BD7679G Datasheet PDF - Rohm

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BD7679G
Rohm

Part Number BD7679G
Description PWM Control Type DC/DC Converter IC
Page 20 Pages


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Datasheet
PWM Control Type
DC/DC Converter IC for AC/DC Driver
BD7679G
General Description
BD7679G is a PWM controller type DC/DC converter
IC for AC/DC that provides an optimum system for all
products that requires an electrical outlet. This product
supports both isolated and non-isolated devices. IC
enables simple design of low-power electrical
converters. With switching MOSFET and current
detection resistor as external devices, it enables more
freedom in design.
Since the peak current control is utilized, peak current
is controlled in each cycles, application excels wide
bandwidth and transient response.
BD7679G includes various protective functions such
as soft start function, burst function, per-cycle over
current limiter, VCC overvoltage protection and
overload protection.
An external stop pin (COMP pin) is provided, so that
switching stopping can be set by external signals. The
function is available as overheating protection and over
voltage protection of secondary output, so on.
The PWM switching frequency is fixed at 65 kHz.
A frequency hopping function is included which contributes
to low EMI.
Key Specifications
Power Supply Voltage range:
8.5V to 25.0V
Operating Current:
Normal: 0.60mA (Typ)
Burst: 0.40mA (Typ)
Oscillation Frequency:
65kHz (Typ)
Operating Temperature range:
-40°C to +85°C
Package
SSOP6
W(Typ) x D (Typ) x H (Max)
2.90mm x 2.80mm x1.25mm
Features
PWM frequency of 65kHz
PWM current mode method
Low circuit current when UVLO is ON
(12μA at VCC=12V)
Low circuit current without load
(Burst operation when load is light)
Built-in SW frequency hopping function
250ns leading-edge blanking
VCC UVLO / OVP (Auto restart)
Per-cycle over current protection circuit
Soft start
Output overload protection(Auto-restart protection)
External stop function for COMP pin (Auto restart)
Applications
AC adapters and household appliances (vacuum cleaners,
humidifiers, air cleaners, air conditioners, refrigerators, IH
cooking heaters, rice cookers, etc.)
Typical Application Circuit
Figure 1, Application Diagram (Isolated type)
Product structureSilicon monolithic integrated circuit
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© 2015 ROHM Co., Ltd. All rights reserved.
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This product is not designed protection against radioactive rays
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TSZ02201-0F2F0A200160-1-2
2015.4.17 Rev.001



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BD7679G
Pin ConfigurationSSOP6
Datasheet
(Unit:mm)
Figure 2, External Dimensions of SSOP6 Package
Pin Description
NO. Pin Name
1 GND
2 FB
3 COMP
4 CS
5 VCC
6 OUT
Table 1 I/O PIN Functions
I/O Function
I/O GND pin
I Feedback signal input pin
I Comparator input pin
I Primary current sensor pin
I Power supply input pin
O External MOS drive pin
ESD protection system
VCC
GND
-
○○
○○
○○
-
○○
I/O Equivalent Circuit
1 GND
GND
2
VREF
FB
FB
20kΩ
3 COMP
VREF
4
VREF
CS
CS
5 VCC
VCC
6 OUT
VCC
OUT
Figure 3, I/O Equivalent Circuit
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BD7679G
Block Diagram
+ FUSE
AC
85- 265Vac
-
Filter
Diode
Bridge
4.0V
LineReg
+
-
VCC UVLO
+ 13.5V / 7.5V
-
VCC OVP
Auto Restart
(27.5V)
+
-
2.0V
Soft Start
0~1msec Maxduty 15%
1~8msec Maxduty 25%
Internal Block
4.0V LineReg
4.0V LineReg
20kΩ
PWM Control
S
RQ
DRIVER
OLP
Comparator
- Timer
+ 250ms
Pulse Skip
Comparator
-
+
+
-
Current Limit
Comparator
Leading Edge
Blanking
(typ=250ns)
PWM
Comparator
-
+
+
MAX
DUTY
OSC = 65 kHz
Frequency
hopping
Slope
Compensation
Figure 4, Block Diagram
FeedBack
With
Isolation
Datasheet
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BD7679G
Description of Each Block
( 1 ) Start Sequences (Soft Start Operation, Light Load Operation, and Overload Protection)
Start sequences are shown in Figure 5. This is also shown the operation of overload protection.
See the sections below for detailed descriptions
Datasheet
VH
VCC=13.5V
VCC=7.5V
VCC=7.0V
VCC
Internal REF
Pull Up
Within
250ms
250ms
FB
Vout
Iout
SwitchSinwgiting
Soft Start
Normal Load
Light LOAD
Over Load
Burst mode
Switching
stop
A
BC D
E
F
GH
IJ
Figure 5, Start Sequence Timing Chart
A: Input voltage VH is applied
B: VCC pin voltage rises by being supplied from VH line through start resistor “Rstart” and the IC starts operating when VCC >
VUVLO1 (13.5V Typ).
Switching operation starts when other protection functions are judged as normal.
From startup to be stable output voltage, application should be set to stabilize output voltage during VCC > VUVLO2 (7.5V Typ)
because the VCC pin consumption current causes the VCC voltage drop.
C: Operated soft start function, maximum duty is restricted to 15% during a 1ms period to prevent any excessive rise in voltage
or current. From 1ms to 8ms, maximum duty is restricted to 25%. Maximum duty is restricted to 75% after 8ms.
D: VOUT voltage rises when the switching operation starts.
Once the output voltage starts, it is set to the rated voltage level within the TFOLP period (250ms Typ).
The output voltage is regulated within TFOLP (=250ms Typ) from starting.
E: During Light Load, when FB pin voltage < VBST (=0.3V Typ), Burst method is operated to keep power consumption down.
F: Over Load condition occurs when FB pin voltage > VFOLP1A (=3.6V Typ).
G: When FB pin voltage is at VFOLP1A (= 3.6V Typ) for more than TFOLP (250ms Typ), the overload protection function is triggered
and switching is stopped. The IC’s internal 250ms timer is reset during the TFOLP period (250ms Typ) if FB < VFOLP1B even
once.
H: If the VCC voltage drops to VUVLO2 (7.5Vtyp) or below, restart is executed.
I: The IC’s circuit current is reduced and the VCC pin value rises. (Same as B).
J: Same as D
In Figure 4, start resistor Rstart is needed to start the application.
When the start resistor Rstart value is reduced, standby power is increased and the startup time is shortened.
Conversely, when the start resistor Rstart value is increased, standby power is reduced and the startup time is lengthened.
Standby current is less than 20uA at VCC UVLO is disable, and it can calculate VCC UVLO voltage from VUVLO1=14.5V
(Max).
exStarting resistor Rstart setting method;
Rstart = (VHmin - VUVLO1Max) / IOFFMax
In the case of Vac=100V (-20% of a margin), Rstart requirement can be found by the following formulas:
VHmin =100 × 2 × 0.8 = 113V
Because of VUVLO1 (Max) =14.5V, Rstart (113V - 14.5V) / 20μA4.975M
Start-up time can be found by the following formulas:
Tstart = -Rstart × CVCC × ln (1-VUVLO1/VHmin)
exRstart=3.0M
Rstart resistor loss in this case is : Pd (Rstart) = (VH-VCC)2 / Rstart = (141V - 14.5V)2 / 3.0M = 5.35mW.
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© 2015 ROHM Co., Ltd. All rights reserved.
TSZ2211115001
4/17
TSZ02201-0F2F0A200160-1-2
2015.4.17 Rev.001



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