LT3804 Datasheet PDF - Linear Technology

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LT3804
Linear Technology

Part Number LT3804
Description Secondary Side Dual Output Controller
Page 16 Pages


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Final Electrical Specifications
LT3804
Secondary Side Dual
Output Controller with Opto Driver
FEATURES
DESCRIPTIO
June 2003
s Regulates Two Secondary Outputs
s Optocoupler Feedback Driver and Second Output
Synchronous Driver Controller
s True Differential Remote Sensing Regulation
s High Switching Frequency: up to 800kHz
s Programmable Current Limit
s Programmable Soft-Start and Power Good
wwws.DaAtuatSohmeeatt4iUc.cForemquency Synchronization
s Available in Thermally Enhanced 28-Lead TSSOP
U
APPLICATIO S
s 48V Input Isolated DC/DC Converters
s Multiple Output Power Supplies
s Offline Converters
s DC/DC Power Modules
, LTC and LT are registered trademarks of Linear Technology Corporation.
The LT®3804 is a high efficiency step-down switching
regulator with optocoupler feedback control for regulating
multiple outputs in single-secondary winding isolated
power supplies.
The LT3804 contains an error amplifier and an optocoupler
driver to regulate the first (main) output. For the second
output regulation, the LT3804 contains a complete PWM
controller to drive dual synchronous N-channel MOSFETs.
With leading edge modulation, it operates with either
current or voltage mode control of the primary side. The
LT3804 is synchronized to the falling edge of the trans-
former secondary winding and can be used in single-
ended or double-ended isolated power converter topolo-
gies. A user selectable discontinuous conduction mode
improves light load efficiency.
True differential Kelvin sensing is used for each output
feedback amplifier to achieve high regulation accuracy
and design simplicity. Other features include soft start,
current limit and power good flags.
TYPICAL APPLICATIO
VIN
36V
TO 72V
TG BG
LT3781
SG
VC + VREF
VFB
VCC
BIAS
L1
1.8µH
0.003
••
Q4
Q3
x2
OUT2
LTC1693-1
OUT1
IN1 IN2
390pF
••
••
VOS1
VOS1+
2.74k
604
LT3804
CL1N SYNC
CL1P TGATE
VCC SW
CSET BGATE
PGND
GNDS1
CL2P
CL2N
VAOUT2
VFB1
VFB2
VAOUT1
GNDS2
OPTO
1.5k
Q1
L2
1.8µH
Q2
x2
+VOS1+
VOS1
VOUT1
3.3V
AT 15A
COUT1
0.003
VOUT2
1.8V
AT 15A
+
COUT2
3.01k
3804 F01
ISOLATION
BOUNDARY
COUT1, COUT2: SANYO POSCAP 4TPE680MF 680µF/4V
L1, L2: SUMIDA CEP125-IR8MC-H
Q1-Q4: SILICONIX Si7892DP
Figure 1. 250kHz, 3.3V and 1.8V Output Isolated DC/DC Converter (Simplified Schematic)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LT3804
ABSOLUTE AXI U RATI GS
(Note 1)
VCC Supply Voltage .................................................. 26V
BOOST Pin Voltage with Respect to SW Pin ............ 10V
BOOST Pin Voltage with Respect to GND Pin .......... 35V
SYNC Pin Voltage (Note 2) ..................................... 30V
GNDS1 Pin Voltage ................................................... 1V
GNDS2 Pin Voltage ................................................... 1V
Operating Junction Temperature Range
LT3804E (Note 3) ..............................–40°C to 125°C
Storage Temperature Range ..................–65°C to 150°C
wwwL.DeaadtaTSheemept4eUr.actoumre (Soldering, 10 sec).................. 300°C
UW U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
CL1P 1
CL1N 2
28 ILCOMP1
27 GBIAS
ILCOMP2 3
BOOST 4
TGATE 5
26 BGATE
25 VCC
24 PGND
SW 6
23 OPTO
CSET 7 29 22 VAOUT1
SYNC 8
21 CL2N
SS2 9
20 CL2P
PGIN1 10
19 PGOOD
PGIN2 11
GNDS2 12
18 VFB1
17 SS1
GNDS1 13
16 BGS
VFB2 14
15 VAOUT2
FE PACKAGE
28-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 38°C/W
EXPOSED PAD IS SGND (PIN 29)
MUST BE CONNECTED TO PCB
ORDER PART
NUMBER
LT3804EFE
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 11V, GNDS1=GNDS2=0V, operating maximum VCC = 25V, no load
on any outputs, unless otherwise noted.
