Solutions specifically designed for advanced control and interface technologies in vehicle systems

As the degree of electronicization of automotive components continues to increase, automotive engineers are actively seeking advanced control and interface technology solutions in vehicle systems. Currently, the space and energy used to embed these functional units in automotive systems are very limited. Automotive engineers are relying on novel high-voltage mixed-signal technologies to integrate complex - and until now incompatible - component functions onto a single chip. Now, the application of I3T high-voltage technology compatible with 42V vehicle voltage has made it possible to integrate complex digital circuits (such as sensors), embedded microprocessors, and power circuits (such as excitation sources or switch drivers) together.

1. LIN bus system

Due to its relatively low cost, LIN bus is widely used in distributed electrical control systems of automobiles, such as controlling stepper motors and DC power supplies for electric windows, adjusting rearview mirrors and headlights, or managing information collected by sensors about temperature or seat position. The transmission byte of LIN bus is up to 20kbps. Based on the structure of single master node and multiple slave nodes, the slave nodes are usually installed around transceivers, microcontrollers, sensor interfaces or excitation drivers composed of discrete components. Recently, a microcontroller with LIN bus asynchronous transceiver (UART) has been developed. This microcontroller can be used with accessories that integrate other slave node modules (such as LIN bus transceivers, voltage regulators, watchdog timers, excitation drivers and sensor interfaces). At present, AMI Semiconductor (AMIS) has integrated all key slave node modules into a chip with dedicated functions, low power consumption and standard IP modules using mixed signal technology, which has taken the development of LIN bus a step further. The characteristics of this solution are:

Integrated RC oscillator, error ≤ 15%;

Dedicated IP modules (such as DC or micro-stepping motor drivers);

Comply with LIN bus V1.3 protocol;

The transmission rate is up to 20kbps (special structure design);

Low frequency transceiver;

Low current consumption in sleep/bypass mode;

Meet potential market demand.

Figure 1 is a block diagram of the main components of a slave node integrated with the LIN bus. The AMIS solution provides all the main functional modules required for the application layer and the data link layer. These functional modules can be programmed with VHDL code and evaluated with the AMIS development board. They will be briefly introduced below.

2. Sampling module with digital filter

The module collects the signal from the receiver and passes the resulting data stream through a digital filter to remove spurious transmissions that may be caused by attenuation of the LIN bus signal. Therefore, the module improves the performance of the LIN protocol in harsh environments and minimizes problems in synchronization and data sampling.

3. Synchronous machine

The synchro module extracts the information needed from the synch field to determine the exact sampling rate of the encoder and decoder. The module has an internal crystal oscillator and uses a technique that minimizes the rounding errors that occasionally occur in traditional UART technology. The main advantage of the synchro is that the LIN protocol can be executed with a lower clock frequency. For example, a 250KHz master clock with a 15% tolerance can be used to obtain accurate and error-free communication. In addition, the AMIS solution achieves a large range of duty cycle variations. A typical UART can achieve a duty cycle variation between 33% and 66% with zero crystal error. However, the AMIS solution can achieve a duty cycle variation between 12% and 88%, and can fully adapt to the crystal error. While providing a large tolerance for physical layer parameters, it also improves electromagnetic compatibility, which has a greater impact on the duty cycle.

4. Identifier Filters and Their Dynamic Management

The master node issues different slave instruction identifiers as needed at the beginning and during the operation of the system. To this end, the slave node must contain a certain number of registers. The ROM instruction array refers to the different instructions executed in the slave node, and the corresponding identifiers are contained in the RAM or EEPROM. The address register module identifies different slave nodes on the same LIN bus, while the second ROM array identifies different slave nodes for different applications and execution processes. The identifier filter determines whether the instruction is executed based on the assigned identifier. If the identifier exists in the queue, the instruction is executed, otherwise it is not executed.

5. Error Correction

The error recognition module is in the data link layer, while error correction is performed in the application layer. Therefore, the error amount is defined in software by the embedded microcontroller. The error correction module in the application layer contains a status register. Each error has a corresponding error flag, which generates an interrupt request to the core of the microprocessor. The error flag can be cleared by performing a read operation on the status register. Each error directly interrupts the communication, resulting in a bit error to stop sending bytes. Then the frame information is ignored and the slave node waits for the next interrupt field.

6. Frame Buffer

The frame buffer is another way to minimize interrupts to the microprocessor core. It is used in conjunction with the identifier filter to reduce the number of interrupts to one per frame. The buffer contains 17 bytes (one identifier, eight transmit bytes, and eight receive bytes).

Core/state machine and application interface AMIS can provide different cores according to needs. The core and LIN controller are connected through interrupt signals and special function registers (SFRs). The LIN controller can be regarded as a peripheral device on the SFR bus. In addition to these LIN bus features, AMIS has developed a wide range of IP module libraries, including II (2) and SAR ADC modules, delay triggers with an output current of up to 0.3A, and H bridges with an output current of up to 3A, just like similar semiconductor processing technology platforms. Of course, using slave nodes is only part of the whole function. Providing them with enough power to integrate them in today's cars is the next important challenge for automotive electrical engineers.

7. 42V power supply technology solution

In an ideal automotive power solution, the power level will be converted from the traditional 12V battery voltage to a 42V power system. In a 42V system, the power level will continue to increase. For example, the maximum operating voltage of the system throughout its life cycle is set at 50V. If there is an 8V maximum dynamic overvoltage, the power supply voltage will reach 58V. Adding a 12V external drive load pump will increase the system voltage requirement to 70V, and adding an ESD protection window will increase the system voltage to 80V. In addition, automotive semiconductor devices must not only withstand higher voltages, but also have sufficient robustness to meet their harsh operating environment, for example, they should meet the requirements of operating temperatures in the range of -40℃ to +200℃. So far, the need to withstand higher voltages and meet harsh operating conditions is a major obstacle to the application of intelligent SoC technology in 42V automotive electronic systems.

AMI Semiconductor's I3T80 is an 80V power intelligent module integration technology based on 0.35mm CMOS process. It meets the harsh operating conditions of 42V automotive systems. The equipment developed by this technology includes motor control drivers, DC-DC converters, high-precision analog circuits with bandwidth filters, ADCs and DACs, etc. Moreover, I3T80 can embed and integrate a total of more than 150,000 gate circuits, and its communication protocol modules include PLL, USB, bus protocol controller, CAN and LIN communication controllers. In addition, it also provides ROM and RAM memory.

8. Conclusion

In new automotive electronic applications, as electronic components continue to increase, automotive designers are looking for a reasonable solution. In this way, highly integrated, high-reliability SoC solutions have emerged. This solution technology requires the ability to simplify execution steps and reduce control and interface costs between different electronic systems. AMIS's high-voltage, mixed-signal technology meets this need. It combines semiconductor solutions with dedicated IP modules to meet any standard interface communication bus (LIN, CAN) node applications, while being compatible with 42V voltage level solutions.