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 should be 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 instabil-

ity. The aluminum electrolytic capacitor is the least expen-

sive solution, but, if the circuit operates at low tempera-

tures (-25¡C to -40¡C), both the value and ESR of the

capacitor will vary considerably. The capacitor manufac-

turers data sheet usually provides this information.

and applications circuit should work for most applica-

tions, however it is not necessarily the optimized solution.

application, start with a tantalum capacitor of the recom-

mended value and work towards a less expensive alterna-

tive part.

Step 1:

Place the completed circuit with a tantalum capac-

itor of the recommended value in an environmental cham-

ber at the lowest specified operating temperature and

monitor the outputs with an oscilloscope. A decade box

connected in series with the capacitor will simulate the

higher ESR of an aluminum capacitor. Leave the decade

box outside the chamber, the small resistance added by

the longer leads is negligible.

Step 2:

With the input voltage at its maximum value,

increase the load current slowly from zero to full load

while observing the output for any oscillations. If no oscil-

lations are observed, the capacitor is large enough to

ensure a stable design under steady state conditions.

Step 3:

Increase the ESR of the capacitor from zero using

the decade box and vary the load current until oscillations

appear. Record the values of load current and ESR that

cause the greatest oscillation. This represents the worst

case load conditions for the regulator at low temperature.

Step 4

: Maintain the worst case load conditions set in step

3 and vary the input voltage until the oscillations increase.

This point represents the worst case input voltage condi-

tions.

Step 5:

If the capacitor is adequate, repeat steps 3 and 4

with the next smaller valued capacitor. A smaller capaci-

0.1

mF

Sense*

CS8221

10

mF

Gnd

Output Stage Protection

The output stage is protected against overvoltage, short

circuit and thermal runaway conditions (Figure 1).

If the input voltage rises above 34V (typ), the output shuts

down. This response protects the internal circuitry and

enables the IC to survive unexpected voltage transients.

Should the junction temperature of the power device

exceed 180ûC (typ) the power transistor is turned off.

Thermal shutdown is an effective means to prevent die

overheating since the power transistor is the principle heat

source in the IC.

Load

Dump

Short

Circuit

Thermal

Shutdown

> 30V

3

Application Notes

Application & Test Diagram

Voltage Reference and Output Circuitry

Stability Considerations

Circuit Description

Figure 1. Typical Circuit Waveforms for Output Stage Protection.

* 8 Lead SO Narrow only

**C1 is required if regulator is distant from power source filter.

***C2 is required for stability.