FIP4F8S datasheet(28/33 Pages) FUJI

28 / 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/

(5) When not using an overload protection

function

As shown in Fig.34, connect a resistor R3 of 18k ohm

between FB pin and GND.

As a result, FB pin voltage does not increase to the

threshold voltage for overload protection and the IC does

not change to the latch mode even at overload.

In this case, the latch protection for over-voltage is also

available.

(6) Correction of overload detection current

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If the power supply output becomes overload, the

current of the MOSFET is limited by the maximum

threshold voltage of the IS pin and power supply voltage

drops. If the state continues as it is, an overload protection

function operates to stop the IC in the latch mode. For

details of an overload protection function, see “9-(8)

Overload protection function.”

When the overload protection operates, the output

current of the power supply varies depending on the input

voltage; and the higher the input voltage is, the larger the

output current.

In such a case, connect R4 between the current

detection resistor Rs and IS pin, and add a correction

resistor R5 as shown in Fig.35. The typical resistance of

R5 is several hundreds of k ohm to several Meg ohm. Note

that the above correction slightly decreases the value of

overload current limit to stop the IC in the latch mode even

if input voltage is low.

Fig.33

Over Voltage protection (2) for FA5536/37/38

Fig.34

When not using overload protection

Fig.35

Correction of overload detection current

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