SLVSD43C May 2015 – February 2019 TPS7B68-Q1
The standard watchdog is able to monitor whether the frequency of the watchdog service signal (WD) is lower than a certain value. A watchdog low-voltage fault is reported when the frequency of the watchdog service signal is lower than the set value.
Figure 25 shows the standard watchdog initialization and operation for the TPS7B68-Q1. Similar to the window watchdog, after output the voltage is in regulation and PG asserts high, the standard watchdog becomes enabled when an external signal pulls WD_EN low. This causes the standard 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 first open window resets the watchdog counter and another open window starts. To prevent a fault condition from occurring, watchdog service must occur during the every 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 proper service and there is not fault condition.
Two different fault conditions occur in Figure 25: