Technical Note

9/11

BD8629FS

www.rohm.com

2009.05 - Rev.A

© 2009 ROHM Co., Ltd. All rights reserved.

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Protection function

Protection circuit is effective for destruction prevention due to accident so that avoid using under continuous protection

operation.

Low voltage protection function (LVP)

The voltage of the terminal FB (2 pins) is compared with internal reference voltage VREF.

the state is fixed. In that case , PDET (3pin) output changes to L.

Table 1 output low voltage protection function

EN terminal

SS terminal

FB terminal

Low voltage protection

function

Low voltage protection

operation

>1.4V(typ)

Effective

ON

OFF

<1.4V(typ)

-

Invalidity

OFF

-

-

Invalidity

OFF

＊

Low voltage protection function is available when SS terminal voltage becomes more than

1.4V (typ) in the transition to ON control (during soft start).

Over voltage protection function(OVP)

The voltage of the terminal FB is compared with internal reference voltage VREF.

If FB terminal voltage is over Vovp (=VREF +60mV) and the state is continues for 500usec, output changes to low voltage

and the state is fixed.

Table 2 output overvoltage protection function

EN terminal

SS terminal

FB terminal

Over voltage

protection function

Over voltage

protection operation

>1.4V(typ)

Effective

ON

OFF

<1.4V(typ)

-

Invalidity

OFF

-

-

Invalidity

OFF

＊

Over voltage protection function is available when SS terminal voltage becomes more than

1.4V (typ) in the transition to ON control (during soft start).

FB terminal

voltage

VREF

0

ON

OFF

Protection

OVP

LVP

VREF＋60ｍV

PDET terminal

HIGH

LOW

VREF-60ｍV

500[us]

500[us]

Fig. 5 Output voltage error detection range