CS8156 Cherry Semiconductor Corporation, CS8156 Datasheet - Page 6

• Manufacturer Part Number: CS8156
• Description: 12V/ 5V Low Dropout Dual Regulator with ENABLE
• Manufacturer: Cherry Semiconductor Corporation

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.
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.
Condition
ENABLE
System
V
V
OUT
OUT
V
IN
1
2
Stability Considerations
2.0V
0.8V
14V
0V
0V
Turn
On
12V
60V
Dump
Load
5V
31V
12V
Typical Circuit Waveform
Low V
Definition of Terms
Application Notes
IN
2.4V
2.4V
3V
6
Line Noise, Etc.
26V
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 C
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.
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 V
The percentage change in output voltage for a thermal varia-
tion from room temperature to either temperature extreme.
To determine acceptable values for C2 and C3 for a par-
12V
Circuit
V
Short
OUT 1
0V
Circuit
V
Short
OUT 2
OUT
12V
Shutdown
Thermal
V
OUT 1
5V
14V
2
12V
will simulate the
Turn
Off
0V