XTR117: XTR117

In our end design, we will be giving input to Pin 2 of XTR117 from DAC,

Thus even if we use Vreg for now, we cant use that in our final design.

All i am confused that how can i connect IRET so that while varying a voltage from 0-3.3V, when we check current through R7,

Currently for testing the functionality of IC we are giving input from external power supply, and looping it with my external board which is having analog input, and all i want that my i can see the current vary through R7, but it is not happening.

the circuit is attached below-

A side is the input either from DAC but currently with external power supply

B  is the external board, this is the actual board which gives 24 V to the loop and takes current input

Thanks for the help, 

As you mentioned we should not give direct power supply to XTR117, so now we used a potentiometer and gave it supply from Vreg and taken it's output to Iin pin 2, and connected GND of Potentiometer to IRET

It is similar to the below circuit given in datasheet.

But still not able to get any output

Figure 1 - my circuit with potentiometer

Figure 2-  as in datasheet

Hi Ankur,

what potentiometer do you use? Remember that only less than 3.8mA is allowed to flow out of the VREG pin to keep the XTR117 in regulation. And don't omit the 10nF decoupling cap between pin 7 and pin 4, as shown in figure 3 of datasheet!!

Kai

hi Sir,

thanks for the help, i am getting the current in loop

but now i am facing another issue

i am using the below circuit for application of giving input of RTD to my circuit and getting 4-20mA loop output.The first one is from datasheet of xtr117

and the second one is the actual one i am implementing.

The issue which i am facing is that, 

Please see A and B in below circuit

when i am connecting B i am not getting any output in my loop, but when i am giving  a separate supply on my wheatstone bridge circuit, i am getting a proper output.

i.e. when i am giving Iret to wheatstone bridge ground as well as my opamp ground, i am not getting any output.

but i have not to do that in my actual design as it will be having just loop power of 24 V and not any other supply.

I tried your suggestion, 

1) As per limiting resistors in XTR106

tried it with 1.2K, 3.4K in both the case my Vreg drops to 4.9 V to 1.2 V and even XTR117 is also getting little bit heated.

In my wheatstone bridge circuit my three resistors are 100 ohms and 4th one is from PT100

2) Please refer the below image as well,

in it when i am connecting point 2 i.e. ground of wheatstone setup with Iret no output  is coming 

3) If we use external supply to my wheatstone, and common ground of wheatstone circuit and opamp ( even if i dont use XTR117) i dont get any output and if we dont do that commoning, we get output from opamp perfectly.

I tried your suggestion,

1) As per limiting resistors in XTR106

tried it with 1.2K, 3.4K in both the case my Vreg drops to 4.9 V to 1.2 V and even XTR117 is also getting little bit heated.

In my wheatstone bridge circuit my three resistors are 100 ohms and 4th one is from PT100

2) Please refer the below image as well,

in it when i am connecting point 2 i.e. ground of wheatstone setup with Iret no output  is coming

3) If we use external supply to my wheatstone, and common ground of wheatstone circuit and opamp ( even if i dont use XTR117) i dont get any output and if we dont do that commoning, we get output from opamp perfectly.

Hi Ankur,

whatever you connect to the input side of XTR117 must be completely powered by Vreg (pin 8) of XTR117. When you want to connect external circuitry to the input of XTR117, you need to provide galvanic isolation as shown in figure 4 of datasheet. Take this figure serioulsy. It's no joke. And also keep in mind that only 3.8mA may be drawn from Vreg.

Or you can take a non loop-powered voltage to current converter, like the XTR111, e.g. This converter is free from these restrictions.

Kai

Hi Ankur,

I think the way you amplify the bridge signal is unsuited. You would need an offset to handle the cases "PT100<100R" and "PT100>100R".

Kai

ankur.TSC

R3 runs from 90R to 150R in the simulation.

You should rework your circuit.

Kai

Thank you so much sir for the help, but i am like trapped in this,

attaching my another circuit and mentioned the current and voltages i am getting,

please help with the changes i should make it to work.

Sir, 

Please if you can help with my issue, would be great help.

Thanks for the help sir, 

I got my PT100 working with some changes in my wheatstone's resistor arrangement NOw our resistors are 10k,10k,100R and PT100, after that we were getting 5V and proper current.

But now,

Since we have to set our system according to above figure, 

1) SInce our MCU draws 150mA current, how can we connect that in our whole arrangement so that there is no limit of current.?

2) Can we common GND1, GND2, GND3 with IRET pin?

3) or is there any other way, i can incorporate MCU in my design.

and since XTR105 is costly, i cant use that in my design.

As i was suggested to use XTR105, thus i am waiting for it to get delivered for testing.

Please, if you could let this thread open.