Tool/software:
Hi,
I am using XTR117 to generate 4-20mA output for the industrial application. In my application, I need to convert the 0.8V-3.9V into 4-20mA current output.
So considering the above requirement, my Slope would be 5.517 & offset would be -0.129.
So to generate -0.129 Do I need to add external -Ve Bias generator like LM7705 or is there any other ways to do it while using XTR117.
thanks
Raghavendra
Hi Raghavendra,
The XTR117 has the current gains of 100 A/A, and the input needs to generate 40uA to 200uA in order to amplify to 4mA to 20mA.
0.8V/40uA = 20kΩ and 3.9V/200uA = 19.5kΩ --> we may remove Ros from the offset current branch, but it will leave a slight error in either upper end of 200uA. We can make some adjustment and put the error on the low end of 40uA --> either way, it will generate some errors because Vin has the odd range.
I would propose that the Vin is from 0.8V to 4.0V, Iout is from 4mA to 20mA, which it will be easier to manage and less errors (more accurate V-I conversion).
XTR117 0.8 to 3.9V 4-20mA 06142024.TSC
Please let me know if this will meet the application requirements.
Best,
Raymond
Hi Raghavendra,
So considering the above requirement, my Slope would be 5.517
What slope are you referring here? what are your 4-20mA accuracy requirements? (20mA-4mA)/(3.9V-0.8) = 5.16 mA/V.
I can adjust the two input voltage end points, 0.8V and 3.9V, and generate 4-20mA at the output, but it will increase the complexity of the circuit. When 0.8V input is present, it needs to supply 40uA in total input current; when 3.9V is present, it needs to supply 200uA in total.
The complexity design option may be as follows, but I would use bandgap reference to generate the negative supply voltage, which is temperature stable in ppm/C range.
LM7705 may not be stable enough over temperature, depending on your accuracy requirements.
The original proposal may have less errors minus complexity vs. LM7705 implementation.
Best,
Raymond
