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TXS0102: Data transfer rate limitation

Part Number: TXS0102

Dear Sir,

Our customer has an LTE module with a 2.85V MDIO bus, needs to interface to a pair of 2.7V powered MDIO slave devices, MDC = 6.25MHz.

About the maximum data rate of this part, the datasheet says the following: 24Mbps for push-pull and 2Mbps for open-drain.

Below is our circuit, any issue using TXS0102 in this scenario? (ex. MDC = 6.25MHz)

  • Do the master and the two slaves drive the MDIO signals with push/pull drivers or with open-drain drivers?

    (A difference of 0.15 V should not require a level translator.)

  • In our product, the master is the LTE module and the slave is QCA8334 only. Both drive the MDIO signals with open-drain drives.

    Does it mean that the maximum data rate depends on the master or slave?

    (if the master or slave is with open-drain drives the maximum data rate for 2Mbps, and with push-pull drives for 24Mbps, right?)

  • The data line is bidirectional. The limit is 2 Mbps if any device uses open-drain drivers.

    Why don't you connect them directly, without a level shifter?

  • Because the recommended operating conditions of QCA8334 slave is 2.83V (max), and the master output signal is at least 2.85V.

  • Hello,

    It's my understanding that the clock line of an MDIO (typically called MDC) signal is a push-pull driver and is unidirectional, while the data line (typically called MDIO) is bidirectional and open-drain.

    If this is the case, then there shouldn't be any problems for the MDC signal. The MDIO signal will probably not function correctly though, since it is likely operating at a similar speed and is open-drain.

    I would recommend against having series resistors at the output of the translator - this device uses a series switch internally and adding resistance will only reduce performance / cause V_OL to drift upwards.

    If the TXS translator is to be used, I would recommend limiting the MDIO speed to 2 Mbps, which likely means reducing the clock frequency to 2 Mbps.

    I would agree with Clemens that there is probably no need for the translator in this case. I would recommend contacting the manufacturer of the device to find out if it can support a 20mV input voltage increase above recommended max.