SLVSD43C May 2015 – February 2019 TPS7B68-Q1
This device works in the standard watchdog mode when the watchdog type selection (WTS) pin is connected to a high voltage level. The same as in window watchdog mode, the user can set the duration of the watchdog window by adjusting the external resistor (RROSC) value at the ROSC pin and setting the voltage level at the FSEL pin. The current through the RROSC resistor sets the clock frequency of the internal oscillator. The user can adjust the duration of the watchdog window (the watchdog timer period) by changing the resistor value. A high voltage level at the FSEL pin sets the watchdog window duration to 5 times as long as that of a low voltage level with same external component configuration.
The duration of the watchdog window and the duration of the fault output are multiples of the internal oscillator frequency as shown by the following equations:
Equation 9. t(WD) = RROSC × 0.5 × 10-6
Equation 10. t(WD) = RROSC × 2.5 × 10-6
Equation 11. t(WD_INI) = 8 × t(WD)
For all the foregoing items, the unit of resistance is Ω and the unit of time is s
Compared with window watchdog, there is no closed window in standard watchdog mode. The standard watchdog receives a service signal at any time within the watchdog window. The watchdog fault occurs when not servicing watchdog during the watchdog window.