LP2980-N_16 Datasheet, PDF (16/30 Pages) Texas Instruments – Micropower 50-mA Ultra Low-Dropout Regulator in SOT-23 Package

LP2980-N
SNOS733O – APRIL 2000 – REVISED JUNE 2015
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8.2.2.2 Reverse Current Path
The internal PNP power transistor used as the pass element in the LP2980-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 34).
V_IN
V_OUT
PNP
GND
Figure 34. LP2980-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 35), to limit the reverse voltage
across the LP2980-N to 0.3 V (see Absolute Maximum Ratings).
SCHOTTKY DIODE
V_IN
V_OUT
PNP
GND
Figure 35. Adding External Schottky Diode Protection
8.2.2.3 ON/OFF Input Operation
The LP2980-N is shut off by pulling the ON/OFF input low, and turned on by driving the input high. If this feature
is not to be used, the ON/OFF input should be tied to IN to keep the regulator on at all times (the ON/OFF input
must not be left floating).
To ensure proper operation, the signal source used to drive the ON/OFF input must be able to swing above and
below the specified turn-on and turn-off voltage thresholds which ensure an ON or OFF state (see Electrical
Characteristics).
The ON/OFF signal may come from either a totem-pole output, or an open-collector output with a pull-up resistor
to the LP2980-N input voltage or another logic supply. The high-level voltage may exceed the LP2980-N input
voltage, but must remain within the absolute maximum ratings for the ON/OFF pin.
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