CS8221YDP3 Ver la hoja de datos (PDF) - ON Semiconductor
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CS8221YDP3 Datasheet PDF : 7 Pages
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CS8221
CIRCUIT DESCRIPTION
VOLTAGE REFERENCE AND OUTPUT CIRCUITRY
Output Stage Protection
The output stage is protected against overvoltage, short
circuit and thermal runaway conditions (Figure 3).
> 30 V
VIN
VOUT
Should the junction temperature of the power device
exceed 180°C (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.
C1*
0.1 mF
VIN
VOUT
CS8221
C2**
10 mF
GND
IOUT
Load
Dump
Short
Circuit
Thermal
Shutdown
Figure 3. Typical Circuit Waveforms for Output
Stage Protection
*C1 is required if regulator is far from the power source filter.
**C2 is required for stability.
Figure 4. Application and Test Diagram
If the input voltage rises above 30 V, the output shuts
down. This response protects the internal circuitry and
enables the IC to survive unexpected voltage transients.
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
instability. The aluminum electrolytic capacitor is the least
expensive 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 capacitor COUT shown in Figure
4 should work for most applications, however it is not
necessarily the optimized solution.
To determine an acceptable value for COUT for a particular
application, start with a tantalum capacitor of the
recommended value and work towards a less expensive
alternative part.
Step 1: Place the completed circuit with a tantalum
capacitor 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 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 oscillations
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
conditions.
Step 5: If the capacitor is adequate, repeat steps 3 and 4
with the next smaller valued capacitor. A smaller capacitor
will usually cost less and occupy less board space. If the
output oscillates within the range of expected operating
conditions, repeat steps 3 and 4 with the next larger standard
capacitor value.
Step 6: Test the load transient response by switching in
various loads at several frequencies to simulate its real
working environment. Vary the ESR to reduce ringing.
Step 7: Increase the temperature to your highest operating
temperature. Vary the load current as instructed in step 5 to
test for any oscillations.
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