FA5604 Datasheet, PDF (26/31 Pages) Fuji Electric – FUJI Power Supply Control IC

FA5604/5605/5606
To shorten the startup period, the capacitor C2 or resistor R1 should be decreased. But in some case, such as when
the load current of the power supply is changed rapidly, you may want to prolong the hold time of the VCC voltage
over the VCC the OFF threshold. In this case, the capacitor C2 cannot be decreased and the resistor R1 should be
decreased. But loss of the resistor R1 increases. In such case, the circuit shown in Fig.24 and Fig.25 is effective to
shorten startup period without increasing the loss of the resistor R1. The capacitor C2 is decreased to shorten the
startup period and, after the IC startup, VCC voltage supplied from C3 to prolong the hold time of the VCC voltage.
The startup period of this circuit also is approximately given by the expression in (7) and (8).
R1 _D1
D2
VCC
6
C2 C3
FA5604/05/06 ^▽
R1
D1 D2
VCC
C2 C3
6
FA5604/05/06 ^{R2 ▽}
Fig.24
Fig.25
(4)Feedback pin circuit
Fig.26 shows an example of connection in which a feedback signal is input to the FB pin. If this circuit causes
power supply instability, connect R3 and C4 as shown in Fig.26 to decrease the frequency gain. Set R3 between
several 10Ω to several kΩ and C4 between several 1000pF to 1F.
In noise is applied to the FB pin, the output pulses may be lacked or disturbed.
In this case, connect a capacitor C5 as shown in Fig.26 to suppress the noise applied to the FB pin. Set the
capacitor of C5 less than 1/10 of capacitance of C4 and connect C5 as near the IC as possible.
5
FA5604/05/06 _OUT
GND ⁴
2 _FB
Rs
▽
▼
C5
R3
PC1
C4
▽▽
Fig.26
Fuji Electric Co., Ltd.
AN-033E Rev.1.2
April-2011
26
http://www.fujielectric.co.jp/products/semiconductor/