Other Parts Discussed in Thread: ADS1281, ADS1282
Looking for a highly accurate ADC. I do not need internal PGA, the logical choice would be ADS1281, but I do not know why ADS1282 has better INL 0.5 ppm vs 0.6 ppm. I assumed that the ADC is identical in the two circuit and the ADS1282 is added PGA and multiplex.As PGA and MUX should INL rather worsen.
What I not see?
Hi Karel,
Welcome to the TI E2E forums!
I think the slight difference in INL is a result of the internal PGA... As with any ADC that samples the input with a switched capacitor circuit, the voltage on the sampling capacitor must settle to within a certain accuracy before a conversion. Therefore, the input signal needs to be provided from a low output impedance source, or buffered, for the sampling capacitor voltage to settle in time. The advantage of the internal PGA in the ADS1282 is that it knows when the sampling capacitor will switch and it can provide the extra drive required to settle the input voltage in time.
You'll notice from the "INL vs INPUT" graph that there is some INL dependence with the input voltage, as well as the PGA gain. Larger inputs need to further recharge the sampling capacitor and the larger gains will result in lower PGA bandwidth (for a constant GBW product) to drive the ADC inputs.
Best Regards,
Chris
