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LSF0102: how should pull up resistor be used in MDIO/MDC

David Lee
Prodigy 50 points
Part Number: LSF0102

Hello 

I am using LSF0102 for mdc/mdio .

I am using Marvell PHY 88E1545 (1.8V mdc/mdio) ,datasheet recommand pull up resistor between 1.5K ohm to 10K ohm,

could you help to check how much resistor should I use.

  • 0
    TI__Guru* 96862 points

    Hi David,

    I would highly recommend watching the video series on the LSF family of translators first:

    https://training.ti.com/LogicMinute

    There are two system factors that affect your pull-up resistor choice:

    (1) Driver sink current

    (2) Parasitic capacitance

    One of these (1) I could look up in the 88E1545 datasheet (although I assume your CPU is also a driver, since I see a bidirectional symbol at CPU_MDIO_2.6). The other (2) is something affected by what's on the bus and the geometry of your traces/wires connecting the two devices.

    Once you have those two numbers for each channel (and each side for bidirectional lines), then you can use the equations found in this video to determine the required pull-up resistor sizes: Up Translation with the LSF Family (4:16)

    Usually you can find a range of values that will work for your application.