LP3878 Datasheet, PDF (10/11 Pages) National Semiconductor (TI) – Micropower 800mA Low Noise Ceramic Stable Voltage Regulator for Low Voltage Applications Designed for Use with Very Low ESR Output Capacitors

Application Hints (Continued)
To assure proper operation, the signal source used to drive
the Shutdown input must be able to swing above and below
the specified turn-on/turn-off voltage thresholds listed in the
Electrical Characteristics section under V_ON/OFF.
REVERSE INPUT-OUTPUT VOLTAGE
The PNP power transistor used as the pass element in the
LP3878 has an inherent diode connected between the regu-
lator output and input.
During normal operation (where the input voltage is higher
than the output) this diode is reverse-biased.
However, if the output is pulled above the input, this diode
will turn ON and current will flow into the regulator output.
In such cases, a parasitic SCR can latch which will allow a
high current to flow into V_IN (and out the ground pin), which
can damage the part.
In any application where the output may be pulled above the
input, an external Schottky diode must be connected from
V_IN to V_OUT (cathode on V_IN, anode on V_OUT), to limit the
reverse voltage across the LP3878 to 0.3V (see Absolute
Maximum Ratings).
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