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LM5161: Why VIN upper limit 80V in eval modules? Why not 100V?

Vlad Blanshey
Intellectual 770 points
Part Number: LM5161
Other Parts Discussed in Thread: LM5116

My battery voltage range is from 64v to 84V , I need to convert to 12V. LM5161 allows up to 100VIN but both evaluation modules limit to 80V . I can't even try eval module as it is too low volts. Interestingly the other TI DC-DC buck converter  LM5116 also allows 100VIN yet it's evaluation module also limited to 80V. Developers surely had some valid reason to not use max voltage allowed for LM5161. What is it? My unqualified guess is that efficiency might drop more dramatically with higher input voltage. Was this the reason? If it is I'd like to know what efficiency can be expected for 84V input to 12v Output.

Webench made a design for my request up to 90V no problem - compared to LM5161 eval modules seems the only difference is a voltage divider for EN-UVLO input.

Thanks in advance for any useful input.

  • 0
    Intellectual 770 points

    I can think of one reason to limit input voltage to 80V : to allow use of the input caps rated for 100V which should be 15-20% higher the rail voltage. If that's the only reason I can still run those eval boards with 100V caps and 84V input volts providing a clean input without too big spikes at turning on. if that's the only reason this would be the answer but...

    If I am missing something else please somebody let me know.

  • 0 in reply to Vlad Blanshey
    TI__Mastermind 40040 points

    Hello Vlad,

    You can use the device for your application, the recommended operating Vin is 100V and below.  

    However, 

    If you decide to run close to 100V, be sure that at no instance you exceed the 100V at any given time as you may cause the device to fail. 

    This can be one of the reasons why the EVM was specified to work at 80V and not 100V.  As we have no control of the input cable length.  If a customer were to take the EVM and use long cables and "hot plug" the input cable into a 100V supply the input will likely overshoot and exceed the 100V max rating.

    Hope this helps?

    David.