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Reverse Input-Output Voltage

Schottky

LP2981

LP2981

100-mA ULTRA-LOW DROPOUT REGULATOR

WITH SHUTDOWN

SLVS521E – JULY 2004 – REVISED MARCH 2008

An inherent diode is present across the PNP pass element of the LP2981.

With the anode connected to the output, this diode is reverse biased during normal operation, since the input

abruptly stepped below the output, this diode is forward biased and can cause a parasitic silicon-controlled

rectifier (SCR) to latch, resulting in current flowing from the output to the input (values in excess of 100 mA can

cause damage). Thus, to prevent possible damage to the regulator in any application where the output may be

pulled above the input, an external Schottky diode must be connected between the output and input. With the

anode on output, this Schottky limits the reverse voltage across the output and input pins to

∼0.3 V, preventing

the regulator's internal diode from forward biasing.

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