LP3879

SNVS396B – MAY 2006 – REVISED APRIL 2013

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For these reasons, X7R and X5R type ceramic capacitors must be used on the input and output of the

LP3879.

SHUTDOWN INPUT OPERATION

The LP3879 is shut off by pulling the Shutdown input low, and turned on by pulling it high. If this feature is not to

be used, the Shutdown input should be tied to VIN to keep the regulator output on at all times.

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

VON/OFF.

REVERSE INPUT-OUTPUT VOLTAGE

The PNP power transistor used as the pass element in the LP3879 has an inherent diode connected between

the regulator 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 VIN (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 VIN to VOUT (cathode on VIN, anode on VOUT), to limit the reverse voltage across the LP3879 to

0.3V (see Absolute Maximum Ratings).

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