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LM5176: LM5176 problem in boost mode and in high power

Part Number: LM5176

Hello,

I am building a buck-boost converter which needs to have the following parameters,

- Input voltage range : [8 - 55] V

- Output voltage : 12.5V

- Max output power : 500W

Currently I am facing two major problems:

- For input voltages less than 13V the output voltage doesn't regulate to 12.5V (in no load), so it doesn't work properly both in buck-boost region and in boost mode.

- For output load more than 20A ( >250W) the converter stops working immediately - the output voltage is not anymore regulated to 12.5V

I have run the design in Webench and everything seemed fine. I attach the schematics.

Thanks for the help

  • Hi Nikos,

    Thank you for considering the Lm5176. Your schematic shows inadequate inductor rating: 39A while you want to support 500W. Also, the single MOSFETs does not support 500W. Even for 200W we recommend parallel MOSFETs to share the power dissipation. I am afraid the single LM5176 cannot support 500W owing to the driver strength limited to 3A. You should consider 2x LM5176 in parallel, each using paralleled MOSFETs, to get 500W. Refer to www.ti.com/.../snva826 for the implementation.

    Regarding your design, recommend you to check against your LM5176 design calculator available at www.ti.com/.../snvc208. If you following snva826, each LM5176 would be 250W, and use 250W as the max power in the calculator.

    Thanks,
    Youhao Xi, Applications Engineering.