I want to use the ADS8317 16-Bit SAR A/D converter and have read through the datasheet. In there, ti recommend using a low ESR 47µF tantalum capacitor to buffer the reference input. Now, my reference is already buffered with a 220µF low ESR aluminum electrolytic capacitor (Panasonic FR 220µF/16V; 130mOhm ESR at 100kHz), and I'm wondering whether that's enough, or if the tantalum has some important advantage.
As far as I can tell, the important factors should be that the capacitor is large enough and "fast" enough to charge the internal capacitors of the ADC to 16 bit accuracy within the required time, similar to the signal inputs. However, I think the reference input might see a charge transfer for every bit of the SAR instead of only once during the acquisition time – if that is the case, the charge transfer would have to be faster. The smallest time I can imagine for this would be half a clock period – 500ns in my case.
Ok, but – is my aluminum electrolytic capacitor up to the task (perhaps assisted by a smaller ceramic right next to the input)? As far as I know they are not good for "high frequency" applications, but I don't know any actual numbers.
Best Answer
They don't appear to be much different electrically.
Tantalums are physically smaller and SMT, which is a big advantage in some applications.
I think you'll be fine from the pov of the ADC if you use that, perhaps with 1uF ceramic X7R in parallel close to the ADC.
Minor nit- I would not call a bypass capacitor a 'buffer'. The OPA350 amplifier is the buffer.