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 LP2978 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 V

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 V

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 V

cal Characteristics).

REVERSE INPUT-OUTPUT VOLTAGE

The PNP power transistor used as the pass element in the

LP2978 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 V

damage the part.

In any application where the output may be pulled above the

input, an external Schottky diode must be connected from

V

verse voltage across the LP2978 to 0.3V (see Absolute

Maximum Ratings).

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