure 14. ICC_OPERATION vs. Temperature
475 35
455
435
415
395
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 15. ICC_LATCH vs. Temperature
125
32
29
26
23
20
−55 −25 5 35 65 95 125
TEMPERATURE (°C)
Figure 16. ICC_OFF−MODE vs. Temperature
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High Performance Current Mode Resonant Controller

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NCP1399 Series
TYPICAL CHARACTERISTICS
9.20 8.4
9.15
9.10
9.05
9.00
8.95
8.90
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 17. VBOOT_ON vs. Temperature
125
8.3
8.2
8.1
8.0
7.9
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 18. VBOOT_OFF vs. Temperature
125
1.72
1.70
1.68
1.66
1.64
1.62
1.60
1.58
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 19. IBOOT2 vs. Temperature
1.202
1.197
1.192
1.187
1.182
125 −55 −25 5 35 65 95 125
TEMPERATURE (°C)
Figure 20. VCLAMP_OVP/OTP_1 vs. Temperature
0.804
0.802
0.800
0.798
0.796
0.794
0.792
−55
−25 5
35 65 95
TEMPERATURE (°C)
Figure 21. VOTP vs. Temperature
2.520
2.515
2.510
2.505
2.500
2.495
2.490
2.485
125 −55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 22. VOVP vs. Temperature
125
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High Performance Current Mode Resonant Controller

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NCP1399 Series
TYPICAL CHARACTERISTICS
96.0 22
95.5 21
95.0 20
94.5 19
94.0 18
93.5
93.0
−55
−25
5
35 65
95
TEMPERATURE (°C)
Figure 23. IOTP vs. Temperature
125
17
16
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 24. RFB vs. Temperature
125
8.1
8.0
7.9
7.8
7.7
7.6
7.5
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 25. tON_MAX vs. Temperature
125
204
203
202
201
200
199
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 26. VCS_OFFSET vs. Temperature
125
185 2.72
175 2.71
165 2.70
155 2.69
145
135
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 27. tpd_CS vs. Temperature
2.68
2.67
125 −55 −25 5 35 65 95 125
TEMPERATURE (°C)
Figure 28. VCS_FAULT vs. Temperature
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High Performance Current Mode Resonant Controller

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1.010
NCP1399 Series
TYPICAL CHARACTERISTICS
5.00
1.005
1.000
0.995
0.990
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 29. VBO vs. Temperature
4.95
4.90
4.85
4.80
4.75
125 −55 −25 5 35 65 95 125
TEMPERATURE (°C)
Figure 30. IBO vs. Temperature
4.70
4.69
4.68
4.67
4.66
4.65
4.64
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 31. VFB_FAULT vs. Temperature
125
50.2
50.0
49.8
49.6
49.4
49.2
49.0
−55
−25 5 35 65 95
TEMPERATURE (°C)
Figure 32. ISKIP vs. Temperature
125
78 16
76 14
74 12
72
70
−55
−25 5
35 65 95
TEMPERATURE (°C)
Figure 33. RCGAIN vs. Temperature
125
10
8
−55 −25 5 35 65 95 125
TEMPERATURE (°C)
Figure 34. IDISCHARGE1 vs. Temperature
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High Performance Current Mode Resonant Controller

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NCP1399 Series
TYPICAL CHARACTERISTICS
28 10
24
20
16
12
8
−55 −25
5
35 65 95 125
TEMPERATURE (°C)
Figure 35. ROH vs. Temperature
8
6
4
2
−55 −25 5 35 65 95
TEMPERATURE (°C)
Figure 36. ROL vs. Temperature
125
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NCP1399 (ON Semiconductor)
High Performance Current Mode Resonant Controller

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NCP1399 Series
VCC Management with High−voltage Startup Current Source
The NCP1399 controller features a HV startup current failure mode that may occur in the application. The HV
source that allows fast startup time and extremely low startup current source is primarily enabled or disabled based
standby power consumption. Two startup current levels on VCC level. The startup HV current source can be also
(Istart1 and Istart2) are provided by the system for safety in
case of short circuit between VCC and GND pins. In
enabled by BO_OK rising edge, auto−recovery timer end,
REMote and TSD end event. The HV startup current source
addition, the HV startup current source features a dedicated charges the VCC capacitor before IC start−up.
over−temperature protection to prevent IC damage for any
Figure 37. Internal Connection of the VCC Management Block
The NCP1399 controller disables the HV startup current
source once the VCC pin voltage level reaches VCC_ON
threshold – refer to Figure 37. The application then starts
operation and the auxiliary winding maintains the voltage
bias for the controller during normal and skip−mode
operating modes. The IC operates in so called Dynamic Self
Supply (DSS) mode when the bias from auxiliary winding
is not sufficient to keep the VCC voltage above VCC_OFF
threshold (i.e. VCC voltage is cycling between VCC_ON and
VCC_OFF thresholds with no driver pulses on the output
during positive VCC ramp). The HV source is also operated
in DSS mode when the low voltage controller enters
off−mode or fault−mode operation. In this case the VCC pin
voltage will cycle between VCC_ON and VCC_OFF
thresholds and the controller will not deliver any driver
pulse – waiting for return from the off−mode or latch mode
operation. Please refer to figures Figure 61 through
Figure 65 to find an illustration of the NCP1399 VCC
management system under all operating conditions/modes.
The HV startup current source features an independent
over–temperature protection system to limit Istart2 current
when the die temperature reaches 130°C. At this
temperature, Istart2 will be progressively to prevent the die
temperature from rising above 130°C.
Brown−out Protection − VBULK/PFC FB Input
Resonant tank of an LLC converter is always designed to
operate within a specific bulk voltage range. Operation
below minimum bulk voltage level would result in current
and temperature overstress of the converter power stage.
