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Original question:

TPS23751: function check

[FAQ] How to calculate Junction Temperature for PoE PD + PWM Controller

Chen Bogey8
Mastermind 9990 points
Part Number: TPS23751

Hi Sir 

May we know how to calculation TPS23751 power dissipation?

As i know, the Tj = Pd * Rjc+ Tc, am i right?

                                                           Bogey

  • 0
    TI__Genius 9230 points
    Hi Chen,

    Rjc (junction to case) would actually be Rja (junction to ambient) for a more effective approximation. However, I would read this app note very closely: www.ti.com/.../spra953c.pdf

    The board layout will be the biggest factor in real world power dissipation.

    Regards,
    Tom A.
  • 0 in reply to Thomas Amlee
    Mastermind 9990 points
    Hi Tom
    May we know how to TPS23751 power dissipation?
    Is it Vdd *Idd? or other way?
    Bogey
  • 0 in reply to Chen Bogey8
    TI__Genius 9230 points
    Hi Chen,

    During normal operation, the approximate total power dissipated would be the TPS23751 power input (Vdd pin) + the supply for the gate drive (VC) + the power dissipated across the hotswap FET (Rdson).

    Ptotal = (Vdd*Idd) + (Ivc_op*Vvc) + (Rds(on)*Irtn^2)

    See "SUPPLY CURRENT" at the bottom of pg 9 for Idd.
    See "VC (GATE DRIVE SUPPLY)" on pg. 6 for Vc-related values.
    See "RTN (PASS DEVICE)" on pg. 9 for hotswap related values.

    In addition to this, you will have some negligible leakage current into the input pins (sleep mode pins, CS, CTL, RTN, APD).

    Regards,
    Tom A.
  • 0 in reply to Thomas Amlee
    TI__Expert 5615 points
    Bogey,

    As the marketing manager, I am going back through some older threads where the customer has not confirmed our answers as "resolved" (answering their questions to satisfaction).

    Is there anything else we could assist you with on this question?

    If not, thank you for your interest in PoE Products from Texas Instruments and it would be great if you could mark this thread as 'Resolved'.

    Thanks,