8/22

2. Short-Circuit Protection Circuit (Latching Type)

When the FB pin is shorted to the Ground or the output voltage drops rapidly because of over load state etc., the P-ch

driver transistor is kept OFF as in the case with the integral protection circuit. (The protection circuit operates when

and the CE pin.

Short-circuit protection circuit

FBVoltage

0.9V

0.7V

VREF

0.9V

Soft-start time ：Tss x 90%

* Protection circuit does not operate.

Less than 100usec = Not latching

Latch

100 usec

* About 100 to 200usec delay time is set

to avoid latching w hen instantaneous

transient response drop

<Protection Circuits>

1. Integral Protection Circuit (Latch Type)

In the circuit of the XC9220/XC9221 A and B series, the more load current becomes larger, the duty of the EXT/ pin

gradually expands, and the duty reaches maximum (EXT/L). When the MAXDUTY state continues a certain amount

resuming the operation from the latching state, please turn off the IC via the CE pin or apply the input voltage again

(operates U.V.L.O. function and release). The latching state does not mean a complete shutdown, but a state in

which pulse output is suspended; therefore, the internal circuitry remains in operation.

However, the integral protection circuit uses the MAXDUTY as a trigger for its operation, it suspends the pulse output

no matter what dropout voltage decreases.

For the specification including small dropout voltage, the

XC9220/XC9221 C or D series, which do not have the integral protection function, are recommended.

Integral protection circuit

Ton < Tpro

Ton > Tpro

EXT/ Waveform

Latch

Protection circuit operates and

EXT/ Output shut dow n

Ton : ON Time ( EXT/ : L)

Tpro : Integral Protection Circuit

Delay Time (Internally set)

■OPERATIONAL EXPLANATION (Continued)