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TIPD126: XTR115 outputs 40mA

Part Number: TIPD126
Other Parts Discussed in Thread: XTR117, , PGA309, XTR115, XTR111

Hi, 

I followed the TIPD126 design with some modifications on my end, primarily switching out the xtr117 for the xtr115 for the extra reference current. I use a 500ohm resistor as the return current load for the 4-20mA output with a 24VDC source. When I turn the circuit on the current draw goes to 40mA, which is strange. I decouple the bias current from the xtr115 vref and the same happens. When I decouple the PGA309 output voltage instead in does the same thing. The only time it doesn't go to 40mA is when both the bias current and the PGA309 are decoupled from the xtr115 with a current draw of about 3mA. Is there a reason for this? I don't see what the issue could be. I attached a schematic of my design below.