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TPS3808: TPS3808 operating voltage and timing

Kean Giap Ng
Prodigy 110 points
Part Number: TPS3808

Hi TI support,

Good day. I have 3 question need advice. The chipset that I use is TPS3808G01DBVRG4

1) Can I connect the SENSE to a voltage source that higher then VDD? Below are my application:

MR = Not connected, CT = not connected, RESET = pull-up to 10Kohm, VDD = 2.8V, SENSE voltage range= 0V - 5V

2) I found that when I connect to a 6KHz square wave (high level = 4.5V; low level = 1.0V). Although VSENSE > VIT, I still get some unexpected LOW RESET (asserted 20ms, please refer to diagram below). My SENSE doesn't connect any capacitance. What could be causing the problem? Is that related to transient? 

Note: The unexpected LOW RESET doesn't occur when there is a 1nF caps at SENSE. 

3) Any dv/dt requirement for SENSE? Any abnormality will occur if I connect SENSE to a switching source eg: 10KHz?

  • 0
    TI__Genius 9375 points

    Hi Kean,

    1) You can, but the RESET output will only show the voltage of what it is pulled up to (eg 2.8V)

    2) This is unusual behavior, and it is interesting that a capacitor solves the problem. I would assume that a glitch wider than the glitch immunity is being caught.

    3) Extremely fast slew rates can cause issues if you are entering or exiting reset too quickly, depending on if you are upsetting the device's glitch immunity feature.

    Thanks,
    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Prodigy 110 points

    Hi Abhinav,

    Thanks for the advice. I have some question to ask in further, please refer below:

    1) Ab: You can, but the RESET output will only show the voltage of what it is pulled up to (eg 2.8V)

        Kean: Okay. 2.8V at RESET output is not a concern for me. Thanks for the advice

    2) Ab: This is unusual behavior, and it is interesting that a capacitor solves the problem. I would assume that a glitch wider than the glitch immunity is being caught.

       Kean: May I know in datasheet, where I can refer regarding the specification on glith immunity? What is the maximum pulse wide that SENSE could immune

    3) Ab: Extremely fast slew rates can cause issues if you are entering or exiting reset too quickly, depending on if you are upsetting the device's glitch immunity feature.

        Kean:  So TPS3808 works better for slower SENSE source rather then a switching voltage with high dv/dt squarewave (eg:6KHz), right?

  • 0 in reply to Kean Giap Ng
    Prodigy 110 points

    Hi TI support,

    Can help to reply my question below? Thank you.

    1) May I know in datasheet, where I can refer regarding the specification on glith immunity? What is the maximum pulse wide that SENSE could immune?


    2) So TPS3808 works better for slower SENSE source rather then a switching voltage with high dv/dt squarewave (eg:6KHz), right?

  • 0 in reply to Kean Giap Ng
    TI__Genius 9375 points

    Hi Kean,

    1) The glitch immunity of the device is specified in section 9.2.2.1 (Immunity to SENSE Pin Voltage Transients)

    2) Quick transitions should actually be better, as long as you are not hopping in and out of reset and constantly putting short pulses on RESET. As long as your pulse is long enough, quick transitions are better.

    Thanks,
    Abhinav.