SPX1121 datasheet(6/9 Pages) SIPEX

6 / 9 page

Date: 12/20/05

SPX1121 150mA Low DropoutVoltage Regulator

EXTERNAL CAPACITORS

The stability of the SPX1121 requires a 1

µF or

greater capacitor between output and ground.

Oscillation could occur without this capacitor.

Most types of tantalum or aluminum electro-

lytic works fine here. For operations below -

°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 capacitor. The capacitors value may be in-

creased without limit.

The SPX1121 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 tantalum

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 220 µF decreases the noise from

430

µV to 160µVRMS for a 100kHz bandwidth

at 5V output.

APPLICATIONS HINTS

SPX1121 Datasheet(PDF) 6 Page - Sipex Corporation