LC2MOS 20-Bit A/D Converter# AD7703CR Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The AD7703CR is a 20-bit sigma-delta analog-to-digital converter (ADC) specifically designed for low-frequency measurement applications requiring high resolution and precision.
Primary Applications:
- Industrial Process Control : Temperature monitoring, pressure sensing, and flow measurement systems
- Weigh Scale Systems : Precision weighing applications requiring 16-20 bit resolution
- Portable Instrumentation : Battery-powered measurement devices due to low power consumption
- Medical Equipment : Patient monitoring systems, biomedical sensors
- Strain Gauge Transducers : Bridge sensor measurements with high accuracy
### Industry Applications
- Manufacturing : Quality control systems, production line monitoring
- Automotive : Sensor interfaces for pressure and temperature monitoring
- Aerospace : Flight control systems, environmental monitoring
- Energy Management : Power monitoring, smart grid applications
- Laboratory Equipment : Precision measurement instruments
### Practical Advantages and Limitations
Advantages:
- High Resolution : 20-bit no missing codes performance
- Low Power : Typically 40 mW power consumption
- Integrated Features : On-chip digital filtering and programmable gain amplifier (PGA)
- Wide Dynamic Range : 120 dB typical at 50 Hz output rate
- Flexible Interface : Simple 3-wire serial interface
Limitations:
- Limited Speed : Maximum output word rate of 4 kHz
- Analog Supply Range : Restricted to ±5V operation
- Temperature Range : Commercial grade (0°C to +70°C) limits harsh environment use
- Noise Performance : May require external filtering in high-noise environments
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Power Supply Noise
- Issue : Switching regulators causing noise in ADC readings
- Solution : Use linear regulators and implement proper decoupling (10 µF tantalum + 0.1 µF ceramic per supply pin)
Pitfall 2: Ground Loops
- Issue : Digital and analog ground contamination
- Solution : Implement star ground configuration and separate analog/digital grounds
Pitfall 3: Clock Jitter
- Issue : External clock instability affecting conversion accuracy
- Solution : Use crystal oscillator instead of RC circuits for master clock
Pitfall 4: Input Signal Conditioning
- Issue : Inadequate anti-aliasing filtering
- Solution : Implement 2nd order anti-aliasing filter with cutoff at 1/2 sampling frequency
### Compatibility Issues with Other Components
Microcontroller Interfaces:
- Compatible with most SPI and microcontroller interfaces
- Requires 3.3V-5V logic level compatibility
- Watch for timing constraints with slower microcontrollers
Sensor Compatibility:
- Excellent for bridge sensors (strain gauges, pressure sensors)
- Compatible with thermocouples and RTDs with external conditioning
- Limited for high-impedance sources (>10 kΩ) without buffer
Power Supply Requirements:
- Requires dual ±5V supplies
- Incompatible with single-supply systems without level shifting
- Sensitive to power supply sequencing
### PCB Layout Recommendations
Power Supply Layout:
- Place decoupling capacitors within 5 mm of supply pins
- Use separate power planes for analog and digital supplies
- Implement ferrite beads for supply isolation
Signal Routing:
- Keep analog input traces short and away from digital signals
- Use guard rings around analog input pins
- Route clock signals away from analog inputs
Grounding Strategy:
- Single-point ground connection between analog and digital grounds
- Use ground plane for analog section
- Avoid splitting ground planes under the ADC
Component Placement:
- Place
