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LP2992 Datasheet, PDF (13/15 Pages) National Semiconductor (TI) – Micropower 250 mA Low-Noise Ultra Low-Dropout Regulator in SOT-23 and LLP Packages Designed for Use with Very Low ESR Output Capacitors
Application Hints (Continued)
It should also be noted that the ESR of a typical Tantalum will
increase about 2:1 as the temperature goes from 25˚C down
to −40˚C, so some guard band must be allowed.
ON/OFF INPUT OPERATION
The LP2992 is shut off by driving the ON/OFF input low, and
turned on by pulling it high. If this feature is not to be used,
the ON/OFF 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 ON/OFF 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. To prevent
mis-operation, the turn-on (and turn-off) voltage signals ap-
plied to the ON/OFF input must have a slew rate which is
≥ 40 mV/µs.
Caution: the regulator output voltage can not be guaranteed
if a slow-moving AC (or DC) signal is applied that is in the
range between the specified turn-on and turn-off voltages
listed under the electrical specification VON/OFF (see Electri-
cal Characteristics).
REVERSE INPUT-OUTPUT VOLTAGE
The PNP power transistor used as the pass element in the
LP2992 has an inherent diode connected between the regu-
lator 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 LP2992 to 0.3V (see Absolute
Maximum Ratings).
LLP Mounting
The LLP package requires specific mounting techniques
which are detailed in National Semiconductor Application
Note # 1187. Referring to the section PCB Design Recom-
mendations, it should be noted that the pad style which
should be used with the LLP package is the NSMD
(non-solder mask defined) type.
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