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LM61440-Q1: LM61440-Q1 Design Consedirations

Mahmoud Tolba
Prodigy 10 points
Part Number: LM61440-Q1
Other Parts Discussed in Thread: LM61440, LM61460

Hello,

- According to LM61440 datasheet, When Vout is 5V and fSW is 400KHz L1 should be 8.2uH. But in the EVK design, the inductor value was 4.7uH. Could you please elaborate on this?
- In the EVK layout design, I noticed that you moved all the VIN_EMI to the bottom side of the PCB while you can keep it on the top layer and made a keepout area in the top layer and layer 1. Could you please elaborate on this? Is it for isolation purposes?
- Also, I noticed that you shielded the VIN traces with GND vias but you didn't do the same with the VIN_EMI. Could you please elaborate on this?

Thanks..

Mahmoud

  • 0
    TI__Mastermind 22299 points

    Mahmoud,

    The EVM is for LM61460 which is a 6A output, it would need higher ripple current compared to a 4A output, that's why the inductance is lower.

    The VIN_EMI node is kept on the bottom layer because the input filter is on the bottom side of the board. 

    For lowest EMI, VIN_EMI node should be kept away from fields, it's separated from the buck inductor for that reason.

    Long skinny traces of high voltage can act antennas, that why the VIN traces are shielded. The VIN_EMI is a short polygon so it wont be a big issue.

    Hope all this helps,

    -Orlando