How Automotive Displays can meet Functional Safety: Page 3 of 7

March 13, 2019 //By Szukang Hsien, Maxim Integrated
How Automotive Displays can meet Functional Safety
Functional safety requirements have long been on the radar for automotive systems like braking and steering. Since vehicle displays now show critical information like speed and blind spot views, they also must be functionally safe to protect everyone inside and around the car. What does it take to design a functionally safe vehicle display?

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).


Table 1: ASIL metrics

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.

 


Figure 3: TFT bias application diagram

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