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LM51772EVM-HP: LM51772 EVM Reverse Current and Voltage and other Questions

Paul H.
Prodigy 10 points
Part Number: LM51772EVM-HP
Other Parts Discussed in Thread: LM51772

Tool/software:

LM51772 EVM Board Setup

  • Left side: power supply

  • Right side: Battery

To force a current flow from right to left, the output voltage of the LM51772 EVM board is set lower than the battery voltage.

Question 1: What happens if the reverse-set current cannot flow into the power supply? How high does the LM51772 EVM board increase the voltage?

General questions:

Question 2: Are there greater electromagnetic issues when using other inductors, for example the Coilcraft SER2915L-472KL, since this one is not completely enclosed?

Question 3: Is it possible to install the board in a steel enclosure without causing additional problems?

  • 0
    TI__Intellectual 1380 points

    Hi Paul,

    LM51772 is a bi-directional buck boost, the current direction is not decided voltage level at battery or the output as you mentioned. You could refer to below apps note, it explains how the current direction is defined and how to change the current direction.

    Reverse Current Operation of the LM5177 Buck-Boost Converter

  • 0 in reply to Alicia Hao
    TI__Guru 68565 points

    Hello Paul,

    If the power supply is not able to take current from the load, then you need to operate the device in DEM which does not allow negative current.

    You can use any inductor as long as it fulfills the basic needs of the converter, like recommended inductance (see quickstart calculator) for your system.

    As long as you make sure that there is no short to the enclosure and the heat can dissipate out of the enclosure, I do not see any issues with putting the board into an enclosure. Be aware that the boards are not for resale, as written on them.

    Best regards,
    Brigitte

  • 0 in reply to Alicia Hao
    Prodigy 10 points

    Hello Alicia,

    actually the current direction is exactly decided by voltage difference at the output as i mentioned. You can find it word by word in the correct application note: www.ti.com/.../sdaa068.pdf where it says under 3.5: "As long as the output voltage is above the set level the power stage operates in reverse operation."

    For everyone that may be as blind as I, the solution for my provlem is of course the IVP Input Voltage Protection. Don't know how I could have missed that one for so long, but I did.