The NCP1399 controller features a VBULK/PFC FB input
in order to precisely adjust the bulk voltage turn−ON and
turn−OFF levels. This Brown−Out protection (BO) greatly
simplifies application level design.
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NCP1399 Series
Figure 38. Internal Connection of the Brown−out Protection Block
The internal circuitry shown in Figure 38 allows
monitoring the high−voltage input rail (Vbulk). A
high−impedance resistive divider made of Rupper and Rlower
resistors brings a portion of the Vbulk rail to the
VBULK/PFC FB pin. The Current sink (IBO) is active below
the bulk voltage turn−on level (Vbulk_ON). Therefore, the
bulk voltage turn−on level is higher than defined by the
division ratio of the resistive divider. To the contrary, when
the internal BO_OK signal is high, i.e. the application is
running, the IBO sink is disabled. The bulk voltage turn−off
threshold (Vbulk_OFF) is then given by BO comparator
reference voltage directly on the resistor divider. The
advantage of this solution is that the Vbulk_OFF threshold
precision is not affected by IBO hysteresis current sink
tolerance.
The Vbulk_ON and Vbulk_OFF levels can be calculated
using equations below:
The IBO is ON:
VBO ) VBOhyst +
(eq. 1)
ǒ ǓVbulk_ON
@
Rlower
Rlower ) Rupper
*
IBO
@
Rlower @ Rupper
Rlower ) Rupper
The IBO is OFF:
VBO
+
Vbulk_OFF
@
Rlower
Rlower ) Rupper
(eq. 2)
One can extract Rlower term from equation 2 and use it in
equation 1 to get needed Rupper value:
ǒ ǓRlower
+
Vbulk_ON@VBO
Vbulk_OFF
*
VBO
*
VBOhyst
IBO @
1
*
VBO
Vbulk_OFF
(eq. 3)
Rupper
+
Rlower
@
Vbulk_OFF *
VBO
VBO
(eq. 4)
Note that the VBULK/PFC FB pin is pulled down by an
internal switch when the controller is in startup phase − i.e.
when the VCC voltage ramps up from VCC < VCC_RESET
towards the VCC_ON level on the VCC pin. This feature
assures that the VBULK/PFC FB pin voltage will not ramp
up before the IC operation starts. The IBO hysteresis current
sink is activated and BO discharge switch is disabled once
the VCC voltage crosses VCC_ON threshold. The
VBULK/PFC FB pin voltage then ramps up naturally
according to the BO divider information. The BO
comparator then authorizes or disables the LLC stage
operation based on the actual Vbulk level.
The low IBO hysteresis current of the NCP1399 brown out
protection system allows increasing the bulk voltage divider
resistance and thus reduces the application power
consumption during light load operation. On the other hand,
the high impedance divider can be noise sensitive due to
capacitive coupling to HV switching traces in the
application. This is why a filter (tBO_FILTR) is added after the
BO comparator in order to increase the system noise
immunity. Despite the internal filtering, it is also
recommended to keep a good layout for BO divider resistors
and use a small external filtering capacitor on the
VBULK/PFC pin if precise BO detection wants to be
achieved.
The bulk voltage HV divider can be also used by a PFC
front stage controller as a feedback sensing network (refer
again to Figure 38). The shared bulk voltage resistor divider
between PFC and LLC stage offers a way how to further
reduce power losses during off−mode and no−load
operation. The NCP1399 features a PFC MODE pin that
disconnects bias of the PFC stage during light load,
off−mode or fault mode operation. The signal from the PFC
MODE pin can be also used to control an external HV switch
in order to disconnect the bulk voltage divider from bulk
during off−mode operation. This technique further reduces
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NCP1399 Series
the no−load power consumption down again since the power
losses of voltage divider are not affected by the bulk voltage
at all.
Please refer to Figure 61 through Figure 65 for an
illustration of NCP1399 Brown−out protection system in all
operating conditions/modes.
Over−voltage and Over−temperature Protection
The OVP/OTP pin is a dedicated input to allow for a
simple and cost effective implementation of two key
protection features that are needed in adapter applications:
over−voltage (OVP) and over−temperature (OTP)
protections. Both of these protections can be either latched
or auto−recovery– depending on the version of NCP1399.
The OVP/OTP pin has two voltage threshold levels of
detection (VOVP and VOTP) that define a no−fault window.
The controller is allowed to run when OVP/OTP input
voltage is within this working window. The controller stops
the operation, after filter time delay, when the OVP/OTP
input voltage is out of the no−fault window. The controller
then either latches−off or or starts an auto−recovery timer −
depending on the IC version − and triggered the protection
threshold (VOTP or VOVP).
The internal current source IOTP allows a simple OTP
implementation by using a single negative temperature
coefficient (NTC) thermistor. An active soft clamp
composed from Vclamp and Rclamp components prevents the
OVP/OTP pin voltage from reaching the VOVP threshold
when the pin is pulled up by the IOTP current. An external
pull−up current, higher than the pull*down capability of
the internal clamp (VCLAMP_OVP/OTP), has to be applied to
pull the OVP/OTP pin above VOVP threshold to activate the
OVP protection. The tOVP_FILTER and tOTP_FILTER filters
are implemented in the system to avoid any false triggering
of the protections due to application noise and/or poor
layout.
Figure 39. Internal Connection of OVP/OTP Input
The OTP protection could be falsely triggered during
controller startup due to the external filtering capacitor
charging current. Thus the tBLANK_OTP period has been
implemented in the system to overcome such behavior. The
OTP comparator output is ignored during tBLANK_OTP
period. In order to speed up the charging of the external
filtering capacitor COVP_OTP connected to OVP/OTP pin,
the IOTP current has been doubled to IOTP_BOOST. The
maximum value of filtering capacitor is 47 nF.
