Datasheet

TLE 7469
Data Sheet 17 Rev. 1.6, 2008-01-22
the closed window is interpreted as a pretrigger failure and results in a reset. After the
closed window the open window with the duration
t
OW
is started again. The open window
lasts at minimum until the trigger process has occurred, at maximum
t
OW
is 32 ms (typ.
value with fast timing).
A HIGH to LOW transition of the watchdog trigger signal on pin WDI is taken as a trigger.
To avoid wrong triggering due to parasitic glitches two HIGH samples followed by two
LOW samples (sample period
t
sam
typ. 0.25 ms) are decoded as a valid trigger (see
Figure 8). A reset is generated (RO goes LOW) if there is no trigger pulse during the
open window or if a pretrigger occurs during the closed window. The triggering is correct
also, if the first three samples (two HIGH one LOW) of the trigger pulse at pin WDI are
inside the closed window and only the fourth sample (the second LOW sample) is taken
in the open window.
Figure 6 Window Watchdog State Diagram
AEA03533.VSD
No Trigger
Closed
Window
Open
Window
Trigger
Reset
Ignore
Window
Always
Always
No Trigger During
Open Window
Trigger During
Closed Window