The TPS36-Q1 offers one or two SET pins based on the pinout option selected. SET pins offer flexibility to the user to program the t_WO timer on the fly to meet various application requirements. Typical use cases where SET pin can be used are

• Use wide open window timer when host is in sleep mode, change to small timeout operation when host is operational. Watchdog can be used to wake up the host after long duration to perform the application related activities before going back to sleep.
• Change to wide open window timer when performing system critical tasks to ensure watchdog does not interrupt the critical task. Change timer to application specified interval after the critical task is complete.

The t_WO timer value for the device is combination of t_WC timer selection based on the CWD pin or fixed timer value along with SET pin logic level. The t_WC timer value is decided based on the Watchdog Close Time selector in the Section 5 section. The SET pin logic level is decoded during the device power up. The SET pin value can be changed any time during the operation. SETx pin change which leads to change of watchdog timer value or enable disable state, terminates the ongoing watchdog frame immediately. SETx pins can be updated when WDO or RESET output is asserted as well. The updated t_WO timer value will be applied after output is deasserted and the t_SD timer is over or terminated.

For a pinout which offers only SET0 pin to the user, the t_WO ratio value is decided based on the Watchdog Open Time Ratio selector field in the orderable part number. Refer Section 5 for available options. Table 8-4 showcases an example of the t_WO values for different SET0 logic levels when using Watchdog Close Time setting as option D = 10 msec.

Pinout which offer both SET0 & SET1 pins to the user, the t_WO ratio value is decided based on the Watchdog Open Time Ratio selector field in the orderable part number. Refer Section 5 for available options. Two SETx pins offer 3 different time scaling options. The SET[1:0] = 0b'01 combination disables the watchdog operation. Table 8-5 showcases an example of the t_WO values for different SET[1:0] logic levels when using Watchdog Close Time setting as option G = 100 msec. The package pin out selected does not offer WD-EN pin.

1. Example for Watchdog Close Time setting = 100 msec.

Selected pinout option can offer WD-EN pin along with SET[1:0] pins (Pin Configuration C, D). With this pinout, the WD-EN pin controls watchdog enable and disable operation. The SET[1:0] = 0b'01 combination operates as SET[1:0] = 0b'00.

Ensure the t_WO value with SETx ratio does not exceed 640 sec. If a selection of close window timer and ratio results in t_WO > 640 sec, the timer value will be restricted to 640 sec.

Figure 8-9 to Figure 8-11 show the timing behavior with respect to SETx status changes.

Figure 8-9 Watchdog Behavior with SETx Pin Status

Figure 8-10 Watchdog Operation with 2 SET Pins

Figure 8-11 Watchdog Operation with 1 SET Pin