Overall Context

️· AD7715: This is an ADC (Analog-to-Digital Converter) device.
️· Two Versions: There are two versions presented:
- "A" Version: Designed for a supply voltage of 3.3V.
- "AD" Version: Designed for a supply voltage of 1.8V.

Key Parameter Comparison

Feature	"A" Version (3.3V Supply)	"AD" Version (1.8V Supply)
Supply Voltage	3.3V	1.8V
Input Range	0 to +VREF/GAIN (typically 3.3V)	0 to +VREF/GAIN (typically 1.8V)
Reference Voltage (VREF)	Typically 3.3V	Typically 1.8V
Input Sampling Rate (fS)	GAIN x fCLK / 64	GAIN x fCLK / 64
Differential Input Range	Up to 1.5V	Up to 1.5V
Input Current (Logic Inputs)	±10μA	±10μA
Output Low Voltage (VOL)	0.4V	0.4V
Output High Voltage (VOH)	DVDD - 0.6V	DVDD - 0.6V
Common Mode Rejection (CMR)	90 dB	90 dB
Input Offset & Gain Error	+/- 0.0015	Typically +/- 0.0004%
Full Scale Drift	0.2 μV/°C	0.2 μV/°C
Gain Drift	0.2 μV/°C	0.2 μV/°C

Important Notes & Other Details

️· Reference Voltage: The reference voltage directly impacts the input range.
️· GAIN: The "GAIN" parameter appears in various calculations related to sampling rate and input range. It likely refers to an internal amplifier gain setting.
️· fCLK: This is the clock frequency, which determines the overall sampling rate.
️· Digital Output Coding: Both versions support Binary and Offset Binary digital output coding.
️· Logic Inputs: The logic input current is the same in both versions.
️· Temperature Sensitivity: Both versions have similar temperature sensitivities.

In short: The main difference between the "A" and "AD" versions is the supply voltage, which affects the input range. The other electrical characteristics are very similar.