• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 320 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

Question on Application report SNVA856A: Working With Inverting Buck-Boost Converters

Kai Cheong Tam
Prodigy 40 points


Hi,

I have come across this document when searching TI web site about positive to negative buck-boost regulator.

I have a question on section 7.4 regarding output clamp. Specifically I have an issue on Figure 13 and the additional clamp diode:

If the negative output is pulled to positive by the biasing circuit in an operational amplifier to +0.1V and cannot start, is there any other techniques that can clamp the -VOUT even closer to ground (I mean practically 0V)?

Thank you.

Best,

Eric

  • 0
    TI__Guru 74475 points

    Hello

    I suppose that you could try to find a very low voltage drop diode, such as a Ge.

    However, I think that the low drop of a Schottky diode is low enough that it would not turn on any junctions

    of the regulator.  The best way to test is to check your particular regulator with your load.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 40 points

    Hi. Thank you for your reply. I have not expected the author of the application report to answer my question so quickly. =)

    Another question that is related to the same document is whether certain control modes, such as current-mode, COT (D-CAP for TI?),etc will be unsuitable for this method?

    I expect different control modes may behave differently under buck-boost topology and the feedback network needs to change but I am not sure if control modes like COT or PFM would work at all.

    Your clarification is much appreciated.

    Eric

  • 0 in reply to Kai Cheong Tam
    TI__Mastermind 23845 points

    Hi,

    We will follow up with your question on the next working day. 

    Thank you

    -Arief

  • +1 in reply to Arief Hernadi
    TI__Guru 74475 points

    Hello

    I believe that a COT or device with PFM mode should work in an IBB topology.  

    Some characteristics may be different between the buck and IBB, but topologies other than

    constant frequency PWM should work in an IBB.

    The best way to determine if any particular device will work as you expect, is to get an EVM

    for that device from TI and test on the bench.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 40 points

    Thanks for your opinion. Please allow me to express my opinion in here a little bit.

    Many EVMs have already soldered the thermal pad of the chip to the ground. This make them impossible to test as IBB.

    The other problem lies on the current chip shortage has severely limited the design choices that are available.

    The few that are already tested by TI (or by other companies) as IBB are not in stock by the major distributors.

    I can also use other untested buck regulators from TI or from other manufacturers but then IBB test boards need to be first constructed and verified before transferring to the actual design. This will increase the development cost and time. This is why I would rather contact TI technical support for their experience  on this kind of conversion, (in which TI has done the most amongst all others) so that I can (hopefully) narrow down the choices.

    Thank you again for your help. It is much appreciated.