cs8151 ON Semiconductor, cs8151 Datasheet - Page 8

• Manufacturer Part Number: cs8151
• Description: 5v, 100ma Low Dropout Linear Regulator With Watchdog, Resetbar, & Wake Up
• Manufacturer: ON Semiconductor

Output Stage Protection
circuit and thermal runaway conditions (see Figure 7).
threshold (e.g. load dump), the output shuts down. This
response protects the internal circuitry and enables the IC to
survive unexpected voltage transients.
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.
Stability Considerations
helps determine three main characteristics of a linear
regulator: startup delay, load transient response and loop
stability.
availability, size and temperature constraints. A tantalum or
aluminum electrolytic capacitor is best, since a film or
V
I
V
OUT
OUT
The output stage is protected against overvoltage, short
If the input voltage rises above the overvoltage shutdown
Should the junction temperature of the power device
V
The output or compensation capacitor C2 (see Figure 8)
The capacitor value and type should be based on cost,
IN
IN
Figure 7. Typical Circuit Waveforms for Output
Figure 8. Test and Application Circuit Showing
**C2 required for stability.
0.1 mF
*C1 required if regulator is located far from the power
supply filter.
C1*
> 50 V
Dump
Load
Output Compensation
Stage Protection
Circuit
CS8151
Short
RESET
V
OUT
Shutdown
Thermal
R
RST
APPLICATION NOTES
C2**
10 mF
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CS8151
8
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 provide this information.
applications circuit should work for most applications,
however it is not necessarily the optimized solution.
application, start with a tantalum capacitor of the
recommended value and work towards a less expensive
alternative part.
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.
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.
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.
3 and vary the input voltage until the oscillations increase.
This point represents the worst case input voltage
conditions.
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.
various loads at several frequencies to simulate its real
working environment. Vary the ESR to reduce ringing.
operating temperature. Vary the load current as instructed in
step 5 to test for any oscillations.
ESR is found, a safety factor should be added to allow for the
tolerance of the capacitor and any variations in regulator
performance. Most good quality aluminum electrolytic
capacitors have a tolerance of ±20% so the minimum value
found should be increased by at least 50% to allow for this
tolerance plus the variation which will occur at low
The value for the output capacitor C2 shown in the test and
To determine an acceptable value for C2 for a particular
Step 1: Place the completed circuit with a tantalum
Step 2: With the input voltage at its maximum value,
Step 3: Increase the ESR of the capacitor from zero using
Step 4: Maintain the worst case load conditions set in step
Step 5: If the capacitor is adequate, repeat steps 3 and 4
Step 6: Test the load transient response by switching in
Step 7: Raise the temperature to the highest specified
Once the minimum capacitor value with the maximum