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LM5060: Large mosfet resistive load blows mosfet

Aurimas Niekis83
Prodigy 30 points
Part Number: LM5060

I have designed a module for switching high current loads like 100A-200A using LM5060 and Mosfet in SOT-227 package (IXFN420N10T) and we have connected a resistive load of around 50A. At first, everything is powered off, then enable is set it opens up, but then its unable to close it anymore and stays always open. Gate to Source is 0.5 ohm and Gate to Drain is 22 ohm.

We use basic example schematic with added 0.01uF capacitor on the gate.

Any idea why this happens?

  • 0
    TI__Expert 5940 points
    Aurimas

    Use the design calculator tool to help with the design. It can be downloaded from the LM5060 product page. It is also at www.ti.com/hotswap along with more app notes and video tutorials. The Ixys FET has good SOA and tremendous heatsink capability, if a stout one is attached with airflow. Is the failure after heat up or during power up? You need to account for a few things at power up. Cout and the fact that you have a resistive load that applies current from 0v to full Vout. The energy dissipated in the FET is the same as the charge for Cout (1/2 Cv^2) + the additional load applied as Vout ramps. It is highly recommended against using a straight resistive load and use the LM5060 PG output to enable downstream loading. This take a large stess off the FET at power up.

    The FET will dissipate ~ 9W during DC 50A conditions. So heatsink theta with airflow needs to be in the 3-5 C/W range I would assume, depending on your ambient.

    Recommend you look at Vin, Vout, Vgate, I-in (not I-out as you want to be sure you look at the FET current), Vtimer at power up. You can then determine the total power vs time the FET sees and check against the SOA plot.

    Brian
  • 0 in reply to Brian Daugherty
    Prodigy 30 points
    As I asked the question in another topic, and I guess the problem was too high Vgate generated by LM5060 as mosfet Vgs max is +/- 20V
  • 0 in reply to Aurimas Niekis83
    TI__Expert 5940 points
    Aurimas,

    LM5060 GS voltage is typically 12v. There is a 16.8v clamp internal you can see on the block diagram. +/- 20v rating is not an issue.

    Brian
  • 0 in reply to Brian Daugherty
    Prodigy 30 points
    Maybe you can direct to that design calculator I can't find it on product page.
  • 0 in reply to Aurimas Niekis83
    TI__Expert 5940 points
    Aurimas,

    Yes, you are correct. It is randomly missing from the product page. Go to www.ti.com/hotswap. This specific landing page has all of the calculator tools, app notes, and tutorials.

    Brian