CS8151

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8

APPLICATION NOTES

Operation Without Watchdog

The CS8151 can be operated without the watchdog

functionality by connecting the WDI and Wake Up Pins.

This will eliminate false resets from occurring. Without the

connection, a reset would occur because a watchdog signal

on WDI would not occur in the required time frame. The

Wake Up Pin provides the watchdog signal into the

WDI Pin.

Figure 7. Device Operation Without Watchdog Function

WDI

RESET

GND

CS8151

Microprocessor

Wake Up

C1

C2

RESET

Battery

Output Stage Protection

The output stage is protected against overvoltage, short

circuit and thermal runaway conditions (see Figure 8).

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.

Figure 8. Typical Circuit Waveforms for Output

Stage Protection

> 50 V

Load

Dump

Short

Circuit

Thermal

Shutdown

Stability Considerations

The output or compensation capacitor C2 (see Figure 9)

helps determine three main characteristics of a linear

regulator: startup delay, load transient response and loop

stability.

Figure 9. Test and Application Circuit Showing

Output Compensation

CS8151

C1*

0.1 mF

RESET

C2**

10 mF

*C1 required if regulator is located far from the power

supply filter.

**C2 required for 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