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PCA9545A: Pull-up resistors on SDx/SCx line between PCA9545 and slave device

zhijian xu
Prodigy 80 points
Part Number: PCA9545A
Other Parts Discussed in Thread: TMP103,

Hi ti team,
We are useing a PCA9545 in our design as a SMBUS switch.
Could you please help to conform whether it is acceptable that there are no pull-up resistors on SDx/SCx line between PCA9545 and slave device?

Thanks & Best Regards

  • 0
    Guru 258990 points

    When the channel 0 is disabled, the two BP_I2C_xxx_M0 lines will be floating. These floating voltages might look like valid I²C communication.

    If you do not have any other I²C device with the same address as this TMP103, then you should keep channel 0 always enabled.

    If at all possible, add pull-up resistors.

  • 0
    TI__Mastermind 20531 points

    Hey Zhijian,

    I2C signals requires pullup resistors on the data lines so that a logic "HIGH" can be passed. It seems that the peripheral device (TMP103) also does not include such pullup resistors internally as well, therefore they are needed. 

    I would also recommend taking a look at the TCA9545A device as it is the newer gen of the PCA9545A while also fixing the /RESET errata the PCA9545A device had. 

    Regards,

    Jack