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Hot Swap controller LM5069MM-1

vinoth kumar
Prodigy 40 points
Other Parts Discussed in Thread: LM5069

Hi,

I am currently using the LM5069 part in one of the power supply application,in which I am switching the 40V from a DC-DC Converter to the output load.Now I am facing a issue of Mosfet failure in two conditions.

There are two power supply boards:

1). 40V,5A Current limit was set to 5.25A

2).40V,18A, Current limit was set to 19A

i). When I add a capacitive load at the output of the controller and mosfet source, the mosfet was failed due to the inrush current offered by the Capacitive load of 2000uF and above, then we increased the timer Capacitor of the controller to1uF from 0.1uF in order to avoid the over-load shutdown due to inrush during the startup. Then the 40V output was coming properly. Then we increased the timer cap to 4.7uF in order to avoid OL- shutdown with 4000uF capacitance. Now the board is working in 5A current application.

The DC-DC Converter used in the board has an inbuilt short circuit protection (Hiccup mode), when we checked for the short circuit test by shorting the Mosfet source to ground the Mosfet failed again. We suspect the problem could be due to the Safe operating area of the mosfet.

Hotswap part number : LM5069mm-1

Mosfet part number : SI7174DP-T1-GE3

The similar problem exists in other 40V,18A board . So request you to help on the same.

Thanks in advance,

Vinoth

  • 0
    TI__Expert 7990 points

    This question was previously submitted by Velmurugan (TI person) through the internal forum.  Please work together to consolidate your questions, avoiding duplication of effort on all parts.

    The response was as below.

    --------------------------------------------------------------------------------------------

    From the looks of the SOA of that device, you can only allow 50W dissipation for 100 ms, or roughly 150W for 10 ms,   and you do not want to come close to this value.  It looks like the timer cap. you have chosen here, in combination with a 1 mOhm sense resistor gives a huge power dissipation.  This will almost surely result in a blown FET.

    By looking at the calculator online (go to http://www.national.com/pf/LM/LM5069.html#Tools,  the LM5069_Component_Calculator.xls) it looks like you can set the power limit to 40W (Rpwr = 4k) and the timer cap. to 2.2 uF to start up in less than 100 ms for an output load of 4400 uF.

    Hope this helps.

    Regards,

    Mike Hartshorne

    (520)751-2363

     

  • 0 in reply to Martin Patoka
    Prodigy 40 points

    Hi Mike,

     

    Thanks for the reply,

     

    Please look in to the attached waveforms and request you suggest the mosfet and also the timer capacitor used is 4.7uF . I need the same for 18A supply.

     

    Regards,

     

    Vinoth

  • 0 in reply to vinoth kumar
    Prodigy 40 points

    Hi Mike,

    The schematic values are mentioned wrong and the actual sense resistor value is 10m ohm and the power limit value is 68K used in the board.

     

    For the 18A board, the current sense resistor is 3mohm and the power limit is 68k.

    Regards,

    Vinoth