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Original question:

TCA9803: B-side Pull-up resister

TCA9803: Is it allowed to connect multiple I2C slaves on the B-side?

Conor
Guru 14780 points

Part Number: TCA9803
Other Parts Discussed in Thread: TCA9617B, TCA39306

Hello,

We are evaluating the TCA9803 and would like to confirm whether the following configuration is supported.

As shown in the attached figure, a CPU is connected to the A-side of the TCA9803, and multiple I2C slave devices are connected in parallel on the B-side (multi-drop configuration).

We would like to confirm the following points based on the TCA9803 datasheet:

  1. Is it acceptable to connect multiple I2C slave devices on the B-side of a single TCA9803, as long as each slave has a unique I2C address?

  2. If this configuration is supported, are there any specific limitations or constraints we should be aware of, such as:

    • Maximum total bus capacitance on the B-side

    • I2C speed limitations (e.g., 100 kHz / 400 kHz)

    • Restrictions regarding external pull-up resistors or other current sources on the B-side

  3. Are there any recommended design guidelines or common pitfalls when using the TCA9803 in this type of multi-slave B-side configuration?

The intention is to use the TCA9803 as a level-translating I2C buffer, with a single master on the A-side and multiple standard I2C slave devices on the B-side.

Thank you for your support.

Best regards,

Conor

  • 0
    TI__Guru 62598 points

    Hi Conor,

    Conor said:
    Is it acceptable to connect multiple I2C slave devices on the B-side of a single TCA9803, as long as each slave has a unique I2C address?

    Yes.

    Conor said:

    If this configuration is supported, are there any specific limitations or constraints we should be aware of, such as:

    • Maximum total bus capacitance on the B-side

    • I2C speed limitations (e.g., 100 kHz / 400 kHz)

    • Restrictions regarding external pull-up resistors or other current sources on the B-side

    B-side of TCA9803 should not include any pull-up resistors. 

    TCA9803 can operate up to 400kHz

    No other current sources can exist on B-side. B-to-B connections of two or more TCA9803's is not allowed. The TCA9803 B-side should not be connected to a static voltage offset of another buffer such as the B-side of the TCA9617B. 

    Maximum bus capacitance is <= 400 pF on B-side for TCA9803. 

    Conor said:
    Are there any recommended design guidelines or common pitfalls when using the TCA9803 in this type of multi-slave B-side configuration?

    Most problems are when TCA9803 is used with other buffers in series or parallel configurations. 

    ALso, any passive level shifter such as TCA39306 that uses pull-up resistors cannot be connected to B-side of the TCA9803. 

    Regards,

    Tyler