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TPS7B63-Q1: Question for WD window tolerance, WD signal and EN pin current

Oba
Genius 17295 points
Part Number: TPS7B63-Q1

Hello

 

I have some question for TBS7B63-Q1. I want to use it as standard watchdog mode.

 

1)

T(WD_TOL) is defined as +-10%. Does this value include tolerance of R(ROSC), +-1%?

 

2)

To clear wathdog counter(to start next OW), rising edge of WD is abolutely reqruied, isn’t it?

If the WD signal is high fixed after WD initialization, watdhdog counter is not cleared and FLT occurrs. Right?

 

3)

When WD signal is High and this signal goes to low for a very short time due the noise, this low signal can be detected as low siganl?

For example, in case of 100usec high à 1nsec low (noise) à High, this 1nsec low à high could be detected as correct riging edge?

 

4)
Could you tell me max value of EN pin input current?

 

Regards,

Oba

  • 0
    TI__Guru 55940 points

    Hi Oba,

    I will answer your questions in the same order you asked them.

    1) T(wd_tol) does not include the tolerance of the external resistor R(rosc).

    2) Correct.  To clear the watchdog counter there must be detected.  The minimum pulse width to ensure the watchdog counter resets is 100us.

    3) The minimum pulse width to ensure the watchdog counter resets is 100us.  a 1ns noise spike will be too fast for the internal circuitry to detect it as a pulse.

    4) Ien max is 3uA

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    TI__Genius 17295 points

    Ryan,

     

    Sorry for my delay response.

    Thanks for your answer.

     

    1)

    If T(WD_TOL) is +-10% without R(OSC) tolerance, I think t(WD) should be +-11% because t(WD) includes R(ROSC) 1% tolerance.

    But t(WD) is +-10%. I think something is wrong. What do you think?

     

    2)

    Thanks. I understand.

     

    3)

    I know 100use active-high pulse is required to reset watchdog counter.

    Let me ask again.

    Could you see the below figure? My question is effect of unexpected low pulse during high pulse.

    Case 2 is my expectation because this low pulse is just noise.

    But I think there is a possiblitly that this unexpected low pulse is detected and next open window is started like case 1.
    I think it depens on the this unexpected low pulse period(A in this figure).

     

    My question is do we have any data how long short pulse can be ignored in this kind of case?

     

     

    4)

    Thanks. I understand.

     

    Regards,

    Oba

     

  • 0 in reply to Oba
    TI__Guru 55940 points
    Hi Oba-san,

    I apologize for the delay in response.

    1) TPS7B63-Q1 is tested with 0.1% resistors for R(osc), the datasheet test conditions for t(wd) are incorrect. The line that you should use as your understanding your system is t(wd_tol) which shows that the tolerance of R(rosc) is excluded from the +/-10% for resistors from 20k to 100k.

    3) Your application will experience case 2 where the noise is ignored. Essentially you have a comparator that will respond to a signal based on the overdrive. A short signal pulse (noise) would need to have much larger overdrive for the comparator to recognize and respond to the change. A noise pulse is too short for the comparator to respond to.

    www.ti.com/.../sbva047.pdf

    Very Respectfully,
    Ryan