CS8151YTHA7G View Datasheet(PDF) - ON Semiconductor

Part Name

Description

Manufacturer

CS8151YTHA7G

5.0 V, 100 mA Low Dropout Linear Regulator with Watchdog, RESET, and Wake Up

ON Semiconductor 

CS8151

APPLICATION NOTES

Output Stage Protection

The output stage is protected against overvoltage, short

circuit and thermal runaway conditions (see Figure 7).

If the input voltage rises above the overvoltage shutdown

threshold (e.g. load dump), the output shuts down. This

response protects the internal circuitry and enables the IC to

survive unexpected voltage transients.

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.

> 50 V

VIN

VOUT

IOUT

Load

Dump

Short

Circuit

Thermal

Shutdown

Figure 7. Typical Circuit Waveforms for Output

Stage Protection

Stability Considerations

The output or compensation capacitor C2 (see Figure 8)

helps determine three main characteristics of a linear

regulator: startup delay, load transient response and loop

stability.

VIN

C1*

0.1 mF

VOUT

CS8151

RESET

RRST

C2**

10 mF

*C1 required if regulator is located far from the power

supply filter.

**C2 required for stability.

Figure 8. Test and Application Circuit Showing

Output Compensation

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 provide this information.

The value for the output capacitor C2 shown in the test and

applications circuit should work for most applications,

however it is not necessarily the optimized solution.

To determine an acceptable value for C2 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: Raise the temperature to the highest specified

operating temperature. Vary the load current as instructed in

step 5 to test for any oscillations.

Once the minimum capacitor value with the maximum

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

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