SLVSD43C May 2015 – February 2019 TPS7B68-Q1
The window watchdog is able to monitor whether the frequency of the watchdog service signal (WD) is within certain ranges. A watchdog low-voltage fault is reported when the frequency of the watchdog service signal is out of the setting range. Figure 24 shows the window watchdog initialization and operation for the TPS7B68-Q1 (WRS is low). After the output voltage is in regulation and PG is high, the window watchdog becomes enabled when an external signal pulls WD_EN (the watchdog enable pin) low. This causes the watchdog to initialize and wait for a service signal during the first initialization window for 8 times the duration of t(WD). A service signal applied to the WD pin during the initialization open window resets the watchdog counter and a closed window starts. To prevent a fault condition from occurring, watchdog service must not occur during the closed window. Watchdog service must occur during the following open window to prevent a fault condition from occurring. The fault output (WDO), externally pulled up to VOUT (typical), stays high as long as the watchdog receives a proper service signal and there is no other fault condition.
Three different fault conditions occur in Figure 24: