SBVS301B October 2016 – September 2021 TPS3850
PRODUCTION DATA
As illustrated in Figure 8-2, there are three options for setting the window watchdog. The design specifications in this application require the programmable timing option (external capacitor connected to CWD). When a capacitor is connected to the CWD pin, the window is governed by Equation 13. Equation 13 is only valid for ideal capacitors, any temperature or voltage derating must be accounted for separately.
The nearest standard capacitor value to 2.5 nF is 2.2 nF. Selecting 2.2 nF for the CCWD capacitor gives the following minimum and maximum timing parameters:
Capacitor tolerance also influence tWDU(MIN) and tWDL(MAX). Select a ceramic COG dielectric capacitor for high accuracy. For 2.2 nF, COG capacitors are readily available with a 5% tolerance, which results in a 5% decrease in tWDU(MIN) and a 5% increase in tWDL(MAX), giving 181 ms and 135 ms, respectively. A falling edge must be issued within this window.