LP2981IM5-3.3 Datasheet, PDF (13/24 Pages) Texas Instruments – LP2981-N Micropower 100 mA Ultra Low-Dropout Regulator in SOT-23 Package

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LP2981-N
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).
LP2981-N
V_IN
PNP
V_OUT
GND
Figure 38. LP2981-N Reverse Current Path
However, if the input voltage is more than a V_BE 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 V_IN 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 V_BE
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 V_IN to V_OUT (cathode on V_IN, anode on V_OUT. See Figure 39), to limit the reverse voltage
across the LP2981-N to 0.3V (see Absolute Maximum Ratings)
SCHOTTKY DIODE
LP2981-N
V_IN
PNP
V_OUT
GND
Figure 39. Adding External Schottky Diode Protection
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