8.3.1 Rail-to-Rail Input

The input common-mode voltage range of the MCP629x family extends 100 mV beyond the supply rails for the full supply voltage range of 2.4 V to 5.5 V. This performance is achieved with a complementary input stage: an N-channel input differential pair in parallel with a P-channel differential pair, as the Functional Block Diagram shows. The N-channel pair is active for input voltages close to the positive rail, typically (V+) – 1.4 V to 100 mV above the positive supply, whereas the P-channel pair is active for inputs from 100 mV below the negative supply to approximately (V+) – 1.4 V. There is a small transition region, typically (V+) – 1.2 V to (V+) – 1 V, in which both pairs are on. This 200-mV transition region can vary up to 200 mV with process variation. Thus, the transition region (with both stages on) can range from (V+) – 1.4 V to (V+) – 1.2 V on the low end, and up to (V+) – 1 V to (V+) – 0.8 V on the high end. Within this transition region, PSRR, CMRR, offset voltage, offset drift, and THD can degrade compared to device operation outside this region.