Shenzhen Mingjiada Electronics Co., Ltd. supplies ADI ADG731 monolithic CMOS 32-channel serial control analog multiplexer.
I. ADG731 product overview
The ADG731 is a high-performance single-chip CMOS 32-channel serial control analog multiplexer. It adopts a single-chip integrated design and realizes a 32:1 signal switching architecture with 32 single-ended analog signal inputs and a single common signal output. It is the core component of a multi-channel analog signal acquisition, detection and control system. This chip abandons the cumbersome design of traditional multiplexer parallel address control, and is equipped with a three-wire serial interface compatible with SPI, which greatly simplifies hardware wiring and main control resource occupation. At the same time, it relies on mature CMOS technology to balance low on-impedance, low signal distortion and high switching speed, making it perfectly suitable for industrial-grade precision analog signal switching scenarios.
The ADG731 uses a 48-TQFP package, which is compact in size, has excellent heat dissipation performance, and covers an industrial-grade temperature range of -40℃ to +85℃. It supports a wide range of single/dual power supply and can flexibly adapt to systems with different power supply architectures such as portable devices, industrial measurement and control, and instruments. It is the preferred device for multi-channel analog signal multi-switching scenarios.
II. Core Functions and Architecture Features of ADG731
1. Channel architecture design
The ADG731 features 32 independently controllable analog switching channels, adopting a single-ended input and common output architecture. It uses 5-bit binary address coding to achieve precise gating of all 32 channels, enabling only one channel to be connected at a time, effectively avoiding signal crosstalk between channels. All analog channels support Rail-to-Rail signal transmission, maximizing the dynamic range of power supply voltages and adapting to the switching needs of low-voltage small signals and conventional amplitude analog signals.
2. Serial control interface
Unlike traditional parallel addressing multiplexers, the ADG731 is equipped with a standardized three-wire SPI-compatible serial interface, consisting of a clock pin, a data input pin, and a chip selection pin, which does not require a large amount of main control GPIO resources. The master controller can accurately control the connection of the corresponding channel by inputting a 5-bit channel address code through serial shift. The serial communication logic is simple and highly compatible, and it can directly connect to mainstream embedded master controllers such as STM32, FPGA, and DSP, greatly simplifying the hardware wiring and program development difficulty of multi-channel switching systems. Meanwhile, the interface supports standard TTL/CMOS logic levels, with clear high and low level thresholds and strong anti-interference capabilities.
3. Advantages of monolithic integrated CMOS process
The ADG731 is manufactured using a high-performance CMOS process, integrating all analog switches, decoding logic, driver circuits, and serial interface circuits. It can independently achieve signal switching functions without the need for external auxiliary devices, resulting in an extremely high degree of integration. Compared to multi-channel switching circuits built on multiple chips and discrete switches, a single-chip architecture effectively reduces system size, power consumption, and wiring complexity, while avoiding the problems of poor consistency and low stability of discrete devices, thus ensuring the consistency and reliability of multi-channel signal switching.
III. Key Electrical Performance Parameters of ADG731
With its excellent electrical parameters, the ADG731 achieves high-precision, low-loss, and low-interference analog signal switching. Its core performance parameters are as follows, and all indicators are based on industry standard test conditions:
- Power supply characteristics: Supports a wide range of flexible power supply, with a single power supply voltage of 1.8V~5.5V and a dual power supply symmetrical power supply of ±2.25V~±2.75V. It can be compatible with low-voltage portable equipment and conventional industrial measurement and control systems, and can still maintain complete performance in low-voltage power supply mode.
- On-impedance characteristics: The typical on-resistance is only 4Ω, and the flatness of the on-resistance is as low as 0.5Ω. The on-resistance consistency of the 32 channels is excellent, which can minimize the signal transmission voltage drop and amplitude distortion and ensure the accuracy consistency of multi-channel signal acquisition.
- Dynamic signal performance: - 3dB signal bandwidth up to 18MHz, which can meet the switching needs of low-frequency to medium-high-frequency analog signals; The typical switching delay time is 42ns, and the switching response speed is fast, making it suitable for high-speed multi-channel signal acquisition scenarios.
- Low interference characteristics: Charge injection is only 1pC, and the interference pulse from the digital circuit to the analog link during the switching process is extremely small; The typical shut-off leakage current is 250pA, and the signal leakage of the unconducted channel is extremely low; The channel crosstalk suppression capability reaches -72dB, effectively eliminating signal interference between channels and ensuring the acquisition accuracy of weak analog signals.
- Leakage current and insulation performance: The leakage current in the on state is extremely small, and the leakage current in the full temperature range is controlled at the nanoampere level, which greatly reduces signal transmission loss and is suitable for high-precision weak signal detection scenarios.
- Working environment: Industrial-grade working temperature range -40℃ to +85℃, with excellent electrical parameter stability in high and low temperature environments, and can adapt to harsh industrial site conditions.
