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LM5116: LM5116

Part Number: LM5116

Hi,

I am developing a DC DC controller with input voltage ranges from 15V to 100V with output voltage of 14V. I have configured the board for about 15A load current. I developed around 5 boards for testing. My observations were as follows:

1. Board 1 and 2 worked fine and i was able to get an output voltage of 14V. I checked the gate terminal voltage of high side MOSFET and found it to be around 10V in all three boards.

2. Board 3,4,5 gave only 4.65V output, even though my components were one to one the same as Board1 and Board2. The gate terminal voltage of high side MOSFET was around 4.6V.

What might be the fault in these three boards? is there any other parameters that i should verify? i checked the UVLO pin voltage which is above 1.215V in all three cases. I have almost implemented the same circuit as that of LM5116 evaluation board except for the Inductor and MOSFET along with changes in feedback loop.

I verified my circuit about 3 to 4 times but found everything almost the same.

- Anushree

  • Hi Anushree,

    Please verify the VCC voltage of the LM5116 is 7.4V. This is approximately equal to the applied gate drive voltage to the power MOSFETs. You may use the LM5116 quickstart calculator available by download from the product folder for further guidance.

    Also, note that the Toff-min spec of the LM5116 is 450ns, so you should verify operation when VIN gets close to VOUT (near dropout).

    Regards,
    Tim
  • In reply to Timothy Hegarty:

    Hi tim,

    thanks for the reply.

    I did verify the VCC voltage but seems to be the same as that of the gate voltage toggling at 4.6V approximately.

    is it because of any other fault in the board? should i cross check any other parameter?

    - Anushree

  • In reply to Anushree N:

    Anushree,

    Please forward your schematic for review. Is the VCCX pin tied to GND or is it connected to an external bias supply?

    Regards,
    Tim
  • In reply to Timothy Hegarty:

    Hi TIm,

    I have attached the TINA file for your reference. Please let me know few solutions regarding the problem.

    -AnushreeNew Design - Copy.tsc

  • In reply to Anushree N:

    Hi Anushree,

    I see that this thread is still open. Did you resolve your issue? If not, please complete the LM5116 quickstart calculator available for download from the product folder: www.ti.com/.../toolssoftware.

    Regards,
    Tim
  • In reply to Timothy Hegarty:

    Hi tim,
    I had attached the TINA file of my schematic for your review. Is the schematic OK?
    Please review and let me know if it is OK.

    In the meanwhile i shall check using the quickstart tool as well. 

    Regards
    Anushree

  • In reply to Anushree n:

    Hi Anushree,

    Were you able to fill out the quickstart file? I reviewed the TINA file. Note that the max operating voltage of VCCX is 15V (quite close to the output voltage of 14V). This level may be exceeded during a load-off transient. Have you tested without connecting VCCX to VOUT?

    Also, the Si7852 MOSFET is rated to 80V, not sufficient for a 100V input. As you know, power MOSFET choice is critical, particularly for such a high-current application.

    Regards,
    Tim
  • In reply to Timothy Hegarty:

    Hi Tim,

    Thank you for your reply.

    I have filled the quickstart file and found some values to be different from the one used in our board. I have made the necessary changes as well, and will test accordingly. 

    Also, i will test without connecting VOUT to VCCX, and analyze the problem as well.

    Thank you,

    Anushree  

  • In reply to Anushree n:

    Hi Anushree,

    I would like to close out this thread. Please click on Resolved if possible.

    Regards,
    Tim

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