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LM5050-1: LM5050 Part overheat when Vs pin connected to Vout

Sergejs Leonovs
Prodigy 20 points
Part Number: LM5050-1
Other Parts Discussed in Thread: LM5050-2

Hello TI,

I have an issue with the O-Ring FET Controller.
FET used  - FDMC8327


When VS pin is connected to the Vout Pin, LM5050 will start to consume a lot of power. As soon as Vout 5V - current  to VS pin is 100mA and will grow with the increase of Vin.
Initially (Vin-5V):  Vds around 50mV  and Vgs = 2.2V with the Increase of the Vin -> LM5050 overheats -> Vgs will decrees and Vds increase.

I then tried to connect VS pin to a separate supply - > VS = 3.3V current consumption 45mA 
The part seems to kind of work Vds - 40mV and Vgs ~ 3.2V  and seem to be roughly the same across the swipe of Vin 5 - 24V and 1A. No Overheat of the Part either.

But. disconnecting LM5050 VS Pin from 3.3V and leaving it floating gives similar result as if it is connected to 3.3V.

So the question is what is the issue with the part? It doesn't seem to work in my application appropriately, or I am missing something?

Testing setup consists of only LM5050 and its required circuitry so nothing else is connected on the Vout, but the electronic load.
Schematic Diagram Is attached Including PCB Layout of LM5050 section

Thank You for the Help!

  • 0
    TI__Genius 16305 points
    Hi

    Can you confirm if you are using LM5050-1 or LM5050-2.
    Schematic shows LM5050-2, but is does not have a Vs pin.

    Also, let us know if you are using electronic load in constant current or constant resistance mode?

    Regards,
    Kari.
  • 0 in reply to Karikalan Selvaraj
    Prodigy 20 points

    Hi Kari !

    Thank you for your reply!
    I complicatedly missed that there is two LM5050's. I was using LM5050-2 for my testings and now see what is the issue. Circuit was designed to be used with LM5050-1 and get it powered trough VS pin. No surprise It overheats.
    The Electronic Load is in CC mode.

    As far as I got it, the main difference between the two is that one has open drain output for the FET test circuit. Is there any other differences between the LM5050-1 and LM5050-2 I need to be aware of?
    Thank You!

  • 0 in reply to Sergejs Leonovs
    TI__Genius 16305 points
    Hi Sergejs,

    No other difference, other that LM5050-1 has seperate Vs pin to provide power.

    If you think your question is answered, please click " this resolved my issue " button at the end .

    Regards,
    Kari.