MCP3425A0T-E/CH

The MCP3425A0T-E/CH from Microchip Technology is a single-channel, 16-bit delta-sigma analog-to-digital converter in a tiny 6-lead SOT-23-6 package with tape-and-reel packaging (3000 units/reel). The A0T suffix denotes the SOT-23-6 package, E denotes extended temperature range (-40C to +125C), CH denotes tape-and-reel packaging.

The MCP3425 integrates all essential ADC functions in a 6-pin package: a delta-sigma modulator, SINC3 digital decimation filter, programmable gain amplifier (PGA), precision 2.048V voltage reference, oscillator, and I2C interface. No external components are required for operation.

The on-board 2.048V reference voltage is accurate to +/-0.05% (typical) with only 5 ppm/C temperature drift, enabling a differential input range of +/-2.048V at PGA = 1x. The PGA provides gains of 1x, 2x, 4x, and 8x, reducing the full-scale input range to +/-1.024V, +/-0.512V, and +/-256mV respectively. The x8 gain is particularly useful for directly measuring small signals from bridge sensors (strain gauges, load cells) without an external instrumentation amplifier.

The conversion resolution and data rate are configurable: 16-bit at 15 SPS, 14-bit at 60 SPS, or 12-bit at 240 SPS. Higher resolution comes at the cost of slower data rate due to the delta-sigma oversampling architecture. The self-calibration of offset and gain occurs automatically with each conversion.

The I2C interface supports standard mode (100 kHz), fast mode (400 kHz), and high-speed mode (3.4 MHz). The device address is configurable via the A0 pin (hardware selectable between two addresses, allowing two MCP3425 devices on the same I2C bus).

The one-shot conversion mode automatically powers down the device after a single conversion, reducing average power consumption to as low as 1 uA at low sampling rates. This is critical for battery-powered applications such as portable instruments and remote sensors.

The MCP3425 is ideal for high-accuracy measurements in space-constrained applications: weigh scales, fuel gauges, temperature sensing (RTD, thermocouple, thermistor), pressure sensors, and strain gauge bridges. For 18-bit resolution, consider the MCP3421 in the same SOT-23-6 package.

**Delta-Sigma ADC Architecture:** The MCP3425 uses a second-order delta-sigma modulator followed by a SINC3 digital decimation filter. The modulator converts the analog input into a high-frequency 1-bit data stream (oversampled at many times the Nyquist rate). The SINC3 filter decimates this bitstream to produce a 16-bit output word at 15 SPS. The oversampling inherently provides anti-aliasing, often eliminating the need for an external anti-aliasing filter.

**Programmable Gain Amplifier (PGA):** The PGA sits before the modulator and amplifies small input signals to utilize more of the ADC’s dynamic range. At x8 gain with a +/-256mV input range, a 1 LSB step corresponds to approximately 7.8 uV, enabling direct measurement of millivolt-level signals from bridge sensors.

**On-Board Reference:** The 2.048V bandgap reference provides the ADC full-scale reference. Because the reference is integrated on-chip, the differential input range is fixed at +/-2.048V/PGA. The reference is brought out on the VDD pin and is not accessible externally. The +/-0.05% initial accuracy and 5 ppm/C drift ensure measurement accuracy over temperature without external calibration.

**Self-Calibration:** The MCP3425 performs offset and gain self-calibration with every conversion. This continuously corrects for drift caused by temperature changes and supply voltage variations, maintaining measurement accuracy without periodic manual calibration.

**I2C Communication:** The device acts as an I2C slave. The master writes to the configuration register (8 bits) to set PGA gain, conversion rate, and conversion mode, then reads the conversion result (3 bytes: 2 data bytes + 1 configuration byte). The RDY bit in the configuration byte indicates when a new conversion result is available.