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SPX1582

3A Ultra Low Dropout Voltage Regulator (Fast Response, Adjustable & Fixed)

Signal Processing Technologies 

APPLICATION INFORMATION

The SPX1582 is designed as a high performance

and low cost solution for applications requiring

a lower dropout than traditional NPN regulators.

The SPX1582 uses a separate input voltage VCTRL

( VCTRL ≥ VOUT + 1.3V) to minimize the dropout

voltage. This allows the 2.5V power for the load

to come from a 3.3V system supply. As an added

benefit this will reduce the heat dissipation*, and

lower heatsink and cooling fan costs.

The SPX1582 can power the 2.5V core voltage

for microprocessors such as a PentiumPCTM,

P55CTM, AMD5k86TM and K6TM and the IBM

PowerPCTM 603EV and 604EV processors.

A typical application would use 3.3V for VIN and

5.0V for VCTRL from a motherboard power sup-

ply to provide a nominal 2.5V output. Using the

sense pin provides a Kelvin measurement of

output for reducing resistance-associated errors.

Power Up Sequencing

The SPX1582 requires a power up sequence in

that VIN must be applied before VCTRL to prevent

a latchup condition. If this is not possible, then a

10Ω series resistor should be added to the VCTRL

input to prevent the device from entering into

latchup if VCTRL is applied before VIN.

Adjustable Regulator Design

1.25V reference voltage is being developed be-

tween the SENSE pin and the ADJ pin of the

SPX1582. 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 at a 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

50μA. This ADJ pin contributes to the final

VOUT but is usually neglected. Connecting the

sense pin to the top of the resistor divider will

improve load regulation.

Lowering Noise

For the fixed voltage device, adding a capacitor

at the GND pin will improve transient response.

This capacitor is chosen in the range of 1μF to

0.1μF and will depend on the amount of output

capacitance in the system.

Jun 17-06 Rev F

SPX1582 3A Ultra Low Dropout Voltage Regulator

4

© 2006 Sipex Corporation

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