AnsweredAssumed Answered

Whats the best Inamp for high speed current sensing?

Question asked by Iand on Jul 19, 2015
Latest reply on Aug 26, 2016 by ScottH

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.

Outcomes