LP2981IM5-3.3 datasheet(13/24 Pages) TI

13 / 24 page

VIN

VOUT

PNP

GND

SCHOTTKY DIODE

LP2981-N

VIN

VOUT

PNP

GND

LP2981-N

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SNOS773K – MARCH 2000 – REVISED APRIL 2013

Figure 37. 3V/10

μF ESR Curves

REVERSE CURRENT PATH

The internal PNP power transistor used as the pass element in the LP2981-N 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 (See Figure 38).

Figure 38. LP2981-N Reverse Current Path

However, if the input voltage is more than a VBE below the output voltage, 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

the VIN pin and out the ground pin, which can damage the part.

The internal diode can also be turned on if the input voltage is abruptly stepped down to a voltage which is a VBE

below the output voltage.

In any application where the output voltage may be higher than the input voltage, an external Schottky diode

must be connected from VIN to VOUT (cathode on VIN, anode on VOUT. See Figure 39), to limit the reverse voltage

across the LP2981-N to 0.3V (see Absolute Maximum Ratings)

Figure 39. Adding External Schottky Diode Protection

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