FIP4F8S datasheet(27/33 Pages) FUJI

27 / 33 page

AN-087E Rev.1.0

April-2011

FA5526/5527/5528/5536/5537/5538

Fuji Electric Co., Ltd.

http://www.fujielectric.co.jp/products/semiconductor/

(3) Protection using CS pin for FA5526/27/28

In steady operation, the CS pin voltage is clamped by a

4V zener diode. Externally forcing CS pin voltage to

increase to the threshold voltage, 8.5V, for the latch mode

allows the IC to stop its operation for protection.

In this case, a current of more than the sink capacity of

4V zener diode, 84uA, shall be applied to the CS pin.

Set the input current to the CS pin at 1mA or less as a

guide.

The following shows examples of overvoltage protection

at an arbitrary voltage using the CS pin.

(3-1) Overvoltage detection on the secondary side

Fig.29 shows an example of an overload detection

circuit on the secondary side to change the IC into the

latch mode.

(3-2) Detection of Vcc (1)

Fig.30 shows a circuit where the IC is stopped in the

latch mode upon detecting Vcc overvoltage. In this case,

Vcc voltage is latched at approximately ZD+8.5V.

Use a ZD whose voltage is larger than the ON threshold

voltage of the low-voltage malfunction preventive circuit.

Otherwise, the IC cannot start.

(3-3) Detection of Vcc (2)

Fig.31 shows another circuit to detect Vcc overvoltage.

In this case, Vcc voltage is latched approximately at ZD

voltage.

Use a ZD whose voltage is larger than the ON threshold

voltage of the low-voltage malfunction preventive circuit.

Otherwise, the IC cannot start.

(4) Protection using CS pin for FA5536/37/38

FA5536/37/38 does not include any latch function.

Therefore, the external latch circuit is necessary for

Over-Voltage Protection as latch mode. Fig.32 shows

the OVP latch circuit by primary side detection at VCC pin

and Fig.33 shows the OVP latch circuit by secondary side

detection through a optocoupler “PC”.

When CS pin voltage is pulled down below 0.68V ( typ. ),

the switching is shut-down. Once the NPN transistor “Q2”

and “Q3” turn-on when the diode “ZD1” or optocoupler

“PC” supplies the current to resistor “R1” by detection of

Over-Voltage, PNP transistor “Q1” turns-on and “Q2” and

“Q3” are maintained in ON-State.

Then, CS pin voltage is maintained at low level until the

current of a diode ZD2 is cut VCC pin voltage decreases

below OFF threshold ( 9V ) .

Fig.29

Over Voltage protection (1) for FA5526/27/28

Fig.30

Over Voltage protection (2) for FA5526/27/28

Fig.31

Over Voltage protection (3) for FA5526/27/28

Fig.32

Over Voltage protection (1) for FA5536/37/38

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