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TPS7A33: We need a negative buck converter for -24V to -16V as a pre-regulator for negative LDOs.

Intellectual 575 points

Replies: 5

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Part Number: TPS7A33

I have similar questions related to this post "TPS7A33: Which negative to negative buck as pre-regulator". We have an industry power source that is the power input to our PCB, which is +24V, GND, -24V. We want to generate positive and negative (clean, low noise, high PSRR) powers of +15V, GND, -15V, using TPS7A33 and TPS7A47. A DCDC pre-regulator is needed for optimum thermal designs using LDO. We have chosen an appropriate power module, lmz14201h, for converting +24V downto +16V. And now I want to find the best DCDC that can be used to convert -24V to -16V. Note that, we do not need to generate -16V from +24V. Is there any power module or design notes from TI that can be used to down-convert -24V to -16V? Thanks in advance, and we are looking forward to your replies.
  • Byliu,

    We have PMP9624 which uses TPS40210 to converter -18VIN (up to -50VIN) down to -3.3VOUT. This is a good starting point for your design.

    We do not have much content on negative input to negative output regulators but this PMP should be a good design to refer to while you make yours.

    -Sam
  • In reply to Samuel Jaffe:

    Can I use an integrated controller DCDC for this functionality?

    BTW, we are now using TPS563240, TPS563249, and TPS56339 for generating 5V digital and 5V analog from 12V, can these chips also be used to generate -5V from -12V?

    I could not understand the principal behind PMP9624, and it seems that there are too many axillary components (R, C, L, PNP) in this design.
  • In reply to byliu:

    Byliu,

    You can use an integrated DCDC boost converter for this application.

    You are using TPS563240, TPS563249, and TPS56339 as bucks for 12V to 5V. You must use a boost converter to go from -12V to -5V so you cannot use these.

    Unfortunately we do not have a dedicated controller or converter for negative to negative conversion. This is the most straight-forward method of achieving your circuit.

    -Sam
  • In reply to Samuel Jaffe:

    Thanks, why there isn't any (easy to use, like TI's SIMPLE and SWIFT) negative in negative out DCDCs?
  • In reply to byliu:

    Byliu,

    The business case is not there. There are many other parts we are building which will sell in higher volumes than a niche part like negative to negative. It's a business :)

    -Sam

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