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Date: 5/25/04

SPX3940 1A Low Dropout Voltage Regulator

© Copyright 2004 Sipex Corporation

APPLICATION INFORMATION

The SPX3940 incorporates protection against

over-current faults, reversed load insertion, over

temperature operation, and positive and nega-

tive transient voltage.

Thermal Considerations

Although the SPX3940 offers limiting circuitry

for overload conditions, it is still necessary to

insure that the maximum junction temperature

is not exceeded in the application. Heat will

flow through the lowest resistance path, the

junction-to-case path. In order to insure the best

thermal flow of the component, proper mount-

ing is required. Consult heatsink manufacturer

for thermal resistance and design of heatsink.

For example, TO-220 design:

Assume that V

T

θ

Where TA = ambient temperature

θ

θ

θ

The power calculated under these conditions is:

P

And the junction temperature is calculated as

T

T

Reliable operation is insured.

Capacitor Requirements

The output capacitor is needed to insure stability and minimize the output noise. The value of the

capacitor varies with the load. However, a minimum value of 10

µF aluminum capacitor will guarantee

stability over all load conditions. A tantalum capacitor is recommended if a faster load transient

response is needed.

If the power source has a high AC impedance, a 0.1

µF ceramic capacitor between input & ground is

recommended.

Minimum Load Current

To ensure a proper behavior of the regulator under light load, a minimum load of 5mA for SPX3940

is required.

SPX3940

V

OUT

V

IN

+

6.8µF

+

10µF

1

2

3

Figure 18. Fixed Output Linear Regulator.