Lens control LSI # Technical Documentation: BU24024GU 24-Bit Delta-Sigma A/D Converter
Manufacturer : ROHM Semiconductor
Document Version : 1.0
Date : October 2023
---
## 1. Application Scenarios
### 1.1 Typical Use Cases
The BU24024GU is a high-resolution, low-power, 24-bit delta-sigma analog-to-digital converter (ADC) designed for precision measurement applications. Its primary use cases include:
* Sensor Signal Conditioning : Direct interfacing with low-output sensors such as bridge sensors (strain gauges, pressure sensors), thermocouples, and RTDs. The integrated programmable gain amplifier (PGA) allows for small signal amplification before conversion.
* Battery-Powered Measurement Devices : Its ultra-low power consumption in active and standby modes makes it ideal for portable multimeters, data loggers, and handheld medical devices (e.g., thermometers, portable monitors).
* Industrial Process Control : Used in 4-20mA current loop receivers, weigh scales, and environmental monitoring equipment where high resolution and good noise rejection are critical.
* Consumer Electronics : Integrated into high-end audio equipment for precise volume/level control and into fitness devices for biometric sensing.
### 1.2 Industry Applications
* Industrial Automation : PLC analog input modules, transducer interfaces, and precision instrumentation.
* Medical Electronics : Patient monitoring systems (blood pressure, SpO₂), diagnostic equipment, and wearable health monitors.
* Test & Measurement : Benchtop multimeters, source measurement units (SMUs), and calibration equipment.
* Automotive : Not typically for safety-critical systems, but suitable for in-cabin sensing, battery management systems (BMS) in low-voltage monitoring, and diagnostic tools.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Resolution & Accuracy : 24-bit output with no missing codes provides excellent dynamic range (up to ~144 dB), enabling the detection of minute signal changes.
* Low Noise & Integrated PGA : Features a low-noise PGA with gains from 1 to 128, simplifying front-end design and improving signal-to-noise ratio (SNR) for small signals.
* Flexible Power Modes : Supports single-shot conversion and auto power-down modes, drastically reducing average power consumption in intermittent sampling applications.
* Robust Digital Interface : Simple SPI-compatible serial interface allows easy connection to most microcontrollers and digital isolators.
* On-Chip Oscillator : Includes an internal clock, reducing external component count.
Limitations:
* Limited Speed : As a delta-sigma ADC optimized for precision, its output data rate (ODR) is relatively low (typically up to 120 SPS). It is unsuitable for high-speed, multiplexed, or audio-bandwidth applications.
* Settling Time with High PGA Gains : When switching input channels or changing PGA settings, sufficient settling time must be allowed, especially at high gain settings, to achieve rated accuracy.
* Sensitivity to Power Supply Noise : Like all high-resolution ADCs, performance is dependent on clean, stable analog and digital power supplies. Poor decoupling will degrade effective resolution.
---
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
* Pitfall 1: Ignoring Input Signal Conditioning. Directly connecting a sensor without filtering can lead to aliasing and noise.
* Solution : Always implement an anti-aliasing filter (RC low-pass) at the analog inputs. For differential inputs, ensure the filter is balanced. The cutoff frequency should be below half the modulator frequency.
* Pitfall 2: Incorrect Reference Voltage (VREF) Design. Noise or instability on VREF directly translates to ADC error.
