• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 64 subscribers
  • Views 545 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS3813I50 - Minimum pulse width of WDI trigger pulse.

Michele Tedeschi
Prodigy 10 points

I need confirmation for the minimum pulse width of WDI trigger pulse, in worst case condition (full temperature+voltage operating range).

In the product datasheet I find two references to "tw parameter".

1) pag. 3:

RECOMMENDED OPERATING CONDITIONS

tw Pulse width of WDI trigger pulse: 50ns min.

2) pag. 4:

TIMING REQUIREMENTS

tw Pulse width at VDD: 3us min.

Is this the same parameter tw of page 3 ?

Which is the minimum pulse width of WDI trigger pulse, valid over the full operating conditions ?

Thank you.

  • 0
    TI__Guru**** 150870 points

    The minimum pulse width required at WDI over temperature and all variations is 50 ns.  The 3usec number is for Vdd.  There are multiple things that could cause a reset, including WDI and Vdd.  If Vdd goes too low for more than 3usec, the IC will generate a resetdue to Vdd.

  • 0 in reply to Chris Glaser
    Intellectual 345 points

    Hi Chris,

    I also had the same question about the pulse width - 50ns vs 3us but now that's answered. Well my other question is about the WDI pulse. How long can it be held high? Since the device senses the rising edge I think the time between two rising edges is most important. I however had the situation that everything looked ok on the scope but my dsp was continually being reset over and again. I have WDT=WDR=Vdd and so my limits for my WDI pulse rising edges are > 23.5ms < 2s as in the datasheet.

    Is there a limit to the duration between a low to high transition? What happens if I hold WDI high for some time (obviously << 2s) and then go low and high in quick succession? Will this rising edge be detected? I couldn't find anything in the datasheet regarding this.

    Thanks

  • 0 in reply to Cecil
    TI__Guru**** 150870 points

    The time that you must hold the WDI pin low should be the same 50 nsec for holding it high.

    I tested this in the lab and verified that 100 nsec was long enough to hold it low.  This was the lowest off time my function generator could output.