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TPS3431: Change CWD Adjustable Capacitor after boot

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Replies: 1

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Part Number: TPS3431

Hi, I was wondering if it would be possible to change the capacitor connected to the CWD pin on the TPS3431 on the fly. 

My thought would be to have a 1uF capacitor connected between the CWD pin and an N-Fet to GND and also connect a 15nF between the CWD pin and ground. So when the Fete was enabled the CWD pin would see them in parallel and then when the fet was disabled it would see just the 15nF.

The idea is to give a ~60s WDI window to allow my processor to boot then when the system is up and running switch out the capacitor and have a ~1s WDI period.

So on power up the WDO is pulled up and wont trigger for 60s. Then I can start clocking the WDI pin when booted and lower the period?

Thanks

 

  • Hi Steven,

    All the TPS3431 sees is a voltage at the CWD pin as it charges the cap.The TPS3431 is designed and tested using CCWD capacitor between 100 pF and 1 μF. So the 1uF + 15nF is already larger than 1uF so just take caution when choosing values.

    The biggest issue is that depending on the charge on the capacitors, the VCWD thresholds can be triggered if you decide to add capacitance later on in the system. Since this is just a start-up i do not see a problem.

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