Can we replace the AMC7135?

[Mike_C]

@DEL

The current sense resistor has to be selected initially for the maximum current that you need.
After that the FET gate is controlled by a ‘pseudo’ analog value in a closed loop control algorithm to get the desired current, as programmed in software.

These small Altmel MCUs do not actually have analog output pins (DAC). The signal is generated using regular PWM and then filtering the result with a hardware (RC) filter to get an (almost) smooth value between 0 and Vcc.

A kind of control loop needs to be programmed in the MCU. Classic control theory uses PID loops (proportional/integral/derivative) where the output of the loop corresponds proportionally to the difference in the set point and actual current (the error), and the integral of the error and the derivative of the error. The loop is tuned by adjusting the weights of these three 3 components. For something simple like this we can probably get pretty good results using just a ‘PI’ loop.

Yeah, I know about them designs too. I got a bit of feedback when I asked in this thread: Methods for constant current (no PWM) in driver design (not existing drivers). Post #14 looks a little like what you describe, and I got an even more advanced drawing sent to me by PM… but it all gave me a headache…