Development of LIN and mixed signal technology improves the performance of automotive sensors and transmission devices

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Development of LIN and mixed signal technology improves the performance of automotive sensors and transmission devices [Copy link]

The increasing importance of electronics in automobiles has led to a growing demand for low-cost, high-reliability sensors and actuators. These devices do not exist independently, but must communicate with the system's main electronic control unit (ECU). In the past, sensor/actuator communication was usually done using one-way analog signals, with each remote device connected to the ECU using its own dedicated line. Since the automotive environment is full of electrical noise, it is difficult to maintain signal integrity on these lines, and the reliability of the system is also affected. Wiring brings other problems - it takes up space, adds weight and cost, and is difficult to maintain. Fortunately, digital multiplexed communication technology can solve these problems. This technology can maintain signal integrity, reduce the number of required lines, and provide new opportunities for intelligent control of the entire vehicle.

　　Two major trends today - standardization of automotive communication buses and semiconductor technology are driving the development of smarter sensors and actuators, while also expanding the application areas of automotive electronic systems through efficient communication. The Local Interconnect Network (LIN) bus architecture has now evolved to version 2.0, which can meet the needs of a simple communication solution for sensors/actuators, reduce costs and improve robustness through standardization. adcode

. The advent of the LIN standard also caters to the development of mixed-signal semiconductor process technology, which together can realize all the typical functions required to connect sensors and actuators to a single integrated circuit (IC). Moreover, the LIN standard and advanced mixed-signal processes also bring opportunities for automakers to introduce low-cost, new electronic systems and reduce the cost of existing systems. While bringing high convenience and safety to car owners, they can also improve maintenance performance and reliability.

Of the current

　　automotive electronic bus standards, LIN offers the best solution for sensor and actuator signal transmission needs. There are a variety of proprietary solutions that can digitize signals through simple schemes such as pulse width modulation (PWM) or variable pulse width (VPW). These schemes are based on various physical layer (PHY) designs, in which each sensor or actuator generally requires a communication line, and sensor-to-ECU or ECU-to-actuator communication is generally unidirectional. Therefore, these network architectures cannot achieve two-way communication and diagnostics, which limits their use. In addition, because they are proprietary solutions, they hinder the industry's economies of scale and design reuse through the implementation of open standards. An

　　alternative option is to use mature communication standards such as the Control Area Network (CAN) bus to transmit signals between the sensor/actuator interface and the ECU. However, CAN and similar communications generally require the use of microcontrollers and auxiliary circuits, resulting in complexity and cost that is beyond the scope of what is needed or reasonable for sensors and actuators. CAN is also based on a two-wire bus, while the best solution only requires a single line for low-speed, low-cost communication.

Simple, open standard

　　Although LIN was originally designed for vehicle body electronics, it has found its way into new applications, one of which is the sensor/actuator interface. The 20.0kbps data rate specified by LIN 2.0 is sufficient for most sensors and actuators, and the LIN PHY and protocol controller can be easily integrated into mixed-signal integrated circuits for remote devices. The LIN 2.0 specification includes protocol definitions that describe the physical and data link layers; a configuration language that defines system configuration and common interfaces between network nodes, which can also be used as input for development and analysis tools; and an application programming interface (API) definition for add-on software. As a standard defined by the LIN Consortium specifically for automotive applications, it enables a seamless development and design tool chain while increasing the speed and reliability of network development.

　　LIN is a single-wire transmission method, which reduces cabling and wiring harness requirements, thereby helping to reduce weight, space, and cost. The standard specifies a single master node with 16 independent slave nodes. Communications are triggered by the master node on a schedule, so there is no need to perform arbitration between simultaneously reporting devices. The self-synchronizing nature of the slave nodes allows the use of on-chip RC oscillators instead of crystals or ceramic resonators, significantly reducing costs. The LIN protocol guarantees signal transmission latency, enabling system predictability—a critical element for most sensor/actuator signals. The protocol is extremely simple and can be run over an asynchronous serial interface (UART/SCI). As a result, silicon implementation costs are low, making LIN an excellent bus solution for mixed-signal process technologies—the same process technologies used to produce signal conditioning and output ICs for automotive sensors and actuators.

The LIN standard is an important advancement in automotive sensor/actuator communications, but its importance is even greater when combined with recent advances in mixed-signal semiconductor processes. IC manufacturers can now achieve

　　levels of system integration that were unattainable just a few years ago, leveraging their expertise in both high-speed CMOS digital processes and advanced analog processes. Typical advanced mixed-signal processes for automotive sensor/actuator applications include linear Bi-CMOS (LBC), high-voltage CMOS, and silicon-on-insulator (SoI) processes. Many of these processes enable monolithic system-on-chip (SoC) implementations of the entire sensor/actuator electronics, including power, high voltage, digital logic, memory, and high-precision analog functions.

