7.5
Window watchdog
Principle of operation
The integrated window watchdog (WWD) can monitor the microcontroller. The microcontroller monitored must
provide periodical triggering during the open windows. Depending on the configuration a trigger event is
•
a falling edge on the WDI pin
•
an SPI write operation to the register
After a trigger event the window watchdog indicates either valid WWD triggering or invalid WWD triggering to
the WWD error counter and the device terminates the open window.
On valid WWD triggering the device starts a closed window.
If there is no triggering during the open window or if triggering occurs during a closed window, then the window
watchdog output indicates invalid WWD triggering to the WWD error counter and a new open window starts.
If the microcontroller does not trigger the window watchdog with a correct timing, then the device indicates
that to the microcontroller. If multiple error events occur, then the device sets ROT "low".
Window
Watchdog
(WWD)
SPI
Invalid WWD triggering
Valid WWD triggering
Window
Watchdog
Failure counter
WWO
Interrupt or
Reset
generation
WDI
WWO
Figure 13
Window watchdog principle of operation
Configuration
The following parameters of the window watchdog can be configured via SPI in ACTIVE:
•
The trigger signal can be configured to be pin triggered (pin WDI) or SPI triggered command (register
). The default configuration is the triggering via SPI.
•
The duration of the open window and closed window cycles can be modified according to the application
needs (combination of cycle time and number of cycles for open window and closed window
).
•
The threshold for the window watchdog error counter overflow can be configured via SPI.
Initialization
As soon as the device sets ROT "high" in INIT state, it activates the window watchdog. After activation the
watchdog opens a long open window (LOW) with a duration of
t
LOW
. With the default configuration the window
watchdog expects a valid trigger event via SPI during the long open window, while it ignores WDI pin signals.
Therefore, glitches at the microcontroller output connected to the WDI have no effect during startup and
initialization. During the long open window cycle the microcontroller can change the window watchdog trigger
source as well as the timing of the open window and of the closed window. On reconfiguration the window
watchdog restarts with the new configuration. The window watchdog starts a regular open window cycle,
waiting for a valid trigger signal from the selected trigger source.
If no valid triggering or configuration of the watchdog occurs during the long open window, then the window
watchdog recognizes invalid WWD triggering. If the INIT timer expires while invalid WWD triggering persists,
then the device generates a soft reset and it sets the ROT pin to "low". After the soft reset the window watchdog
OPTIREG
™
PMIC TLF30681QVS01
Power management IC
Microcontroller interface and supervisory functions
Datasheet
68
Rev. 1.0
2020-04-08