The OVP/OTP ON signal is set after the following events:
the VCC voltage exceeds the VCC_ON threshold during
first start−up phase (after VCC pin voltage was below
VCC_RESET threshold)
BO OK signal is received from BO block
Auto−recovery timer elapsed and a new restart occurs
IC returns to operation from skip−mode (VFB_SKIP_IN +
VFB_SKIP_HYST threshold was reached)
IC returns to operation from off−mode (VREM_ON or
VFB_REM_ON signal is received by off−mode control
block)
The IOTP current source is disabled when:
VCC falls below VCC_OFF threshold
BO OK signal goes to low state (i.e. Brown−out
condition occurs on the mains)
Fault signal is activated (Auto−recovery timer starts
counting or Latch fault is present)
IC goes into the skip−mode operation (VFB_SKIP_IN
threshold was reached)
IC goes into the off−mode operation (VREM_OFF or
(VFB_REM_OFF & VCC_OFF) signal was reached)
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NCP1399 Series
The latched OVP or OTP versions of NCP1399 enters
latched protection mode when VCC voltage cycles between
VCC_ON and VCC_OFF thresholds and no pulses are provided
by drivers. The controller VCC pin voltage has to be cycled
down below VCC_RESET threshold in order to restart
operation. This would happen when the power supply is
unplugged from the mains.
SKIP/REM Input and Off−mode Control
The NCP1399 implements an ultra−low power
consumption mode of operation called off−mode. The
application output voltage is cycled between the nominal
and lower levels that are defined by the secondary side
off−mode controller (like NCP435x secondary off−mode
controller). The output voltage is thus not regulated to
nominal level but is always kept at a high enough voltage
level to provide bias for the necessary circuits in the target
application – for example this could be the case of
microcontroller with very low consumption that handles
VCC management in a notebook or TV. The no−load input
power consumption could be significantly reduced when
using described technique. The NCP1399 implements two
different off−mode control system approaches:
Active ON off−mode control − available on the
NCP1399By device family
Active OFF off−mode control − available on the
NCP1399Ay device family
These two off−mode operation control techniques differ in
the way the off−mode operation is started on the primary
side controller. Both of these methods are described
separately hereinafter.
Active ON Off−mode Control – NCP1399B Device
Family
The NCP1399B device family uses a SKIP/REM pin only
for off−mode operation control– i.e. the pin is internally
connected to the Active ON off−mode control block and the
skip mode threshold level is not adjustable externally. The
skip mode comparator threshold can be adjusted only
internally (by IC option) in this package option. The
SKIP/REM pin when used for off−mode control allows the
user to activate the ultra−low consumption mode during
which the IC consumption is reduced to only very low HV
pin leakage current (IHV_OFF−MODE) and very low VCC pin
consumption (ICC_OFF−MODE). The off*mode is activated
when SKIP/REM pin voltage exceeds VREM_OFF threshold.
Normal operating mode is resumed when SKIP/REM pin
voltage drops below VREM_ON threshold – refer to
Figure 40 for an illustration.
Figure 40. SKIP/REM Input Internal Connection – Active ON Version
The off−mode operation is activated by the secondary side
off−mode controller. The auxiliary bias for primary side
off−mode control is provided by a circuit composed from
components D2, C1, R1, R2 and C2. The SKIP/REM pin is
pulled up by this auxiliary supply circuit once the REM
optocoupler (REM OK) is released. The application then
operates in off−mode until the secondary side off−mode
controller activates the REM optocoupler or until the
auxiliary bias on C1 is lost. Normal operation mode is then
recovered via power stage startup. The application is thus
switching between ON−mode and OFF−mode states when
off−mode control is implemented. The OFF mode period
last significantly longer time (tens of seconds or more)
compared to the secondary capacitor refilling period (few
tens of milliseconds) – this explains why the no−load input
power consumption can be drastically reduced. The
auxiliary off−mode supply capacitor C1 can stay charged
while the secondary bias is lost – this can happen during
overload or other fault mode conditions. A REM TIMER is
thus implemented in the system to allow fast application
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NCP1399 Series
restart in such cases. The controller blanks the SKIP/REM
input information and pulls down the SKIP/REM input for
tREM_TIMER time during controller restart so that the
secondary side bias can be restored and the secondary
off−mode controller can activate the REM optocoupler. This
REM TIMER blank sequence is activated each time the
VCC pin voltage reaches VCC_ON threshold – except in the
situation when after IC left off−mode operation by standard
way and VCC is restored – i.e. when the REM optocoupler
is activated by the secondary off−mode controller.
The SKIP/REM input blanking is activated in following
cases:
VCC pin voltage reaches VCC_ON threshold during first
start−up phase (i.e. when VCC was below VCC_RESET
threshold before)
Auto−recovery timer elapsed and new start is initiated
The REM TIMER helps to assure fast application re−start
from fault conditions by forcing controller operation after
tREM_TIMER . However, the secondary controller drives the
remote pin via REM optocoupler during normal operating
conditions in order to switch between ON and OFF
operating modes. The controller is active for very short time
during no−load conditions − just during the time needed to
re−fill the secondary side capacitors to the nominal output
voltage level. In this case we do not use REM TIMER
because it would increase the no−load power consumption
by forcing the application to run for a longer time than
necessary. The REM TIMER blank period is thus not
activated in no−load conditions.
