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SPX3819

500mA, Low-Noise LDO Voltage Regulator

Signal Processing Technologies 

APPLICATION INFORMATION

The SPX3819 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 SPX3819 is sourcing

less current, a lower output capacitance may be

sufficient. For example, a regulator outputting

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 2.2µF alumi-

num electrolytic capacitor works in most appli-

cation circuits, but the same stability often can

be obtained with a 1µF tantalum electrolytic.

With the SPX3819 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 the BYP pin will signifi-

cantly reduce output noise, but it may be left

unconnected if the output noise is not a major

concern. The SPX3819 start-up speed is in-

versely proportional to the size of the BYP

capacitor. Applications requiring a slow ramp-

up of the output voltage should use a larger

CBYP. However, if a rapid turn-on is necessary,

the BYP capacitor can be omitted.

The SPX3819’s internal reference is available

through the BYP pin.

Figure 1 represents a SPX3819 standard appli-

cation circuit. The EN (enable) pin is pulled

high (>2.0V) to enable the regulator.

To disable the regulator, EN < 0.4V.

The SPX3819 in Figure 2 illustrates a typical

adjustable output voltage configuration. Two

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

output voltage is calculated using the formula:

VOUT = 1.235V x [ 1 + R1/R2]

R2 must be > 10 kΩ and for best results, R2

should be between 22 kΩ and 47kΩ.

VIN

1

5

VOUT

+

2

+ GND

SPX3819

3

EN

4 BYP

(Opt.)

ENABLE may be tied directly to VIN

TOP View

Figure 1. Standard Application Circuit

VIN

1

5

+ GND

EN

Hi-ON

Lo-OFF

2

SPX3819

SOT-23

3

4

TOP View

+

R1

VOUT

R2

Figure 2. Typical Adjustable Output Voltage Configuration

Jun 5-07 Rev E

SPX3819 500mA, Low Noise LDO Voltage Regulator

7

© 2007 Sipex Corporation

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