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TPS54386PWPR Inductors getting hot

Ed Wilinski
Prodigy 120 points

We’re running our units and we noticed that the 2 inductors used in our TI dual power supply switcher (part # TPS54386PWPR) are running hot. We’re using the Wurth 74477110 and 74477112 for a +3.8V and +5V supplies respectively.

The +3.8 supply is powering a Cell Module Simcom SIM5320AD and the +5V supply is powering an LCD and is also feeding a 3.3V LDO that powers the rest of our board.


What we would like help with is why are the inductors getting hot? Should we use a different inductor?

  • 0
    TI__Guru**** 191445 points
    The 74477110 should be ok-ish. it is rated for 5 A dT of 40 C. The 74477112 is only rated for 3.37 A. It is probably getting pretty hot. What is your input voltage and output currents? The values look a little low (the EVM uses 22uH). You can calculate the minimum recommended value. I wpuld probaly size the inductors for current at or above the current limit for each channel.
  • 0 in reply to JohnTucker
    Prodigy 120 points
    The input Voltage is 12VDC and +3.8Vout @ worst case 0.7A and +5V @ worst case 1A.

    Regards,

    Ed
  • 0 in reply to Ed Wilinski
    TI__Guru**** 191445 points
    Using the standard design equation for inductors:
    For 3.7 V output, if you design for the full rated output current of 3 A, then 4.7 uH. For 0.7 A, 22 uH.
    For 5 V output, if you design for the full rated output current of 3 A, then 4.7 uH. For 1 A, 18 uH.

    So those 10 and 12 uH inductors you chose are about midway. It just depends on how much ripple you want and how much of your load range you want to operate in DCM vs CCM.