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Bias Current Generation

Question asked by nikitagusev on Oct 16, 2017
Latest reply on Jan 10, 2018 by idris

Hello,
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.

 

Problem:
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.

 

Thank you!

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