In page 20 of the AD7689 both options are shown in Figs 30A and 30B.
If I want 8 Single Ended channels, what should I do:
- Use CFG[12:10] = 111 and leave COM open
- Use CFG[12:10] = 010 and connect COM to GND?
Thanks in advance!
Yes, that's correct.
Sorry, the 2 options considered should be Single Ended or Unipolar Diffferential:
- Use CFG[12:10] = 110 and connect COM to GND?
If you want to use the 8 single-ended (unipolar) channels referenced to ground (figure 30A), set CFG [12:10] = ‘111’ and if you want to use the 8 single-ended (unipolar) channels referenced to COM, set CFG [12:10] = ‘110’, where COM is always connected to absolute GND±0.1V. In both the cases, all inputs (IN[7:0]) have a range of GND to VREF and you will get the same output result.
If you want to use the unipolar differential pairs configuration (figure 30c), the positive input channels have the range of GND to VREF and the negative input channel is always referenced to absolute GND±0.1V set by CFG [12:10] = '10X'.
So there's basically no performance difference between using them referenced to ground with COM open (CFG [12:10] = ‘111’) or using them referenced to COM, with COM connected to ground (CFG [12:10] = ‘110’)?
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