CS5203−3

http://onsemi.com

4

Time (ms)

Figure 7. Transient Response

0

+200

0

−200

3

2

1

510

0

Figure 8. Short Circuit Current vs.

1.0

6

5

4

3

2

1

0

1.5

2.0

2.5

3.0

3.5

APPLICATIONS INFORMATION

The CS5203−3 linear regulator provides a fixed 3.3 V

output voltage at currents up to 3.0 A. The regulator is

protected against overcurrent conditions and includes

thermal shutdown.

The CS5203−3 has a composite PNP−NPN output

transistor and requires an output capacitor for stability.

Stability Considerations

The output or compensation capacitor helps determine

three main characteristics of a linear regulator: start−up

delay, load transient response, and loop stability.

The capacitor value and type is based on cost, availability,

size and temperature constraints. A tantalum or aluminum

electrolytic capacitor is best, since a film or ceramic

capacitor with almost zero ESR can cause instability. The

aluminum electrolytic capacitor is the least expensive

solution. However, when the circuit operates at low

temperatures, both the value and ESR of the capacitor will

vary considerably. The capacitor manufacturer’s data sheet

provides this information.

A 22

mF tantalum capacitor will work for most

applications, but with high current regulators such as the

CS5203−3 the transient response and stability improve with

higher values of capacitance. The majority of applications

for this regulator involve large changes in load current so the

output capacitor must supply the instantaneous load current.

The ESR of the output capacitor causes an immediate drop

in output voltage given by:

DV + DI

ESR

For microprocessor applications it is customary to use an

output capacitor network consisting of several tantalum and

ceramic capacitors in parallel. This reduces the overall ESR

and reduces the instantaneous output voltage drop under

transient load conditions. The output capacitor network

should be as close to the load as possible for the best results.

Protection Diodes

When large external capacitors are used with a linear

regulator it is sometimes necessary to add protection diodes.

If the input voltage of the regulator gets shorted, the output

capacitor will discharge into the output of the regulator. The

discharge current depends on the value of the capacitor, the

CS5203−3 linear regulator, the discharge path is through a

large junction and protection diodes are not usually needed.

If the regulator is used with large values of output

capacitance and the input voltage is instantaneously shorted

to ground, damage can occur. In this case, a diode connected

as shown in Figure 9 is recommended.

Figure 9. Protection Diode Scheme for Large

Output Capacitors

CS5203−3

GND

IN4002 (Optional)