The types of capacitors best suited for the noise bypass

capacitor are ceramic and film. High quality ceramic capaci-

tors with NPO or COG dielectric typically have very low

leakage. Polypropolene and polycarbonate film capacitors

are available in small surface-mount packages and typically

have extremely low leakage current.

Unlike many other LDO’s, the addition of a noise reduction

capacitor does not effect the transient response of the de-

vice.

ENABLE OPERATION

The LP3995 may be switched ON or OFF by a logic input at

the ENABLE pin, V

device on. When the enable pin is low, the regulator output is

off and the device typically consumes 3 nA. If the application

does not require the shutdown feature, the V

be tied to V

To ensure proper operation, the signal source used to drive

the V

specified turn-on/off voltage thresholds listed in the Electrical

Characteristics section under V

FAST TURN OFF AND ON

The controlled switch-off feature of the device provides a fast

turn off by discharging the output capacitor via an internal

FET device. This discharge is current limited by the RDSon

of this switch. Fast turn-on is guaranteed by control circuitry

within the reference block allowing a very fast ramp of the

output voltage to reach the target voltage.

micro SMD MOUNTING

The micro SMD package requires specific mounting tech-

niques which are detailed in National Semiconductor Appli-

cation Note AN-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 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

incorrect operation of the device. Light sources such as

halogen lamps can affect electrical performance if they are

situated in proximity to the device.

Light with wavelengths in the red and infra-red part of the

spectrum have the most detrimental effect thus the fluores-

cent lighting used inside most buildings has very little effect

on performance. Tests carried out on a micro SMD test

board showed a negligible effect on the regulated output

voltage when brought within 1 cm of a fluorescent lamp. A

deviation of less than 0.1% from nominal output voltage was

observed.

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