FA7703 Datasheet, PDF (15/21 Pages) Fuji Electric – FUJI Power Supply Control IC

FA7703/04
FA7703/7704
occurrence of a short-circuit in the output and
the triggering of the short-circuit protection
function can be calculated with
tp[s] ≈ ^{0.7 × CCS}
ICS
where, CCS: Capacitance of CS terminal [μF]
ICS: Output source current of CS terminal [μA]
(2.2μΑ, typ.)
You can reset the timer latch action for the
short-circuit protection function by changing the
voltage of either VCC terminal or CS terminal to
the following values.
VCC terminal: below UVLO voltage (1.85V typ.)
CS terminal: below 1.83V(typ.)
2.2V
2.0
DO NOT leave SEL1 terminal open in operation,
and be sure to connect it to either GND terminal
or REG terminal.
(8)Power good signal/Undervoltage lockout
protection circuit (UVLO)
To protect FA7703/04 from malfunction when
the supply voltage drops, there is built-in
undervoltage lockout as a protection circuit.
When the supply voltage rises from 0V, the
UVLO circuit is canceled at VCC of 2.0V(typ.).
When the supply voltage drops, the UVLO circuit
shuts off the output at VCC of 1.85V(typ.). In this
case, CS terminal is reset to Low level.
Power good signal circuit monitors the voltage
of REG terminal, and it stops the output of
FA7703/04 until the voltage of REG terminal
exceeds approximately 1.9V in order to protect
the ICs from malfunction.
1.5
1.27V
1.0
Start-up
0.5
short circuit
tp ^protection
short circuit
momentary short circuit
soft start
0
Time
Fig.7
(7)Output circuit
FA7703/04 contain a push-pull output stage and
can directly drive MOSFETs. The peak current of
OUT terminal is the maximum sink current of
+150mA, and the source current of -400mA.
FA7703/04 can also drive both NPN and PNP
type transistors. And in such cases, the
maximum continuous current is ±50mA. When
designing the value of output current, be sure to
consider the allowable loss accordingly. (See
Design advice)
Ch1 of FA7703/04 is available for driving both
types of MOSFETs and you can determine the
type of MOSFET, which is connected externally
by selecting the connection of SEL1 terminal
(Pin11). If SEL terminal is connected to GND
terminal, FA7703/04 can drive a Pch MOSFET. If
SEL terminal is connected to REG terminal, they
can drive Nch MOSFET.
You can accordingly design a buck converter
circuit by Pch MOSFET driving, and a boost
circuit or a fly-back converter circuit by Nch
MOSFET driving.
Fuji Electric Systems Co., Ltd.
AN-057E Rev.1.0
Jun-2010
15
http://www.fujielectric.co.jp/fdt/scd/