SNVSB66A July 2018 – October 2021 TPS3431
Adjustable capacitor timing is achievable by connecting a capacitor to the CWD pin. If a capacitor is connected to CWD, then a 375-nA, constant-current source charges CCWD until VCWD = 1.21 V. Table 8-2 shows how to calculate tWD using Equation 1 and the SET1 pin. The TPS3431 determines the watchdog timeout with the formulas given in Equation 1, where CCWD is in nanofarads and tWD is in milliseconds.
The TPS3431 is designed and tested using CCWD capacitors between 100 pF and 1 µF. Note that Equation 1 is for ideal capacitors and capacitor tolerances vary the actual device timing. For the most accurate timing, use ceramic capacitors with COG dielectric material. If a CCWD capacitor is used, Equation 1 can be used to set tWD for the watchdog timeout. Table 8-3 shows the minimum and maximum calculated tWD values using an ideal capacitor.
|INPUT||WATCHDOG TIMEOUT WDT (tWD)(1)||UNIT|
|CCWD||1||tWD × 0.905||tWD Equation 1||tWD × 1.095||ms|
|CCWD||WATCHDOG TIMEOUT WDT (tWD)||UNIT|