6

Date:12/

18/04

SPX5205 150mA, Low Noise LDO Voltage Regulator

© Copyright 2004 Sipex Corporation

+

+

GND

EN

BYP

(Optn)

Hi-ON

Lo-OFF

SPX5205

1

2

3

4

5

V

IN

V

OUT

R1

R2

ADJ

TOP View

Figure 1. Typical Adjustable Output Voltage.

APPLICATION INFORMATION

The SPX5205 requires an output capacitor for

device stability. Its value depends upon the

application circuit. In general, linear regulator

stability decreases with higher output currents.

In applications where the SPX5205 is putting

out less current, a lower output capacitance may

be sufficient. For example, a regulator sourcing

only 10mA, requires approximately half the

capacitance as the same regulator sourcing

150mA.

Bench testing is the best method for determining

the proper type and value of the capacitor since

the high frequency characteristics of electro-

lytic capacitors vary widely, depending on type

and manufacturer. A high quality 2.2

µF alumi-

num electrolytic capacitor works in most appli-

cation circuits, but the same stability often can

be obtained with a 1

µF tantalum electrolytic.

With the SPX5205 adjustable version, the mini-

mum value of output capacitance is a function of

the output voltage. The value decreases with

higher output voltages, since closed loop gain is

increased.

Typical Applications Circuits

A 10nF capacitor on BYP pin will significantly

reduce output noise but it may be left uncon-

nected if the output noise is not a major concern.

The SPX5205 start-up speed is inversely pro-

portional to the size of the BYP capacitor. Ap-

plications requiring a slow ramp-up of the out-

if a rapid turn-on is necessary, the BYP capaci-

tor can be omitted.

The SPX5205’s internal reference is available

through the BYP pin.

The Typical Application Circuit shown on page

1 represents a SPX5205 standard application

circuit. The EN (enable) pin is pulled high

(>2.0V) to enable the regulator. To disable the

regulator, EN < 0.4V.

The SPX5205 in Figure 1 illustrates a typical

adjustable output voltage configuration. Two

resistors (R1 and R2) set the output voltage. The

output voltage is calculated using the formula:

R2 must be > 10 k

Ω and for best results, R2

should be between 22 k

Ω and 47kΩ. A capacitor

placed between adjustable and ground will pro-

vide improved noise performance.