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TPS92513: about ΔIL (inductor ripple current)

ACGUY
Guru 11170 points

Part Number: TPS92513
Other Parts Discussed in Thread: TPS92515

Hello E2E,

Our customer is using TPS92513 for light source of scanner.
Fail at function test for lack of light intensity.

They exchanged the device and verified it on EVM.
Symptoms are as follows;
  -  Failed device operates normally at ΔIL 160 mA or more. Passed device ΔIL is 75 mA or more.
  -  Start-Up time is vely slow.
    -  Failed device : 500-msec
    -  Passed device : 8.7-sec. No-msec, sec.
  -  It does not follow the voltage of IADJ.

Please let us know the cause and measures.

Best regards,
ACGUY

  • 0
    TI__Mastermind 25500 points

    Hello ACGUY,

    I am not sure I understand the first symptom. Are you saying on the same board with the same components two devices have very different inductor current ripple during normal operation? Or is this just during startup?

    As for the startup time, this is not the fastest device since it uses open loop startup, and certain conditions can affect it. For example if IADJ is at a low voltage during startup COMP can take a very long time to charge enough to begin switching. IADJ generally needs to be above about 0.8V to avoid excessive delays and then it can be adjusted lower after startup. What are your startup conditions? Does it not follow IADJ after you have full regulation or only during startup?

    In any case if the conditions are right this device can be fast enough for strobe and scanner applications, but the TPS92515 is better suited for them since it starts very fast every time regardless of what dimming level you have.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 11170 points
    Hi Clinton,

    Sorry, I accidentally clicked on green.

    >> Are you saying on the same board with the same components two devices have very different inductor current ripple during normal operation?

    Yes. Same board, same L, C, and same LED load. They changed TPS only.

    >> What are your startup conditions?
    - Vin is 24V .
    - ILED is about 600mA.
    - L is 47-uH.
    - Fsw is 1MHz, then RT = 100-kΩ.
    - IADJ is 0.8V from DAC output wehn start up.

    By the way, Sho Ogane is my coworker.
    e2e.ti.com/.../600456

    I think that failed device has issue at slope compensation.

    Regards,
    ACGUY
  • 0 in reply to ACGUY
    TI__Mastermind 25500 points

    Hello ACGUY,

    At full current after startup the inductor ripple between two devices should be the same. Maybe one of the devices had an ESD event and sustained damage?

    The long startup would be due to the IADJ voltage. I needs to be higher for quick startup, 1.8V ideally then adjusted down, but from my experience at least 1V on IADJ. If that isn't possible for the application the 515 I mentioned would work much better starting with a low IADJ voltage.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 11170 points
    Hello Clinton,

    No, that didn't have ESD damages.
    IADJ is clamped 0.8V when before start.

    Regards,
    ACGUY
  • 0 in reply to ACGUY
    TI__Mastermind 25500 points

    Hello ACGUY,

    Understood. If the ripple is different then the switching frequency must be different as well, so there is some error somewhere. Do you have a way of making sure the DAP is fully soldered down in both cases? If it isn't, or one of the pins isn't, that could cause an error in the switching frequency. It would also likely cause some error in the average output current.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 11170 points
    Hello Clinton,

    I obtained update information about NG sample from customer.
    Symptoms of NG samples have deteriorated, and the ripple current required now is 400 mA or more.
    I explained to them, "This is not defective, malfunction.".

    New question from customer.
    - How much the min / max (typ:75mApp) of ripple current required for normal operation?

    Could you answer it?

    Regards,
    ACGUY
  • 0 in reply to ACGUY
    TI__Mastermind 25500 points

    Hello ACGUY,

    Could they verify the DAP as I mentioned? If it isn't a good connection it could deteriorate over time due to expansion and contraction. Also, did you verify if the switching frequency is the same in all cases or is it changing?

    As for the ripple current, 75mA is the minimum and there really isn't a maximum. Ideally you would keep it <1A peak-to-peak to keep the AC losses under control.

    Regards,

    Clint