TPS3850-Q1: there is a way to shorten WDO active time?

Alan Xia

Genius 9680 points

Part Number: TPS3850-Q1
Other Parts Discussed in Thread: TPS3850

Hi team，

Would like to check one question for TI TPS3850.

We would like to connect WDO of TPS3850 to NMI of SoC (DRA78x) as data sheet describes.
Due to we cannot disable NMI once it is enabled unless code-reset is triggered (TI SoC issue/limitation), in NMI ISR (Interrupt Service Routine) we have to dessert WDO immediately before triggering warm-reset.
I try to disable TPS3850 via SET1 and SET0, but the WDO will still keep asserted for 10 ms. Do you know there is a way to shorten WDO active time?

over 2 years ago

0 Joshua Garcia over 2 years ago

TI__Genius 11780 points

Hi Alan,

We can shorten the tRST time below 10ms by adding a capacitor to the CRST Pin. As outlined in section 8.1.1.2 Programmable Reset Delay Timing for example: placing a 100pF capacitor on this pin will shorten the reset time to a typical of 0.7ms. (*Just note this will change the reset time for both WDO and RESET*)

Thanks,
Joshua

0 Alan Xia over 2 years ago in reply to Joshua Garcia

TI__Genius 9680 points

Hi Joshua，

Sorry, I did not describe it clearly.

I want to let WDO to go to de-asserted via SW method in NMI interrupt, previously I though disabling TP3850 can help, but after quick test, seems it is not working..

Because I will do a reset in end of NMI interrupt, I do not want the still-asserted WDO impacts bootloader.

0 Alan Xia over 2 years ago in reply to Alan Xia

TI__Genius 9680 points

the customer is just looking for a way to turn WDO from asserted into de-asserted once it is not needed.

0 Joshua Garcia over 2 years ago in reply to Alan Xia

TI__Genius 11780 points

Hi Alan,
The customer would have to wait until the entire tRST period expired before the WDO goes from asserted into de-asserted, there is no logic input that can alter this state besides the programming of tRST through the CRST pin and this pin can only do as descibed above.

Thanks,

Joshua

0 Alan Xia over 2 years ago in reply to Joshua Garcia

TI__Genius 9680 points

Hi Joshua，

Thanks for the answer.
If there is no way to de-assert WDO when it is asserted (even disabling external watchdog cannot de-assert it), we have to wait for tRST period (max 11.5 ms) in NMI interrupt before resetting the SoC.

0 Trailokya Rai over 2 years ago in reply to Alan Xia

TI__Genius 11401 points

HI Alan

Josh will reply tomorrow, as there is holiday in US today. Thanks for your patience.

Regards

Trailokya

0 Joshua Garcia over 2 years ago in reply to Alan Xia

TI__Genius 11780 points

Hi Alan,

As you stated even when you disable the watchdog it is recommended to wait for the tRST period (max 11.5ms) to ensure that the WDO is de-asserted.

Thanks,
Joshua

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TPS3850-Q1: there is a way to shorten WDO active time?