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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  • Have you looked at the AD8130? it's intended as  a differential line receiver, but is very fast ( a faster variant of the AD8420 mentioned above).  It uses indirect current feedback, so for example you can refer the output signal to mid supply for bipolar input to a differential ADC. It only uses a single gain resistor, so it is possible to change the gain without the CMRR issues. and it works nearly rail to rail, so no issues with the "hexagon".

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  • Have you looked at the AD8130? it's intended as  a differential line receiver, but is very fast ( a faster variant of the AD8420 mentioned above).  It uses indirect current feedback, so for example you can refer the output signal to mid supply for bipolar input to a differential ADC. It only uses a single gain resistor, so it is possible to change the gain without the CMRR issues. and it works nearly rail to rail, so no issues with the "hexagon".

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