　　If intelligence is required on the chip, advanced mixed-signal processes allow for a reasonable level of digital logic to be integrated outside of the LIN protocol controller. For example, a design might include logic that can report sensor or actuator status to enable diagnostics for both timely maintenance and the development of a lifetime reliability database. Next-generation mixed-signal process technology will allow microcontrollers to integrate LIN communications into mixed-signal devices, such as touch-type window lifters that need to run an algorithm to prevent fingers from being squeezed when the glass rises. For applications that require more complex and faster communications, semiconductor functions that enable LIN communications integration also allow CAN functions to be integrated into mixed-signal devices.

Sensor/Actuator Example

　　The Texas Instruments (TI) TPIC1021 LIN-2.0 transceiver is the foundation for using advanced mixed-signal integration to increase the robustness and keep the cost of LIN-compatible sensor and actuator communications low. Based on TI's LBC4 linear Bi-CMOS process, the transceiver operates from the vehicle battery voltage, so no external power supply is required. Fault protection allows the device to withstand voltages of -40V to +40V on the LIN bus, while on-chip electrostatic discharge (ESD) protection can withstand peak voltages of up to 17kV (International Electrotechnical Commission) and 21kV (Human Body Model). On this basis, more components required to connect the sensor or actuator to the vehicle power grid and LIN network can be integrated. Typical on-chip functions include: automotive voltage regulator to meet system requirements, analog filtering functions for front-end inputs in sensor outputs, analog-to-digital converters (ADCs), digital filtering and control, and LIN-compatible protocol controllers. Figure 1 illustrates an example of a fully integrated sensor interface based on LBC4. The high level of integration and circuit protection features of this device make it ideally suited for the harsh automotive environment where space and cost are very limited.

　　The TPIC10271 transmission interface is a device designed specifically for automotive applications based on LBC-4 D. It integrates a 3.3V voltage regulator/monitor using battery power, a high-voltage interface to the user switch, a high-side FET (field effect transistor) driver for position sensors or other types of sensors, two low-side FET drivers for motor control relays, feedback operational amplifiers, protection circuits, and a LIN-compatible PHY (Figure 2). The output is directly connected to a microcontroller for control algorithms, such as the anti-crush monitoring function of a window lift. Like the TPIC1021 and other devices in TI's mixed-signal portfolio, the TPIC10271 enters a power-saving sleep mode during non-operation and has low electromagnetic interference (EME) and high electromagnetic interference immunity (EMI).

　　For other applications, the same mixed-signal process technology can integrate the functional blocks in addition to the above two devices, including: low-dropout and switching voltage regulators for single and multi-rail, high/low-side drivers in different configurations, various operational amplifiers, digital logic devices, and communication interfaces such as LIN interfaces. Available drive interfaces include: H-bridges, smart drivers for DC brush/three-phase DC brush motors, and relay drivers. These drivers are used for power seats and mirrors, door locks, windshield wipers and defrosters, glass and antenna lifts, heating, ventilation and air conditioning systems (HVAC), and various other electronic systems for user comfort and safety.

System Benefits

　　Changing the sensor/actuator signal and communication interface to a LIN-compatible mixed-signal IC can yield several system-level benefits. The first is improved system robustness and diagnostics. Fewer wires reduces cost and potential sources of failure, and because LIN allows bidirectional communication, the master can obtain diagnostic information from the slave, while the slave can provide fault information when a system problem occurs. In addition, LIN eliminates the need for proprietary interfaces, allowing both component and software development by adopting a common communication scheme based on an open, reliable standard.

　　LIN can be used to build sensors or actuators with only three wires (battery, ground, and LIN), reducing wiring and harness requirements. Smaller device housings allow for better sensor/actuator placement without much wiring considerations. LIN and advanced mixed-signal processes can reduce system cost in many ways: fewer components; reduced inventory; more compact and simpler printed circuit boards and sensor/actuator housings; use of on-chip oscillators instead of crystal or resonator systems as clock sources; and higher reliability. Some of these factors can also reduce weight and space consumption - a constant pursuit in automotive design.

　　This advancement is just the first step in the evolution of automotive sensor and actuator intelligence and functionality. The next generation of mixed-signal automotive ICs will integrate smaller microcontrollers, enable programmable functionality, and provide greater flexibility to meet future automotive needs. As automotive sensors and actuators continue to become more intelligent, automotive designers will be free to envision intelligent applications for automotive systems.