Other Parts Discussed in Thread: LM4140
Datasheet question regarding bypass caps for the adc128d818 VREF - in the adc128d818 datasheet it states
1) on page 4 it states "ADC128D818 allows two choices for sourcing VREF: internal or external. If the 2.56-V internal VREF is used, leave this pin unconnected." Below that it states "Bypass with the parallel combination of 1-μF (electrolytic or tantalum) and 0.1-μF (ceramic) capacitors" The second comment is its own paragraph about the pin, and seems to indicate the bypass is required whether one uses an external source or not. For example, it does NOT say.....in the event of external sources, bypass as follows....
2) On page 38 it states "VREF source must have a low output impedance and needs to be bypassed with a minimum capacitor value of 0.1 µF. A larger capacitor value of 1 µF placed in parallel with the 0.1 µF is preferred. VREF of the ADC128D818, like all ADC converters, does not reject noise or voltage variations". This does not state whether that source is external, internal or both.
3) On page 35 is figure 38. That shows an LM4140 external reference marked as "optional". However, there is no such "optional" comment about the bypass caps to the right of the external reference, seeming to indicate that the bypass caps to the right of it are required whether or not you have an LM4140.
Thus, the datasheet is vague on the VREF bypassing subject. So given the above comments....
1) are the bypass caps required when using the internal VREF source?
2) if they are not required using the internal source, what would happen if one had these two bypass caps installed when using the internal reference.
A) would it make the internal vref more quiet
.....or
B) would it make the part not function properly.
