XC9220 Datasheet, PDF (8/22 Pages) Torex Semiconductor – 16V Input Voltage, Step-Down DC/DC Controller ICs.

XC9220/XC9221 Series
˙OPERATIONAL EXPLANATION (Continued)
<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
of time (TPRO), the EXT/ pin holds high level (latching) and keeps the P-ch output driver transistor in OFF state. For
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.
z Integral protection circuit
EXT/ Waveform
Ton < Tpro
Ton > Tpro
Latch
Ton : ON Time ( EXT/ : L)
Tpro : Integral Protection Circuit
Delay Time (Internally set)
Protection circuit operates and
EXT/ Output shut dow n
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
the FB voltage becomes 0.7V or lower.) For releasing the latching state, the circuit is needed to restart via the VIN
and the CE pin.
z Short-circuit protection circuit
F B Vo lta g e
VREF
Sof t-start time ：Tss x 90%
* Protection circuit does not operate.
Less than 100usec = Not latching
* A bout 100 to 200usec delay time is set
to avoid latching w hen instantaneous
transient response drop
Latch
0.9V
0.7V
0.9V
100 usec
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