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Recommended current sensing amplifier

Ramakrishna Challa
Prodigy 160 points
Other Parts Discussed in Thread: INA282, INA285, INA212, INA193

Dear all,

I need your assistant for choosing the correct high side current sensing amplifier.

Specification:

1) need to sense the current in both the directions ( +20 mA to -20mA)

2) current sensing resistor is as low as possible.

I found INA282 is one which has 70uV offset voltage. The inbuilt gain is low (50V/V).

I think INA285 is suitable for my application. It has inbuit gain of 1000V/V.

Calculations:
 INA285 Specifications
Gain = 1000;
Vsupply  = 5V
Vref = Vsupply/2
min current = -20mA
Max current = 20mA
Vsensemax = (Vsupply-0.4-Vref)/Gain
Vsensemax = 2.1mV
Rsensemax = Vsensemax / maxcurrent
Rsensemax = 105mOhm

Is this current sensing amplifier(INA285) is in production?

Is there any amplifier that will provide bi-directional current sensing with high gain then we can use very low current sensing resistor (~10mOhm)?

Please provide your comments on this application.

Thanks

Regards

Ram

 

  • 0
    TI__Mastermind 25805 points

    Hello Ram,

     

    The highest-gain, lowest Vos current shunt monitor that is currently in production is the INA212.  The offset is 35uV(max) and it has a gain of 1000V/V.  It is also bi-directional and can be used for high-side sensing.

     

    One difference between the INA212 and the INA28X family, however, is the common-mode voltage.  The INA28X family can accept             -14V<Vcm<80V.  The INA212, however, can accept -0.3V<Vcm<26V.

     

    I have attached a TINA simulation that you can work with.  I used the INA212 with 35mohm & 100mohm shunts and performed a DC sweep.  

     

    ram.TSC
  • 0 in reply to Pete%20Semig
    Prodigy 160 points

    Dear Pete Semig,

    Thanks for your reply.  I already went throught it. It has low -ve common mode mode voltage.

    But we need atleast -10V common mode voltage and Gain is as HIGH as possible.

    Please suggest a suitable high side bi-directional current sensing amplifier.

    I think INA285 is suitable for my application. Please tell me is it in production.

    Thanks.

    Regards,

    Ram

     

  • 0 in reply to Ramakrishna Challa
    TI__Guru 62905 points

    Hi Ram,

    Pete is out so I'll try to fill in while he's gone.  INA285 is not in production yet.  The INA282 is the only product in that family that has been released.

    Besides the INA282, we unfortunately do not have any other bi-directional dedicated current shunt monitors that will meet your -10V common-mode voltage. 

    A solution would be to use two of our uni-directional current shunt monitors that can handle the -10V negative common-mode voltage and then use a difference amplifier to determine the bi-directional current value from difference of the two outputs.   An example of this can be seen in Figure 25 in the INA193 datasheet:

     

    The same priniciple can be applied to any of the other voltage-out current shunt monitors as long as their datasheet limited specs are abided by.

    Hope this helps,
    Collin Wells
    Precision Analog

  • 0 in reply to Collin Wells
    Genius 5430 points

    Ram;

    Let me add another approach to what Colin has already posted. This attached circuit Figure 6-7 on page 6 has high accuracy with low values of shunt resistance, has the ability to measure current in both directions, and can withstand a CMV of up to +/-200V.

    7a- Curr Meas Apps.doc
  • 0 in reply to Neil Albaugh
    TI__Guru 62905 points

    Thanks Neil,

    Neat circuit!

    Regards,
    Collin

  • 0 in reply to Collin Wells
    Prodigy 160 points

    Dear all,

    I don`t have much space for putting three devices.

    If I use INA285 space must be saved.

    Please give the information when it will goto production.

    we need 300 units

     

    Thanks

     

    Regards

    Ram