A car’s instrument cluster houses the various displays and indicators that enable a driver to operate the vehicle. Among these are several gauges – often a speedometer, odometer, tachometer, oil pressure gauge, fuel gauge, etc. – as well as various indicators for system malfunctions and warnings. Instrument clusters provide drivers with a centralized and easily viewable location for displaying all critical system information.
Major subsystems include:
Load drivers: Each physical (i.e. non-graphical) gauge is actuated by an individual stepper motor. Also, virtually all instrument clusters include LED backlighting. All of these devices require an appropriate load driver to operate properly. Often the instrument cluster MCU will have integrated stepper motor drivers; however, the LED backlight driver is implemented as a discrete IC.
Connectivity: Being the de facto standard for high integrity serial communications, an automobile’s CAN (Controller Area Network) bus forms the “backbone” of the vehicle network. CAN is meant for applications that have to communicate numerous but small pieces of data consistently among nodes, as well as self-diagnose and repair data errors. Likewise, LINs (Local Interconnect Network) handle network communication within a node. Inexpensive and relatively simple to implement, a LIN network uses a broadcast topology with a single master – typically an MCU – and up to 12 slave devices.
Processor: Automotive applications are inherently safety-critical, so the processor or microcontroller must offer a level of performance that is high enough to ensure reliable, real-time control. In addition to its ability to execute code rapidly, the microcontroller is also chosen for its application-specific integrated peripherals. Instrument cluster MCUs typically include an integrated CAN and/or LIN transceiver for communicating with various sensors located throughout the vehicle. As previously mentioned, the microcontroller may also feature stepper motor drivers for actuating various gauges.
Power Management: Low-dropout (LDO) regulators can be particularly useful for instances of heavy loading, such as when engaging an electric starter. An instrument cluster can include external memory, stepper motors, one or more MCUs, CAN interface, LIN interface, and LED backlighting – all of which may operate at different voltage levels. With so many different power rails, careful consideration is required when designing for efficiency, compactness, low cost, and low EMI.
