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TCA9803: Does an I2C multiplexer operate the same as a FET-based translator when placed on the b-side of the TCA9803?

Kirk Festing
Prodigy 70 points
Part Number: TCA9803
Other Parts Discussed in Thread: PCA9517, TCA9517

Does an I2C multiplexer, such as a PCA9548 or PCA9543, operate the same as a FET-based translator when placed on the b-side of the TCA9803?  We are running into problems where our SMBus segments are locking up when trying to access I2C devices through multiplexers.  The multiplexers are on the b-side of a TCA9803.  We have the option of using a PCA9517 instead.

  • 0
    TI__Guru 62920 points
    Hi Kirk,

    Yes, those multiplexer devices are essentially several FET-based translators that connect to a common I2C bus, and so devices on one side of the mux would need to sink the pull-up currents from the opposite side whenever the bus is low and the FETs are conducting. If the pull-up resistance values are low enough, then, the IEXT-I specification of TCA9803 could be violated. PCA9517 would not have this limitation, although I would recommend using the pin-for-pin equivalent TCA9517 device over the PCA9517. TCA9517 addresses some issues related to glitch/noise susceptibility and data corruption under certain configurations (see Section 8.2 of the PCA9517 datasheet for details).

    Max