On my ADuC7121 evaluation board, i am not able to achieve the datasheet specifications for the IDACs.
When I look at the IDAC output pins with an oscilloscpe, i am seeing an oscillation of +/-100mV at a frequency of ~25khz.
What is causing this?
Firstly, to fix the issue, remove the capacitor C5 from the board.
This cap is in parallel to the external low ppm reference resistor. R8. R8 is used to generate an internal reference current for the IDAC circuits.
On some builds of the evaluation boards, C5 is populated with a 100nF cap. This cap makes the internal buffer circuit for the reference current unstable and causes the oscillation on the IDAC outputs.