PARAMETER
Overall
Supply Voltage (VCC)
Supply Current (IVCC)
BOOST Pin Current
Voltage Amplifier VA1,VA2
Reference Voltage (VREF1,VREF2)
VFB1, VFB2 Pin Input Current
Remote Ground Pin (GNDS1,GNDS2) Current
VAOUT1 High at OA1 Threshold 1.5V
VAOUT1 High at OA1 Threshold 1.25V
VAOUT1 Low
VAOUT2 High
VAOUT2 Low
VAOUT1 Source Current
VAOUT2 Source Current
Open-Loop Gain
Gain Bandwidth Product
Soft-Start Current (SS1,SS2)
CONDITIONS
VAOUT2 1.2V (Switching Off)
VBOOST = VSW + 8V, 0V VSW 24V
TGATE High
TGATE Low
Common Mode: ±20mV (0°C to 125°C)
(–40°C to 125°C)
VREF over Common Mode: ±100mV
VFB1 = VREF1, VFB2 = VREF2
–100mV GNDS1, GNDS2 100mV
VFB1 = VREF1 – 10mV, IVAOUT1 = –50µA
VFB1 = VREF1 – 10mV, IVAOUT1 = –50µA
VFB1 = VREF1 + 10mV, IVAOUT1 = 100µA
VFB2 = VREF2 – 10mV, IVAOUT2 = –50µA
VFB2 = VREF2 + 10mV, IVAOUT2 = 100µA
MIN TYP MAX UNITS
q8
25
9 13
23
23
V
mA
mA
mA
0.591 0.6 0.609
q 0.587
0.609
–3 3
0.2 0.5
q –50 –100
1.75
1.45
0.7
4.5
0.8
q 100 230 400
q 70
150 250
100
10
5 10 24
V
V
mV
µA
µA
V
V
V
V
V
µA
µA
dB
MHz
µA
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LT3804
ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 11V, GNDS1=GNDS2=0V, operating maximum VCC = 25V, no load
on any outputs, unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Opto Driver Amplifier OA1
OA1 Upper Threshold
q 1.4
1.55 1.65
V
OA1 Threshold Hysteresis
0.25 V
OA1 Voltage Gain (VOPTO/VAOUT1)
VOPTO High
VOPTO Low
IOPTO Short-Circuit Current Limit
wwwP.oDwaetraGSohoedet4U.com
1.2V < VOPTO < 4V, ROPTO = 1k
VAOUT1= 0.9V, IOPTO = –10mA
VFB1 = VREF1 – 10mV, ROPTO = 1k
VFB1=VREF1 – 10mV, GNDS1 = 0V,
VOPTO = 4V
q 5.6
q 4.5
q0
6 6.4
5.2 6
0.1 0.25
q –50 –25 –12
V
V
V
mA
Power Good Window Threshold
(PGIN1-GNDS1, PGIN2-GNDS2)
Input Current (PGIN1,PGIN2)
–100mV < GNDS1, GNDS2 < 100mV
0V < PGIN1, PGIN2 < 1V
0.85 1.15
0.2 0.35
VREF
µA
Delay Time for Power Bad
25mV Overdrive on PGIN1,PGIN2
q 100 200 300
µs
Output Low (PGOOD)
2mA into the Pin
q
150 300
mV
Current Limit Amplifier CA1, CA2
Current Limit Threshold (CL1P-CL1N, CL2P-CL2N)
BGATE Off Threshold at (VCL2P-VCL2N), BGS Pin Float
Switching Off Threshold at ILCOMP2
Input Current (CL1P, CL1N, CL2P, CL2N)
Oscillator
Common Mode Voltage from 0V to VCC – 2.5V
VAOUT1 = 1.2V, VAOUT2 = 2.5V,
Commond Mode Voltage from 0V to VCC – 2.5V
VILCOMP2
VCL2P = VCL1N, VCL2P = VCL2N
q 40
0
50 60
8 15
0.15
100
mV
mV
V
µA
Switching Frequency
Synchronization Frequency Range
