SPX1129 datasheet(3/5 Pages) SIPEX

3 / 5 page

Date: 5/25/04

SPX1129 400mA Low Dropout Voltage Regulator

External Capacitors

The stability of the SPX1129 requires a 2.2

µF or

greater capacitor between output and ground.

Oscillation could occur without this capacitor.

Most types of tantalum or aluminum electrolytic

works fine here. For operations of below -25

°C

solid tantalum is recommended since the many

aluminum types have electrolytes that freeze at

about -30

°C. The ESR of about 5Ω or less and

resonant frequency above 500kHz are the most

important parameters in the value of the capaci-

tor. The capacitor value can be increased with-

out limit.

The SPX1129, unlike other low dropout regula-

tors will remain stable and in regulation with no

load in addition to the internal voltage divider.

This feature is especially important in applica-

tions like CMOS RAM keep-alive.

If there is more than 10 inches of wire between

the input and the AC filter capacitor, or if a

battery is used as the input, then a 0.1

µF tanta-

lum or aluminum electrolytic capacitor should

be placed from the input to the ground.

Reducing Output Noise

It may be an advantage to reduce the AC noise

present at the output. One way is to reduce the

regulator bandwidth by increasing the size of

the output capacitor. Increasing the capacitor

from 1

µF to 220µF decreases the noise from

430

µV to 160µV rms for a 100kHz bandwidth

at 5V output.

APPLICATION INFORMATION

SPX1129 Datasheet(PDF) 3 Page - Sipex Corporation