The highly integrated Application Specific Standard Product (ASSP) has emerged as a beneficial alternative to electronic control units (ECUs) for discrete devices, providing damper position control for automotive heating, ventilation, and air conditioning (HVAC) applications. In addition to improving reliability, it also saves space, cost and weight, and provides precise position control and flexible design. As the automotive HVAC system becomes more complex, these advantages of ASSP become even more important.
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The HVAC system is the standard equipment for most cars today. This system is designed to achieve high efficiency, enhance reliability, improve passenger safety and comfort, while reducing size, weight and greenhouse gas emissions. Advanced sensing and closed-loop control functions are also being integrated into this system.
The sensor elements include temperature, humidity, and gas sensors, as well as sensors that measure solar radiation levels and determine the level of contaminants in the passenger compartment. Real-time data from this sensor array will be sent to various embedded intelligent electronic modules. These electronic subsystems are designed to achieve efficient adjustment of airflow in the passenger compartment by controlling the movement of various electromechanical components (Fig. 1).
The airflow from the HVAC system to the passenger compartment is primarily controlled by a mechanical damper that is integrated with the airflow duct. These dampers are used to direct the flow of air in various areas of the passenger compartment (multi-zone climate control) to control the mixing of hot and cold air, as well as the mixing of external and recirculated air (to control the pollution inside the cabin, thereby regulating the temperature). The damper is in turn connected to a DC motor machine (usually a stepper motor) to form a multitude of electromechanical subsystems.
The main challenge associated with the design of these electromechanical subsystems is to achieve real-time, fast and accurate airflow closed-loop control (the damper moves and positions while reducing the cost, size and weight of the system. In addition, to maintain passenger comfort Degree, requiring nearly zero noise operation of the motor and damper, while extending the operating life of the entire system and enhancing its reliability is also a key factor. To meet this series of demanding requirements, it is clear that the electronic module consisting of a large number of discrete integrated circuits will not Then there is a viable method.
The newly introduced AMIS-3052X step motion control ASSP enables automotive HVAC system designers to develop a final solution that is extremely flexible and efficient in solving system-level design challenges. It is based on a range of innovative integrated on-chip features that provide comprehensive programmable data communication, power management, motor control (speed, direction and position) and system protection. In addition, these devices are compatible with 5V and 3.3V microcontrollers and provide bidirectional data transfer via the SPI interface. The schematic of the device is shown in Figure 2. The typical motor drive application circuit is shown in Figure 3.
This paper describes the novel features and functions of the AMIS-3052X ASSP and its advantages in the design and operation of automotive HVAC systems.
Programmable microstepping and intelligent motor current converter
The stepper motor is a synchronous DC motor, so the stable rest position of the rotor is synchronized with the induced magnetic flux of the stator. In the stepper motor, the microstepping mode allows the rotor to increase the number of dwell positions in a complete rotation, thereby greatly reducing the vibration and noise of the motor.
The AMIS-3052X offers seven microstepping programmable modes along with an intelligent “step command motor current†converter (complete, 1/2, 1/2 compensation, 1/4, 1/8, 1/ 16 and 1/32), thereby achieving real-time and fast response, and smooth and precise operation of the HVAC damper. This micro-stepping feature also significantly reduces out-of-step, zero-noise operation while improving the comfort of the passenger compartment environment.
Other important features of the AMIS-3052X are the integrated "next" and "rotation direction" input/output pins. Once incorporated into the system microcontroller, they enable rapid changes in the microstepping mode and the direction of rotation of multiple stepper motors (HVAC damper movement resolution and direction) while reducing system microcontroller overload.
Programmable H-Bridge Motor Driver
The AMIS-3052X integrates two full H-bridge output stages with up to 1.6A programmable output current. The output current is regulated by current mode pulse width modulation (PWM) and is used in conjunction with an integrated measurement actual motor current sensing circuit. In addition to eliminating the need for external H-bridge motor ICs (reducing system cost, size and weight), improved motor current regulation makes HVAC damper movements more accurate.
Speed ​​and load angle output
An innovative feature of the AMIS-3052X device is the "Speed ​​and Load Angle" output pin, which provides an output voltage that is proportional to the motor's measured back EMF voltage. This output signal can be sent to the system microcontroller so that the user can program the stall detection function and the rotor stall condition can be detected. With this sensorless stall detection feature, external position sensors are no longer needed, further reducing the cost, size and weight of the HVAC system.
Power management and system protection
The AMIS-3052X series is developed through proprietary high voltage mixed signal technology. Therefore, the device can operate over a wide input supply voltage (~6V to ~30V). This eliminates the need for an external voltage regulator. In addition, the AMIS-30522 has an additional 5V/50mA regulated output for powering external microcontrollers. Therefore, there is no need to power the microcontroller from an external voltage regulator.
AMIS ASSP also has power-saving (sleep) mode, as well as short-circuit, open-circuit and over-temperature detection and protection circuit functions.
Future trend
As global people pay more attention to energy efficiency, cleaner environment and reduction of greenhouse gas emissions, it is becoming more and more important to improve the efficiency, size and parts of automotive HVAC systems. In addition, in order to provide passengers with safer, more comfortable and user-defined HVAC functions, the number of environmentally friendly sensors will continue to increase, so the demand for electronic data processing and control content will also increase. In addition to reducing the audible noise level caused by the engine inside the car and the external environment, efforts should be made to reduce the noise caused by the HVAC system itself in the passenger compartment.
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