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TPS23861: will the noise measured on sense resistor be a problem?

Chris Zhao1
Expert 1240 points
Part Number: TPS23861


Hi experts,

I measured the voltage of two 0.51ohm resistors in parallel, the waveform is shown blow, will this be a problem? 

In my board, I have to disable the  Disconnect Detection in 0x13h, otherwise the PD would be keeping power cycling. once I thought it might be caused by Maintain Power Signature, after measurement i found the minimum current of my board is like 80mA, which is much higher than 7.5mA.

By the way, the 54V is generated by a DC/DC switch, and the frequency is 500kHz.

Is there any other registers I should check?

Thanks

Chris

  • 0
    TI__Genius 15685 points
    Hi Chris,

    I would suggest to connect your load to TPS23861EVM-612 which will help you to isolate the problem. If TPS23861 can turn on the load without any power cycling issues, we will need to take a look at your schematic and layout. Thanks.

    Best regards,
    Penny
  • 0 in reply to Penny Xu
    Expert 1240 points

    Hi Penny,

    Thanks for comments, I was able to find a PD designed by 3rd vendor, which receives power from POE, and generates 5V/4.7A power. 

    So I could connect my board with this PD, then connect PD with DC Electronic load, after that I can set different current and run test.

    I listed my result below,

    Load current value in register  Real Current PD status Notes
    None 0xda 13.3mA Always on
    5V/0.1A 0x16f 22.4mA Always on
    5V/0.2A 0x20a 31.8mA Always on
    ... ... ... Always on
    5V/0.7A 0x52c 80.8mA Always on
    5V/0.8A 0x5b8 - 0x5cf 89.3mA - 90.7mA Always on The current value read back is not stable
    5V/0.9A 0x3eb - 0x415 61.2mA - 63.8mA Always on The current value read back is un-stable, and lower
    5V/0.95A 0x1bf - 0x214 27.3mA - 32.5mA Always on The current value read back is un-stable, and even lower
    5V/0.97A 0xcc - 0x144 12.5mA - 19.8mA Always on The current value read back is un-stable, and very small
    5V/0.98A 0x0 - Keeping ON/OFF PD is keeping power cycling, and current read back is zero.

    it seems the current sensing is wrong when current is larger than 80mA, can you give me some advice on this?

    Thanks

    Chris

  • 0 in reply to Chris Zhao1
    TI__Genius 15685 points

    Hi Chris,

    Have you tried with TPS23861EVM-612? Did you see the same behavior? Can you also send me waveform capturing RESET,VDD and VPWR in one screen and I want to check the power on sequence. Basically you need to follow the power on sequence described in this app note: http://www.ti.com/lit/an/slua818/slua818.pdf. Thanks.

    Best regards,

    Penny

  • 0 in reply to Chris Zhao1
    TI__Genius 15685 points
    Hi Chris,

    It has been a while since my last reply. Did you solve the problem? I am planning to close this thread. Thanks.

    Best regards,
    Penny