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Hi guys,

I am using AD8420 in 4-20mA current loop receiver configuration. Referring document is https://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0314.pdf

I am using 3.3V external reference instead of ADR02 for voltage reference. I calculated the scaling resistor values for 3.3V reference voltage and they found to be following.

R10 = 1K, R11= 1.526K, R12 = 15.5K

This gives me a output voltage swing of 0.2V to 2.302V for 4-20mA input.

The output voltage equation seem to be Vout = R6*I1*(1+R11/R10) - Vref(R11/R12)

R6=50, I1=4mA, R11 = 1.526K, R10 = 1K

Then Vout = 0.1804. But simulated result is 0.202V. There is a discrepancy in the voltage.

Am i using the correct formula for converting current to voltage.?? Parents
• Hi PavithraR,

I did the calculations and the value of the resistors should be:

R10  =1 Kohms, R11 =1.544 Kohms, R12 =14.557 Kohms

Let me know if this gives you the correct output voltage.

Best regards,

Emman

• Hi PavithraR,

I did the calculations and the value of the resistors should be:

R10  =1 Kohms, R11 =1.544 Kohms, R12 =14.557 Kohms

Let me know if this gives you the correct output voltage.

Best regards,

Emman

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