This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

INA226: Pullup resistors on SDA and SCL lines for Address Pins

Part Number: INA226

Our customer is concerned that the pullup resistors on the SDA and SCL lines will affect the slave address configurations when connecting either or both of the two address pins (A0 and A1) to the SDA or SCL line.

If the voltage on each of the SDA and SCL lines pulled high by the pullup resistors when the bus is idle meets the range of High-level input voltage (VIH) to the two address pins (A0 and A1), can the slave address be configured correctly?

Best regards,

Daisuke

  • The beginning of an I²C transaction requires both low and high voltages on both the SCL and SDA lines.

    The INA226 samples the state of the A0 and A1 pins when SCL and SDA are both low and high. When the Ax pin is always low, it is connected to GND; when it is always high, it is connected to VCC; when it changes, it is connected to SCL/SDA.

    The pull-up resistors are required for this. There is no problem.

  • Hi Daisuke,

    Clemens is correct – the idle state of the SCL/SDA doesn’t affect addressing. The algorithm that deciphers address is also idling when there is no activity on the bus.

    There is no problem using this option. It is always a good practice to allow sufficient timing to avoid potential racing conditions between the SCL and SDA edges. This helps to ensure the robustness of the communication protocol.

    Regards, Guang

  • Hi Guang-san and Clemens-san,

    Thank you for your reply.

    I would like to know how to choose the appropriate pullup resistors on the SDA and SCL lines for the two address pins (A0 and A1).

    The post below describes how to choose an appropriate pullup resistor for a general I2C bus, including the INA226.

    https://e2e.ti.com/support/amplifiers/f/14/p/699655/2578752#2578752

    The following application report also describes how to calculate an appropriate pullup resistance for a general I2C bus

    https://www.ti.com/lit/an/slva689/slva689.pdf

    I will need to know the input characteristics of the two address pins (A0 and A1) to calculate the appropriate pullup resistance.

    Do the input characteristics for DIGITAL INPUT in the data sheet apply to the two address pins (A0 and A1) as well as the SDA and SCL?

    Best regards,

    Daisuke

  • The A0/A1 pins indeed are digital inputs.

    If you do not have extremely long traces or many I²C devices, common pull-up such as 4.7 kΩ will be fine.

  • Hi Daisuke,

    To select SCL/SDA pull ups, you may refer to the documents quoted. Common values are between 2K to 10K. If you choose a 4.7KΩ as Clemens mentioned, it most definitely will work.

    A single pull up is needed for each of SCL/SDA. You could directly short the address pins to SCL/SDA near the device.

    And yes the electrical specifications apply to address pins as well; otherwise it will be explicitly stated.

    Regards, Guang

  • Hi Guang-san and Clemens-san,

    Thank you for your reply.

    Best regards,

    Daisuke