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Reverse Input-Output Voltage

Schottky

LP2985

LP2985

150-mA LOW-NOISE LOW-DROPOUT REGULATOR

WITH SHUTDOWN

SLVS522F – JULY 2004 – REVISED AUGUST 2005

APPLICATION INFORMATION (continued)

There is an inherent diode present across the PNP pass element of the LP2985.

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

voltage is higher than the output. However, if the output is pulled higher than the input for any reason, this diode

is forward biased and can cause a parasitic silicon-controlled rectifier (SCR) to latch, resulting in high current

flowing from the output to the input. Thus, to prevent possible damage to the regulator in any application where

the output may be pulled above the input, an external Schottky diode should 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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