The TCAN1469-Q1 provides three methods for setting up the watchdog. If more frequent, < 64ms, input trigger events are desired it is suggested to us the Time-out timer as this is an event within the time event and not specific to an open window.

When using the window watchdog, it is important to understand the closed and open window aspects. The TCAN1469-Q1 are set up with a 50%/50% open and closed window and is based on an internal oscillator with a ± 10% accuracy range. To determine when to provide the input trigger, this variance needs to be considered. Using the 60ms nominal total window provides a closed and open window that are each 30 ms. Taking the ± 10% internal oscillator into account means the total window could be 54ms, t_WINDOW, MIN or 66ms, t_WINDOW MAX. The closed and open window would then be 27ms, T_WDOUT MIN, or 33ms, T_WDOUT MIN. From the 54ms total window and 33ms closed window the total open window is 21ms. The trigger event needs to happen at the 43.5ms ± 10.5ms, safe trigger area. The same method is used for the other window values. Figure 8-29 provides the above information graphically. Once the WD trigger is written, the current Window is terminated and a new Closed Window is started.

Figure 8-29 Window Watchdog Timing Diagram