[quote user="Jens-Michael Gross"]
First, if you don't need to draw significant analog current (such as for a D/A), you can rise the resistor to 100Ohms. It gives a better low-pass effect and a cleaner AVcc.
In addition, the capacitors between AVcc and AVss should be a 10µF Tantalum/100nF ceramic combo, which combines low ESR with high capacitance and still low leakage current.
[/quote]
I ran a simulation in LTSpice on the proposed RC filter where R = 100 Ohms and C = 10.1 uF. The image below shows that the voltage difference between DVCC (blue) and AVCC (green) exceeds 0.3V. The red is a plot of the difference between DVCC and AVCC.
It has been recommended in previous posts and throughout app notes not to use different sources for AVCC and DVCC because they may have different start up times that could lead to a voltage difference greater than 0.3V that could cause latch up conditions and dissipate large amounts of current through the internal protection diodes.
It appears that the proposed RC filter may cause the same issues due to the voltage lag of the RC. Has anyone noticed any problems with an RC filter this big (R=100 and C = 10.1uF)?
