Other Parts Discussed in Thread: XTR117, , XTR111, XTR305, XTR300
Dear Support team,
I want to couple the DAC81416 and XTR117 to generate voltage to current conversion 4-20mA.
Regards
Wasim
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Hi,
I had a look at the schematics. There are mistakes.
1, ISO7310 is a digital isolator, you cannot use the same for analog source. Please change the same.
2. 24V loop power supply is used by another LDO in the system which is feeding the DAC. This scheme is not OK, since you want isolation. I suggest have the isolation on the digital side for the DAC.
Regards,
AK
Hi,
In place of ISO7310 which one do we have to use?
Which isolation needs to use for the DAC isolation?
Regards
Wasim
Hi,
The problem with your approach is DAC81416 needs more than 4mA current to operate, so you cannot power the DAC within the loop. You need to have external power supplies for that.
The XTR117 is a two-wire transmitter, the IRET has to be independent for each, since the IOUT pin potential for each transmitter is a function of the produced Iout (load current) as shown on the image below. Since the IOUT will have different voltage potential with respect to the loop ground depending on the output current; IRET is required to float to a potential slightly above IOUT, as a function of the transmitter current output and the load resistor.
Therefore, unfortunately, it is not possible to configure the circuit to have multiple DAC circuits feeding multiple XTR117s (2-wire current transmitters) referred to the same IRET.
- One option is to use independent DAC circuits for each XTR117, with each DAC connected to each independent IRET.
- A second option may be to isolate the DACs as you have mentioned above.
- Alternatively, you could consider using a 3-wire transmitter such as the XTR111, where all the circuitry is biased with respect to the same loop GND and a multiple channel DAC could be used to drive multiple XTR111s. However, 3-wire transmitters are in most cases locally powered as discussed on the attached presentation.
Attached is a presentation that discusses 2-wire vs 3-wire transmitters in detail:
Below are a couple of blogs that discuss isolation briefly when driving 2-wire transmitters that could be useful.
2-Wire 4-20mA Sensor Transmitters: Background + Compliance Voltage
https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/11/04/two-wire-4-20-ma-transmitters-background-and-common-issues
2-Wire 4-20mA – IRET Can’t connect to Vloop GND
https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/12/09/part-2-two-wire-4-20-ma-transmitters-background-and-common-issues
2-Wire 4-20mA – Controlling 2-Wire Transmitters with Externally Powered Sources
https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/02/24/two-wire-4-20ma-transmitters-background-and-common-issues-part-4
2-Wire 4-20mA – Input Isolated Sensor Transmitter
https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/03/10/2-wire-4-20ma-sensor-transmitters-background-and-common-issues-part-5
2-Wire 4-20mA – Increasing Sensor Power
https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/04/14/2-wire-4-20ma-sensor-transmitters-background-and-common-issues-part-6
I still suggest go for three wire transmitter with local supplies
Regards,
AK
Yes, we have an external power supply for DAC81416 separately, then how to connect the DAC output to the XTR117?
because XTR117 is having iret pin all we cant mix 16 channels?
what is the way forward for this kind of application? where we are connecting DAC81416 to 16 no of XTR117 to make a 16channel 4-20mA loop power signal.
Regards,
Wasim
Hi,
Like I said, the best approach is to go for 3 wire 4-20mA.
What is your actual requirement? DAC is generating PWM or DC? Please clarify the same.
Regards,
AK
Dear AK,
My requirement is 16 channel 4-20mA 2-wire transmitter for my application, for this application I used DAC81416 for 16channel 0-5 VDC signal and XTR117 for 4-20mA generation, and ISO7310 for signal isolation for Iret pin of XTR117.
Can you guide me in place of ISO7310 isolation on how to do it and what component we have to use for avoiding the Iret conflict with the ground signal?
Regards
Wasim
Hi,
Got it. Give me a day's time and I will provide you with our suggestions.
Regards,
AK
Hi Wasim,
Using a single multiple channel DAC to drive several 2-wire current transmitters becomes a challenge, since each XTR117 driving circuitry needs to be referred to a independent IRET (local GND) potential, where each transmitter (each channel) IRET potential changes with IOUT current independently. For this reason, we don’t typically recommend 2-wire transmitters for these type of applications, and most users select a 3-wire current transmitters for a multiple channel DAC.
The XTR111, XTR300 and XTR305 are 3-wire current transmitters that are typically used for these type of multiple channel DAC applications, where all circuitry can be referred to the same GND potential, greatly simplifying the design. TIPD155 is a good example of a two channel current output/voltage output transmitter using the XTR300, but a similar approach could be used with a multiple channel DAC and the XTR111 (3-wire current transmitter).
Regards,
AK
Dear AK,
I understand the 3-wire details but I want to do with the 2-wire system because in my loop 4-20mA the other end PLC is feeding 24V but in the 3-wire system, it will conflict with both side's power then how to implement that?
I don't want 24V in the loop from XTR side so that we selected the XTR117,
Regards,
Wasim
Hi,
Please have a look at the TIPD155 Which is dual channel version, and you can extend the same to 16 channel with DAC81416.
Regards,
AK
Dear AK,
I think you are not able to understand my question or I am unable to give you more details to understand you let know.
My question is it possible to make in XTR111 for 24v loop power from the receiver side?
below schematic is my application, in XTR111 or 300 we cant give a 24V loop from the receiver side as my understanding (If I am wrong let me correct it)
Regards,
Wasim
Hi,
Both XTR111 and XTR300 is not suitable for loop powered systems.
Can you post the same to XTR forums, they will be in a better position to comment on this design.
Regards,
AK