12-bit SAR ADC in a SOT-23-5 — fit for space-constrained single-channel conversion
The MCP3221A4T-E/OT is a 12-bit successive-approximation-register (SAR) ADC from Microchip, sampling at 22.3 kS/s with a single-ended input and an I²C interface. It operates from a single 2.7V to 5.5V supply — the analog and digital rails share the same pin, so no separate reference or dual-supply routing is needed on the board. The 12-bit resolution gives 4096 codes across the supply voltage range, so the LSB size scales with VDD — at 5V it is 1.22 mV, at 3.3V it is 0.81 mV. This is a workhorse ADC for reading a single sensor or voltage rail where 0.1% accuracy is enough and the 22.3 kS/s throughput covers slow-changing signals like temperature, pressure, or battery voltage.
Supply and temperature range — single-rail simplicity with 125°C headroom
The -40°C to +125°C operating temperature covers automotive under-hood and industrial oven-adjacent environments; the 125°C ceiling gives margin above the 105°C typical for engine-bay electronics. The SOT-23-5 package (SC-74A) is a five-pin footprint that hand-solders easily and fits into tight mixed-signal layouts. The I²C interface uses only two bus lines (SCL, SDA) plus VDD and GND, leaving one pin for the analog input — the 1:1 S/H:ADC ratio means the sample-and-hold is dedicated to that single channel, so no input multiplexer settling delay.