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TPS23731: Accuracy for Class resistor

Satoshi
Guru 19645 points
Part Number: TPS23731

・Please let me know about guaranteed accuracy for Class resister (RCLS) value.

・Example case, when set CLASS 4 and RCLS: 32Ω, can RCLS use the condition of 33Ω±0.5% or 33Ω±5%?

Best regards,

Satoshi

  • 0
    TI__Genius 15275 points

    Hi Satoshi,

    It is mainly dependent on the return current measured by the PSE which must fall in the specified range in the table below. The PSE will apply a voltage of 1.25V accross the classification resistor, when the voltage differential between VPD and VSS lies between 11 to 22V. The current drawn by the resistor along with the internal current drain of the controller and any leakage through the internal pass FET will create classification current. As long as the current falls in the range for the desired power class, that will give your tolerance for the classification resistor. 

    Very Respectfully,

    Brandon Beader

  • 0 in reply to Brandon Beader
    Guru 19645 points

    Hi Brandon

    Thank you for reply,

    Although I calculate referenced by your advice, results are differ from typ value by datasheet. (about 1mA lower than datasheet)

    I think that measure the ICLS need to addition the IDEN and IRTN, is below equation correct? 

    ⇒ICLS = (1.25V / RCLS) + 1mA

    ※Maximum IDEN is 1mA_max

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Genius 15275 points

    Hi Satoshi,

    Yes that is correct, per my statement above this is to include the internal current drain of the controller and any leakage through the internal pass FET.

    Therefore, ICLS = (1.25V / RCLS) + IDEN + IRTN

    Where, IDEN max value is 1mA and IRTN is internally limited.

    Very Respectfully,

    Brandon Beader