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INA233: Asking for the INA233 schematic review

Part Number: INA233

Hi Team,
Customer uses INA233 to monitor the 5V USB port 2A and 3A case.
Would you please review and provide your comment on the schematic?

BR,
SHH

  • Hello SHH,

    I am a little confused. It seems there is no shunt resistor in this schematic. The 5mOhm resistors (R7223 and R7224) will not actually sense any current because they are not in-series with the 5V_USBBC rail. Usually R7223 and R7224 are 10 Ohms and placed at the input pins to provide RC filtering along with the input differential capacitor (C7212).

    Unless customer is planning to use PCB trace resistance as the sense resitance, they need to place a sense resistor in between R7223 and R7224. Note that measuring voltage through a trace can be problematic given the temperature coefficient of metal and tolerances required in manufacturing.

    If they want to measure up to 3 Amps of current, then want to limit the input sense voltage to 81.9175mV, which is the specified positive input shunt voltage range for the device. Using Ohm's Law, this means customer should use 81.9175mV/3A = 27.3 mOhm. This resistor will need at the least 246 mW power rating.

    Also, I am not sure what customer is doing for their SDA/SCL bus lines, but SDA and SCL should have pull-up resistors to the power supply at some point in the system. The 100 Ohm resistors in series with SDA and SCL might slow down communication signal rise time, but this should be only minimal to effect. 
     
    Hope this helps. Thanks for coming to the forum.

    Sincerely,
    Peter Iliya
    Current Sensing Applications