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LM5122: Dual Phase Boost Schematic

Lee Jong Chul
Prodigy 20 points
Part Number: LM5122
Other Parts Discussed in Thread: PMP7921,

Tool/software:

I've seen the PMP7850 and PMP7921 designs.

It is designed with LM5122 Dual Phase Boost.

I am trying to design Vin 6~35V Vout 12V Iout 84A by referring to the PMP7850 and PMP7921 models, but I am having difficulty.

If you modify which part of the circuit, what results will you get?

  • 0
    TI__Mastermind 20620 points

    Hi Lee,

    Thanks for using the e2e forum.

    The two reference designs you found should already be very good starting point for your design.
    My main question would be, what is causing difficulties for your design.

    The effect of each device pin functionality is described in detail in the LM5122 datasheet. Here you will find what results can be expected when changing parts of the circuit.

    General checks for the power stage that I can recommend are:
    - Are the current and voltage ratings of inductors, FETs, and input/output caps fit for the power requirements?
    (You can use our power stage designer tool to calculate expected peak currents/voltages in a boost topology: https://www.ti.com/tool/POWERSTAGE-DESIGNER )
    - Is switching frequency, softstart time and loop compensation fit for your design application as well?
    - Are you following the design guidelines of the datasheet to account for good thermal and EMI behavior?

    Please let me know if you have any additional questions.
    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 20 points

    I have checked the contents carefully. Can't PMP7921 output 84A continuously? Additionally, please recommend Power N-Mosfet for continuous operation at 100A in the PMP7921 circuit.

  • 0 in reply to Lee Jong Chul
    TI__Mastermind 20620 points

    Hi Lee,

    The PMP7921 is rated for 84A peak load condition, meaning 42A per phase. There is nothing mentioned on how long the application can support these peak load conditions, but I would assume thermal behavior can be a risk if the application runs under peak load for long periods of time.

    Unfortunately, I am not an expert for FETs, so I cannot give a good component recommendation.
    Important checks are that voltage ratings of Vgs and Vds match with the application requirements. Low Rds-on will reduce conduction losses. FETs normally do not break from overcurrent, but actually from overheat due to high current flow, so please keep this in mind when comparing FET parts.

    Best regards,
    Niklas