The bias on VCC pin needs to be assured when off−mode
operation takes place. The auxiliary winding is no more able
to provide any bias thus the HV startup current source is
operated in DSS mode – i.e. the VCC pin voltage is cycling
between VCC_ON and VCC_OFF thresholds. This approach
keeps IC biasing in order to memorize the current operation
sate.
Please refer to Figure 64 for an illustration on how the
NCP1399 Active ON off−mode system works under all
operating conditions/modes.
Active OFF Off−mode Control – NCP1399A Device
Family
The NCP1399A device family uses LLC FB pin voltage
information for off−mode operation detection − refer to
Figure 41. The SKIP/REM pin is internally connected to the
skip mode block in this case and serves as a VFB_SKIP_IN
threshold voltage adjust pin. The secondary off−mode
controller reuses the LLC stage regulation optocoupler in
order to reduce total system cost. The off−mode operation is
initiated once the LLC FB pin is pulled down below
VREM_ON threshold and the VCC pin voltage drops below
VCC_OFF threshold in the same time. The optocoupler has to
be active at all time the application is held in off−mode. No
biased is then provided by the secondary off−mode
controller during normal operation – this is why this
approach is called Active OFF off−mode operation. The
application no−load input power consumption is slightly
higher compared to Active ON off−mode solution,
previously described, because the optocoupler needs to be
biased during off mode operation
Figure 41. Active OFF Off−mode Internal Detection Based on the LLC FB Pin Voltage
The controller monitors the LLC FB pin voltage level and
restarts via regular startup sequence (including VCC pin
voltage ramp−up to VCC_ON level and soft−start) once the
FB pin is released by the secondary off−mode controller.
The HV startup current source is working in DSS mode
during application off−mode operation – i.e. the VCC pin
voltage is cycling between VCC_ON and VCC_OFF
thresholds. This approach keeps IC biased so that the actual
operation sate is memorized. The LLC FB pin pull−up
resistor is disconnected when off−mode operation is
activated in order to reduce IC power consumption and also
needed current for optocoupler driving from secondary side.
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Please refer to Figure 65 for an illustration on how the
NCP1399 active ON off−mode system works under all
operating conditions/modes.
PFC MODE Output and P ON/OFF Control Pin
The NCP1399 has two pins P ON/OFF and PFC MODE
that can be used to disable or enable PFC stage operation
based on actual application operating state – please refer to
Figure 46. The PFC MODE pin voltage is changed
(VPFC_M_ON or VPFC_M_BO) based on the actual P ON/OFF
input logic signal state. Minimum impedance connected to
P ON/OFF pin is 1 kW. The PFC stage operation can thus be
disabled/enabled via external logic signal. This option
should be used with the wide range input voltage LLC tank
designed to assure correct operation of the LLC stage
through whole bulk voltage range. The PFC MODE output
pin can be used for two purposes:
1. to control the external small signal HV MOSFET
switch that connects the bulk voltage divider to the
VBULK/PFC FB input
2. to control the PFC front stage controller operation
via PFC controller supply pin
5V
0.1 V
Figure 42. Internal Connection of the PFC MODE and P ON/OFF Blocks
There are three possible states of the PFC MODE output
that can be placed by the controller based on the application
operating conditions:
1. The PFC MODE output pin is pulled−down by an
internal MOSFET switch before controller startup.
This technique ensures minimum VCC pin current
consumption in order to ramp VCC voltage in a
short time from the HV startup current source
which speeds up the startup or restart process. The
PFC MODE output pin is also pulled−down in
off−mode or protection mode during which the HV
startup current source is operated in DSS mode.
This reduces the application power consumption in
both cases.
2. The pull−down switch is disabled and the internal
regulator enabled by the controller to provide
VPFC_M_BO reference when an external logic
signal on the P ON/OFF pin is at “high” state. An
internal regulator includes current limitation for
the PFC MODE output that is set to IPFC_M_LIM
when VPFC_M_BO reference is provided. The PFC
MODE pin drives external small signal HV
MOSFET switch to keep bulk voltage divider
connected. The LLC power stage Brown−out
protection system thus works when the LLC stage
is switching while PFC stage disabled.
3. The pull−down switch is disabled and the internal
regulator is switched to bypass mode in which it
connects VCC pin voltage to PFC MODE output
with minimum dropout (VPFC_M_ON). This state of
the PFC MODE output appears in case an external
signal on the P ON/OFF pin is at “low” state.
The output power level is derived internally from the
actual FB pin voltage. This information could be compared
on external comparator with the reference level and control
the P ON/OFF input, thus the user has possibility to adjust
power below which the PFC stage is disabled in order to
increase efficiency in light load conditions. The P ON/OFF
comparator features an hysteresis (P ON/OFFHYST)
proportional to the set P ON/OFF level in order to overcome
PFC power stage oscillations (periodical ON/OFF
operation). The P ON/OFF timer (tP ON/OFF_TIMER) is
implemented to ensure a long enough propagation delay
from the PFC turn OFF detection to PFC MODE output
deactivation. This timer is unidirectional so that it resets
immediately after PFC ON condition is detected by the
P ON/OFF comparator. This technique is used in order to
avoid a PFC stage deactivation during load or line transients.
The PFC MODE pin output current is limited when the VCC
to PFC MODE bypass switch is activated. The current
limitation avoids bypass switch damage during PFC VCC
decoupling capacitor charging process or short circuit. A
minimum value PFC VCC decoupling capacitance should
be used in order to speed up PFC stage startup after it is
enabled by the NCP1399 controller.
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Please refer to Figure 61 through Figure 65 for an
illustration of NCP1399 PFC operation control.
