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SPX1580

7A Ultra Dropout Voltage Regulator Fast Response, Adjustable & Fixed

Signal Processing Technologies 

Output Capacitor

An output capacitor for SPX1580 is for circuit

compensation for the device to prevent

oscilliation. The minimum size of the output

capacitor is either a 330µF aluminum electro-

lytic capacitor or 33uF tantalum. Larger capaci-

tor values improve the regulator transient re-

sponse performance and increase surge load

capability. The output capacitor should have an

ESR not more than 0.3Ω.

Adjustable Regulator Design

1.25V reference voltage is being developed be-

tween the SENSE pin and the ADJ pin of the

SPX1580. Adding two external resistors (see fig

1.) will allow setting the output voltage from

1.25V to 6V. R1 is chosen so that this current is

specified minimum load current of 10mA. R2 is

given by the formula: VOUT = VREF (1+ R2/R1)

+ IADJ (R2). The current flowing from the ADJ

pin is typicaly 50uA. This ADJ pin contributes

to the final VOUT but is usually neglected.

Connecting the sense pin to the top of the resis-

tor divider will improve load regualtion.

APPLICATION INFORMATION

Lowering Noise

Using the SENSE pin to Kelvin the load will

increase accuracy of the output voltage during

load regulation. For the fixed voltage device,

adding a bypass capacitor from ADJ pin to

ground improves transient response. A 330pF

ceramic capacitor is recommended.

3.3V

VIN

5V

VCTRL

VIN

5

3

C1

SPX1580

33µF

4

1

VCTRL

2

ADJ

C2

10µF

VOUT

SENSE

C4

0.033µF

R1

124Ω

R2

124Ω

2.5V

VOUT

C3

68µF

(1) VCTRL needed when VIN < 5V.

(2) VOUT = VREF (1+R2/R1)+IADJ R2.

(3) VREF is measured across adjust to sense.

Figure 1. Adjustable Regulator.

Date: 5/14/04

SPX1580 7A Ultra Dropout Voltage Regulator

4

©Copyright 2004 Sipex Corporation

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