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INA181: Using INA181 for inline current sense

Tomer Bruchiel
Intellectual 640 points
Part Number: INA181
Other Parts Discussed in Thread: INA240, INA300

Hi Everyone,

I wanted to know if I can use the INA181 for inline current sense.

Usually I will use it in the low side but I am driving a DC motor with an IC with integrated FETs so it is not possible.

My supply is 11V so it should be OK as the Common mode range is up to 26V.

If I'll set the Ref voltage to be 0.5 VCC it should be OK if I understand correctly right?

Alternatively, if this part cannot be used for inline current sense, can you offer a device that can and is cost effective.

I don't need high accuracy and the system is cost sensitive so device like INA240 are too expansive.

Thanks,

Tomer

  • 0
    TI__Mastermind 31915 points

    Hey Tomer,

    It is possible to use INA181 in-line; however, there are two primary risks/concerns. First, is inductive kickback which could pull Vcm < -0.3V. This will require system validation and testing. If Vcm could go below -0.3V, you will need to protect INA181 input pins either with or both input resistance (RF) and clamping Schottky diodes with low forward voltage drop. Equation to determine RF is RF > Vcm_min/5mA. The downside is that RF > 10-Ω will begin to significantly decrease shunt voltage gain error (and also increase gain error range) as explained in datasheet Section 8.1.3. To determine exact new gain error range, refer to the following video/pdf.

    The other performance risk is the output disturbance every time Vcm switches between high and low. How high the peaks go and how long they last can be system dependent and would need to be validated to make sure your system can handle/blank out the output peaks and settling delays. See example of Vcm output disturbance from datasheet below.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Intellectual 640 points

    Thank you Peter,

    What device would you suggest instead of the INA181 that is cost effective?
    I do not need high accuracy, just to Identify over voltage.

    Thanks

  • 0 in reply to Tomer Bruchiel
    TI__Mastermind 31915 points

    Hey Tomer, 

    The INA181 is the cheapest bidirectional current sense amplifier.

    For over voltage detection, could you use a comparator? Was this a typo?

    Any other cheaper current sense circuit would involve a discrete solution with a rail-trail input op amp in a difference amplifier network, but this requires well matched resistor, so this may make savings negated.

    Could the INA300 work? This provides simple over current detection.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Intellectual 640 points

    Thanks,

    I'll use the INA240 or similar.