3

Date: 5/25/04

SPX1521 300mA Low Dropout Voltage Regulator

©Copyright 2004 Sipex Corporation

External Capacitors

The stability of the SPX1521 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 SPX1521, 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 220µF only decreases the noise

from 430

µV to 160µVrms for a 100kHz band-

width at 5V output.

APPLICATION INFORMATION

Top View

SPX1521

13

2

SOT-223 (M3)

Top View

TO-263-3 (T)

1

SPX1521

2

3

Front View

TO-220-3 (U)

SPX1521

12

3

Front View

TO-252 (R)

3

2

1

V

IN

GND V

OUT

V

V

IN

V

V

IN

V

OUT

GND

V

IN

PINOUTS