FA5604 Datasheet, PDF (18/31 Pages) Fuji Electric – FUJI Power Supply Control IC

FA5604/5605/5606
Further details on the above four major functions of the CS pin are given below.
(i)Soft start function
Fig.9 shows the soft start operation timing chart. The CS pin is connected to capacitor Ccs. When the power is
turned on, the constant current source (10A) begins to charge the capacitor. As shown in the timing chart, the CS
pin voltage rises slowly. The CS pin is connected to the IC internal PWM comparator, and then the comparator
output pulse slowly widens to cause a soft start as shown in the timing chart. After the soft start, the CS pin voltage
is clamped at 3.8V by internal zener diode.
FB pin voltage
Oscillator output
CS pin voltage
OUT pin output
Fig.9
(ii)Overload shutdown function
Fig. 10 shows the timing chart of the CS terminal voltage (VCS) under overload condition. To achieve intermittent
operation at overvoltage, apply a voltage proportional to the output voltage to VF terminal. If the output voltage is
reduced by overvoltage or the like, the VF terminal voltage is reduced. If the VF terminal voltage is 3 V or more, the
CS terminal voltage is clamped at 3.8 V and perform an output drooping operation. Subsequently, when the output
voltage is reduced due to overload, short circuit, or the like, and the VF terminal voltage becomes less than 3 V, the
CS terminal voltage oscillates between 3.8 V and 5.7 V. Intermittent operations are performed at switch-on during
the count period of 1 to 64 and at switch-off during the count period of 65 to 512 (switching period ratio: 64/448 = 1 :
7) at FA5604/06, and at switch-on during the count period of 1 to 64 and at switch-off during the count period of 65
to 1024 (switching period ratio: 64/960 = 1 : 15) at FA5605. The intermittent function is achieved by three terminals:
CS, FB, and VF terminals. For the detailed description, see item (6) below.
VCS
5.7V
3.8V
SS ^3V
1V
ON/OFF
12
64 65
1024
(512)
Switching ON Switching OFF
VVF＜3V
Type
12
FA5604
FA5606
FA5605
VVF＞3V(3.8V Clamp)
Switching
ON
0～64
0～64
Switching ON
Switching
ON:OFF
OFF
65～512
1:7
65～1024 1 : 15
Fig.10
Fuji Electric Co., Ltd.
AN-033E Rev.1.2
April-2011
18
http://www.fujielectric.co.jp/products/semiconductor/