ON−time Modulation and Feedback Loop Block
Frequency modulation of today’s commercially available
resonant mode controllers is based on the output voltage
regulator feedback only. The feedback voltage (or current)
of output regulator drives voltage (or current) controlled
oscillator (VCO or CCO) in the controller. This method
presents three main disadvantages:
1. The 2nd order pole is present in small signal
gain−phase characteristics the lower cross over
frequency and worse transient response is imposed
by the system when voltage mode control is used.
There is no direct link to the actual primary current
– i.e. no line feed forward mechanism which
results in poor line transient response.
2. Precise VCO (or CCO) is needed to assure
frequency modulation with good reproducibility,
fmin and fmax clamps need to be adjusted for each
design need for an adjustment pin(s).
3. Dedicated overload protection system, requiring
an additional pin, is needed to assure application
safety during overload and/or secondary short
circuit events.
The NCP1399 resolves all disadvantages mentioned
above by implementing a current mode control scheme that
ensures best transient response performance and provides
inherent cycle−by−cycle over−current protection feature in
the same time. The current mode control principle used in
this device can be seen in Figure 43.
Figure 43. Internal Connection of the NCP1399 Current Mode Control Scheme
The basic principle of current mode control scheme
implementation lies in the use of an ON−time comparator
that defines upper switch on−time by comparing voltage
ramp, derived from the current sense input voltage, to the
divided feedback pin voltage. The upper switch on−time is
then re−used for low side switch conduction period. The
switching frequency is thus defined by the actual primary
current and output load conditions. Digital processing with
10 ns minimum on−time resolution is implemented to
ensure high noise immunity. The ON−time comparator
output is blanked by the leading edge blanking (tLEB) after
the Mupper switch is turned−on. The ON−time comparator
LEB period helps to avoid false triggering of the on−time
modulation due to noise generated by the HB pin voltage
transition.
The voltage signal for current sense input is prepared
externally via natural primary current integration by the
resonant tank capacitor Cs. The resonant capacitor voltage
is divided down by capacitive divider (Ccs1, Ccs2, Rcs1,
Rcs2) before it is provided to the CS input. The capacitive
divider division ratio, which is fully externally adjustable,
defines the maximum primary current level that is reached
in case of maximum feedback voltage – i.e. the capacitive
divider division ration defines the maximum output power
of the converter for given bulk voltage. The CS is a bipolar
input pin which an input voltage swing is restricted to ±5 V.
A fixed voltage offset is internally added to the CS pin signal
in order to assure enough voltage margin for operation the
feedback optocoupler − the FB optocoupler saturation voltage
is ~ 0.15 V (depending on type). However, the CS pin useful
signal for frequency modulation swings from 0 V, so current
mode regulation would not work under light load conditions
if no offset would be added to the CS pin before it is stabilized
to the level of the on−time comparator input. The CS pin
signal is also used for secondary side short circuit detection
– please refer to chapter dedicated to short circuit protection.
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The second input signal for the on−time comparator is
derived from the FB pin voltage. This internal FB pin signal
is also used for the following purposes: skip mode operation
detection, PFC MODE control, off−mode detection (in
NCP1399A device family) and overload / open FB pin fault
detection. The detailed description of these functions can be
found in each dedicated chapters. The internal pull−up
resistor assures that the FB pin voltage increases when the
optocoupler LED becomes less biased – i.e. when output
load is increased. The higher FB pin voltage implies a higher
reference level for on−time comparator i.e. longer Mupper
switch on−time and thus also higher output power. The FB
pin features a precise voltage clamp which limits the internal
FB signal during overload and startup. The FB pin signal
passes through the FB processing block before it is brought
to the ON−time comparator input. The FB processing block
scales the FB signal down by a KFB ratio in order to limit the
CS input dynamic voltage range. The scaled FB signal is
then further processed by subtraction of a ramp
compensation generator signal in order to ensure stability of
the current mode control scheme. The divided internal FB
signal is overridden by a Soft−start generator output voltage
during device starts−up.
The actual operation frequency of the converter is defined
based on the CS pin and FB pin input signals. Please refer to
Figure 44 and below description for better understanding of
the NCP1399 frequency modulation system.
Figure 44. NCP1399 On−time Modulation Principle
The Mupper switch is activated by the controller after
dead−time (DT) period lapses in point A. The frequency
processing block increments the ON−time counter with
10 ns resolution until the internal CS signal crosses the
internal FB set point for the ON−time comparator in point B.
A DT period is then introduced by the controller to avoid any
shoot−through current through the power stage switches.
The DT period ends in point C and the controller activates
the Mlower switch. The ON−time processing block
decrements the ON_time counter down until it reaches zero.
The Mlower switch is then turned−OFF at point D and the
DT period is started. This approach results in perfect duty
cycle symmetry for Mlower and Mupper switches. The
Mupper switch on−time naturally increases and the
operating frequency drops when the FB pin voltage is
increased, i.e. when higher current is delivered by the
converter output – sequence E.
The resonant capacitor voltage and thus also CS pin
voltage can be out of balance in some cases – this is the case
during transition from full load to no−load operation when
skip mode is not used or adjusted correctly. The current
mode operation is not possible in such case because the
ON−time comparator output stays active for several
switching cycles. Thus a special logic has been implemented
in NCP1399 in order to repeat the last valid on−time until the
current mode operation recovers – i.e. until the CS pin signal
balance is restored by the system.
