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TPS3824: TPS3824: TPS3824-33: WDI & /RESET During RS Testing

Jai Kumar Reddy
Prodigy 120 points
Part Number: TPS3824

Hi Team,

We are using TPS3824-33DBVR in our Design. During normal Operation, WDI will be provided with the Transitions within the Timeout Period of 1.6sec and the /RESET Output will be High. When we are not providing Transitions on WDi pin the Watchdog is resetting the Controller as required.

But, During RS Testing the WDI Pin will have only 1.2V constant Voltage and the /RESET Output is high and not generating low signal to reset the Controller. We are testing DUT with a RS field of 10V/m.

Is Watchdog considering 1.2V WDI signal as High Impedance State? But, we are providing the Transitions on WDI pin before it is going to 1.2v so that we are activating the watchdog function.

Is Watchdog Freezing because of RS field?

Can we connect the WDI pin to GND through 1K and then make high or low using Controller so that if Controller is hanged then the WDI pin will be low and Watcdog will reset the controller(If 1.2V is coming because of Controller hang)?

Please find the attached Waveforms before and during RS Testing.

Regards,

Jai kumar.

  • 0
    TI__Genius 9375 points

    Jai,

    I'm going to ask one of our experts for these products to help you out with your issue. He should get back to you tomorrow.

    Thanks,

    Abhinav.

  • 0
    TI__Genius 12630 points

    Jai,

    Can you please describe what you mean by "RS" testing? The WDI pin should not be held at constant voltage. This is not the same as leaving high impedance because during high impedance, the device creates its own pulse internally to prevent the watchdog from causing a reset. But when you hold the WDI pin at constant voltage, this does not allow the device to pulse the WDI pin correctly. Adding the pull-down resistor to WDI prevents the device from generating the pulse when WDI is in high impedance which will also prevent the constant voltage from causing an undefined behavior. If you look at table 7.3 in the datasheet, you see that the WDI pin is a digital input and must be above 0.7xVDD to be logic high and below 0.3xVDD to be logic low. This means if you provide a constant voltage between the logic high and logic low, the WDI logic is undefined and thus may or may not cause a reset.

    If you want the WDI to cause a reset, the WDI pin should be high or low for the timeout. Please meet the logic requirements of the WDI pin and see if this fixes your issue.

  • 0 in reply to Michael_DeSando
    Prodigy 120 points

    Hi Michael,

    Thank you for your Quick Response.

    RS Testing is the Radiation Susceptibility Testing. Yes, I got that during High Impedance state, the Watchdog creates its internal pulses to prevent reset and WDI is Digital Pin.

    We had same doubt that if the constant voltage is in between the logic levels of WDI the device may or may not be generating reset signal. When have tested for the same, got the following results:

    During Normal Conditions, When we apply Constant voltages at WDI Pin the watchdog is generating Reset signal for the range of 0-3.3VDC (Regulated Power supply). But, if we see the picture i have shared earlier during Radiation testing chamber(Device under RS testing) the when the WDI is constant the Reset is not generating.

    Is the Watchdog is freezing because of Radiation? Where to find the EMI/EMC levels for the watchdog?

    Regards,

    Jai Kumar.

  • 0 in reply to Jai Kumar Reddy
    TI__Genius 12630 points

    Jai,

    Sorry for the delay. I investigated the radiation susceptibility and EMI/EMC data for TPS3824 and unfortunately we do not have any data for these tests. This is not a standard test we do for our devices so I can't comment on if this is the reason you are having issues. I do want to emphasis that under recommended operating conditions and normal environmental conditions, the device will not have any issues as described. But we do not have information on how the device will behave under RS testing.

    Please let me know if you have any additional questions.