How to Use ADS1220: Examples, Pinouts, and Specs

The ADS1220 is a high-performance, 24-bit analog-to-digital converter (ADC) manufactured by Texas Instruments (TI). It is designed for precision measurement applications, offering a low-noise, low-drift architecture. The ADS1220 integrates programmable gain amplifiers (PGAs), a multiplexer, and an internal oscillator, making it an ideal choice for sensor interfacing and data acquisition systems.

• Industrial process control
• Medical instrumentation (e.g., temperature or pressure sensors)
• Weigh scales and load cell measurements
• Portable instrumentation
• Thermocouple and RTD temperature measurements

The ADS1220 is available in a 16-pin TSSOP package. Below is the pinout and description:

1. Power Supply: Connect AVDD and DVDD to appropriate supply voltages (e.g., 3.3 V for DVDD and 5 V for AVDD). Ensure GND is connected to the system ground.
2. Input Configuration: Connect the analog inputs (AIN0–AIN3) to the desired sensors or signals. For differential measurements, use pairs of inputs (e.g., AIN0 and AIN1).
3. Reference Voltage: Provide a stable reference voltage to REFP and REFN. Alternatively, use the internal reference by configuring the device via SPI.
4. SPI Communication: Connect the SPI pins (SCLK, CS, DIN, and DRDY/DOUT) to a microcontroller or processor. Ensure proper SPI settings (Mode 1: CPOL = 0, CPHA = 1).
5. Start Conversion: Use the START pin or send the appropriate SPI command to initiate conversions.
6. Read Data: Monitor the DRDY pin for data-ready status, then read the conversion result via SPI.

• Bypass Capacitors: Place decoupling capacitors (e.g., 0.1 µF and 10 µF) close to the AVDD and DVDD pins to reduce noise.
• Input Impedance: Ensure the source impedance is low enough to avoid signal degradation.
• Thermal Management: Operate the device within the specified temperature range to maintain accuracy.
• SPI Timing: Follow the timing requirements specified in the datasheet for reliable communication.

Below is an example of interfacing the ADS1220 with an Arduino UNO via SPI:

#include <SPI.h>

// Pin definitions
#define CS_PIN 10    // Chip select pin
#define DRDY_PIN 9   // Data ready pin
#define START_PIN 8  // Start conversion pin

void setup() {
  // Initialize SPI
  SPI.begin();
  SPI.setDataMode(SPI_MODE1); // CPOL = 0, CPHA = 1
  SPI.setClockDivider(SPI_CLOCK_DIV16); // Adjust as needed for your setup

  // Configure pins
  pinMode(CS_PIN, OUTPUT);
  pinMode(DRDY_PIN, INPUT);
  pinMode(START_PIN, OUTPUT);

  // Set initial states
  digitalWrite(CS_PIN, HIGH);  // Deselect ADS1220
  digitalWrite(START_PIN, LOW); // Ensure conversion is stopped

  // Start conversion
  digitalWrite(START_PIN, HIGH);
}

void loop() {
  // Wait for data ready signal
  if (digitalRead(DRDY_PIN) == LOW) {
    digitalWrite(CS_PIN, LOW); // Select ADS1220

    // Read 3 bytes of data (24-bit result)
    byte data1 = SPI.transfer(0x00);
    byte data2 = SPI.transfer(0x00);
    byte data3 = SPI.transfer(0x00);

    digitalWrite(CS_PIN, HIGH); // Deselect ADS1220

    // Combine bytes into a 24-bit result
    long result = ((long)data1 << 16) | ((long)data2 << 8) | data3;

    // Print result to serial monitor
    Serial.println(result);
  }
}

1. No Data Output:

   • Ensure the SPI connections are correct and the SPI mode is set to Mode 1.
   • Verify that the CS pin is toggled correctly during communication.

2. Incorrect Conversion Results:

   • Check the reference voltage and ensure it is stable.
   • Verify the input signal is within the specified range.

3. High Noise in Measurements:

   • Use proper grounding and shielding techniques.
   • Add bypass capacitors near the power supply pins.

4. Device Not Responding:

   • Confirm that the RESET pin is not held low.
   • Ensure the power supply voltages are within the specified range.

• Use an oscilloscope to verify SPI signals (SCLK, DIN, DOUT).
• Check the DRDY pin to ensure the device is completing conversions.
• Refer to the ADS1220 datasheet for detailed timing diagrams and configuration options.