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TCA4311A: How to use TCA4311A for long Cable

Kane Zhang
Intellectual 585 points

Part Number: TCA4311A
Other Parts Discussed in Thread: TCA4311

Dear:

Our customer use the TCA4311A for long cable, like the below connection.

MCU(Master) -> TCA4311(IN) -> TCA4311(Out) -> Cable -> TCA4311(Out) -> TCA4311(IN) -> Slave(MCU)

Is it correct? or need to change the IN and Out direction?

  • 0
    TI__Guru* 78111 points

    Hey Kane,

    This device uses a dynamic voltage offset so as your stack them in series, the VoL gets larger from "TX" to "RX" (keep in mind I2C is bidirectional though).

    For example, if you have a VoL of 0.3V on the TX line and the dynamic offset value is 0.150V then the first TCA4311A would see 450mV. The second would see 600mV, the third TCA4311A would see 750mV and finally the last TCA4311A would see 750mV. This may be a problem if the receiver does not accept 750mV or if the TX were larger...

    The second reason I would be careful about using the TCA4311A for transmission over cable is that the RTAs would cause a large di/dt which would generate large oscillations if the cable had large inductance. The undershoots or overshoots could also damage the device.

    You may also have issues with the RTA of one side triggering earlier/prematurely as they use 'or' logic and you likely will not have all of them equally loaded.

    Do you have to use the TCA4311A for cable transmission or can you use a different buffer?

    Thanks,

    -Bobby