I would like to use the delta sigma ADC from 5LP in one of my application and I have some questions:
1. I intend to monitor 3 single-ended signals using the inherent analog multiplexer and the delta sigma ADC available. The monitored signals range from 0 to 5.15V and I need to adapt my input voltage to the ADC input ranges available in datasheet using a voltage divider alongside a filter capacitor. For single ended operation I thought to go with the 0-2.048V range, hence I need to divide my input signal by 2, approximately (I do not have a very stable Vdda available on my board therefore the Vssa to Vdda option does not fit my needs).
According to the datasheet this option sets automatically the buffer gain to 1, which normally would clip the input voltage range to both upper and lower rails. However the datasheet also states that the single-ended option will bypass the low side buffer.
Does it mean than when configured as single-ended the input signal will not be affected by the lower voltage limit of the buffer, VOL?
2. I did not found any information about the leakage current of the ADC pin and maximum allowed current into the ADC pin (or GPIO as a matter of fact), inside the document. The leakage component will affect my readings due to the voltage drop across the series external resistor.
3. Another point concerns the external capacitor – is it ok if I foresee a filter capacitor 1000 x the value of the hold capacitor? The cut-off frequency of the external filter is not a big concern as I am monitoring some rather sluggish signals.
4. The last point that I am interesting in: could I use the differential mode configuration to measure single ended signals?
The datasheet states that in differential mode I can tie the negative input to 2.028V and obtain a usable input range between 0 and 4.096V. Does it mean that even if in differential mode I can monitor a single-ended signal ranging from 0 to 4.096V? This would be more appropriate for my application as it is closer to the input signal range. Please let me know if possible!
Also, I presume there is no bypass of the rails when configured as differential, so for monitoring low voltage signals (under 100mV) is should bypass the buffer.
Many thanks for your support,