CSET Ramp Valley Voltage
CSET Peak-to-Peak Voltage
Synchronization Pulse Threshold on SYNC Pin
Maximum Duty Cycle
Gate Drivers (TGATE, BGATE)
CS = 500pF (NO SYNC)
CS = 333pF (NO SYNC)
CS = 200pF (NO SYNC)
CS = 500pF
CS = 333pF
CS = 200pF
CS = 1000pF (NO SYNC)
CS = 1000pF (NO SYNC)
Falling Edge VSYNC
VFB2 = VREF2 – 5mV, CS > 333pF
q 170 200 240
q 240 280 340
q 400 470 570
q 245
q 345
q 575
400
500
800
0.90 1.15
1.4
2.4
2.5
q 75
80
kHz
kHz
kHz
kHz
kHz
kHz
V
V
V
%
VGBIAS
VTGATE High (VTGATE – VSW)
VBGATE High
VTGATE Low (VTGATE-VSW)
VBGATE Low
Peak Gate Drive Current
IGBIAS < 25mA
ITGATE < 50mA, VBOOST = VGBIAS – 0.5V
IBGATE < 50mA
ITGATE < –50mA
IBGATE < 50mA
10nF Load
q 7.5 8 8.5
5 6 7.5
q5
6 7.5
q 0.5
q 0.5
1
V
V
V
V
V
A
Gate Drive Rise and Fall Time
1nF Load
25 ns
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: If highter than 30V on SYNC pin is needed, add a 10kresistor in
series with the pin.
Note 3: The LT3804E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
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LT3804
TYPICAL PERFOR A CE CHARACTERISTICS
VGBIAS vs IGBIAS Over Junction
Temperature
8.1
–40°C
8.0 25°C
7.9
www.Da7.t8aSheet4U.com
125°C
7.7
0
10
IGBIAS (mA)
20 26
3804 G01
VREF vs VCC, FREQ vs VCC
CSET = 500pF
3 TA = 25°C
2
1
VREF
0
–1
FREQ
1
0
–1
10 15
VCC (V)
20 25
3804 G04
Switching Frequency vs
Temperature
CSET = 500pF
215
210
205
200
195
–40 –20 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
3804 G07
ICC vs VCC (Switching Off)
13
TA = 25°C
12
11
10
9
8
7
6
5
8 10 12 14 16 18 20 22 24
VCC (V)
3804 G02
Voltage Amplifier VA1, VA2 Gain
and Phase
120
TA = 25°C
–0
GAIN
80
(–111°)
–50
PHASE
40 –100
0 –150
0dB, 10MHz
–20 –180
10 100 1k 10k 100k 1M 10M 100M
FREQUENCY (Hz)
3804 G03
CSET vs Switching Frequency
TA = 25°C
800
CSET
600
400
200
1.00
MAXIMUM DUTY CYCLE
0.95
0.90
0.85
0.80
0.75
0.70
100 200 300 400 500 600 700 800 900 1000
CSET (pF)
3804 G05
VREF vs Temperature
0.602
0.601
0.600
0.599
0.598
0.587
0.596
–40 –20 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
3804 G06
GBIAS vs IGBIAS (Charging 2.2µF)
CGBIAS = 2.2µF
300 TA = 25°C
250
200
150
100
50
0
VGBIAS
IGBIAS
12
10
8
6
4
2
0
0
500µs
1ms
TIME
3804 G08
Current Limit Amplifier CA1 Gain
at VCC = 11V, VCL2N = 5V
8
7
VCC = 11V
VCL2N = 5V
TA = 25°C
6
5
4
CSET PEAK
3
2
CSET VALLEY
1
0
30 40 50 60 70
VCL2P – VCL2N (mV)
3804 G09
3804i
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