The TPS3430-Q1 features three options for setting the watchdog reset delay: connecting a capacitor to the CRST pin, connecting a pull-up resistor, and leaving the CRST pin unconnected. If the CRST pin is either unconnected or pulled up the minimum timing requirement cannot be met, thus an external capacitor must be connected to the CRST pin. Because a minimum time is required, the worst-case scenario is a supervisor with a high CRST charging current (I_CRST) and a low CRST comparator threshold (V_CRST). For applications with ambient temperatures ranging from –40°C to +125°C, C_CRST can be calculated using I_CRST(MAX), V_CRST(MIN), and solving for C_CRST in Equation 5:

Equation 5.

When solving Equation 5, the minimum capacitance required at the CRST pin is 0.086 μF. If standard capacitors with ±10% tolerances are used, then the minimum CRST capacitor required can be found in Equation 6:

Equation 6.

Solving Equation 6 where C_tolerance is 0.1 or 10%, the minimum C_CRST capacitor is 0.096 μF. This value is then rounded up to the nearest standard capacitor value, so a 0.1-μF capacitor must be used to achieve this reset delay timing. If voltage and temperature derating are being considered, then also include these values in C_tolerance.