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DAC8871: voltage drift at voltages lower than -8.5V

Part Number: DAC8871

Hello,

     I have a dac8871 that is being used with an SBC. I'm using the dac to send a signal to a galvo drive.  My reference input values are at -10V to +10V.  The DAC uses 16 bit resolution, and it works very well above -8.5V.  However, when I send it a value that corresponds to a voltage below about -8.5 volts (between -8.5 and -10), I see the voltage drift in the positive direction at a rate of no more than 0.1 v per minute, but it does seem to eventually stabilize near -8.5v. 

     I've gone through and checked that all our voltages (especially our references) are staying stable, and have confirmed that there are no changes there. 

     With all of this in mind I am at a loss for what is causing this issue, and I can't seem to find anything in the setup that would cause an issue like this. 

     Any help would be greatly appreciated. 

Christian. 

  • Hi Christian,

    Thanks for using the e2e forum! Do you think you could post your schematic for you design?  Specifically, what are you using for your supplies?  Do you have an output buffer?  

    Thanks!

    Paul

  • Hi Paul,

         I do have a schematic, which will be attached. For power I'm using a pair of lab supplies and I'm using a first order filter right now.  However, I'll be putting together a more sophisticated buffer at some point.

    Thanks,

         Christian

  • Thanks for the schematic. I do not see anything obviously wrong with the design or the power supplies, but I think we need some insight on how the 'galvo' works. This DAC is unbuffered, meaning that the resistor network is exposed to the VOUT pin. If the galvo is sinking or sourcing current it could change the output of the DAC. If you could share the model number/part number of the galvo you are using we could look into this together. Otherwise I would suggest that you buffer the output of the DAC and see if you get better performance.