8-/10-Channel, Low Voltage, Low Power, ADCs# AD7708BR Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The AD7708BR is a complete 16-bit analog-to-digital converter (ADC) designed for low-frequency measurement applications. Typical use cases include:
Direct Sensor Interface Applications
- Strain Gauge Bridges : The AD7708BR's programmable gain amplifier (PGA) and high resolution make it ideal for precision strain measurement in load cells and pressure sensors
- Thermocouple Measurements : With its low noise performance and ability to handle small differential signals, the device excels in temperature measurement applications
- RTD (Resistance Temperature Detector) Systems : The integrated excitation current sources enable direct 2-, 3-, or 4-wire RTD configurations
- Industrial Process Control : 4-20mA current loop monitoring with the ADC's flexible input ranges
Multi-Channel Data Acquisition
- 8-Channel Differential Inputs : Simultaneous monitoring of multiple sensor inputs with individual channel configuration
- Battery-Powered Systems : Low power consumption (3.3mW typical) enables portable instrumentation
- Medical Instrumentation : ECG, blood pressure monitors, and patient monitoring systems
### Industry Applications
Industrial Automation
- Process Control Systems : PLC analog input modules for temperature, pressure, and flow monitoring
- Motor Control : Current sensing and position feedback in servo drives
- Smart Transmitters : Field instrumentation with HART communication compatibility
- Environmental Monitoring : Air quality sensors, water quality analysis systems
Medical Equipment
- Patient Monitoring : Vital signs measurement with high CMRR for noise rejection
- Portable Medical Devices : Blood glucose meters, portable ECG monitors
- Laboratory Instruments : Precision measurement equipment
Consumer and Automotive
- Automotive Sensing : Pressure monitoring, temperature sensing in engine management
- Home Automation : Smart thermostat systems, environmental controls
### Practical Advantages and Limitations
Advantages:
- High Integration : Complete analog front-end with PGA, reference, and digital filtering
- Flexible Power Supply : Operates from 2.7V to 5.25V single supply
- Low Power Operation : 3.3mW typical power consumption
- Excellent Noise Performance : 16-bit no missing codes, 0.003% nonlinearity
- On-Chip Calibration : System calibration and background calibration modes
- SPI-Compatible Interface : Simple microcontroller interface
Limitations:
- Limited Speed : Maximum throughput of 500Hz may be insufficient for high-speed applications
- Input Range Constraints : Limited to ±VREF/PGA gain input ranges
- Temperature Range : Commercial temperature range (0°C to +70°C) limits industrial applications
- No Internal Clock : Requires external crystal or clock source
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Power Supply Decoupling
- Pitfall : Inadequate decoupling causing noise and accuracy degradation
- Solution : Use 10μF tantalum and 100nF ceramic capacitors close to AVDD and DVDD pins
- Implementation : Place decoupling capacitors within 5mm of power pins with short traces
Reference Voltage Stability
- Pitfall : Poor reference performance affecting overall accuracy
- Solution : Use low-noise, low-drift reference sources like AD780 or REF19x series
- Implementation : Buffer reference output if driving multiple ADCs or heavy loads
Digital Interface Issues
- Pitfall : SPI communication errors due to timing violations
- Solution : Ensure proper setup and hold times for digital signals
- Implementation : Use series termination resistors (22-100Ω) on clock and data lines
### Compatibility Issues with Other Components
Microcontroller Interface
- SPI Compatibility : Works
