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TPS63900: Noisy Current Waveforms on Some Boards

Calvin
Prodigy 10 points
Part Number: TPS63900

Tool/software:

My design is using the TPS63900 along with some mosfets and resistors to change the current at which a supercapacitor charges. Below are current traces of switching between a 1mA limit and 2.5mA limit. The 2.5mA seems to consistently be about 3mA, but that is not the problem. On about 130 of 150 boards, the waveform looks like the first image. Nice and stable. However on about 20 of my boards, the waveform very consistently and repeatably looks like the 2nd picture. The average current is the same, but the waveform is very noisy. It is worth noting that the 1mA curve is very steady on all of the boards

I am hoping that someone can provide insight as to why this is happening and if this behavior is expected and/or if it will cause damage to the TPS63900.

Thank you

  • 0
    TI__Mastermind 32350 points

    Hi  Calvin,

    Thanks for using TI's device in your design.

    I am wondering if the the status of supercapacitor(such as voltage) is same or not, asking because the current limit of this device is averange limit, which means the ripple of input current is not same.

    Regards

    Tao

  • 0 in reply to Tao Zhang
    Prodigy 10 points

    Sorry that I was unclear about that. This testing was done on a single board automated test fixture before the supercapacitor is soldered to the pcb. For the input I have a 5V switching supply fed through a 3.6V LDO into a current meter and then into the input of the TPS63900. On the output I just have a 1.2k resistor as my load for consistency. The load resistor and power input is all on my tester, so those are all constants between the many different PCBAs I was testing.

  • 0 in reply to Calvin
    TI__Mastermind 32350 points

    Hi  Calvin,

    Thanks for your explaination, could you try with a EC load but not tester? Asking because want to screen out unexpected instable behavior of your tester.

    Regards

    Tao

  • 0 in reply to Tao Zhang
    Prodigy 10 points

    Due to the repeatability of the behavior on specific board that do and do not have the "issue" I am very confident that this is not a tester issue. Also, like you said the average current is correct so it also isn't really an issue for my application. I just want to make sure that this is reasonably expected behavior that is not a defect and will not cause damage to the TPS63900 itself if this behavior is present over 10 years of regular use.

  • 0 in reply to Calvin
    TI__Mastermind 32350 points

    Hi Calvin,

    Understand, i am sure that this behavior will not cause device damaged.

    But if Vin,Vout and Iout are all same between boards, the different havihor here seems not reasonable. 

    Could you help to capture Vin/Vou/IL waveforms with different boards to help me to address the root cause?

    Regards

    Tap

  • 0 in reply to Tao Zhang
    Prodigy 10 points

    I certainly can do that! I will aim to follow up next week with those waveforms from at least a few boards both with and without the noisy current waveform. Thank you.

  • +1 in reply to Calvin
    TI__Mastermind 32350 points

    Hi  Calvin, 

    Thanks, let us check what happened according waveforms you got.

    Regards

    Tao