FA5626 FUJI [Fuji Electric], FA5626 Datasheet - Page 19

• Manufacturer Part Number: FA5626
• Description: Fuji Switching Power Supply Control IC
• Manufacturer: FUJI [Fuji Electric]

(6) Short circuit detection
AN-071E Rev.1.2
April-2011
(7)Over voltage protection circuit
FA5626 has a protection function for output short-circuit
without delay time.
If output of PSU is shorted, FB pin voltage goes high. In
addition, Vcc voltage drops because auxiliary winding
voltage almost zero. IC stops switching operation at the
instance when IC detects that FB pin voltage exceeds
overload detection voltage and Vcc drops below
Vthshort (11V typ.).
As in the case of overload, IC restart switching
operation after 1600ms and repeats it until short circuit
condition is removed.
To cancel the latch mode, shut down the input voltage
to cause brownout, as in the case of the overload
protection.(latch type)
Since 65s (typ) delay time has been set to the set input
of the latch circuit, the latch mode is not entered even if
the VCC pin exceeds the detection voltage temporarily.
The IC integrates an overvoltage protection circuit for
monitoring the VCC pin voltage. (See Fig.12)
If the VCC voltage increases and exceeds 26V typ,
which is the reference voltage of the comparator (OVP),
the comparator output is reversed to High level, setting
the latch circuit to perform latch shutdown.
At this time, the startup circuit is subjected to ON/OFF
control to maintain the latch mode, thus keeping the
VCC voltage within the 12V or 13V (typ) range.
Fuji Electric Co., Ltd.
Fig.14 Overvoltage protection circuit
FA5626
(8) Latch shutdown circuit by an external signal
-Overheat protection-
(9) Under voltage lockout circuit (VCC pin)
(10)Output circuit
The push/pull structure output circuit drives the MOSFET
directly. The peak output current of the OUT pin is 0.5A
(source) and 1.0A (sink) in the maximum absolute ratings.
In a state in which the IC is stopped in the under voltage
lockout circuit or operation is suspended in the latch mode,
or in an auto reset wait state by overload protection function,
the OUT pin is brought into the Low level, and the MOSFET
is interrupted.
TH
The IC integrates an under voltage lockout (UVLO) function
to prevent circuit malfunction that might occur when power
supply voltage decreases. When the VCC voltage
increases from 0V and reaches 18V (typ), the circuit starts
operating. When the VCC decreases down to 9V (typ), the
circuit stops operating.
In a state in which the under voltage lockout function is
actuated to stop IC operation, the OUT pin is forcibly made
to enter the Low state. The latch mode of the protection
circuit is also reset.
The LAT pin is equipped with a latch shutdown function.
(See Fig.13)
By decreasing the LAT pin voltage to 1.05V or lower, the IC
enters the latch mode.
To cancel the latch mode, interrupt the input voltage,thus
decreasing the VCC voltage to the OFF threshold voltage
(9.0V typ.) or lower.
LAT function operates after LAT pin voltage rises to more
than 2.1V once.
If the external latch shutdown function by the LAT pin is not
to be used, connect a capacitor only.
Connect an NTC thermistor to the LAT pin to use the
overheat protective function.
(See Fig.13, P23 9-(4) Lat pin)
Fig.13 Overheat protection function using a thermistor
19
LAT
1
5V
http://www.fujielectric.co.jp/products/semiconductor/
LAT
UVLO
Latch
Set
Reset