Data Sheet

31

Rev. 1.1, 2007-11-08

TLE7368

Detailed Internal Circuits Description

5.10

Watchdog Circuit

Figure 8

Window Watchdog State Diagram

Principle of Operation:

A Window Watchdog is integrated in the TLE7368 to monitor a microcontroller. The Window Watchdog duty cycle

consists of an "Open window" and a "Closed window". The microcontroller that is being monitored has to send a

periodic falling edge trigger signal to the watchdog input pin WDI within the "Open Window". If a trigger signal is

not sent or if it is sent during the "Closed Window", then Watchdog Output (WDO) switches from high to low

signaling a potential microcontroller fault has occurred. The watchdog cycle time

T

T

Initialization:

The Watchdog is switched off per default and activated by pulling WDI to low at least for the time

t

has turned to high. Watchdog input pin WDI has an integrated pull-up resistor

R

transitions to high before

t

the watchdog input WDI should transition to high within the "Ignore Window". The WDI signal may also transition

to high during the following "Open Window", but sufficient time must be left for a falling edge transition before the

end of the "Open Window". The watchdog function is turned off following a RO_2 reset, and must be reinitialized

to be turned back on.

Normal Operation:

Please refer to Figure 8.

The Watchdog starts operating in the "Ignore Window" state for a duration of

t

the microcontroller is given time to initialize. Any signal to watchdog input WDI within the "Ignore Window" is

ignored. After time

t

a maximum duration of

t

AEA03533.VSD

No Trigger

Closed

Window

Open

Window

Trigger

WDO = LOW

Ignore

Window

Always

Always

No Trigger During

Open Window

Trigger During

Closed Window