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2016.04.06 Rev.A
© 2016 ROHM Co., Ltd. All rights reserved.
Quasi-Resonant type AC/DC converter IC
BD768xFJ-LB series Quasi-Resonant converter Technical Design
24V / 1A ( SIC TO-3PFM SCT2H12NZ)
This application note describes the design of Quasi-Resonant converters using ROHM’s AC/DC converter IC BD768xFJ-LB
series devices. It explains the selection of external components and PCB layout guidelines.
● Description
The BD768xFJ-LB series are Quasi-Resonant switching AC/DC converter for driving SiC (Silicon Carbide)–MOSFET. Using
external switching MOSFET and current detection resistors provides a lot of flexibility in the design. Power efficiency is
improved by the burst function and the reduction of switching frequency under light load conditions.
This is the product that guarantees long time support in the Industrial market.
● Key features
Quasi-resonant method（Maximum frequency control 120kHz）/Current mode
Low power when load is light ( Burst operation) / Frequency reduction function
VCC pin : under voltage protection / over voltage protection
Leading-Edge-Blanking function
Over-current protection (cycle-by-cycle)
ZT trigger mask function
ZT Over voltage protection
AC voltage correction function
Soft start
Brown IN/OUT function
Gate Clamp circuit
MASK Function
● Basic specifications
Operating power supply voltage range(VCC): ：VCC：15.0V～27.5V
Operating current Normal mode ：0.80mA (Typ.)
Burst mode ：0.50mA(Typ.)
Maximum frequency ：120kHz(Typ.)
Operating temperature range ：-40℃ to +105℃
(＊) Product structure：Silicon monolithic integrated circuit This product has no designed protection against radioactive rays
(＊) Operating the IC over the absolute maximum ratings may damage the IC. The damage can either be a short circuit between
pins or an open circuit between pins and the internal circuitry. Therefore, it is important to consider circuit protection measures,
such as adding a fuse, in case the IC is operated over the absolute maximum ratings.
● BD768xFJ-LB Series line-up
FBOLP VCCOVP
BD7682FJ AutoRestart Latch
BD7683FJ Latch Latch
BD7684FJ AutoRestart AutoRestart
BD7685FJ Latch AutoRestart
● Applications
Industrial equipment, AC Adaptor, Household appliances
Application Note
2/24
www.rohm.com
2016.04.06 Rev.A
© 2016 ROHM Co., Ltd. All rights reserved.
BD768xFJ-LB series Quasi-Resonant converter Technical Design
● Block Diagram
NOUT
+
-
+
VOUT
FUSE
Filter
Diode
Bridge
Leading Edge
Blanking
5
OUT
GND
VCC
CS
+
-
Internal
Supply
ZT
ZT
Comp.
RS
Czt
FB
VREF(4V)
3
1
7
4
2
18.5V/14.0V
28.0V
Timer
(128ms)
FBOLP_OH
+
-
100mV
/400mV
1 shot
OSC
Cfb
ERROR
AMP
PC
OSC
Rzt1
7V
AND
ZT Blanking
OUT(H->L)
0.60us
NOUT
TimeOut
( 15 usec )
AND
AND
PRE
Driver
POUT
FB/2
+
-
-
DCDC
Comp.
1.00V
+
-
VCC OVP
CURRENT SENSE (V-V Change)
Normal : ×1.0
+
-
FBOLP_OH
MAX
Blanking
Frequency
(120kHz)
1.00V
0.50V
+
-
OLP
200kΩ
200kΩ
VCC UVLO
Burst
Comp.
8
BO
4.0V
Regulator
Soft Start
+
-
1.0V
RH
RL
BO
Comp.
OR
OR
15uA
20k
MASK
0.5μs
Delay
6
NOR
+
-
ZT ACSNS Comp.
SS1ms
SS4ms
Va
Rstart
Cvcc
VH
Rzt2
+
-
ZT OVP Comp.
(LATCH)
S
Q
R
NOUT
18.0V
Clamper