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Current sense amplifier

Timur Ha
Prodigy 110 points

Other Parts Discussed in Thread: INA190, INA237, INA186, INA2191, INA228

Hello,

I need to sense a current for AC system - charging/discharging of the Capacitor.

Do you have any current sense amplifiers that support AC signal 20Vpp and can sense currents as low as 60uA RMS

Best regards,

Timur

  • 0
    TI__Mastermind 32395 points

    Hello Timur,

    I am looking into this and will reply shortly.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    TI__Mastermind 32395 points

    Hey Timur,

    The number of current sense amplifiers (CSA) options become limited when needing to operate at -10V input common mode (VCM). Here are all of the bidirectional CSAs that can operate at -10V VCM.

    https://www.ti.com/amplifier-circuit/current-sense/products.html#p726min=-14;-15;-16;-22&p2192=Bi-directional&sort=p726min;desc

    Unfortunately, the CSAs in the above link for the most part have relatively low input impedance (high input bias currents), thus using them to measure 60uA RMS is difficult because IB will moving with VCM and will already be in the tens of uA. So I would not recommend these devices unless you have ability to use firmware to calibrate every device before use.

    If you do want to use a CSA, then I would recommend using a high impedance option (e.g. INA190, INA186, INA2191, INA228, INA237, etc.), and additionally find a way to to rectify the input VCM or clamp the negative VCM to 0V. I am not sure what is allowed in your system, but if these products were used, their VCM cannot go below -0.3V or they will break. 

    A second option is to use an instrumentation amplifier, but this will requires a dual supply greater than +/-10V, which may not be desirable. The same goes for using a fully differential amplifier as well.

    Hope this helps.

    Best,

    Peter