Datasheet

V
IN
V
OUT
PNP
GND
LP2982
LP2982
SNVS128J –MARCH 2000–REVISED APRIL 2013 www.ti.com
Figure 37. 5V/2.2 μF ESR Curves Figure 38. 3V/4.7 μF ESR Curves
BYPASS CAPACITOR
The 0.01 μF capacitor connected to the bypass pin to reduce noise must have very low leakage.
The current flowing out of the bypass pin comes from the bandgap reference, which is used to set the output
voltage.
This capacitor leakage current causes the output voltage to decline by an amount proportional to the current.
Typical values are −0.015%/nA @ −40°C, −0.021%/nA @ 25°C, and −0.035%/nA @ +125°C.
This data is valid up to a maximum leakage current of about 500 nA, beyond which the bandgap is so severely
loaded that it can not function.
Care must be taken to ensure that the capacitor selected will not have excessive leakage current over the
operating temperature range of the application.
A high quality ceramic capacitor which uses either NPO or COG type dielectric material will typically have very
low leakage. Small surface mount polypropylene or polycarbonate film capacitors also have extremely low
leakage, but are slightly larger than ceramics.
REVERSE CURRENT PATH
The internal PNP power transistor used as the pass element in the LP2982 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 39).
Figure 39. LP2982 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 40), to limit the reverse voltage
across the LP2982 to 0.3V (see Absolute Maximum Ratings).
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