24-Bit, Single-Channel, Ultra Low Power, Sigma Delta A/D Converter# AD7791BRM Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The AD7791BRM is a low-power, 24-bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC) specifically designed for precision measurement applications requiring high resolution and low noise performance.
Primary Use Cases:
- Bridge Sensor Measurements : Direct interface with strain gauges, load cells, and pressure sensors
- Temperature Monitoring : RTD and thermocouple measurements with high precision
- Medical Instrumentation : Patient monitoring equipment, portable medical devices
- Industrial Process Control : 4-20mA current loop monitoring, process variable measurement
### Industry Applications
Industrial Automation
- Advantages : Excellent for PLC analog input modules, providing 24-bit resolution for precise process variable monitoring. The integrated PGA (Programmable Gain Amplifier) handles small signal amplitudes from various transducers.
- Limitations : Maximum sampling rate of 16.7 Hz may be insufficient for high-speed control loops requiring faster response times.
Medical Devices
- Advantages : Ultra-low power consumption (350 μA typical) makes it ideal for battery-powered portable medical equipment. Excellent common-mode rejection ratio (CMRR > 100 dB) ensures accurate measurements in noisy environments.
- Limitations : Limited to single-channel operation, requiring external multiplexers for multi-parameter monitoring systems.
Weighing Scales and Force Measurement
- Advantages : Outstanding noise performance (1.1 μV peak-to-peak noise with gain = 128) enables high-precision weight measurements. Internal clock eliminates external crystal requirements.
- Limitations : External reference voltage requirement adds component count and cost.
Environmental Monitoring
- Advantages : Low offset drift (10 nV/°C) ensures long-term measurement stability for climate monitoring applications.
- Limitations : Single-ended input configuration may require additional circuitry for differential sensor interfaces.
### Practical Advantages and Limitations
Key Advantages:
- Power Efficiency : 350 μA operating current with power-down mode (1 μA typical)
- High Resolution : 24-bit no missing codes performance
- Integrated Features : On-chip PGA with gains from 1 to 128
- Simple Interface : 3-wire serial interface compatible with SPI, QSPI, and MICROWIRE
- Small Form Factor : 10-lead MSOP package saves board space
Notable Limitations:
- Single Channel : Lacks internal multiplexing capability
- Limited Speed : Maximum output data rate of 16.7 Hz
- External Reference : Requires stable external voltage reference
- Temperature Range : Commercial temperature range (0°C to +70°C) limits harsh environment applications
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Power Supply Decoupling
- Pitfall : Inadequate decoupling causing noise and performance degradation
- Solution : Use 10 μF tantalum capacitor in parallel with 100 nF ceramic capacitor placed close to AVDD and DVDD pins
Reference Voltage Stability
- Pitfall : Using unstable reference sources leading to measurement drift
- Solution : Implement low-noise, low-drift reference IC (e.g., ADR381, REF19x) with proper bypassing
Digital Interface Noise
- Pitfall : Digital noise coupling into analog signals through poor layout
- Solution : Separate analog and digital ground planes with single-point connection near device
### Compatibility Issues with Other Components
Microcontroller Interfaces
- SPI Compatibility : Fully compatible with standard SPI interfaces, but requires attention to timing specifications
- Voltage Level Matching : Ensure digital I/O voltages match microcontroller logic levels (2.7V to 5.25V operation)
Sensor Compatibility
- Bridge Sensors : Excellent compatibility with
