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LSF0204: Schematic Review and Queries Regarding its Functionality

Aditya Singh
Intellectual 280 points
Part Number: LSF0204

Hi E2E Team,

We are using LSF0204 into our design for below purpose-

1) Voltage level translation for MDC/MDIO. MCD will work in push-pull configuration and MDIO will work in open drain confirmation.

2) Voltage level translation for control signals which works in push-pull configuration.

Below is the screen shot of the schematic-

Please review the schematic and share your queries. Also, we are using 3 pins in push-pull configuration and one pin in open-drain configuration. Do you see any issue into the same?

Best Regards,

Aditya Kumar Singh

  • 0
    TI__Guru* 97016 points

    Hi Aditya,

    I don't see any problem with your schematic for the voltage reference, enable, and ground connections.

    MDIO has pull-up resistors on both sides, which is correct and required for open-drain signals. MDC I assume is coming in from the A side (up-translation from 1.8V to 3.3V), in which case the pull-up resistor locations are correct (only one pull-up on the B side).

    I'm not sure what's going on with the other 2 channels (no pull-up resistors shown). Assuming down-translation (B -> A) with push-pull drivers, no pull-up resistors would be correct.

    The only question left would be regarding the data rate and capacitive loading. The main area of concern for this will be up-translation, so the B1 and B2 connections -- do you know the expected maximum data rate and capacitive loading (including parasitics from the board/cables)?

  • 0 in reply to Emrys Maier
    Intellectual 280 points

    Hi Emrys,

    Thanks for your quick response. We have connected MDC/MDIO with four PHYs on board. Trace length would be around 5~6 inches. Expected frequency of operation is around 1MHz. Please let us know if you see any concern here.

    Also, LSF0204 datasheet recommends to use a pull-up resistor of 300 ohm. Please refer to below screenshot from the datasheet-

    Please suggest what pull-up values we should use into our design. Also, We have have observed that mixed-mode voltage translation is not mentioned for LSF0204 family and we are using a combination of open-drain and push-pull signals on a single IC. Is it ok or we can face issues during bring-up? If yes, please let us know the solution.

    Best Regards,

    Aditya Kumar Singh

  • 0 in reply to Aditya Singh
    Guru 302310 points

    The datasheet recommends many values. The actual value to use depends on capacitive load of your circuit, and is a compromise between speed and power usage. Try multiple values with the actual board and check with an oscilloscope.

    All channels work independently.