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LM5116-HT: High temperature issues

Roger Jefferies
Prodigy 80 points
Part Number: LM5116-HT
Other Parts Discussed in Thread: LM5116

Tool/software:

I have a high temperature issue with a LM5116 regulator. The design is for a 24V 4A power supply with an input voltage range from 30V to 70V.

The regulator works well until the ambient temperature reaches 130C, when the output reduces to 13.5V at a 4A load

The deltaT< (regulator-heat sink), is 15C.

The schematic is:

24V buck supply.pdf

Can you think of any reason for the voltage to reduce this badly

Regards

Roger Jefferies

  • 0
    TI__Guru* 75882 points

    Hi Roger,

    You can complete the LM5116 quickstart to check the loop. Also check that the 33uH inductor is not saturating at hot.

    If Vin = 70V, consider using 80V FETs (no need for 100V). This will help with power loss and the overall temperature rise of the PCB. 

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 80 points

    Hi Tim.

    We have been playing with inductors. We have fitted a 47uH inductor that is rated to 200C.

    We also re-ran the quick start and changed a few vales in the compensation network.

    We have now acheived the following

    New Inductor New Snubber 22r 100pF Current Sense 5mR
    Temperature Vin I in A V out Load Hold Time
    24 50 1.11 23.4 2 Initial
    24 50 1.1 23.4 2 20m
    24 50 2.1 22.6 4 n/a
    120 50 1.12 23.5 2 40m
    120 50 4 V Drops
    130 50 1.13 23 2 20m
    130 50 4
    140 50 1.12 23.01 2 20m
    140 50 4
    150 50 1.12 22.98 2 20m

    Any further suggestions please

    Regards

    Roger

  • 0 in reply to Roger Jefferies
    TI__Guru* 78675 points

    Hi Roger,

    The responsible engineer is current out of office and he will return on Friday.  Please wait for his advices no latter than next Monday. 

    Regards,

    Youhao

  • 0 in reply to Youhao Xi
    TI__Guru 61601 points

    Hello Roger 

    Looks like it is current limited. Please try ~ 10m-15mOhm at R6 and check if an improvement.

    -EL

  • 0 in reply to EricLee
    TI__Guru 61601 points

    I am closing this thread since I have not heard from you for sometime.
    If you are still trying to resolve the issue, please feel free to open a new thread. Thanks
    - EL