Enhancing Automotive Embedded Systems with Mixed-Signal Microcontrollers
Automotive applications are becoming more sophisticated as different in-vehicle systems are networked together to share information, monitor performance and enhance safety. In addition to growing more complex, automotive systems demand more cost-efficient electronic components with smaller footprints for space-constrained applications. This translates to fewer components in the automotive network, which requires more integration and performance enhancements from semiconductors, and in particular, automotive microcontrollers (MCUs).
From powertrain management to safety and chassis systems to body electronics, MCUs are widely used in automotive applications, and they are being asked to control more system features to reduce network complexity, component count and board space. Highly integrated, mixed-signal 8-bit MCUs offer a number of ways to address the need to simplify automotive system designs. By adding a wide range of peripheral features to hardware, mixed-signal MCUs help eliminate the need for extra components on the bill of materials. The MCUs also can be enhanced to increase speed, reduce memory size and extend chip peripherals, but all of this integration must be accomplished in a very small footprint.
In addition reducing board space, on-chip integration can reduce component costs by as much as $0.70, in some instances. Mixed-signal MCUs can eliminate the need for external components such as a voltage reference source, regulator and resonator. These savings result in a smaller system footprint as well, further improving reliability since more interconnections on the PCB usually equate to more reliability problems.
A practical example is the C8051F58x 8-bit MCU family from Silicon Laboratories. This MCU family includes many on-chip peripherals not typically integrated on board other 8-bit MCU alternatives. These on-chip features and integrated peripherals help automotive electronics engineers create more efficient designs. For example, the F58x family includes a high-accuracy oscillator, high-precision voltage reference and a 5 V regulator. It offers highly optimized peripherals that reduce overall system cost, including an automatic adjustment feature that replaces the need for high-cost sensors, a high-speed MCU core that can reduce required memory, and an innovative I/O scheme that can reduce manufacturing and testing costs.
Offering up to 128 kB of Flash and 50 MIPS processing power in a 25 mm2 package, the F58x family has a combination of memory, performance and small size that enables designers to solve problems that until now were expensive to address. Complex algorithms and computations can now be performed at run-time opposed to look-up tables which saves memory that can be used to further enhance existing applications.
The F58x automotive microcontrollers provide internal oscillator accuracy to ±0.5% over the entire operating temperature and voltage range. By using the on-chip analog-to-digital converter (ADC) and temperature sensor, a designer can further improve the accuracy to ±0.25% across voltage and temperature. Off-chip resonators cost an additional $0.20 to perform the same function. This capability enables designers to operate high-speed CAN networks without any external timing components saving them money and improving their system reliability.
The 12-bit ADC offers outstanding performance and supports up to 32 channels and sampling rates up to 200 ksps. It includes an internal precision voltage reference that has stability of approximately ±30 ppm/ºC. An external component performing the same function would add to the footprint and the cost of the design.
Another unique feature of the integrated ADC is variable attenuation. This feature allows designers to dynamically attenuate the input signal so that it always matches the voltage reference. This has two distinct advantages:
* First, all input signals greater than the voltage reference can take advantage of the full range of output codes. This means the designer’s signal will not be clipped and can take advantage of all output codes for the maximum amount of dynamic range.
* Second, this technique can be used to eliminate part-to-part variation (i.e., calibration) in sensors and can have the added benefit of allowing designers to use lower cost sensors, calibrate them in system, and achieve the same performance as expensive precision sensors at a much lower system cost.
Dedicated automotive serial busses also can offer performance advantages to designers. For example, a CAN 2.0 engine that offers 32 discrete message objects can support heavy network traffic. By integrating a dedicated LIN 2.1 controller (not LIN emulated in software), automotive designers can further improve the network performance of their designs. The 8-byte message buffer, hardware synchronization and checksum generation – all performed in hardware – frees valuable CPU resources and enables more complex LIN topologies.
Flexibility is another key concern for automotive embedded designers. Traditionally, MCUs use a fixed multiplexing scheme that forces designers to choose which resource they are going to use for a particular pin. Mixed-signal MCUs have the ability to use a digital cross bar that is a programmable switch-fabric that allows designers to route digital peripherals to available I/O pins. This flexibility simplifies the design effort.
One example would be the ability to multiplex a resource. A designer could have two independent LIN busses and re-map the pins dynamically during run-time. This would save money and provide flexibility unique to a mixed-signal MCU.
Another example is using the crossbar to reduce programming and calibration costs. Many designers must calibrate their systems using some test text fixture at the end of the PCB assembly. During this step, a special “calibration firmware” can be programmed in the device with the express purpose of interfacing with the test fixture. MCU resources can be used in conjunction with the test fixture to accelerate the calibration and greatly reduce the overall test time. Once the system is calibrated, the parameters are stored in flash memory, and the application firmware is programmed into the MCU.
Taking the design a step further, a digital isolator enables an isolation stage between the CAN physical layer and the MCUs that are running on the bus. This isolates the MCUs from any effects of noise that are typically common in automotive systems, further enhancing performance. This is well-suited to eliminate ground loops that are present in automotive CAN and LIN networks and ideal for applications in electrically noisy environments.
Automotive electronics designers face more design options, more system requirements and more complexity than ever before. A mixed-signal 8-bit MCU can play an important role in simplifying the design effort, improving performance, reducing cost and addressing space constraints.
The ability to integrate noisy digital circuits with sensitive analog circuits without degrading performance is an enormous benefit to automotive system designers who work with both digital and analog components. The ability to integrate analog-intensive mixed-signal capabilities on 8-bit MCUs results in cost-effective system-on-chip devices with smaller footprints that enable reduced system cost and complexity. These benefits are particularly helpful for body electronics on modern vehicles that rely more and more on MCUs to deliver intelligent features.
For more information about Silicon Laboratories’ automotive MCU solutions, please visit www.silabs.com/mcu.
Keith Odland, Manager, MCU Products
Silicon Laboratories Inc.
Keith Odland is a product manager focused on Silicon Laboratories’ MCU products. Prior to joining Silicon Laboratories, Odland served as a technical solutions manager for Future Electronics Corporation where he developed and deployed marketing and business development programs for 8/16-bit microcontrollers. He also co-founded Technology Kitchen Corporation where he developed a specialty instrument for the general aviation industry, which was adopted by an established aircraft instrumentation manufacturer. Odland has also served in various engineering management roles at Dell Computer Corporation and Eaton Corporation. Odland holds a bachelors degree in electrical engineering from The University of Texas at Austin.