LP2985 Datasheet, PDF (16/24 Pages) National Semiconductor (TI) – Micropower 150 mA Low-Noise Ultra Low-Dropout Regulator Designed for Use with Very Low ESR Output Capacitors

LP2985
150-mA LOW-NOISE LOW-DROPOUT REGULATOR
WITH SHUTDOWN
SLVS522F – JULY 2004 – REVISED AUGUST 2005
APPLICATION INFORMATION (continued)
Reverse Input-Output Voltage
There is an inherent diode present across the PNP pass element of the LP2985.
V_IN
V_OUT
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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.
Schottky
V_IN
LP2985
V_OUT
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