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AD57xx and AD54xx current loop transmitters

Question asked by AnalogDave on Oct 15, 2011
Latest reply on Oct 28, 2011 by DerrickH

Hi:

 

I am new to current loop transimitters (CLT) in general but noticed that they might fit my need of a high precision (< 0.01%), load indepedent(1 ohm to 10kohm)  current source, though my range is 0 - 2mA and not the standard 4-20mA / 0-20mA. The 54xx have an internal DAC which would save the cost and board space of using an external one. My questions are:

 

1. Is there a way i could use the AD54xx to sweep to 2mA only while using the full scale range of the ADC? RIght now, i believe i would be using only 10% of it if i output 2mA maximum. I want to maximize the dynamic range of the internal 16-bit DAC to swing from 0-2mA? do i need to use the 5757 for this as it has gain & offset registers to accomplish this task? Is it fast enough for a 16-bit accurate settling time of under 10us?

 

2. What does Total Unadjusted Error (TUE) mean? From its name, the implication is that this error can be removed or adjusted out of the system. How does one do this?

 

3.  What are the minimum and maximum resistive load requirements for these CLTs? Is the accuracy load depedent and if so, how so? The datasheets don't list these specs?

 

Thanks for your time :-),

David

 

PS

 

If other alternatives exist for design a precision current source(1uA to 2mA) with < 0.01% TUE, with 16-bit settling times < 10usecs, very high output impedance and is completely load invariant from 1 ohm to > 10K, please let me know  :-)! Our current legacy design of the standard DAC + OPAMP + FET is highly non-linear at currents under 0.5mA :-(

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