Part Number: XTR116
Hello, we created an 8 channel 4-20mA output/driver based off the XTR116. We are experiencing three problems:
1. The datasheet clearly states that the XTR116 has a VREF of 4.096 volts. The chips we received are correctly labeled as XTR116, but they are outputting 2.5 volts and not 4.096.
2. No matter what current we provide on the IIN pin, we get roughly 40mA on the current loop, it doesn't change. We have a digital-to-analog converter providing voltages/currents to the XTR116 to control this.
3. We are using the VREF off the channel 1's XTR116 for the digital-to-analog converters reference voltage. If we don't have anything hooked up to this current loop, the XTR116 no longer outputs a voltage on VREF... it becomes zero.... which causes all of the other 7 channels to fail.
Here is the circuit schematic showing the 8 channel 4-20mA drivers, the digital-to-analog converter for setting IIN, and the power supply. The idea is that any device that receives a 4-20mA signal can just hook up to 2 of the 4 terminals labeled as ISOLATED_POWER, and ISOLATED_GND. The power supply is already tied into the current loop:
Any help or advice on these 3 problems would be greatly appreciated, as we already have PCB's of these made, thanks!
In reply to Robin Maeder:
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In reply to kai klaas69:
Hi Kai, thanks again for the help.
I put in the 8x DAC for 8x XTR116, am using a I2C multiplexer, and using an optocoupler for digital isolation, does this look correct?
This DAC (MCP4725) does not have a reference pin; it uses its VDD as the reference. Because of this I am powering it directly off the VREF pin on the XTR116 since its more accurate than the VREG pin. It was not clear in the datasheet how much mA this pin could support, but it seems to be able to at least support this DAC and pullups? It sounded like as long as the DAC and pullups don't exceed 4mA then it should work, and I can leave VREG disconnected.
p.s. This adds a lot of extra components to the PCB. Are you sure there is no way to just use a single 8 channel DAC for 8x XTR116's? You mentioned it might be possible with "galvanic isolation", but I am having a difficult time imagining how that would work?
Thanks again for the help and advice!
In reply to Matt Roybal:
In reply to Luis Chioye:
Is that an acceptable solution though? The schematic I posted above with the 8x DACs?
you might also want to read this:
Hi Kai, thanks for the article. Isn't this what I implemented above? And to re-iterate my question again, is it ok for me to power this stuff off the VREF pin instead of the VREG pin? (leaving the VREG pin disconnected). Because as I said above, the DAC doesn't have a reference input voltage.... and the VREF on the XTR116 will be more accurate than the VREG pin. I will post my schematic again:
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