The current consumption of a 2-wire transmitter, sensor, and its driving circuitry needs to be below 4mA. As seen in the current flow diagram below for the XTR116, the output current, IO, is a summation of IIN, IRET, and IBJT. IIN and IBJT are always positive…
The minimum output current of my 2-wire 4-20mA transmitter is greater than 4mA.
Why is that? How can I lower it?
Why does my 2-wire 4-20mA transmitter output not reach the full 20mA? When I change the load resistance or decrease the supply, the output changes.
What can I do to fix this?
From the XTR116 data sheet:
MINIMUM-SCALE CURRENT
The quiescent current of the XTR115/6 (typically 200µA) is the lower limit of its output current. Zero input current (IIN = 0) will produce an IO equal to the quiescent current. Output current will not…
Hi AK. I will get the exact dependence of the voltage on the code and post it a little later.
The idea was as follows:
Сode 0x800 gives 0.8V. Current before XTR 0.8V/20k=40mkA. Then 40mkA*100(XTR)=4mA.
Code 0xFA0 gives 4V. 4/20k=0.002mA and 0.0002mA*100…
Hi Jason,
Are you looking for suggestions on how to dissipate the heat? The output stage with the external transistor for the XTR106 is going to look the same as the output stage of the reference deign for the XTR116 that I linked previously. Page 12 of…
Hello Jason,
The XTR106 datasheet advises that the external transistor have a VCEO = 45V min, β = 40 min and PD = 800mW. Power dissipation requirements may be lower if the loop power supply voltage is less than 36V. Since the external transistor…
Feel free to check out this blog post which goes into more detail on 2-Wire 4-20mA Sensor Transmitters: Sensor and Transmitter Current Consumption Limitations. The rest of the blog series might be helpful if you have any other questions with your design…
Hi Remya,
Page 4 of the XTR116 datasheet shows the regulator voltage vs current, VREG is able to source 4mA and sink 1mA; and the VREF precision is specified for a 0mA to 2.5mA current load in the specifications table on page 2.
As Kai has correctly…
Hi Remya,
think about where the VREG and VREF currents are coming from. It's just a portion of the 4mA output current of XTR116. So if the XTR116 draws a supply current of 300µA, then 4mA - 300µA = 3.7mA maximum can be delivered by VREG and VREF in total…
Hi Kai,
Is it possible to load 10mA@3.3V from VREG pin at input current of 4mA?
If it is not possible, what will be the maximum current that can load from VREG pin at an input current of 4mA.
Hi,
Can you please share the continuous output current of VREG pin of XTR116.
Its short circuit current observed as 12mA in the datasheet.
Hi John,
Many Thanks,
Kind Regards,
Luis
HI Kovach,
As long as the compensation capacitance (with the recommended Rcomp or Riso) is inside the range 2.2uF to 22uF, the circuit offers a conservative phase margin, and circuit is stable per the datasheet recommendation.
One effect of having a larger…
Louis,
Thank you for verifying my assumptions. You have hopefully save a lot of field people much grief.
Last question(s):
The Option A drawing has Clf with a range of 2.2 - 22uF.
Would a value higher than 2.2uf be better or have a greater chance of stability…
HI John,
Essentially the XTR116 voltage reference requires the specified load/compensation capacitance and compensation resistors shown on Figure 5 for reliable or stable operation. If the reference does not have the proper compensation, the reference…
I have built and deployed many boards out into the field using the XTR116 in an isolated configuration.
This design has always worked well and is stable on the bench, but now I being told that the the 4-20 output occasionally "drifts…
Hi,
carefully compare the circuits shown in the datasheets of XTR111 and XTR116/7. Shift your attention to the signal and power grounds :-)
Kai
Hi,
this issue has already been discussed here for many times. Make a search for "XTR116" and "XTR117". See this one for example:
The individual pin 3 (Iret) of each XTR117 must be galvanically isolated from each other. Otherwise…
Hi Shawn,
You can also refer to TI design and some technical blogs in as below in regard to the design guideline for XTR116.
https://www.ti.com/tool/TIPD126?keyMatch=TIPD126&tisearch=Search-EN-everything&usecase=GPN#0
Hi Shawn,
I would recommend the circuit shown in figure 4 of datasheet. By other words, take a 10nF/100V X7R and add D1. If you use the diode bridge, better take 4 x 1N4002.
Kai
Are there any app notes on the XTR116 that discuss the selection purpose, selection criteria and guidelines for the output capacitor. The datasheet doesn’t mention how to select this component, what effect the value has on the output…
