Other Parts Discussed in Thread: OPA2350, THS4522
1. I am trying to follow the recommended operating conditions of the ADC, with AVDD set to 5[V] and DVDD set to 3.3[V]. I am confused as to where to connect the ground of both power supplies. Pin 15 is labeled as GND, and the description of it says it is a Digital ground. If this is the case, then where is the ground for AVDD? Is it the same as the REFGND?
2. Page 57 of the Datasheet, under Power Supply Recommendations, asks to decouple the AVDD and DVDD pins with the GND pins using 10microF capacitors (pin numbers are not for the ADS8354, so I was wondering if this still applies to the ADS8354). I read on the web the following:
"Some high-speed ICs have their analog circuits powered by +5V, but the digital interface is powered by +3.3V or less, to interface to external logic. In this case, the +3.3V pin of the IC should be decoupled directly to the analog ground plane. It is also advisable to connect a ferrite bead in series with the power trace that connects the pin to the +3.3V digital logic supply".
What I get from here is that a capacitor needs to be connected from DVDD to the ground of AVDD? But the datasheet tells me that it needs to be connected from DVDD to the ground of DVDD.
3. Page 29 of the Datasheet, under the Reference Section, also has a 10microF capacitor connected in between the REFGND and REFIO pins. Is this only necessary when using the internal referece voltage of the ADC? Or do I need to add it when I am using an external reference voltage? I tried just connecting the capacitor in between the pins just to see if I would get the internal reference voltage of 2.5[V], but was not getting any voltage from those pins.
4. Do I need at some point connect all my grounds to a single ground?
Thank you so much for your help.