by Willie Fitzgerald, Director, Product Marketing; and Greg Robinson, Manager, Applications Engineer
The continued advancements of electronics within the vehicle are being driven by the challenges that automotive OEMs face in making their vehicles safer, smarter and more energy efficient. Electronics continues to be the fastest growing sector of automotive content, over mechanical, pneumatics and hydraulics. Embedded systems designers continue to develop new electronic control modules (ECMs), to enable targeted vehicle features that address the desires of the driver. Most of the growth in automotive electronics can be attributed to the growing demand for more safety, comfort, security, and driver-information applications.
STAYING WITHIN POWER BUDGET Flash-based, highly integrated, power-managed microcontrollers (MCUs) are not only the cornerstone of the ECM, but are the key enablers that support embedded system designers in overcoming the significant challenges that are encountered in implementing new features. Challenges range from powerconsumption and space constraints to ECM connectivity for diagnostics capability, while remaining cost sensitive.
With increased electronics penetration across the spectrum of applications within the vehicle, the number of ECMs continues to expand-taxing the vehicle power budget. Some higher end vehicles can have over 80 ECMs, which means that current loads are increasing. An increase in battery size to support the growing power requirements is an alternative to overcoming this challenge. However, larger batteries do not always provide a good tradeoff in an environment where space is limited and weight is critical, due to the negative impact on fuel consumption.
A better alternative is to address the power-consumption requirements of those ECMs that consume power when the ignition is off. With more power loads present when the ignition is off, such as keyless entry and infotainment systems, automotive OEMs are moving toward tightening their ignition-off power budget to less than 1mA per ECM. A family of power-managed microcontrollers is a key enabler for embedded system designers, in this environment where a high value is placed on energy-efficient operations without sacrificing performance.
Power-managed microcontrollers offer the designer onchip Flash memory, maximized system efficiency, increased system robustness, and minimized costs and board space, by eliminating external components. Multiple power-managed modes offer designers the flexibility of switching between modes, and incorporate power-saving routines in the application software. The nanoWatt technology features of Microchip Technology’s PIC microcontrollers provide flexible power-managed technology over their operating-frequency range. nanoWatt technology was developed to give designers technically feasible and costeffective options to address the complex challenges associated with reliable low-power operation.
Table 1 summarizes the outstanding power-management features that the PIC microcontroller family provides the designer.
Microchip provides the designer with a platform to innovate creative power-saving routines. This platform includes a comprehensive array of on-chip peripherals with selectable oscillator options and multiple crystal modes, external clock modes, external RC oscillator modes, plus an internal oscillator block that generates multiple clock frequencies under software control. Figure 1 shows a power-saving example based on the proprietary nanoWatt technology from Microchip.
OSCILLATOR OPTIONS With a number of oscillator options available on the microcontroller, the designers are able to gain tighter control of their ECM’s power consumption, adapt to changes on-the-fly and reduce external components, delivering enhanced performance with reduced system cost. Powermanaged microcontrollers provide designers with the flexibility to create the appropriate embedded solutions for their project, with minimized current draw and reduced power consumption.
Addressing increasing performance requirements in a spaceconstrained environment.
The growth of bodycontrol ECMs can be attributed to the desire of carmakers to address the functional requirements of targeted automotive buyers. As a result of this ECM growth, available space is limited. The microcontrollers being used are expected to have a high level of on-chip peripherals, both digital and analog, to support the overall goal of conserving space. Figure 2 shows the wide range of on-chip peripherals available on most microcontroller families.
As microcontrollers can be viewed as building blocks for ECMs, it’s important to note that one size does not cover all requirements. It’s critical that the broad range of compatible microcontrollers is available to designers, which allows the selection of the appropriate microcontroller for the specific application being designed. The compatible-family concept is most powerful when both software and pin-out compatibility are sustained.
Strong migration compatibility facilitates reusable engineering blocks that are instrumental in saving valuable development time and overall costs. Compatibility is the key to re-using PIC microcontroller designs. The standardized pin-out schemes of the PIC microcontroller families support the development of a code library that is not traditionally available from other suppliers of microcontrollers. Uniquely, the PIC microcontroller architecture also provides socket, software and peripheral compatibility, which delivers superior flexibility to the designers. As an example, each pin is capable of accommodating several peripheral functions which allows designers to add or swap functionality without changing the printed circuit board. The end result is minimized or eliminated redesign costs.
Reuse of proven engineering blocks not only saves time and costs, but it can also directly improve the overall system quality—since the engineer has access to performance from earlier designs and is able to apply the appropriate lessons learned to the current design. Ultimately, overall product development efficiency is gained from compatibility and reusability, which is critical in the current industry environment where experienced embedded designers are limited.
COST-EFFECTIVE CONNECTIVITY The growing number of ECMs within the vehicle creates an environment for the “networked” vehicle. Body-control electronics improve the comfort and safety of vehicle occupants. Advancing bodycontrol electronics is essential, in order for car manufacturers to produce smarter vehicles that are pleasing to drive, reliable and safer. Body-control electronics improve the vehicle’s safety factor by simplifying its operation and releasing the driver from distracting secondary activities. Networks are a key element of the vehicle’s electrical architecture. Figure 3 shows the various communication networks utilized within the vehicle, along with the relative cost to implement a node for each. Two of the most popular automotive networks are the controller area network (CAN) and local interconnect network (LIN).
CAN offers a multi-master hierarchy, which support the development of intelligent, redundant systems. In this type of network, if a network node is defective, the network remains functional. Messages are broadcast across the network. All nodes receive the messages, and are able to read the message and determine whether it is relevant to them and requires any action. In this environment, data integrity is ensured—as all nodes of the system use the same information. Data integrity is supported via errordetecting mechanisms and retransmission of faulty messages.
The LIN protocol is a holistic communication concept for smaller vehicle networks. The specification covers the definition of the protocol and the physical layer, as well as the definition of interfaces for development tools and application software. LIN enables a cost-effective communication network for vehicle switches, smart sensor and actuator applications where the bandwidth and versatility of CAN is not required. This communication protocol is based on the SCI (UART) data format, with a single-master/ multiple-slave concept, with a single-wire 12V bus, and clock synchronization for nodes without a stabilized time base.
CRITICAL FACTORS With LIN residing in low-end applications, two factors are critical: (a) the communication cost per node must be significantly lower, compared with CAN, and (b) the performance, bandwidth and versatility of CAN are not required. The main cost savings of LIN versus CAN are derived from: (1) the single-wire transmission, (2) the low cost of implementation as hardware or software in silicon, and (3) the avoidance of crystals or ceramic resonators in slave nodes.
Microcontrollers with on-chip peripherals to support the CAN and LIN communication protocols are available to embedded-system designers. Gateway microcontrollers are used to provide the transition between the high-speed and low-speed CAN busses, as well as between the low-speed CAN bus and other networks-such as the multimedia, fiberoptic point-topoint network and the Media Oriented Systems Transport (MOST) protocol. LIN is a sub-bus network that can directly connect to the CAN network. The integrated microcontroller support of these communication protocols facilitates the trend to reduce component count and system costs for the increasing number of ECMs within the vehicle.
We are now more than a decade into the 21st century, and on an ever-accelerating fast track to technological innovation in electronics. The transistor and progression into the IC, or microchip, lit the fuse leading to the explosion of innovations in electronics that is now taking place. Since the wi ...
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