CS5205−2

http://onsemi.com

4

APPLICATIONS INFORMATION

The regulator is protected against short circuit, and

includes thermal shutdown and safe area protection (SOA)

circuitry. The SOA protection circuitry decreases the

maximum available output current as the input−output

differential voltage increase.

The CS5205−2 has a composite PNP−NPN output

transistor and requires an output capacitor for stability. A

detailed procedure for selecting this capacitor is included in

the Stability Considerations section.

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

CS5205−2 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

CS5205−2 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 7 is recommended.

Figure 7. Protection Diode Scheme for Fixed

Output Regulators

CS5205−2

GND

IN4002 (Optional)

Output Voltage Sensing

Since the CS5205−2 is a three terminal regulator, it is not

possible to provide true remote load sensing. Load

regulation is limited by the resistance of the conductors

connecting the regulator to the load. For best results the

regulator should be connected as shown in Figure 8.

Figure 8. Conductor Parasitic Resistance Effects

Can Be Minimized With the Above Grounding

Scheme for Fixed Output Regulators

CS5205−2

Conductor Parasitic

Resistance