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DC/DC converter help needed - background on power calculations and whether device specs exceeded

PeterH
Prodigy 125 points
Other Parts Discussed in Thread: TPS40042

Hi there,

I have a pcb where I would like to add an Arria 2GX125 FPGA.  At present the pcb doesn't have the supply for the 0.9V rail.

I'm considering the TPS40042 using the design generated by SwitcherPro with Vin = 3.3V and Vout = 0.9V with Iout = 9A.

The pcb resides in a housing with no airflow & heatsink only and has a measured temp = 63.5 degC on the board.  Can you tell me if I'm going to exceed the TPS40042 specs on junction temp/operating temp and go thru some power dissipation calculations relating to temperature.  If there are any tutorials or background materials relating to DC/DC power calculations please forward.

Also, how high of an ambient or pcb temp can I tolerate above 63.5 degC before device shutdown or I violate the recommended operating junction temp?

Thanks,

Peter

  • 0
    TI__Guru**** 150670 points

    I suggest that you read the ground rules post at the top of this forum and re-title your post appropriately.  We have thousands of DC/DC converters, so you'll need to make sure the right engineer sees this post by putting the part number at the beginning of the title.

  • 0
    TI__Genius 17240 points

    Hi Peter,

    As described in the Package Power Dissipation section on page 15 of the datasheet, the total power dissipation PT in the controller IC can be calculated. The maximum power capability of the package is dependent on the layout as well as air flow. For rough estimate, the junction-to-ambient thermal impedance (theta_ja) of the DRC package is 48C/W as given on page 3 of the datasheet. Then to maintain the junction temp below Tj = 125C, the max ambient temp will be Ta = Tj - PTx theta_ja.

    Regards,

    Na