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Delay Superviser TPS3808G09DBVR - regarding stability of reset output

vijayavani raju
Prodigy 220 points
Other Parts Discussed in Thread: TPS3808

Hi,

     We are working on a project where we use Delay Superviser TPS3808G09DBVR for voltage monitoring. We used dot matrix board and when we left the Ct pin floating, we got the reset output with fixed delay. When we tried with ct pin pulled up to 51k ohms, we got the reset output with fixed delay. But when ct capacitance varied from 1nf to 390pf, no consistent output is observed as in below table. Please help to resolve the issue

Capacitance Ct

Calculated Delay (ms)

Measured Delay(ms)

1nF

6.2ms

30ms

680pF

4.4ms

 No O/P

390pF

2.7ms

5.4ms

218pF

1.74ms

 No O/P

150pF

1.35ms

 No O/P
  • 0
    TI__Guru 55940 points

    Hi Vijayavani,

    Would it be possible to share some scope shots with Vdd, Vsense, and /Reset monitored?  

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 220 points

    Hi Ryan,

                     We found that the issue was due to handling of the IC. Its resolved now.

    After MR is released, the delay time after which Reset goes high is not specified in datasheet of TPS3808G09DBVR. Is it same as the delay calculated using Ct? Can somebody help on this

  • 0 in reply to vijayavani raju
    TI__Guru 55940 points

    Hi Vijayavani,

    Glad to hear you resolved it!

    After MR is released, for TPS3808, the same user configurable delay will occur before /RESET goes high.  This is the same delay that is calculated using the Ct.  For your reference, this is indicated in the timing diagram on page 5 of the datasheet and the Manual Reset (/MR) Input description on page 8.

    Very Respectfully,

    Ryan