The upper boundary of the watchdog timer can be set by an external capacitor connected between the WDT pin and GND. Common consumer electronic capacitors can be used to implement this feature. The capacitors that are used should have low ESR and low tolerances because the tolerances must be considered to perform the calculations. The first formula is used to calculate the upper window frame. After calculating the upper window frame, the lower boundary can be calculated. As in the last example, the most important values are the t_boundary,max and t_window,min. The trigger pulse must fit into this window frame.

The external capacitor should have a value between a minimum of 155 pF and a maximum of 63 nF.

Equation 2.