So I have been working on a project for a while now that requires two dacs to output values that are different from each other. They one way or another even if they were working the day before, find a way to get stuck at 2.5V. What is happening with them? Is this their eeprom default value?
My guess is this is likely due to having both sets of pullup resistors active which is passively causing gain/drift over time; disable one set https://learn.sparkfun.com/tutorials/mc … -overview- (leave one set active per bus) and see how that goes
That sounds like you are triggering a POR (power-on-reset) condition. According to the datasheet, a POR will bring the DAC back to factory default of mid-scale value (unless internal EEPROM has been reprogrammed for other value). Assuming you have not re-programmed the internal EEPROM for a different POR value, then you are clearly describing a POR condition.
Per the datasheet, the reset condition is initiated by one of two independent events: (a) by POR or (b) by I2C General Call Reset Command. The I2C general call requires you to program some registers a certain way to initiate it, while the POR is triggered by the supply voltage dipping below +2Vdc. Assuming you are not purposely writing an I2C General Call Reset Command to both DACs at the same time, and that most likely both DACs are tied to the same supply voltage, you are most likely seeing a voltage supply dip at both DACs which would then be causing the same POR behavior at both of them.
If this is the case, you could monitor this on the voltage supply line to be sure. Also, if you are using the SFE breakout board you could add the 10uF recommended capacitor to the power supply input pin - this capacitor is useful when you have high transitions on the DAC (e.g. going from zero scale to full scale) as the power input has to supply a near instantaneous energy during this transition.