TI E2E Community
Precision Data Converters
Precision Data Converters Forum
DAC8581 Voltage Offset
I am using a DAC8581 for high precision stimulation in a biological setting. I have ordered multiple batches of DAC8581's and have noted a substantial voltage offset. The most recent DAC I measured had an offset of about -6.5mV, which is a fairly typical magnitude. The power inputs were all +/- 5V. I tried fooling around with the DAC such as setting it to the maximum and minimum voltages (about 4.63V and -4.67V) before setting it back to 0, but the offset persisted. I've double checked each of the input power/ground pins and they are all within 1 mV of what they should be.
Is this a known issue? Is there something I could do to fix this aside from individually finding the offset for each DAC and using a lookup table when stimulating?
Where are you measuring the offset voltage at? The DAC8581 being a bipolar device, measuring offset error is a little different; you want to look at -Vref. Are you writing code 0x0000 to the device and comparing it to ground or are you writing 0x8000 to reach -FS and comparing that to -Vref? You want to write 0x8000 to get minus full scale and then look at the voltage value for -FS to compare to the reference voltage to solve for the offset error of a bipolar DAC.
This offset of about -6.5 mV is when I write 0x0000 and compare it to ground. When I write 0x8000 I get an output from pin 2 of about -4.67V. The negative reference voltage going to pin 3 is -5V.
You are running into a headroom problem between the output voltage swing set by the reference voltage and the analog negative power supply. If you test a few other codes near near the full scale negative supply, 0x8000 (0x8001, 0x8002, 0x8003), you will notice that they all produce the same output of -4.67V without a change. This has to do with the headroom of the built in output buffer amplifier. My recommendation is to try a 4V reference with +/-5V supplies, giving the output swing 1V headroom from both the negative and positive supply. You should then see offset error that reflects the data sheet.
+4V applied to pins 1,4
-4V applied to pin 3
+5V applied to pins 13, 14, and 16
The resulting voltage offset was approximately -5.2mV. The negative swing was -3.734V and the positive was 3.699. When I tested other codes near the full scale +/- supplies they did not produce the same output - they made approximately the correct voltage steps (hard to tell exactly though).
You will want to apply +4V to only pin 1 (Vref). Set pin 4 (AVDD) to +5V, pin 3 (AVSS) to -5V and DVDD (pin 13/16) to your logic level voltage. Pull pin 14 to your DVDD level to keep it out of /CLR mode. This will be the best way to measure the offset voltage. Do you have a schematic of the system you are using to measure the offset voltage that I can take a look at?
I can't do that with my current setup, but I don't think that is the issue. We tried swapping out a different DAC from a new batch on the stimulator we are using and there was no offset. The stimulator we are using uses 5V for the power and +/- 5V for the references, like my test board.
A different DAC from the new batch gives me an offset on a testing board though.
How would you prefer I send you my schematic? Do you have an email I should send it to?
It can be posted on the forum or sent to me directly using a private conversation.
hi....tony and guy...i am also using DAC8581....are there any sample codes available on how to send data to DAC...if yes...cold u plz post the links....thnx
We do not have sample code directly for the DAC8581. Please refer to your other post.
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.