CS8481
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4
DEFINITION OF TERMS
Current Limit − Peak current that can be delivered to the
output.
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 100 mV from the nominal value
obtained at 14 V input, dropout voltage is dependent upon
load current and junction temperature.
Input Output Differential − The voltage difference
between the unregulated input voltage and the regulated
output voltage for which the regulator will operate.
Input Voltage − The DC voltage applied to the input
terminals with respect to ground.
Line Regulation − The change in output voltage for a
change in the input voltage. The measurement is made under
conditions of low dissipation 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 conditions after 1000 hours with
maximum rated voltage and junction temperature.
Quiescent Current − The part of the positive input
current that does not contribute 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.
Short Circuit Current Limit − Peak current that can be
delivered by the outPut when forced to 0 V.
Temperature Stability of V
OUT
− The percentage
change in output voltage for a thermal variation from room
temperature to either temperature extreme.
14 V
0 V
5.0 V
2.0 V
0.8 V
V
IN
ENABLE
V
OUT1
V
OUT2
System
Condition
Load
Dump
Low V
IN
Line
Noise, Etc.
V
OUT1
Short
Circuit
Thermal
Shutdown
Turn
Off
Turn
On
V
OUT2
Short
Circuit
3.3 V 3.3 V 3.3 V 3.3 V 3.3 V 3.3 V
5.0 V 5.0 V 5.0 V 5.0 V 5.0 V 5.0 V
2.4 V
2.4 V
0 V 0 V 0 V
0 V
3.0 V
74 V
34 V
30 V
14 V
Figure 2. Typical Circuit Waveform
APPLICATION NOTES
General
The CS8481 is a Micropower dual regulator. All bias
required to operate the internal circuitry is derived from the
standby output, V
OUT2
. If this output experiences an over
current situation and collapses, then V
OUT1
will also
collapse (see Figure 2).
If there is critical circuitry that must remain active under
most conditions it should be connected to V
OUT2
. Any
circuitry that is likely to be subjected to a short circuit, e.g.,
circuitry outside the module, should be connected to V
OUT1
.
External Capacitors
Output capacitors are required for stability with the
CS8481. Without them, the regulator outputs will oscillate.
Actual size and type may vary depending upon the
application load and temperature range. Capacitor effective
series resistance (ESR) is also a factor in the IC stability.
Worst−case is determined at the minimum ambient
temperature and maximum load expected.
Output capacitors can be increased in size to any desired
value above the minimum. One possible purpose of this
would be to maintain the output voltages during brief
conditions of negative input transients that might be
characteristic of a particular system.
Capacitors must also be rated at all ambient temperatures
expected in the system. To maintain regulator stability down
to −40°C, capacitors rated at that temperature must be used.
More information on capacitor selection for SMART
REGULATORs is available in the SMART REGULATOR
application note, “Compensation for Linear Regulators,”
document number SR003AN/D, available through the
Literature Distribution Center or via our website at
http://www.onsemi.com.
