TD340

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Watchdog circuit

An integrated Watchdog circuit resets the microcontroller when a periodic signal

coming from the

microcontroller is missing after an externally adjustable Time out delay.

Watchdog timeout is adjustable by means of a capacitor Cwd between CWD pin and GND. This capacitor

should be placed as close as possible to the CWD pin.

Watchdog function can be inhibited by tying the CWD pin to ground.

Timeout range is from about 1ms to 1s, approximate value is given by:

Twd = 1 + (20 x Cwd)

(Twd in ms, and Cwd in nF).

When the watchdog timeout triggers, the reset output is pulsed once low for 20 microseconds, and the

driver outputs are set to ground (MOS switched off). TD340 stays in disable state (MOS off) until pulses

appear again on WD pin.

Figure 7 : Watchdog waveforms

Temperature output

The TD340 provides a temperature indicator with the TEMP output.

TEMP voltage is 2.68V at 25

°C with a temperature coefficient of -7.5mV/°C.

The goal of this function is to provide a rough temperature indication to the uP. It allows the system

designer to adapt the behavior of the application to the ambient temperature.

The TEMP output must be connected to a high impedance input. Maximum available current is 1uA.

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