Whats the best Inamp for high speed current sensing?

Question

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.

ScottH · Accepted Answer

Hi Ian, 
 In addition to Phil's response, I just wanted to point out that there are a few issues using a digi-pot or solid-state mux to set the gain for a standard in-amp. There are several threads about this, such as this one: https://ez.analog.com/message/175432#175432 . Also, see this short article that has some more detail: Use a PGIA to avoid getting burned by switch parasitics . 
 If you need more granularity in gain than the AD8250/AD8251/AD8253 integrated PGIA family can provide, the best option is generally to take the minimum gain that you will need with the first stage in-amp and follow it with a programmable-gain op amp stage based on the digipot. There is a good discussion on how to build a good PGA with solid-state switches in the op-amp applications handbook (Section 2.2) , which I would suggest reading. 
 Generally, the widest bandwidth in-amps that we offer are dual-supply products. For single-supply, there might be a few products such as AD8422 or AD8226 with enough bandwidth, but I think if you check the in-amp tool that Phil linked above, you'll find that you probably need a dual supply anyway due to input/output headroom requirements. AD8421 is a great product, but it may have more bandwidth than you really need (2MHz at G=100, whereas you're talking about Nyquist rates in the 50kHz to 75kHz range). I would suggest that you consider using a dual supply and something like an AD8228 on the first stage (AD8228 is similar to AD8221, but with fixed gains, and therefore lower gain drift which will be important because 10µV in 100mV full-scale is 100ppm). Then you should have plenty of options to choose from as the op amp for your PGA. 
 Best regards, 
 Scott

bobsbots · Answer

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".