Overload and Open FB Protections
The overload protection and open FB pin detection are
implemented via FB pin voltage monitoring in this
controller. The FB fault comparator is triggered once the FB
pin voltage reaches its maximum level and the VFB_FAULT
threshold is exceeded. The fault timer or counter (depending
on IC option) is then enabled – refer to Figure 43. The time
period to the FB fault event confirmation is defined by the
preselected tFB_FAULT_TIMER parameter when the fault
timer option is used. The FB fault counter, once selected as
a FB fault confirmation period source, defines the fault
confirmation period via Mupper DRV pulses counting. The
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FB fault confirmation time is thus dependent on switching
frequency. The fault timer/counter is reset once the FB fault
condition diminishes. A digital noise filter has been added
after the FB fault comparator to overcome false triggering of
the FB fault timer/counter due to possible noise on the FB
input. The noise filter has a period of 2 ms for FB fault
timer/counter activation and 20 ms for reset/deactivation to
assure high noise immunity. A cumulative timer/counter IC
option is also available on request. The FB fault
timer/counter is not reset when the FB fault condition
diminishes in this case. The FB fault timer/counter is
disabled and memorizes the fault period information. The
cumulative FB fault timer/counter integrates all the FB fault
events over the IC operation time. The Fault timer/counter
can be reset via skip mode or VCC UVLO event.
Figure 45. Internal FB Fault Management
The controller disables driver pulses and enters protection
mode once the FB fault event is confirmed by the FB fault
timer or counter. Latched or auto−recovery operation is then
triggered – depends on selected IC option. The controller
adds an auto−recovery off−time period (tA−REC_TIMER) and
restarts the operation via soft start in case of auto−recovery
option. The application temperature runaway is thus
avoided in case of overload while the automatic restart is still
possible once the overload condition disappears. The IC
with latched FB fault option stays latched−off, supplied by
the HV startup current source working in DSS mode, until
the VCC_RESET threshold is reached on the VCC pin – i.e.
until user re−connects power supply mains.
Please refer to Figure 61 and Figure 62 for an illustration
of the NCP1399 FB fault detection block.
Secondary Short Circuit Detection
The protection system described previously, implemented
via FB pin voltage level detection, prevents continuous
overload operation and/or open FB pin conditions. The
primary current is naturally limited by the NCP1399
on−time modulation principle in this case. But the primary
current increases when the output terminals are shorted. The
NCP1399 controller will maintain zero voltage switching
operation in such case, however high currents will flow
through the power MOSFETS, transformer winding and
secondary side rectification. The NCP1399 implements a
dedicated secondary side short circuit protection system that
will shut down the controller much faster than the regular FB
fault event in order to limit the stress of the power stage
components. The CS pin signal is monitored by the
dedicated CS fault comparator − refer to Figure 43. The CS
fault counter is incremented each time the CS fault
comparator is triggered. The controller enters
auto−recovery or latched protection mode (depending on IC
option) in case the CS fault counter overflows refer to
Figure 46. The CS fault counter is then reset once the CS
fault comparator is inactive for at least 50 Mupper upcoming
pulses. This digital filtering improves CS fault protection
system noise immunity.
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Figure 46. NCP1399 CS Fault Principle
Dedicated Startup Sequence and Soft−Start
Hard switching conditions can occur in a resonant SMPS
application when the resonant tank operation is started with
50% duty cycle symmetry – refer to Figure 47. This hard
switching appears because the resonant tank initial
conditions are not optimal for the clean startup.
Figure 47. Hard switching cycle appears in the LLC application when resonant tank is
excited by 50% duty cycle during startup
The initial resonant capacitor voltage level can differ
depending on how long delay was placed before application
operation restart. The resonant capacitor voltage is close to
zero level when application restarts after very long delay –
for example several seconds, when the resonant capacitor is
discharged by leakage to the power stage. However, the
resonant capacitor voltage value can be anywhere between
Vbulk and 0 V when the application restarts operation after
a short period of time – like during periodical SMPS
turn−on/off. Another factor that plays significant role during
resonant power supply startup is the actual load impedance
seen by the power stage during the first pulses of startup
sequence. This impedance is not only defined by resonant
tank components but also by the output loading conditions
and actual output voltage level. The load impedance of
resonant tank is low when the output is loaded and/or the
output voltage is low enough to made secondary rectifies
conducting during first switching cycles of startup phase.
The resonant frequency of the resonant tank is given by the
resonant capacitor capacitance and resonant inductance
−note that the magnetizing inductance does not participate
in resonance in this case. However, if the application
starts−up when the output capacitors is charged and there is
no load connected to the output, the secondary rectification
diodes is not conducting during each switching cycle of
startup sequence and thus the resonant frequency of resonant
tank is affected also by the magnetizing inductance. In this
case, the resonant frequency is much lower than in case of
startup into loaded/discharged output.
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These facts show that a clean, hard switching free and
parasitic oscillation free, startup of an LLC converter is not
an easy task, and cannot be achieved by duty cycle imbalance
and/or simple resonant capacitor pre−charge to Vbulk/2 level.
These methods only work in specific startup conditions.
This explains why the NCP1399 implements a proprietary
startup sequence − see Figure 48 and Figure 49. The resonant
capacitor is discharged down to 0 V before any application
restart − except when restarting from skip mode.
Figure 48. Initial Resonant Capacitor Discharge
before Dedicated Startup Sequence is Placed
Figure 49. Dedicated Startup Sequence Detail
The resonant capacitor discharging process is simply
implemented by activating an internal current limited switch
connected between the HB pin and IC ground – refer to
Figure 48. This technique assures that the resonant capacitor
energy is dissipated in the controller without ringing or
oscillations that could swing the resonant capacitor voltage
to a positive or negative level. The controller detects that the
discharge process is complete via HB pin voltage level
monitoring. The discharge switch is disabled once the HB
pin voltage drops below the VHB_MIN threshold.
The dedicated startup sequence continues by activation of
the Mlower driver output for Tl1 period (refer to Figure 49).
This technique ensures that the bootstrap capacitor is fully
charged before the first high−side driver pulse is introduced
by the controller. The first Mupper switch on−time Tup1
period is fixed and depends on the application parameters.
