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LM51231-Q1: LM51231-Q1 MOS heat dissipation design

Imelda Zhang
Expert 5025 points
Part Number: LM51231-Q1
Other Parts Discussed in Thread: LM5155-Q1

Hi Expert,

Thanks a lot for your warm help on my daily work!

My customer using LM5155-Q1 as a power supply to audio amplifier.

Pout=160W, Vout=14.4, Vin=10.7,Fsw=2.1M, Ambient temprature=80℃

If customer using 4 Mosfet as we shown on EVM, the power dissipation of Mos is too high. What's more the Fsw is around 400KHz on EVM. Should Customer do external  MOS heat dissipation design on PCB? 

If customer using 2 Mosfet, is there any recommanded MOS for them to use?

Kind Regards

Imelda

  • 0
    TI__Mastermind 19575 points

    Hello Imelda,

    Nice to talk to you via e2e as well.

    I guess that LM5155-Q1 is a typo, right?

    I cannot really propose any FET other than those that you know from our various EVMs.

    For a high switching frequency the parasitic capacitances of the FET should be small to keep the switching losses low.

    The RDS On of the High Side FET must NOT be too low, otherwise the zero current detection of the LM51231 will no longer work. 

    The conduction losses should be pretty independent from the switching frequency.

    The EVM is configured for 24V output voltage. Has this been modified?
    Also, has an EVM been modified for 2.1 MHz?       This would at least require a replacement of the inductor.

    On the NON-modified EVM, when going from VIN=14V to VOUT=24V and connecting a160W load, I would estimate that the FETs will heat up to about 100°C at room temperature without any airflow.

    Running at 2.1MHz the switching losses will be even higher.

    So, if the ambient temperature is already sitting at 80°C, I would definitely expect that the FETs will need some means of cooling.

    Best regards

    Harry