Whats the best Inamp for high speed current sensing?

Hi all,

I am working on a device to measure the current of a supply in real time.  The purpose of this, is to help with software development of ultra-low power 'always on' devices to be more efficient.  The biggest market for this currently is IoT.

I want to have both speed and accuracy from an amplifier and I have therefore discarded all of the purpose made current sense amplifiers as they don't provide sufficient bandwidth for my application.

The specifications required are as follows:

  • The highest voltage supply to be measured will be +5V to 0V. and the maximum current will be 1A.  I will most likely use a 50mohm shut resistor, giving the maximum differential voltage of 50mV.  I would also like for it to be accurate to the 100'suA scale, meaning that the differential voltage accuracy needs to be < 10uV (although I may use a 0.1ohm resistor for the lower scale). 
  • I need a high bandwidth across the gain range as I plan to use a 500ksps ADC to digitize the analog voltage, although will most likely be using 100-150ksps.
  • It needs to have very good common mode rejection ratio.
  • It needs to have the voltage offset as low as possible to get the best accuracy.
  • Adjustable gain is a must ideally from an external resistor, that I will drive from a digital Pot.

I have been looking at the AD8220 for a rail to rail inamp, or the AD8221 which appears to be a better device for me, but will require a dual supply to get the full swing.

Can anyone suggest any better suited iamps that I have missed, or do these 2 seem the best suited for this application?

Any support will be very much appreciated.

Many Thanks Ian.

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  • Hello Ian,

    Yes, I agree that your choice would be sufficient enough in your application. But you may also want to consider AD8420 or AD8421. AD8420 is a wide supply range, micropower, rail to rail inAmp but the bandwidth is a little lower. AD8420's CMRR is also excellent. While AD8421 is a low noise low power In Amp. It has low voltage offset of 25uV.

    I also want to share our tool for in amp. It is a In amp operating range tool that will show common mode voltage vs the output voltage, this might help you in choosing the proper inamp considering your input signal and your supply. You can visit the tool here.

    Apologies for late response.

    Regards,

    Phil

Reply
  • Hello Ian,

    Yes, I agree that your choice would be sufficient enough in your application. But you may also want to consider AD8420 or AD8421. AD8420 is a wide supply range, micropower, rail to rail inAmp but the bandwidth is a little lower. AD8420's CMRR is also excellent. While AD8421 is a low noise low power In Amp. It has low voltage offset of 25uV.

    I also want to share our tool for in amp. It is a In amp operating range tool that will show common mode voltage vs the output voltage, this might help you in choosing the proper inamp considering your input signal and your supply. You can visit the tool here.

    Apologies for late response.

    Regards,

    Phil

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