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LM7481-Q1: schmatic review

Sky Kao
Prodigy 100 points
Part Number: LM7481-Q1

Tool/software:



Would you have any suggestions for modifications to the schematic?

  • 0
    TI__Genius 15485 points

    Hi Sky,

    Welcome to e2e!

    Looks like the FETs are connected incorrectly. Or maybe the image is not very clear.

    DGATE is supposed to be diode FET and HGATE is supposed to be a blocking FET. Are they connected that way?

    Next, if you don't want the internal switch between VSNS and SW, you can short them together and connect it to VS. Then, connect the resistor ladder directly to VIN.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 100 points

    Let me update the schematic and explain that I've used two parallel MOSFETs to reduce the Rdson resistance. Could you please check if there are any issues with the circuit design?


  • 0 in reply to Sky Kao
    TI__Genius 15485 points

    Hi Sky,

    My previous comments still apply.

    Next, please add a 0.1uF cap from VS to ground. 

    Increase VCAP from 0.1uF to 0.22uF.

    Next,Is this an automotive application? This is to know the requirement of TVS at the input.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 100 points

    Hi  Shiven

    I have been considering the improvement suggestions you mentioned initially, and while confirming the correctness of my circuit, I noticed that the recommended circuit in the datasheet differs from the one in the LM74810 Evaluation Module. The datasheet uses a P-channel MOSFET and an N-channel MOSFET, whereas the Evaluation Module uses two N-channel MOSFETs. Additionally, I spoke with the engineer who designed the previous circuit, and she mentioned that the design was based on the Evaluation Module. The previous design was verified and worked correctly, and this revision aims to lower Rds(on) by paralleling MOSFETs.

    Based on the above, I would like to confirm the following points:
    1. What are the design considerations that led to the differences between the circuit in the datasheet and the Evaluation Module?
    2. Regarding the capacitors, I originally followed the Evaluation Module's design. Is it okay to continue using this design, or should there be any modifications?

  • 0 in reply to Sky Kao
    TI__Genius 15485 points

    Hi Sky,

    Can you share where does the datasheet suggest a PMOS?

    1. We require an N-channel MOSFET only for LM7481-Q1.

    2. EVM capacitors are fine, although you can add a 0.1uF on EN/UVLO pin. Capacitors like INPUT and OUPUT capacitors usually depend on your conditions. 

    Regards,

    Shiven Dhir