AD5696 16-Bit 4-Channel DAC - Periodic signal distortion


I am currently using your AD5696 to drive a galvanometric mirror and noticed periodic disturbance in my experiment. I then monitored two channels of the AD5696 on an oscilloscop when setting them to a constant value. I use one write and update to both channels and then just measure the resulting signal.

There is a periodic disturbance visuable (period of a couple of seconds) consisting of a series of Voltage spikes with about 20ms delay between them (see attached images). In the zoom you see that they seem to be initiated by a bigger spike. They occur simultaneously on both channels.

Do you have any idea what could be the reason behind this? Do I need to continously update the signal to be output because some internal reset is happening? (Edit: I tested updating the output every 10ms but the result is the same)

Thank you in advance for your help!

Best regards,

Edit: To add on to my configuration I am using a Raspberry Pi 3 with your inward facing I2C Shield.

Furthermore, the problem seems to be worse at higher output voltage:

I ran some additional tests the problem seems to be in the 5V supply for the board that is taken from the raspberry pi 5V out. Do I see it correctly that the DAC has no own reference voltage but that the 5V supply is used as a reference?

This would explain that the signal distortion is directly correlated to Voltage fluctuations on the 5V line from the adapter to the dac board.
Futhermore, the fluctuations are influenced by the activity level of the pi: I can see directly when I am connecting via SSH as well as running a program on the pi a resulting distortion on the 5V line and the DAC output. When I shutdown the raspberry but leave the power supply on everything is quiet (see the attached images).

I don’t think that our power supply to the pi is the problem here. The first time I noticed this behaviour I was using a standard USB power supply - but by now we use our own switching power supply more than high enough current rating as well as a 5V linear regulator to stabilize the power supply for the pi.

If the problem is the raspberry could I - as a workaround - just connect SDA and SCL lines to the adapter and directly connect ground and 5V of the DAC board to our power supply? Or is there a possibility to use a different reference voltage than the 5V?

Best regards,

HI Tim,
yes, the AD5696 board usages 5V as voltage ref. so if there is any noise on 5V line the DAC will pick it up.
Yes, you can connect the 5V to a stable power supply which does not produce any noise.