XTR115: Multiple 4-20mA loops with same loop GND

Robin Maeder

Part Number: XTR115

Hello everyone

I have the following circuit:

V_4_20_OUT is an external loop voltage referenced to GND_LOOP (not referenced to GND). When only one of the four jumpers is set everything works fine. But as soon as I set a second jumper I measure a currentflow in the first loop of up to 30mA (depending which jumper is set). And on the pin 2 of the XTR115 I measure -0.5V (output of the DAC is 0V). I do not see what the problem is and where/why the wrong current is flowing.

Thank you for your help.

over 6 years ago

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Robin,

you might want to have a look into this thread:

e2e.ti.com/.../770353

Kai

0 Robin Maeder over 6 years ago in reply to kai klaas69

Intellectual 450 points

Hi Kai,

thank you for your answer.
Of course I've read the datasheet but I do not know why it does not work otherwise. I do not use VREG and VREF so there is no return current that must flow into IRET. And the current IIN flows through R1 and R2 inside the XTR115 same as when supplied from IREG. So I do not see why it does only work with isolated input control? And as I already said it works fine when only 1 jumper is set. There only is a problem when more than 1 jumper is set what I also do not understand?

Robin

0 kai klaas69 over 6 years ago in reply to Robin Maeder

Guru 140200 points

Hi Robin,

I have it explained here:

e2e.ti.com/.../2849472

Kai

Amplifiers

Amplifiers forum

XTR115: Multiple 4-20mA loops with same loop GND