Hi,
I personally would not do it. Because the IC is designed for an R to set the current.
Your text gives no requirements: Your schematic shows:
* 5V supply
* high side operation (true current source)
If it is for 20mA only what is the DAC used for?
I can only guess: You want the current source to be adjustable ... but what range?
But what output voltage range do you need? (or what is the max allowed dropout voltage)
Any accuracy requirements, any load requirements, any requirement about settling time?
Is there a reason for using especially this IC?
Here a short tutorial how to design a
DAC controlled High Side current source
(This forum has a search engine.... Free to use ;-) )
Klaus