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CS8156YT5

12V, 5V Low Dropout Dual Regulator with ENABLE

Cherry semiconductor 

Definition of Terms

Dropout Voltage

The input-output voltage differential at which the circuit

ceases to regulate against further reduction in input voltage.

Measured when the output voltage has dropped 100mV

from the nominal value obtained at 14V input, dropout volt-

age is dependent upon load current and junction temperature.

Input Voltage

The DC voltage applied to the input terminals with respect

to ground.

Input Output Differential

The voltage difference between the unregulated input volt-

age and the regulated output voltage for which the regulator

will operate.

Line Regulation

The change in output voltage for a change in the input volt-

age. The measurement is made under conditions of low dis-

sipation or by using pulse techniques such that the average

chip temperature is not significantly affected.

Load Regulation

The change in output voltage for a change in load current at

constant chip temperature.

Long Term Stability

Output voltage stability under accelerated life-test condi-

tions after 1000 hours with maximum rated voltage and

junction temperature.

Output Noise Voltages

The rms AC voltage at the output, with constant load and no

input ripple, measured over a specified frequency range.

Quiescent Current

The part of the positive input current that does not con-

tribute to the positive load current. i.e., the regulator ground

lead current.

Ripple Rejection

The ratio of the peak-to-peak input ripple voltage to the

peak-to-peak output ripple voltage.

Temperature Stability of VOUT

The percentage change in output voltage for a thermal varia-

tion from room temperature to either temperature extreme.

Typical Circuit Waveform

VIN 14V

60V

31V

26V

3V

14V

ENABLE 2.0V

0.8V

VOUT1 0V

12V

5V

VOUT2 0V

System

Condition

Turn

On

Load

Dump

12V

12V

2.4V

2.4V

12V

0V

12V

0V

5V

Low VIN

Line Noise, Etc.

VOUT1

Short

Circuit

VOUT2

Short

Circuit

VOUT1

Thermal

Shutdown

Turn

Off

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 cheapest

solution, but, if the circuit operates at low temperatures

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

will vary considerably. The capacitor manufacturers data

sheet usually provides this information.

The value for the output capacitors C2 and C3 shown in

the test and applications circuit should work for most appli-

cations, however it is not necessarily the best solution.

To determine acceptable values for C2 and C3 for a par-

ticular application, start with a tantalum capacitor of the

recommended value and work towards a less expensive

alternative part for each output.

Step 1: Place the completed circuit with the tantalum

capacitors of the recommended value in an environmental

chamber at the lowest specified operating temperature

and monitor the outputs with an oscilloscope. A decade

box connected in series with capacitor C2will 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 any oscillations on

the output. If no oscillations are observed, the capacitor is

large enough to ensure a stable design under steady state

conditions.

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