This period can be adjusted internally – various IC options
are available. The Mupper switch is released after Tup1
period and it is not followed by the Mlower switch
activation. The controller waits for a new ZVS condition for
Mupper switch instead and measures actual resonant tank
conditions this way. The Mupper switch is then activated
again after the Mlower blank period is used for measurment
purposes. The second Mupper driver conduction period is
then dependent on the previously measured conditions:
1. The Mupper switch is activated for 3/2 of previous
Mupper conduction period in case the measured
time between previous Mupper turn−off event and
upper ZVS condition detection is twice higher than
the the previous Mupper pulse conduction period
2. The Mupper switch is activated for previous
Mupper conduction period in case the measured
time between previous Mupper turn−off event and
upper ZVS condition detection is twice lower than
the previous Mupper pulse conduction period
The startup period then depends on the previous
condition. Another blank Mlower switch period is placed by
the controller in case condition 1 occurred. A normal
Mlower driver pulse, with DC of 50% to previous Mupper
DRV pulse, is placed in case condition 2 is fulfilled.
The dedicated startup sequence is placed after the
resonant capacitor is discharged (refer to Figure 48 and
Figure 49) in order to exclude any hard switching cycles
during the startup sequence. The first Mupper switch cycle
in startup phase is always non−ZVS cycle because there is
no energy in the resonant tank to prepare ZVS condition.
However, there is no energy in the resonant tank at this time,
there is also no possibility that the power stage MOSFET
body diodes conducts any current. Thus the hard
commutation of the body diode cannot occur in this case.
The IC will not start and provide regular driver output
pulses until it is placed into the target application, because
the startup sequence cannot be finished until HB pin signal
is detected by the system. The IC features a startup watchdog
timer (tWATCHDOG) which activates a dedicated startup
sequence periodically in case the IC is powered without
application (during bench testing) or in case the startup
sequence is not finished correctly. The IC will provide the
first Mlower and first Mupper DRV pulses with a
tWATCHDOG off−time in−between startup attempts.
Soft−start
The dedicated startup sequence is complete when
condition 2 from previous chapter is fulfilled and the
controller continues operation with the soft−start sequence.
A fully digital non−linear soft−start sequence has been
implemented in NCP1399 using a soft−start counter and
D/A converter that are gradually incremented by the Mlower
driver pulses. A block diagram of the NCP1399 soft−start
system is shown in Figure 50.
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Figure 50. Soft−start Block Internal Implementation
The soft−start block subsystems and operation are
described below:
1. The Soft−Start counter is a unidirectional counter
that is loaded with the last Mupper on−time value
that is reached at the dedicated startup sequence
end (i.e. during condition b occurrence explained
in previous chapter). The on−time period used in
the initial period of the soft−start sequence is
affected by the first Mupper on−time period
selection and the dedicated startup sequence
processing. The Soft−Start counter counts up from
this initial on time period to its maximum value
which corresponds to the IC maximum on−time.
The Soft−Start counter is incremented by the
soft−start increment number (tSS_INCREMENT)
during each Mlower switch on−time period. The
soft−start start increment, selectable via IC option,
thus affects the soft−start time duration. The
Mlower clock signal for the Soft−Start counter can
be divided down by the SS clock divider
(KSS_INCREMENT) in case the soft−start period
needs to be prolonged further – this can be also
done via IC option selection. The Soft−Start period
is terminated (i.e. the counter is loaded to its
maximum) when the FB pin voltage drops below
VFB_SKIP_IN level.
2. The ON−time counter is a bidirectional counter
that is used as a main system counter for on−time
modulation during soft−start, normal operation or
overload conditions. The ON−time counter
counts−up during Mupper switch conduction
period and then counts down to zero – defining
Mlower switch conduction period. This technique
assures perfect 50 % duty cycle symmetry for both
power switches as afore mentioned. The ON−time
counter count−up mode can be switched to the
count−down mode by either of two events: 1st
when the ON−time counter value reaches the
maximum on−time value (tTON_MAX) or 2nd when
the actual Mupper on−time is terminated based on
the current sense input information.
3. The Maximum ON−time comparator compares
the actual ON−time counter value with the
maximum on−time value (tTON_MAX) and
immediately activates the latch (or auto−recovery)
protection mode. The minimum operating
frequency of the controller is defined the same
way. The Maximum ON−time comparator
reference is loaded by the Soft−Start counter value
on each switching cycle during soft−start. The
Maximum ON−time fault signal is ignored during
Soft−Start operation. The converter Mupper switch
on−time (and thus operating frequency) is thus
defined by the Soft−Start counter value indirectly
– via Maximum ON−time comparator. The
Mupper switch on−time is increased until the
Soft−Start counter reaches tTON_MAX period and
Maximum on−time protection is activated, or until
ON−time comparator takes action and overrides
the Maximum ON−time comparator.
4. The Soft−Start D/A converter generates a
soft−start voltage ramp for ON−time comparator
input synchronously with Soft−Start counter
incrementing. The internal FB signal for ON−time
comparator input is artificially pulled−down and
then ramped−up gradually when soft−start period
is placed by the system – refer to Figure 51. The
FB loop is supposed to take over at certain point
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when regulation loop is closed and output gets
regulated so that soft−start has no other effect on
the on−time modulation. The Soft−Start counter
continues counting−up until it reaches its
maximum value which corresponds to the IC
maximum on−time value – i.e. the IC minimum
operating frequency. The Soft−Start period is
terminated (i.e. counter is loaded to its maximum)
when the FB pin voltage drops below VFB_SKIP_IN
level. The D/A converter output evolve
accordingly to the Soft−Start counter as it is
loaded from its output data bus.
