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INA226-Q1: schmatic review

Sky Kao
Intellectual 260 points
Part Number: INA226-Q1
Other Parts Discussed in Thread: INA226, INA238, INA228

Tool/software:

Would you have any suggestions for modifications to the schematic?

  • 0
    TI__Mastermind 22315 points

    Hello Sky,

    Thank you for using the TI forum. Here are my comments for your schematic:

    1. It looks like all 3 devices have the same address, so if they are on the same I2C BUS then you won't be able to read from them individually. If they are on separate boards, then it won't be a problem. 
    2. I don't see the I2C pullup resistors, so I will assume they are on a different section of the schematic
    3. Only the schematic with UIC1302 shows the shunt resistor connection, so I can't review it for the others. However, it is fine on this one, so if the others are the same or similar then they would be fine also.

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Intellectual 260 points

    Thank you for your response. The schematic has been updated as described below:

    Model: INA226-Q1, Shunt Resistor: 1mΩ,
    - UIC2619, Function: Exterior Lighting - Reverse Light Power (Lamp), Maximum Current: 0.33A
    - UIC2729, Function: Exterior Lighting - Rear Fog Light Power (Lamp), Maximum Current: 0.2A
    - UIC2730, Function: Exterior Lighting - CHMSL Power Supply (Lamp), Maximum Current: 1.8A

    We have also added 2.2K pull-up resistors to the I2C lines.

    Do we need to adjust the shunt resistor value? Are there any other suggestions?

  • 0 in reply to Sky Kao
    TI__Expert 4340 points

    Sky,

    Thank you for your patience. Mitch is out of the office today but will reply when he returns on Tuesday.

    Louis

  • 0 in reply to Sky Kao
    TI__Mastermind 22315 points

    Hello Sky,

    With a 1mΩ shunt resistor, here is the required measurement range for each device:

    - UIC26190: 0.33mV
    - UIC27290: 0.2mV
    - UIC2730:   1.8mV

    For each of these, this is a very small percentage of the device full scale range, which is ±81.92 mV.  This will make measurement accuracy very low, and I recommend increasing the shunt resistor size. Similarly, if you plan to use the current result register, then this shunt value will not work because the calculated calibration value to put in the register would be too large to fit in the register (increasing the shunt resistor would help with this also). Here is a link to an app note and calculator tool that can help you pick a better shunt value for your application:

    https://www.ti.com/lit/pdf/sboa511 (App Note)

    https://www.ti.com/tool/download/SBOR021 (Calculator Tool)

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Intellectual 260 points

    Hi  Mitch

    I have modified the shunt resistor values according to the documentation:
    - UIC2619, Function: Exterior Lighting - Reverse Light Power (Lamp), Maximum Current: 0.33A: 20mΩ
    - UIC2729, Function: Exterior Lighting - Rear Fog Light Power (Lamp), Maximum Current: 0.2A: 20mΩ
    - UIC2730, Function: Exterior Lighting - CHMSL Power Supply (Lamp), Maximum Current: 1.8A: 10mΩ

    Is there anything else that needs to be corrected in the circuit?


  • 0 in reply to Sky Kao
    TI__Expert 4340 points

    Sky,

    Again, thank you for your patience. Mitch is currently out of the office but will reply as soon as he returns Wednesday.

    Thanks,

    Louis

  • 0 in reply to Louis L
    TI__Mastermind 22315 points

    Hey Sky,

    Those shunt resistors will still be too small. I recommend using our error calculator tool to find a good balance between acceptable error and shunt resistor size, that can be found here:

    https://www.ti.com/tool/download/CS-AMPLIFIER-ERROR-TOOL

    Also, you may be interested in using the INA228 or INA238 instead. These devices are footprint compatible with the INA226, but have a lower input bias current so they will be able to measure small currents more accurately. 

    Regards,

    Mitch