IV. ADG731 Working Principle and Control Logic
The core working logic of the ADG731 is "serial address decoding + single-channel gating", and the overall workflow is clear and efficient. After the system is powered on, the chip completes internal circuit initialization and is in standby mode, with all analog channels turned off by default. The main control device transmits 5-bit channel address data to the chip bit by bit through a three-wire serial interface. After the address data is latched by a serial shift register inside the chip, it is sent to the decoding circuit to complete decoding.
Based on the parsed address signal, the decoding circuit accurately gates the corresponding one analog channel, while the remaining 31 channels remain off, achieving 32-to-1 analog signal switching. External analog signals are transmitted to the common output terminal through a conductive channel, and can then be connected to back-end processing modules such as ADC sampling circuits and operational amplification circuits. When channel switching is required, the main controller resends the new address code, and the chip automatically turns off the original channel and turns on the new channel to complete the signal path switching. The switching process is stable and glitch-free. Combined with the low charge injection characteristic, it can effectively avoid signal interference at the moment of switching.
Meanwhile, the chip has a switching timing characteristic of disconnecting before connecting, which can effectively avoid signal short circuits and link conflicts during channel switching, further improving system stability.
V. Typical Application Scenarios of ADG731
Leveraging its core advantages of multi-channel integration, low distortion, low interference, and ease of control, the ADG731 is widely used in various multi-channel analog signal acquisition and control systems, with the following core application scenarios:
1. Industrial multi-channel data acquisition system
In multi-channel acquisition scenarios of analog sensor signals such as industrial temperature, pressure, humidity, voltage, and current, the ADG731 can expand the 32-channel sensor signal input. The single chip achieves multi-channel signal time-sharing switching and completes multi-channel data sampling with a high-precision ADC, greatly simplifying the circuit design of industrial measurement and control boards and improving system integration and detection accuracy.
2. Precision instruments and testing equipment
It is used in precision testing instruments such as oscilloscopes, signal analyzers, impedance testers, and high-precision multimeters for switching and gating multiple analog test signals. Its extremely low on-impedance, minimal signal distortion, and crosstalk suppression capabilities can preserve the original signal characteristics to the greatest extent, ensuring the detection accuracy and measurement consistency of the instrument.
3. Battery management and power supply detection system
In the multi-node voltage and current detection system of power battery packs and energy storage power supplies, the simulation parameters of each individual cell of the battery pack are collected through 32 channels in time-sharing to achieve real-time monitoring of battery status. The low voltage and low noise characteristics can be adapted to the detection needs of weak battery signals and ensure the monitoring reliability of the battery management system.
4. Portable measurement and control equipment
Leveraging its advantages of wide voltage power supply, low power consumption, and small size, it is suitable for lightweight products such as portable data recorders and handheld testing equipment. It achieves multi-channel signal acquisition functions within limited equipment space, while reducing overall power consumption and improving battery life.
VI. ADG731 Hardware Design and Application Precautions
1. Power supply design
The power supply needs to be equipped with a 0.1μF high-frequency decoupling capacitor and a 10μF high-capacity filter capacitor, which are close to the chip's power pin and ground to filter out high-frequency ripples and low-frequency fluctuations in the power supply and avoid power supply noise from introducing analog signal interference. When powered by dual power supplies, it is necessary to ensure that the positive and negative power supplies are symmetrical and the grounding is reliable to prevent signal distortion caused by potential offset.
2. Signal wiring
The analog input channel wiring should be as short and straight as possible, away from high-interference cables such as digital clocks and power supplies, and the analog and digital channels should share a single point of ground to avoid digital noise coupling to the analog link. The 32 input traces maintain consistent wiring length and impedance, ensuring consistent signal transmission across all channels.
3. Serial interface design
Impedance matching of SPI serial communication cables reduces signal reflection and interference, ensuring accurate address data transmission. In high-speed switching scenarios, the communication clock frequency is reasonably configured to balance switching speed and communication stability, avoiding channel gating abnormalities caused by data errors.
4. Heat dissipation and operating condition adaptation
The 48-TQFP package has excellent heat dissipation performance and does not require an additional heat dissipation structure under normal operating conditions; In high-temperature and high-load scenarios, the copper cladding area can be appropriately increased to improve heat dissipation efficiency and ensure that the chip operates stably within the full temperature range.
7. Summary of ADG731 Product Advantages
As ADI's classic 32-channel serial analog multiplexer, the ADG731 boasts four core advantages: high integration, excellent signal performance, easy control, and high stability. Compared with traditional parallel control multiplexers, the serial interface greatly saves main control resources and wiring space; Compared to discrete switch combination circuits, monolithic architectures have higher consistency, lower power consumption, and smaller volume; Extremely low on-impedance, charge injection, and crosstalk, perfectly suited for precise analog signal switching scenarios.
With its mature process, stable performance, and wide adaptability, the ADG731 has become the core preferred device for multi-channel analog signal switching in many fields such as industrial measurement and control, precision instruments, energy testing, and portable equipment. It effectively reduces the difficulty of system design and improves the detection accuracy and operational reliability of the equipment.
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