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 LP2985 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

LP2985 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

reverse voltage across the LP2985 to 0.3V (see Absolute

Maximum Ratings).

MICRO SMD MOUNTING

The micro SMD package requires specific mounting tech-

niques which are detailed in National Semiconductor Appli-

cation Note # 1112. Referring to the section Surface Mount

Technology (SMT) Assembly Considerations, it should be

noted that the pad style which must be used with the 5-pin

package is the NSMD (non-solder mask defined) type.

For best results during assembly, alignment ordinals on the

PC board may be used to facilitate placement of the micro

SMD device.

MICRO SMD LIGHT SENSITIVITY

Exposing the micro SMD device to direct sunlight will cause

misoperation of the device. Light sources such as Halogen

lamps can also affect electrical performance if brought near

to the device.

The wavelenghts which have the most detrimental effect are

reds and infra-reds, which means that the fluorescent light-

ing used inside most buildings has very little effect on per-

formance. A micro SMD test board was brought to within 1

cm of a fluorescent desk lamp and the effect on the regu-

lated output voltage was negligible, showing a deviation of

less than 0.1% from nominal.

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