A digitally controlled DC to DC converter:
You can easily add margining capability (digital adjustment of the output voltage) to a DC/DC converter by adding a 2- or 4-channel, I²C-adjustable current DAC (DS4402 or DS4404) at the converter’s feedback input. Because each DAC output is 0mA at power up, the extra circuitry is transparent to the system until a command is written via the I²C bus.
Thanks for the tip rsdio!
actually I wanted to do the same thing for a DIY bench supply. I think, one other method is to use PWM and a low pass filter although I haven’t tested yet.