I want to generate a variable bias current for an IC from 5uA to 20uA. I am doing this with a TI current source and AD SPI programmable variable resistor, the datasheet set up and my schematic are attached in the pictures. Looks simple enough, I change the programmable resistance values through SPI and this changes the Bias Current.
I supply 5V power to the PCB which is used to power most of the ICs on the board.
When I connect the Vsupply (which is 3.3V generated by a TI LDO: http://www.ti.com/lit/ds/symlink/tps7a8300.pdf) to the current source by means of a jumper then there seems to be a short circuit.
I assume that somewhere in my schematic I connected the ICs incorrectly because when I measure the resistance between the 5V line and GND I get 500Ohms. When I removed these components from the PCB the shorting problem went away.