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LM5000: Negative in, Positive out buck-boost

Ryan.Bishop
Expert 3900 points
Part Number: LM5000

Hello,

I am working with one of our customers on a power supply design using LM5000 based on this app note: www.ti.com/.../snva740.pdf

Vin= -12V
Vout= 3.3V
Load= 300mA
Topology: Non-Isolated Buck-Boost

We have two questions:

  1. Compensation: How should we go about selecting Rc, Cc, and Cc2? Should we follow the guidelines in the LM5000 datasheet even though that isn't meant for a buck-boost topology?

  2. We found this app note for buck-boost topology. We are planning to use this document to selected the inductor, input/output capacitors, and diode. Is that okay, or should we stick to the datasheet for those components (even thought the datasheet is not written for buck-boost).
      1. www.ti.com/.../slva059a.pdf

Thank you,
Ryan Bishop

  • 0
    TI__Guru 68495 points
    Hi Ryan,

    The inverting buck-boost is still a boost if you reference all signal to the negative input rail. Namely (Vo-Vin) and (-Vin) satisfy the boost operating principle. So, please follow the datasheet loop compensation equations to select the compensation component values.

    Yes you can follow slva059a.pdf to select those components.

    Thanks,
    Youhao