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TPS7B7702-Q1: Thermal performance

Arie Li
Expert 3390 points
Part Number: TPS7B7702-Q1

Hi experts,

For TPS7B7702-Q1, do you have a curve of RθJA vs. copper area like below?

For VIN=16, VOUT=8V, IOUT1=0.2A, IOUT2=0.2A, the total power dissipation will be 3.2W, if using RθJA=40.3C/W in datasheet, TA=75C, the calculated TJ will exceed the max operating TJ 150C. So can TPS7B7702-Q1 support this application? Is it necessary to add heat-sink? Thank you.

Arie

  • 0
    TI__Guru 50025 points

    Hi Arie,

    This is not a typical curve that we measure during validation/characterization. This app note shows empirical data for the same idea that this plot shows:

    An empirical analysis of the impact of board layout on LDO thermal performance

    Thermal shutdown for TPS7B77 is 175C (typ). To get the junction temperature below 175C the customer would need to reduce the RθJA to about 31.25C/W plus some margin by adding more copper around the part, which is doable if they have the space for a large GND copper pour around the part, thermal vias under the package, and they connect the NC pins to GND as well. I'll note that the copper on the layer that the LDO is on is the best layer for dissipating heat since the heat does not have to go through vias. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Expert 3390 points

    Hi Nick,

    Thanks for your quick reply. The thermal shutdown TJ is 175C while the max operating TJ is 150C. Why using 175C for thermal calculation instead of 150C? If using 150C, then the RθJA should be reduced to 23.4C/W, is it still doable by optimizing the PCB layout? Thanks.

    Arie

  • 0 in reply to Arie Li
    TI__Guru 50025 points

    Hi Arie,

    I meant to include - thermal shutdown is 175C (typ), 150C (min), 200C (max). So you are correct in that to be sure it will never enter thermal shutdown it should be designed for less than 150C junction temperature operation. It is possible to reduce the RθJA by more than half given there is sufficient copper as in the plot and as the app note shows. If they cannot have at least 100cm^2 of copper or more around the TPS7B77-Q1 then it may not be enough to have enough margin to be confident it will not enter thermal shutdown.

    Regards,

    Nick