I need to create a constant current sink circuit such that I can simulate current draws from a battery, and analyze the battery behavior. I'll be testing a battery that is 3.1V with 12mAh capacity. I need to draw current in various patterns (i.e. repeated cycles of 15 minutes 1.5microamp, then 5 seconds 7mA, 30 minutes 1.0microamp, then 3 seconds 10mA, etc).
The battery voltage remains at 3.1V when a microamp current is drawn, but the voltage drops when 7mA is drawn. This voltage drop is what I need to analyze. Thus, I need a circuit that will ensure constant current is drawn regardless of what the battery voltage drops to (expected drop is to between 2.4V and 1.8V after repeated cycles).
This is what I am able to find online (picture of schematic below): http://www.ti.com/lit/an/slaa868/slaa868.pdf
However, I am having a hard time finding appropriate parts and setting appropriate resistor currents to achieve the current sink range of 1.5uA to 7mA. Can anybody point me in the right direction to appropriate MOSFETs and op-amps I should be using here? The circuit needs to be very precise, I can't think I'm drawing 1.5uA but actually be drawing 30uA or 30uA.
I also plan to measure the battery voltage as I run different tests using an Arduino, and control the DAC with an Arduino. I've found this DAC that should be pretty easy to use with Arduino: https://cdn-shop.adafruit.com/datasheets/mcp4725.pdf. 2.7-5.5V max output.
[![enter image description here][1]][1] [1]: https://i.sstatic.net/pL2x3.png
