12-bit SAR at 250k SPS — the MUX is the bottleneck
The MAX1261AEEI+ is a 12-bit successive-approximation ADC that samples at 250k samples per second. That 250k rate is shared across the input multiplexer — with all 8 channels active, each channel sees an effective throughput of 31.25 kSPS. If your application needs faster per-channel sampling, you either reduce the number of enabled channels or move to a simultaneous-sampling architecture. The input mux can be configured as 4 or 8 inputs, each selectable as pseudo-differential or single-ended. The pseudo-differential mode rejects common-mode noise on the signal return path, which is useful when the sensor ground and the ADC ground are separated by a few millivolts of noise.
Dual-supply rails — analog and digital domains
If your host runs at 3.3 V, both supplies can share the same rail, but the separate digital domain gives you the option to save power on the logic side. The reference can be either internal or external. An external reference gives you control over the full-scale range and noise floor; the internal reference simplifies the BOM at the cost of a fixed 2.5 V (typical) reference voltage. The S/H-to-ADC ratio is 1:1, meaning the sample-and-hold acquires the input in one clock cycle before the SAR conversion starts.
The QSOP has a tighter lead pitch (0.635 mm) than the standard SSOP — verify your PCB footprint matches the QSOP land pattern, not the wider SSOP. The package ships in a tube.