LP2981 Datasheet, PDF (8/17 Pages) National Semiconductor (TI) – Micropower 100 mA Ultra Low-Dropout Regulator

LP2981
SLVS521F – JULY 2004 – REVISED AUGUST 2008 ......................................................................................................................................................... www.ti.com
Reverse Input-Output Voltage
An inherent diode is present across the PNP pass element of the LP2981.
V_IN
V_OUT
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 one V_BE higher than the input, or if the input is
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.
Schottky
V_IN
LP2981
V_OUT
8
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