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TMDSCNCD28388D: Question about the pull-up resistor of MDIO

Green Deng
Expert 4490 points
Part Number: TMDSCNCD28388D
Other Parts Discussed in Thread: C2000WARE, DP83822I

Dear team:

TMDSCNCD28388D: C:/ti/c2000/C2000Ware_4_00_00_00/boards/controlCARDs/TMDSCNCD28388D/Rev.B/MCU063B(002)_Sch.PDF

On page 8 of the above schematic diagram, 2.2k pull-up resistors (R127 & R152) are added to the MDIO pins of the two DP83822IRs and then connected to the GPIO153 of the F28388D:

However, Figure 31-5 on page 3301 of the chip TRM states:  that MDIO must have a pull-up resistor (4.7 kOhm recommended) externally.

In this case, is the resistance value too small after the two 2.2k resistors on the schematic diagram of TMDSCNCD28388D are connected in parallel?

Best regards

  • +1
    TI__Mastermind 38295 points

    Hi Green,

    Checking the DP83822I datasheet as well it mentions a 2.2 kOhm pull-up resistor requirement on MDIO, but the two 2.2k in parallel is still not correct for that spec either. I think this is a mistake, that it should just be just one 2.2k resistor on the signal. The lower total resistor value doesn't seem to have an impact on the F2838x ControlCard EtherCAT usage, but following the DP83822I spec on a custom board would be best.

    I will make a record of this finding on the ControlCard.

    Thanks,

    Kevin