Q:

Change current using PWM, for specific range outside PWM boundaries

I have a circuit where I use a digital potentiometer (namely MCP41100) to change current, and I use duty between 0 and 255 (thus, I have 256 steps).  The current changes from 25 micro to 50 micro.  And things are running great for these numbers, but I want a different range. 
What I would like to have is a current that goes between 0 and 16 milliampere with very small steps (each step is like 10 to 20 micro, thus I will have over 500 steps (16000/20)). 
If you know the right component(s) to make my circuit work, please let me know.  Any hint in the right direction is appreciated. 

A:

According to the datasheet, these devices can be daisy chained. 
So if you add another MCP41100 (or use a dual, MCP42100 for 100k devices) in series, you will add one effective bit, for 9 bit (512 step) resolution. 
Note that the accuracy of these devices is very limited; I would probably put 4 in series for 10 bit resolution if I wanted to achieve decent precision. 
There are quad devices available, incidentally.