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Low Frequency Noise In Eval-AD5791/91SDZ

Question asked by wlunden on Jun 3, 2015
Latest reply on Jun 5, 2015 by harryh

I've got myself an Eval-AD5781/91SDZ board (with an AD5791 onboard) and an SDP board for communicating with it over usb. Using the default jumper configurations, such that the positive and negative references are derived from a 5V reference input and the digital +5V and ground are derived from the SDP board, I have supplied the circuit with power rails derived from a pair of 9V's and a 5V reference from a circuit built around an LT1019. The low frequency noise in the reference circuit is something like +/-10uV. I have experienced two issues with this setup:

 

1) The Vout shows a lot of low-frequency (ie sub-Hz to a few Hz) noise. The amount of noise is something like +/- 10's of mV. This persists if I replace the 9V rails with a +/-10V from a linear power supply with ~100uV ripple.

 

2) The software included with the board allows me to send DAC codes without any software errors, but the output voltage of the board is slightly non-monotonic with DAC code (it jumps backwards in voltage after every 1000 codes or something like this). Any ideas here?

 

Thanks!

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