If you want the controller to go more than 2.1A, you will need more voltage at the MOSFET gate then 5V that the DAC could give. For that use this second schematic below with an OPAMP between the DAC and the MOSFET gate. The gain is 2 so the output from the OPAMP will eb around 5V * 2 so around 10V which should be enough to go up to 5A or more. See the other schematic here without the OPWMP.