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TPS2HB16-Q1: Sampling error when switching channels

SUN xuran
Prodigy 40 points
Part Number: TPS2HB16-Q1

Tool/software:

Current Configuration:

EN1=1,EN2=0,SEL1=0 ,DIA_EN=3.3V, Channel1 OL,Channel 2 OL

Ideally, when SEL2=0, Vsns≈0, and when SEL2=1, Vsns=Isnsfh*Rsns≈5V. However, we observed that the voltage at the SNS point takes about 4ms to change to 5V when SEL1 switches from 0 to 1, and quickly changes from 5V to 0V when SEL1 switches from 1 to 0. Why is this? What is the chip doing in these 4ms? How can we set the switching time of SEL1 and the sampling time of SNS to ensure that the correct voltages of the two channels are read?

The yellow line is SEL2, and the blue line is the voltage on Rsns

  • 0
    TI__Mastermind 34935 points

    Sun,

    For reference, here is the truth table for the fault output:

    When SEL1 = 1 and SEL2 = 1, the output state of SNS is undefined so this is likely why you are seeing the quick/sharp decrease when toggling SEL1x. 

    Could you confirm what the input supply voltage is? It seems like it should be quicker than 4ms to be able to detect the open load condition via the sense pin. 

    Best Regards,
    Tim

  • 0 in reply to Timothy Logan
    Prodigy 40 points

    I can't understand your answer. SEL1 is always pulled down to ground, and my question is not why SEL2 drops quickly when switching from 1 to 0, but why SEL2 rises after a delay of 4ms when switching from 0 to 1.
    In addition, the supply voltage is 14V, which is a constant voltage, so why is it quicker than 4ms? What is the connection between the two?

  • 0 in reply to SUN xuran
    TI__Mastermind 34935 points

    Sun,

    I am confused here- from your original question you said, "when SEL1 switches from 0 to 1, and quickly changes from 5V to 0V when SEL1 switches from 1 to 0.", however in the follow up you said that SEL1 is always pulled to ground? To clarify, is it always pulled to ground or are we toggling the logic level?

    The SELx pins are just logic level digital inputs and would not output any voltage or current outside of what the MCU connected to said pins sources. I would expect the device to detect the open load condition quicker and report the fault via the SNS pin when switching SEL2 and SEL1 within the following timing parameters:

    Best Regards,
    Tim 

  • 0
    Prodigy 40 points

    Sorry, I made a typo。I mean "my question is not why SNS drops quickly when SEL2 switching from 1 to 0, but why SNS rises after a delay of 4ms whenSEL2  switching from 0 to 1."As you can see in the first picture I posted, SNS did not report the error immediately, but only reported the error 4ms after SEL selected the channel.

  • 0 in reply to SUN xuran
    TI__Mastermind 34935 points

    SUN,

    So it should only take tens of microseconds... nowhere near the millisecond range.

    I will dig deeper into this- but first could you provide me with a few sanity questions:

    • Does this happen on every device or just a subset of devices?
    • Was this part procured either directly from TI or from a TI authorized distributor?
    • The load is completely floating in this test condition, correct?

    Best Regards,
    Tim

  • 0 in reply to Timothy Logan
    Prodigy 40 points
    • Does this happen on every device or just a subset of devices? ----------everyone
    • Was this part procured either directly from TI or from a TI authorized distributor?-------from TI
    • The load is completely floating in this test condition, correct?--------yes,completely floating