XTR116: PWM control for 4-20mA current loop with Microcontroller

Hi Ivan,

Ivan Vargas said:

I need to know the considerations that I must have to find the values of R3 and R4 in the circuit.

XTR116 is 2-wire V-to-I converter with 4-20mA current loop transmitter when input voltage, Viso is ranged from 0-5V. 

1. Viso is the average voltage of the PWM input signal from PWM_OUT of the CMU's GPIO pin. The higher the PWM frequency, the better the accuracy of the PWM to Viso voltage signal (0-5Vdc is proportional to 0-100% PWM duty cycles, and LPF is used to obtain the average DC voltage from the PWM signals, which is in 50% duty cycles).

2. IRET node is the floating node for XTR116 and ISO7310-Q1 isolator. The XTR116's GND signal is located at Vloop or 24Vdc supply as simulated. 

3. V_REF or R4 should be measured at 4.096V wrt IRET pin, where Riso = V_REF/40uA = 4.096V/40uA = 102.400kΩ (this needs to a precision resistor, 0.1% or better, prefer 0.01%). 

4. Rset or R3 should be configured as Viso/160uA =5Vdc/160uA = 31.25kΩ (this needs to a precision resistor, 0.1% or better, prefer 0.01%). 

5. I_in = Io + Iiso = 40uA +160uA = 200uA, where the current gain of the XTR116 is 100 A/A (1 + R3/R4 = 1 + 2.475kΩ/25 = 100)

6. When Viso = 0Vdc, Iout = 100A/A * Io = 100*40uA = 4mA (when there is no input signal or Viso = 0Vdc)

7. When Viso=5Vdc, Iout = 100A/A(40uA + 160uA) = 20mA (when Viso = 5Vdc)

8. The Iout responses from 4mA to 20mA are linear to the input voltage of 0Vdc <= Viso <=5Vdc 

XTR116 03162023.TSC

Enclosed is the reference information and videos about the 4-20mA current loop transmitter application, and we have many in the subjects. 

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1021937/faq-how-to-select-amplifiers-for-4-20ma-field-transmitter-applications

If you have additional questions, please let me know. 

Best,

Raymond