FIP4F8S datasheet(21/33 Pages) FUJI

21 / 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/

(10) Over-Voltage Protection of FA5526/27/28

FA5526, FA5527 and FA5528 have built-in over-voltage

protection circuits to monitor Vcc voltage. Fig.16 shows

its block diagram and Fig.17 its timing chart.

When VCC voltage increases and exceeds comparator

(OVP) reference voltage, 28V, an internal 1.3mA constant

current source is tuned on.

Since sink capability of the zener diode which clamps

the CS pin at 4V is 55uA, CS pin voltage quickly

increases when the 1mA constant current source is turned

on. When CS voltage exceeds comparator (Latch)

reference voltage, 8.5V, the IC changes to the latch mode.

The delay time td (OVP), the time from over-voltage

detection to the latch mode, is given as follows.

td (OVP) [ ms ] = 2.85 * Cs [ uF ]

( typical value )

Here, Cs is a capacitance connected to CS pin [ uF ].

In the latch mode, an internal power supply source, 5V

“Reg” circuit, is turned off and OUT pin voltage is held to

be low., and the current form the CS pin changes to 5µA.

The latch mode can be reset through decreasing Vcc

voltage due to cutting off of input voltage or through

forcibly decreasing CS pin voltage to 7.4V or less.

Moreover, pay attention to the relationship between wiring

at the VH pin and reset time in the latch mode.

（See “9-(1) Start-up circuit.”）

(11) Over-Voltage Protection of FA5536/37/38

FA5536, FA5537 and FA5538 have built-in over-voltage

protection ( OVP ) circuits to monitor Vcc voltage similar

to FA5526/27/28.

However, the OVP of FA5536/37/38 is Auto-Recovery

mode.

Therefore, when you need the OVP as latch mode, the

additional external circuit is necessary as mentioned on

page 28 to 29 ( See “10-(4)” ).

(12) Under-Voltage Lock-Out circuit

The IC has a built-in undervoltage lockout circuit to

prevent malfunction when Vcc voltage drops. When Vcc

voltage increases from 0V, the IC starts operation at Vcc =

15V (typ.). As the supply voltage decreases, the IC stops

operation at Vcc = 9V(typ.).

When the undervoltage lockout circuits operates and

the IC stops operation, OUT pin and CS pin voltage are

forced to be low, resetting soft start, and overload and

overvoltage timer latch protection.

ENB

VCC

5V Reg.

UVLO

5V Reg.

ENB

UVLO

F.F.

1.3mA

8.5V/7.7V

4.8V

2.8V

OUT

VCC

Overload

Latch

28V

OVP

Fig.16

Over Voltage protection circuit

( only for FA5526 / 5527 / 5528 )

Fig.17

Over-Voltage protection timing chart

( only for FA5526 / 5527 / 5528 )

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