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CS8164

8V/5V Low Dropout Dual Regulator with ENABLE

Cherry semiconductor 

Circuit Description: continued

to bias VOUT2 up to this point. Approximately 60µA will

suffice, resulting in a 10k½ external resistor for most appli-

cations.

VIN

High Current Output

Unlike the standby regulated output, which must remain

on whenever possible, the high current regulated output is

fault protected against overvoltage and also incorporates

thermal shutdown. If the input voltage rises above

approximately 30V (e.g., load dump), this output will

automatically shutdown. This protects the internal circuit-

ry and enables the IC to survive higher voltage transients

than would otherwise be expected. Thermal shutdown is

effective against die overheating since the high current out-

put is the dominant source of power dissipation in the IC.

VOUT2

RD

10kW

VOUT2

+

C3

ENABLE

Disabling VOUT2 when it is not needed. C3 is no longer needed.

The enable function controls VOUT1 When ENABLE is high

(5V), VOUT1 is on. When ENABLE is low, VOUT1 is off.

Test & Application Circuit

C1*

0.1 mF

VIN

VOUT1

CS8164

ENABLE

+

C2**

10mF

NOTES:

* C1 required if regulator is located far from power

supply filter.

** C2, C3 required for stability.

Gnd

VOUT2

+

C3**

10mF

Application Notes

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 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.

The value for each output capacitor shown in the test and

applications circuit should work for most applications,

however it is not necessarily the optimized solution.

To determine acceptable values for C2 and C3 a particular

application, start with a tantalum capacitor of the recom-

mended value and work towards a less expensive alterna-

tive part for each output.

Step 1: Place the completed circuit with the tantalum

capacitors of the recommended values in an environmen-

tal chamber at the lowest specified operating temperature

and monitor the outputs with an oscilloscope. A decade

box connected in series with the capacitor C2 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 on

the output under observation. look for oscillations on the

output. If no oscillations are observed, the capacitor is

large enough to ensure a stable design under steady state

conditions.

6

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