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LMG5200 Thermal Management

user4294430
Prodigy 10 points
Other Parts Discussed in Thread: LMG5200

Hello! I am having some problems with thermal management when trying to build a 60 W  ZVS buck-converter. I know that it is very inaccurate to use the thermal information given in the datasheet to calculate the junction temperature but, by the way, I would like to know in which conditions have you measured that parameters. Was made in the evaluation board? or in another better conditions?

Thanks a lot.

  • 0
    TI__Expert 4840 points

    Hello,

    I would like to make a few comments that might point you in the right direction.

    The datasheet contains calculations to get a close estimate of the power losses inside the LMG5200 for a hard-switched converter case.

    The junction temperature is then determined by how well the power generated inside the IC is conducted out i.e. how good of a heat-sink you have and the ambient temperature.

    If you know the thermal resistance for your heat-sink  and for your TIM (Thermal Interface Material) thermal resistance, you can sum those two with the Junction-to-board thermal resistance of the LMG5200, and depending on your ambient temperature you can determine the junction temperature.

    This calculation is purely a thermal calculation and has no correlation with the electrical parameters.

    In your particular case, when dealing with a ZVS circuit, instead of Coss and switching losses, you will have to consider the  conduction losses for the  circulating currents in the resonant tank (which include the output capacitance of the FETs).

    Finally consider what the losses associated with the circulating currents are, and compare them with switching losses in a hard-switched equivalent circuit; because of the elevated dv/dt of GaN, you might find the latter to be lower.