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INA181-Q1: Is there any reference schematic for bidirectional current sensing?

Chase Jeong
Mastermind 9355 points

Part Number: INA181-Q1
Other Parts Discussed in Thread: INA181

Tool/software:

Dear TI experts,

My customer wants to sense the current of 12V system, from 0A to 40A.

And It need to be measured bidirectionally. (clockwise and counter-clockwise)

I saw EVM schematic but it is too simple.

Do you have any detailed reference schematic for bidirectional current sense?

Please check this issue. Thanks.

Best regardcs,

Chase

  • 0
    TI__Mastermind 20060 points

    Hello Chase, 

    Thank you for your post. 

    Can you please confirm that their range is -40A to 40A?

    I will assume this is the case for my response. 

    The difficulty will be the wide current range and low currents causing large error contributions from the 500µV input offset voltage of the INA181. 

    I ran some calculations and if they use the 20V/V variant and a 2.5mΩ shunt resistor, then they will be operating in the linear range of the INA181 (0.5V to 4.5V, assuming a 5V supply voltage).

    At ±1A, the error contribution from the 500µV offset voltage alone is 20%.

    If this is acceptable then I would recommend the topology shown in the datasheet with a 5V supply, 2.5V VREF, and 2.5mΩ shunt that can handle more than 4W of power. 

    I hope this helps, 

    Joe

  • 0 in reply to Joe Vanacore
    Mastermind 9355 points

    Dear Joe,

    Thank you for your support.

    1. Yes you are right. It is bidirectional, sensing range is -40A ~ 40A.

    2. Customer uses 5V for other IC (MCU, etc) in the PCB. Is it okay to apply 5V to REF pin?

    3. Could you confirm the accuracy between the range -40℃ to 85℃?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Mastermind 20060 points

    Hello Chase, 

    Please see my responses to your questions below:

    2) They need the reference to be 1/2 of supply voltage for proper bidirectional use. For a 5V supply, I would recommend a 2.5V reference. If you want to look into accuracy trade-offs for driving the reference pins for our devices, please see: Driving Voltage Reference Pins of Current-Sensing Amplifiers

    3) Please see the over temperature errors from the EC table and the provided plots from the datasheet. 

    I hope this helps, 

    Joe