Datasheet

TLE7368
Detailed Internal Circuits Description
Data Sheet 33 Rev. 2.1, 2010-11-22
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
WD
is derived from the time base
T
Cycle
. An external capacitor connected between pins RT and GND determines T
Cycle
.
Initialization:
The Watchdog is switched off per default and activated by pulling WDI to low at least for the time
t
WD,start
after RO_2
has turned to high. Watchdog input pin WDI has an integrated pull-up resistor
R
WDI
connected to Q_LDO2. If WDI
transitions to high before
t
WD,start
has elapsed, then the watchdog will not start operation. To initialize the Watchdog
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
WD,IW
. Within the "Ignore Window"
the microcontroller is given time to initialize. Any signal to watchdog input WDI within the "Ignore Window" is
ignored. After time
t
WD,IW
, the watchdog transitions from the "Ignore Window" state to the "Open Window" state for
a maximum duration of
t
WD,W
. Within the "Open Window" a valid trigger signal must be applied to the watchdog
AEA 0 3 5 3 3.VSD
No Trigger
Closed
Window
Open
Window
Trigger
WDO = LOW
Ignore
Window
Always
Always
No Trigger During
Open Window
Trigger During
Closed Window