Figure 51. Soft Start Behavior
The Controller Operation during Soft−start Sequence
Evolves as Follows:
The Soft−Start counter is loaded by last Mupper on−time
value at the end of the dedicated startup sequence. The
ON−time counter is released and starts count−up from zero
until the value that is equal to the actual Soft−Start counter
state. The Mupper switch is active during the time when
ON−time counter counts−up. The Maximum ON−time
comparator then changes counting mode of the ON−time
comparator from count−up to count−down. A dead−time is
placed and the Mlower switch is activated till the ON−time
counter reaches zero value. The Soft−Start counter is
incremented by selected increment during corresponding
Mlower on−time period so that the following Mupper switch
on−time is prolonged automatically – the frequency thus
drops naturally. Because the operating frequency of the
controller drops and Mlower DRV signal is used as a clock
source for the Soft−start counter, the soft−start speed starts
to decrease on each (or on each N−th) Mlower driver pulse
(where N is defined by KSS_INCREMENT) of switching cycle.
So we have non−linear soft−start that helps to speed up
output charging in the beginning of the soft−start operation
and reduces the output voltage slope when the output is close
to the regulation level. The output bus of the Soft−Start
counter addresses the D/A converter that defines the
ON−time comparator reference voltage. This reference
voltage thus also increases non−linearly from initial zero
level until the level at which the current mode regulation
starts to work. The on−time of the Mupper and Mlower
switch is then defined by the ON−time comparator action
instead of the Maximum ON−time comparator. The
soft−start then continues until the regulation loop is closed
and the on−time is fully controlled by the secondary
regulator. The Soft−Start counter then continues in counting
and saturates at its maximum possible value which
corresponds to IC minimum operating frequency. The
maximum on−time fault detection system is enabled when
Soft−Start counter value is equal to tTON_MAX value.
The previous on−time repetition feature, described above
in the ON−time modulation and feedback loop chapter, is
disabled in the beginning of soft start period. This is because
the ON−time comparator output stays high for several cycles
of soft start period – until the current mode regulation takes
over. The previous on−time repetition feature is enabled
once the current modulation starts to work fully, i.e. in the
time when the ON−time comparator output periodically
drops to low state within actual Mupper switch on−time
period. Typical startup waveform of the LLC application
driven by NCP1399 controller can be seen in Figure 52.
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Figure 52. Application Startup with NCP1399 −
Primary Current − green, Vout − magenta
Skip Mode Operation
An LLC resonant converter efficiency reaches high values
under medium and full load conditions thanks to ZVS
operation for the primary MOSFETs and ZCS operation for
the secondary rectifiers. The light−load and no−load
efficiency however drops unacceptably when a normal
frequency modulation control technique is used. This is
because the converter operating frequency needs to be
increased quite a lot compared to nominal load operating
frequency in order to maintain regulation under light load
conditions. High operating frequency increases driving
losses in the controller and also losses in the converter power
stage. Moreover, the magnetizing current that becomes
major primary current component during light load
conditions, circulates in the resonant tank and creates power
losses in the power switches despite minimum energy
transfer to the secondary side. This is why the majority of
resonant converter controllers implement skip mode
operation under light load conditions.
The NCP1399 controller implements a proprietary skip
mode technique that assures maximum light−load efficiency
and low acoustic noise. The FB pin voltage level below
which the application enters skip mode operation is fully
user adjustable for the NCP1399A device family − via
SKIP/REM adjust pin or via IC option for the NCP1399B
device family. The skip mode operation can be initiated by
the skip comparator only during actual Mupper driver
on−time period. This technique assures defined and
synchronous transition from normal to skip mode operation.
The SKIP/REM pin voltage (NCP1399Ay) or internal
voltage level (NCP1399By) defines the FB pin voltage
threshold under which is the skip mode initiated – the
maximum operating frequency of the converter is thus
defined indirectly.
The Mlower switch is always activated for a defined
on−time period at the beginning of each skip burst to
re−charge the bootstrap capacitor and thus assure enough
charge for high side driver powering during the following
Mupper pulse. The resonant capacitor average voltage level
is maintained below Vbulk/2 level during the skip mode
operation. This technique helps to minimize power loses
during the initial Mlower MOSFET switch activation – refer
to Figure 53.
Figure 53. The average voltage of resonant capacitor is maintained below Vbulk/2 during the skip mode operation
to reduce turn−on losses during 1st Mlower skip burst pulse
The first pulse in the skip burst is always non−ZVS
because there is no magnetizing energy in the resonant tank
that could prepare ZVS condition for lower MOSFET
switch turn−on. The reduced resonant capacitor voltage thus
helps to decrease C*V^2 losses related to the total HB line
capacitance (composed from output capacitances of the
power stage MOSFETs and stray capacitance seen by the
HB line). However, too low of a resonant capacitor voltage,
during 1st Mlower driver pulse initiation, would result in a
too low resonant tank current at the end of the first Mlower
switch conduction period and thus a non ZVS condition for
the following Mupper switch turn−on process. This is why
a full discharge of resonant capacitor is not needed before
skip mode.
The reduced resonant capacitor average voltage
requirement imposes a specific turn−off sequence to be used
at the end of each skip burst and also during transition from
normal operation mode to skip mode– refer to Figure 54.
The Mlower driver is always activated the latest during
transition to skip mode. However, the latest Mlower driver
activation on−time is equal to 3/2 of previous Mupper pulse
width when the skip mode is entered. This technique
naturally imbalances the resonant tank so that the average
resonant capacitor voltage stays below Vbulk/2 level. – i.e.
application is prepared for optimal initialization of the
following skip burst.
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