Since these automotive displays are providing safety-critical information via advanced driver assistance systems (ADAS), they must comply with functional safety standards. ISO 26262 is an international standard for functional safety of automotive electronic/electrical systems. A key part of the standard is the Automotive Safety Integrity Level (ASIL), which classifies the inherent safety risk in an automotive system. There are four ASIL levels, with ASIL D requiring the most safety-critical process and testing, based on severity (of injuries), exposure (probability), and controllability. Typical automotive systems requiring ASIL D compliance include windshield wipers, electric power steering, side-view cameras (mirror replacements), airbag deployment, braking, and engine management. Table 1 highlights common ASIL metrics for single-point fault (a fault that leads directly to a safety violation) and for latent-point fault (a multiple-point fault that is not detected by a safety mechanism nor the user).
Achieving ASIL B Compliance
Automotive displays, such as the instrument cluster display and the side mirror replacement display, typically require ASIL B compliance. Within the instrument cluster display are various blocks that should meet functional safety standards. Let’s take a look at how two of them, thin film transistor (TFT) bias for power management and the light-emitting diode (LED) backlighting driver, can be designed for ASIL B compliance. TFT bias typically consists of these voltages: AVDD and NAVDD for the TFT source driver, VGON and VGOFF for the TFT gate driver and, in some cases, VCOM for the liquid-crystal display (LCD) backplane. I2C and a fault pin are used to communicate with the host microcontroller unit (MCU). See Figure 3 for a diagram of a typical TFT bias application.