24 Bit ADC with Two Differential Input Multiplexer and Internal Oscillator# ADS1226 Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The ADS1226 is a precision, 24-bit, delta-sigma (ΔΣ) analog-to-digital converter (ADC) designed for high-resolution measurement applications requiring excellent accuracy and low noise performance.
Primary Measurement Applications:
- Temperature Measurement : Direct thermocouple and RTD measurements with built-in programmable gain amplifier (PGA)
- Pressure Sensing : Bridge sensor measurements for industrial pressure transducers
- Strain Gauge Systems : High-resolution force and weight measurement applications
- Current Shunt Monitoring : Precision current measurement in power management systems
### Industry Applications
Industrial Automation
- Process control instrumentation
- Factory automation sensors
- PLC analog input modules
- Motor control current sensing
Medical Equipment
- Patient monitoring devices
- Portable medical instruments
- Diagnostic equipment sensors
- Biomedical signal acquisition
Energy Management
- Smart grid monitoring
- Power quality analysis
- Solar inverter systems
- Battery management systems
Test and Measurement
- Laboratory instruments
- Data acquisition systems
- Calibration equipment
- Environmental monitoring
### Practical Advantages and Limitations
Advantages:
- High Resolution : 24-bit conversion with no missing codes
- Low Noise : 90nV RMS noise at 20SPS with gain=128
- Flexible Input : Supports differential and single-ended measurements
- Integrated PGA : Programmable gains from 1 to 128
- Low Power : 350μA typical current consumption
- Temperature Range : -40°C to +125°C operation
Limitations:
- Speed Limitation : Maximum 2kSPS conversion rate
- External Reference : Requires stable external voltage reference
- Complex Configuration : Multiple register settings for optimal performance
- PCB Sensitivity : Performance dependent on careful layout practices
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Power Supply Decoupling
- Pitfall : Inadequate decoupling causing noise and accuracy degradation
- Solution : Use 10μF tantalum + 100nF ceramic capacitors close to AVDD and DVDD pins
Reference Voltage Stability
- Pitfall : Using noisy or unstable reference voltage
- Solution : Implement low-noise reference IC (e.g., REF5025) with proper filtering
Input Signal Conditioning
- Pitfall : Direct sensor connection without anti-aliasing filtering
- Solution : Implement RC low-pass filter with cutoff frequency below Nyquist rate
Digital Interface Noise
- Pitfall : Digital noise coupling into analog signals
- Solution : Use separate analog and digital ground planes with single-point connection
### Compatibility Issues with Other Components
Microcontroller Interface
- SPI Compatibility : Standard 4-wire SPI interface compatible with most microcontrollers
- Voltage Level Matching : Ensure DVDD matches microcontroller I/O voltage levels
- Timing Requirements : Verify SPI clock frequency compatibility (max 4.1MHz)
Sensor Compatibility
- Bridge Sensors : Optimal for full-bridge and half-bridge configurations
- Thermocouples : Requires cold-junction compensation circuitry
- RTD Sensors : Supports 2-wire, 3-wire, and 4-wire RTD configurations
Power Supply Requirements
- Analog Supply : 2.7V to 5.25V AVDD range
- Digital Supply : 1.65V to 3.6V DVDD range
- Supply Sequencing : No specific sequencing requirements between AVDD and DVDD
### PCB Layout Recommendations
Power Distribution
- Use star-point configuration for analog and digital power supplies
- Implement separate power planes for analog and digital sections
- Place decoupling capacitors within 2mm of
