TLE7368_10 Datasheet, PDF (33/41 Pages) Infineon Technologies AG – Next Generation Micro Controller Supply

5.10
Watchdog Circuit
TLE7368
Detailed Internal Circuits Description
WDO = LOW
Always
Ignore
Window
Trigger During
Closed Window
No Trigger During
Open Window
Always
Closed
Window
Trigger
No Trigger
Figure 8 Window Watchdog State Diagram
Open
Window
AEA03533.VSD
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
Data Sheet
33
Rev. 2.1, 2010-11-22