• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 64 subscribers
  • Views 196 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMR51420: Can this converter be used as an inverting buck boost regulator reliably

Craig Javid
Prodigy 40 points
Part Number: LMR51420
Other Parts Discussed in Thread: LMR36510, LMR38010

My understanding from this device's topology that I can use it in the classic inverting case as shown in your literature with the positive output grounded as shown below.  My application is for 24V input and a -12V output at 800 mA.  Am I missing any considerations that would make the LMR51420 a bad choice?

  • 0
    TI__Mastermind 23630 points

    Hi Craig,

    Usually we would recommend an IC with a higher maximum input rating to reduce stress on the switch. I would recommend something around the 42Vin range or higher. But other than that, a converter can be used in the IBB design.

    Thanks,

    Richard

  • 0
    Prodigy 40 points

    Hi Richard:

    I do not think that either output MOSFET in the LMR51420 sees the absolute value of 24V - (-12V) = 36V in the inverting buck topology.  Am I wrongt?  Assuming I am correct then are you saying that the 36V Vin rating of the LM51420 does not provide enough margin ?

    If that is true, would a device such s the LM38020-Q1 be a better choice.  I was trying to stick with the SOT package and avoid the HSOIC8 package.  Can you make a better recommendation?  I was trying to use the same part for four separate buck converters as well as one inverting buck converter.

    Thank you

  • 0 in reply to Craig Javid
    Prodigy 40 points

    Hi Richard:

    I understand that Vin is limited to Vin(max) + Vout  so at a 36V Vin and -12V Vout our maximum input would be 36-12=24V so I understand your concern about too much stress.  If I substituted the LMR36510 with a Vinmax of 65V is a better choice given that I require less than 1.0A.  Do you agree?

    Thanks

  • +1 in reply to Craig Javid
    TI__Mastermind 23630 points

    Hi Craig,

    Yes, the LMR36510 or LMR38010 would both be suitable. They're both HSOIC8, the main difference is that the LMR36510 is a fixed 400kHz, and the LMR38010 is a fixed 2p2MHz, so your inductor would be smaller with the LMR38010.  

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 40 points

    Thank you for your support!