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Calculate Tj from power dissipation of body diode

S.Satoshi
Guru 21675 points
Other Parts Discussed in Thread: CSD17382F4

Hi,

Please let me ask how to calculate junction temperature. 

In case of CSD17382F4, the Pd of body diode at ISD=0.02A will be 0.6V so Pd=12mW. Then can I calculate Tj by using RθJA and this Pd, and Tj can allow up to Tj(max)?

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Mastermind 18200 points
    Sonoki-san,
    Your calculation of the power dissipation is correct. I would caution against using the RthJA on the datasheet because RthJA is a very board specific parameter, especially for these tiny parts. The RthJA for your board might be quite different, or somewhere in between the min and max RthJA's provided on the datasheet.

    Also, make sure you pay attention to the Id vs Temp curve provided in the datasheet, as that shows how max allowable current for your device deviates as the ambient environment decrease. This curve can easily be recalculated for any RthJA, but again we would have to know that parameter specific to your board.
  • 0 in reply to Brett Barr1
    Guru 21675 points

    Hi Brett,

    Thank you for your comment. I'll pay attention to Id vs Temp curve. Again please let me clarify following question.

    • Can Id in datasheet be applied both current through Ron and body diode?

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    TI__Mastermind 18200 points
    Sonoki-san,
    From an electromigration or package perspective, the answer is yes.

    From a thermal perspective, it all comes down to thermals, which can be calculated from the Pd provided on the curve above and the given junction to ambient thermal impedance for your board.