How to Use MCP3421: Examples, Pinouts, and Specs

The MCP3421 is a high-resolution, low-power, 18-bit analog-to-digital converter (ADC) manufactured by Microchip. It features a single-channel input and an integrated programmable gain amplifier (PGA), allowing for precise measurements of small signals. The device communicates via the I2C protocol, making it easy to interface with microcontrollers and other digital systems. Its compact design and low power consumption make it ideal for battery-powered and portable applications.

• Sensor signal acquisition (e.g., temperature, pressure, and light sensors)
• Portable medical devices
• Industrial process control
• Data logging systems
• Battery monitoring

• Resolution: 18-bit
• Input Channels: Single-ended
• Programmable Gain Amplifier (PGA): Gains of 1x, 2x, 4x, and 8x
• Input Voltage Range: ±2.048V (PGA = 1x)
• Supply Voltage: 2.7V to 5.5V
• Communication Interface: I2C (up to 3.4 MHz)
• Conversion Modes: Continuous or One-Shot
• Current Consumption:
  • 145 µA (typical) during conversion
  • 0.1 µA (typical) in standby mode
• Package: 6-pin SOT-23

The MCP3421 is available in a 6-pin SOT-23 package. The pinout and descriptions are as follows:

1. Power Supply: Connect the VDD pin to a 2.7V to 5.5V power source and the GND pin to ground.
2. Analog Input: Connect the signal to be measured to the VIN+ pin. If measuring differential signals, connect the reference signal to the VIN- pin.
3. I2C Interface:
   • Connect the SCL and SDA pins to the corresponding I2C pins on the microcontroller.
   • Use pull-up resistors (typically 4.7 kΩ) on the SCL and SDA lines.
4. Addressing: The MCP3421 has a fixed I2C address of 0x68.

Below is a basic connection diagram for the MCP3421 with an Arduino UNO:

MCP3421       Arduino UNO
---------     ------------
VDD           3.3V or 5V
GND           GND
SCL           A5 (SCL)
SDA           A4 (SDA)
VIN+          Signal Input
VIN-          Ground or Reference Signal

The following Arduino code demonstrates how to read data from the MCP3421:

#include <Wire.h>

#define MCP3421_ADDRESS 0x68 // I2C address of the MCP3421

void setup() {
  Wire.begin(); // Initialize I2C communication
  Serial.begin(9600); // Initialize serial communication for debugging
}

void loop() {
  Wire.beginTransmission(MCP3421_ADDRESS);
  Wire.write(0x10); // Configuration byte: 18-bit resolution, PGA = 1x
  Wire.endTransmission();

  delay(100); // Wait for conversion to complete

  Wire.requestFrom(MCP3421_ADDRESS, 3); // Request 3 bytes of data
  if (Wire.available() == 3) {
    // Read the 3 bytes of data
    byte msb = Wire.read();
    byte lsb = Wire.read();
    byte config = Wire.read();

    // Combine the bytes into a 2's complement 18-bit value
    long rawData = ((long)msb << 16) | ((long)lsb << 8);
    rawData >>= 8; // Shift to remove the unused bits

    // Convert to voltage (assuming PGA = 1x and Vref = 2.048V)
    float voltage = (rawData * 2.048) / 131072.0;

    Serial.print("Voltage: ");
    Serial.print(voltage, 6); // Print voltage with 6 decimal places
    Serial.println(" V");
  }

  delay(1000); // Wait 1 second before the next reading
}

• Input Voltage Range: Ensure the input voltage does not exceed the specified range for the selected PGA setting.
• I2C Pull-Up Resistors: Use appropriate pull-up resistors on the SCL and SDA lines to ensure reliable communication.
• Noise Reduction: Minimize noise in the analog input signal by using proper grounding and shielding techniques.

1. No I2C Communication:

   • Verify the pull-up resistors on the SCL and SDA lines.
   • Check the wiring and ensure the correct I2C address (0x68) is used.

2. Incorrect Voltage Readings:

   • Ensure the input voltage is within the specified range.
   • Verify the PGA setting and adjust the voltage calculation formula accordingly.

3. Device Not Responding:

   • Confirm that the power supply voltage is within the 2.7V to 5.5V range.
   • Check for loose or incorrect connections.

Q: Can the MCP3421 measure negative voltages?
A: Yes, the MCP3421 can measure differential signals, allowing it to measure negative voltages relative to the VIN- pin.

Q: What is the maximum sampling rate of the MCP3421?
A: The maximum sampling rate is 240 samples per second (SPS) at 12-bit resolution. At 18-bit resolution, the sampling rate is reduced to 3.75 SPS.

Q: Can I use the MCP3421 with a 3.3V microcontroller?
A: Yes, the MCP3421 operates with a supply voltage as low as 2.7V, making it compatible with 3.3V systems.

Q: How do I change the resolution or PGA settings?
A: The resolution and PGA settings are configured using the configuration byte sent via the I2C interface. Refer to the datasheet for details on the configuration byte format.