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This uC board is supposed to have two 12-bit DACs. But when I sweep from 0 to 4095, the DAC output stops increasing after around 4032 and settles to around 2.8V.

I power the board by its USB port.

What could be the reason for this?

Edit:

I want to increase the resolution.

On page 433 it is mentioned: "An input reference pin, VREF+ (shared with ADC) is available for better resolution"

VDDA is an input which is an analog power supply. Absolute maximum ratings at page 203 of the datasheet:

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Does that mean if I power this board via VDDA pin with 4V DC, I can power the VREF+ with 4V(to increase the resolution)?

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    \$\begingroup\$ Check the electrical specs which are in the datasheet, not the reference manual. I'm not sure you can expect rail-to-rail anyways due to transistor voltage drops. Your DAC probably doesn't go to zero either. \$\endgroup\$
    – DKNguyen
    Feb 21 at 15:50
  • \$\begingroup\$ Please see my edit. What do you think? \$\endgroup\$
    – pnatk
    Feb 21 at 16:11
  • \$\begingroup\$ You're looking for the electrical specs for the DAC in that section. \$\endgroup\$
    – DKNguyen
    Feb 21 at 16:15
  • \$\begingroup\$ What is the DAC output connected to? \$\endgroup\$ Feb 21 at 16:29
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    \$\begingroup\$ Ignore the "Absolute Maximum" ratings section. Forget you ever saw it. It's not relevant to anything you might want to do with the device under normal circumstances. The DS explicitly tells you "These are stress ratings only and functional operation of the device at these conditions is not implied." \$\endgroup\$
    – brhans
    Feb 21 at 19:04

1 Answer 1

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I am assuming you expect the output to be ideal but it isn't.

It is perfectly normal for the output to not reach GND or supply voltage.

How close it goes depends on if you use the onboard DAC buffer op-amp or not, and how much load you have on the DAC output pin.

See the DAC characteristics part of the MCU datasheet.

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  • \$\begingroup\$ Please see my edit. What do you think? \$\endgroup\$
    – pnatk
    Feb 21 at 16:11
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    \$\begingroup\$ What I think is that it's absolutely poor idea to raise supply voltage beyond recommended ratings where it may not function properly to the limit of absolute maximum rating at which there is already a risk of permanent damage. \$\endgroup\$
    – Justme
    Feb 21 at 16:44

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