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■OPERATIONAL DESCRIPTION (Continued)

<Short-Circuit Protection>

the block diagram shown in the previous page). In case where output is accidentally shorted to the Ground and when

the Pch MOS driver transistor, the short-circuit protection quickly operates to turn off and to latch the driver transistor.

For the D/E/F/G series, it does not matter how much the current limit, once the FB voltage become less than the

latch mode, the operation can be resumed by either turning the IC off and on via the CE/MODE pin, or by restoring

<UVLO Circuit>

or higher, switching operation takes place. By releasing the UVLO function, the IC performs the soft start function to

the UVLO operating voltage. The UVLO circuit does not cause a complete shutdown of the IC, but causes pulse output to

be suspended; therefore, the internal circuitry remains in operation.

<PFM Switch Current>

on. In this case, time that the Pch MOS driver transistor is kept on (TON) can be given by the following formula.

TON= L

< PFM Duty Limit >

duty increases (e.g. the condition that the step-down ratio is small), it’s possible for Pch MOS driver transistor to be turned

図 IPFM ①

Ton

Lx

I Lx

0mA

図 IPFM ②

0mA

Lx

I Lx

FOSC

PFMデューティ制限

PFM Duty Limit