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TPS40425: Current monitor Accuracy

T Kishi
Genius 4425 points
Part Number: TPS40425

Hi

My customer has question.

The customer uses TPS40425 +CSD95378B in the 3 Phase circuit.

An alarm was raised with a current value lower than [OCW] [OCF] set during high load evaluation.

The customer is using [FUSION DIGITAL POWER DESIGNER].

〇set
　OCW:40A
　OCF:42A

〇OCW
　Master ch1:31.75A
　Master ch2:31.75A
　Slave   ch1:33.4A

〇OCF
　Master ch1:33.9A
　Master ch2:33.9A
　Slave   ch1:35.7A

※An alarm stands only on the master side.

Is there anything you can think about about the cause of the gap?

Also, when trying to measure the IOUT / REFIN line [OCF] and it can not be measured well.
Is there a correct measurement method?

Best Regad

T Kishi

  • 0
    TI__Mastermind 24075 points
    Hello,

    Which falut is declared, OC warning or OC fault?
    TPS40425 use inductor peak current (not average current) for OCW and OCF detection. Can you calculate the inductor peak current?
    Also, the OCW/OCF itself has tolerance.

    To measure the current sense signal from CSD85378B, you can use a different probe to measure the voltage between IOUT and REFIN.
    If different probe is not available, use a portable multimeter to measure the DC voltage value between IOUT and REFIN, then add calcuated ripple to get peak voltage.

    Thanks
    Qian
  • 0 in reply to Qian Chen
    Genius 4425 points
    Hi Qian

    Thank you for reply.

    Both are about 7 A below the set value and an alarm is occur.
    〇Load to be OC warning
    　Master ch1:31.75A
    　Master ch2:31.75A
    　Slave ch1:33.4A

    〇Load to be OC fault
    　Master ch1:33.9A
    　Master ch2:33.9A
    　Slave ch1:35.7A

    Customers use CSD95378B in "Smart Power Mode".
    Is CSD95378B also detected by Peak current of Inductor?

    Regard
    T Kishi
  • 0 in reply to T Kishi
    TI__Mastermind 24075 points

    Hello,

    The inductor current has DC value (average value) and AC value (peak to peak ripple). 

    The CSD95378B current sense signal (voltage between IOUT and REFIN) includes both DC value and AC value. 

    Thanks

    Qian