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the TPS40305 inductor is very hot !

Carlton
Prodigy 20 points
Other Parts Discussed in Thread: TPS40305

I'm using TPS40305 for my modules.

12Vin, Output 5V, 3.3V, 1.8V, 1.2V. But I found the output inductor is very hot (around 70Deg.C) at output current 1A.

I changed the output inductor to Vishay part and the inductor is still hot.

What is the possible root cause for this issue?

thanks!

  • 0
    TI__Guru 52445 points

    Carlton,

     

    Inductor heating is typically a result of 2 items:

     

    1) Copper Losses due to RMS current through the inductor

    2) Core losses due to the AC flux in the inductor.

     

    The later may be an issue depending on the ripple current in the inductor and the inductor core material at the 1.2MHz switching frequency of the TPS40305 converter.

    The prior would likely require a lot more than 1A of RMS current.

    1) What is the ambient temperature?  Is it 25C so the inductor surface temperature is 45C rise above ambient?

    2) Have you checked to make sure the output and switching waveforms are stable?

    3) What is the input current at 1A output current?

    4) Have you tried Vishay's core loss estimator for the Vishay inductor?

  • 0 in reply to Peter James Miller
    TI__Guru 52445 points

    Carlton,

     

    I used Vishay's Inductor Loss calculator http://www.vishay.com/inductors/calculator/calculator/ for your parameters:

     

    12V to 5V @ 1.2MHz using the 0.33uH IHPL2525BD inductor at 1A DC load current.

    The core loss is 1.171W

    The AC conduction loss is 433mW

    The total power loss is 1.608W for an expected surface temperature of 71.5C at 25C ambient.

    With a lower output voltage (1.2V) the temperature should be much lower, about 35C due to the much lower ripple current.  Depending on your design requirements, you may want to consider a higher inductor value for the higher output voltages.  the 0.33uH inductor is producing more than 7A of peak to peak ripple current, which is dissipating most of your power in core losses.

  • 0 in reply to Peter James Miller
    TI__Guru 52445 points

    If you can afford the additional height of a 3mm tall inductor, the IHLP2525CZ series 0.33uH inductor http://www.vishay.com/inductors/list/product-34172/ has about 20% lower losses due to the larger magnetic volume available.  This would reduce the surface temperature about 9 degrees C and save a little more than half a watt.

    The pulse inductor series NEW! PG0426NL is a little taller at 3.2mm max, but offers much better core loss characteristics in a 7.5mm x 7mm footprint.

  • 0 in reply to Peter James Miller
    Prodigy 20 points

    Hi Peter ,

         Thank you very much! I will try to use the PG0426NL for my power moudle.

         thank you !

  • 0 in reply to Carlton
    TI__Guru 52445 points

    Carlton,

    I'm really glad that we could help you.