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TPS3808G09DBVR - regarding stability of Reset delay

vijayavani raju
Prodigy 220 points
Other Parts Discussed in Thread: TPS3808G01DBVEVM

Hi,

     We are working on a project where we use Delay Supervisor TPS3808G09DBVR for voltage monitoring. We used dot matrix board and tested the circuit with Ct of 270pF which should give a reset delay of 2.04ms. When it is tested for different iterations, we found that the reset delay not being consistent and varying to 20ms. Is this because of testing locally on Dot Matrix Board? Will the reset delay be consistent if PCB is used? Have somebody experienced the same? Please help to resolve the issue.

  • 0
    TI__Guru 55940 points

    Hi Vijayavani,

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

    Could you also check that you have a solid connection between the capacitor and the Ct pin?  An intermittent connection would explain the variation.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 220 points

    Hi Ryan,

                  We had solid connection between capacitor & Ct Pin. Please find the scope shots below

    Test Inputs

    Ct=270pF, Vin=3.3v for resistor divider, Vdd=3.3v, 10k pullup added on RESET pin, R1=7.5K Ohms & R2=4.02k Ohms

    Iteration1

    Capacitance Ct

    Calculated Delay (ms)

    Measured Delay(ms)

    270pF

    2.04ms

    1.9ms


    Iteration 2

    Test Inputs

    Ct=270pF, Vin=3.3v for resistor divider, Vdd=3.3v, 10k pullup added on RESET pin, R1=7.5K Ohms & R2=4.33k Ohms

    Iteration2

    Capacitance Ct

    Calculated Delay (ms)

    Measured Delay(ms)

    270pF

    2.04ms

    20ms

     

  • 0 in reply to vijayavani raju
    TI__Guru 55940 points

    Hi Vijayavani,

    The delay going to 20ms is very interesting.  As indicated in the datasheet, this is the delay associated with floating the CT pin.  

    As indicated in your first post, you are using a dot matrix board and asked about if using a PCB would remove the intermittent results.  The dot matrix board can introduce variables that are not present in the final system.  We recommend evaluations be performed on our Evaluation Module tps3808g01dbvevm.  You can order the EVM here: http://www.ti.com/tool/tps3808g01dbvevm.  By using the EVM, you would better replicate a final system with the device and components soldered on the PCB.

    Very Respectfully,

    Ryan