Voltage swing from Due DAC

Dear guys,

I have concerns about DAC of Due as below;

1) The output voltage does not go 0 Volt even if I write 0 as output value. The DMM readings of DAC0 pin was as below;

0: 0.548V 100: 0.599V delta 51mV 1000: 1.078V 1100: 1.131V delta 53mV 2000: 1.610V 2100: 1.664V delta 54mV 3000: 2.143V 3100: 2.196V delta 53mV 3995 : 2.673V 4095: 2.727V delta 54mV

It seems that voltage swings from 0.548V to 2.727V when I wirte 0~4095. The linearity of the DAC sems OK for my application.

2) The Voltage at 3.3V rail was 3.235V.

3) I need voltage swing starting from 0 Volt to 10 Volt.

4) I know I have to use OP amp to amplify the output of DAC0.

5) The problems are; a) The voltage is not starting from 0 Volt. How can I make it Zero Volt using OP Amp?? I also need to amplify Max output to 10 Volt. My requirement is to make DAC0 outpout of 0.548V to Zero Volt after OP Amp and 2.727V to 10V. How?? b) I need the DAC output stays Zero when booting and stay Zero until I write new value BUT I found the DAC0 output went to 3.235V when booting.. How can I solve this problem??

6) I tried external 12bit DAC, MCP4728, and the voltage swing was from 0V to 3.3V which is OK but I really want to use internal DAC if at all possible.

I found that the output of DAC0 and DAC1 swings from 1/6 to 5/6 of the VCC which is consistant with my DMM readings.

You can level shift and amplify with just one op-amp. This link explains how.

Dear dlloyd,

Thanks for your great help. This solves level shift and amplify problem..

I still have problem of DAC output rising up to 3.3V when booting. Any idea to make it zero until I write new DAC value??

Cheers, Young

You could try a 10K pulldown resistor on the Due's DAC output to keep it low while it's un-configured during bootup (untested). Another idea might be to use an analog switch ... but more information on your application and circuit would be helpful.

Dear dlloyd,

Thanks for your advice. I will try with a Pull down resistor. If it fails, I will use a small FET grounding non inverting input of the OP amp where DAC output is connected ( I may need a series resistor to prevent overload to DAC output when grounding) until I write a DAC value..

Thanks, Young