FA5546 Datasheet, PDF (19/27 Pages) Fuji Electric – Switching Power Supply Control IC

FA5546/47
(6) Overload protection circuit (latch shutdown
type)
Fig.14 shows a latch shutdown type circuit block, and
Fig.15 shows the protection operation timing chart.
The latch shutdown type operates on the same principle as
the auto reset type up to switching stop.
After the overload protection delay time TdOLP (200ms typ)
has elapsed, the switching pulse output is stopped and the
latch mode is entered.
After the latch mode is entered, the one-time clamp circuit
discharges the VCC voltage rapidly down to 14.5V (typ) (as
in the case of the overvoltage protection).
To maintain the latched state in the latch mode, the startup
circuit is subjected to the ON/OFF control, and the VCC
voltage is maintained within the 12V or 13V (typ) range.
By interrupting the input voltage to decrease the VCC
voltage to the OFF threshold voltage (9.8V typ) or lower, the
latch mode can be reset.
As described in the section of the auto reset type, in the
case of a load with which overload and light load are
repeated, latch shutdown may occur within the period of
200ms or shorter.
Start up
Start up VCC
Management
8
Current
Logic
VH
Monitor Ctrl
ON
ON
DBL
5
OUT
5V
Rfb
FB ^20kΩ
2
INV.
AMP
A
Over
OLP
Load
T1
Ctrl
T2
OLP Timer
IS comp.
UVLO
Latch
Set
Reset
VthIS1
4
3
GND
IS
Fig.14 Overload protection circuit (timer latch)
Fig. 15 Overload protection timing chart (timer latch type)
Fuji Electric Co., Ltd.
AN-027E Rev.0.4
April -2011
19
http://www.fujielectric.co.jp/products/semiconductor/