I want to use an ADC (AD7124 that is a 24 bit sigma/delta) for 14 bit readings of an external voltage. My power source is a fairly stable 24v DC supply and the ADC runs on 3.3v. I will be using the internal 2.5v voltage reference of the ADC.
I'm planning on using a MC34063 switching dc-dc converter to reduce the voltage down to 3.3 volts. Some say this is a bad idea because of the voltage ripple and spikes on the output of switching supplies.
The only effect I can think of that voltage ripple has on ADC readings, is on the internal voltage reference. According to the datasheet, the internal reference has a "power supply rejection" value of 85 db. I'm guessing power supply ripple is attenuated by 85 db and then appears as an error on the internal reference.
Question 1: Is this correct? If yes does this change with frequency? The datasheet has nothing on frequency.
Question 2: How else does power supply ripple affect ADC readings?
Question 3: If using a step down switching supply is a bad idea, will adding a L200c linear regulator solve the problem? (L200c is probably overkill but I need the current limiting function and that is the only thing I have available)