How to Power the Automotive TFT-LCD Displays Future

With the rapid evolution of driver information technology, we can expect the automobile of the future to be equipped with multiple displays, possibly a dozen per car or even more (Fig. 1). These “infotainment” displays will include an instrument cluster, a central information display, mirror replacement displays, and optionally, multiple entertainment displays for the rear seats.

1. The typical smart car will have multiple displays.

While the size and resolution of automotive displays have grown, their electronics have become more complex yet limited in both PCB size and cost. One example of increasing complexity is found in the array of power rails that bias the TFT-LCD (thin-film-transistor liquid-crystal display) panel and power its backlight. Another example is the stringent level of diagnostics required for display systems that relay safety-relevant information to the driver.

This article reviews the shortcomings of a typical power-management solution for evolving automotive infotainment clusters. It then provides a solution to the size problem while facilitating the dynamic orchestration of the complex protocol required to operate the display while meeting automotive safety levels.

TFT-LCD Display

The standard display used in automotive systems is the active-matrix color TFT-LCD, which has become ubiquitous due to its high brightness, high resolution, reasonable cost, and demonstrated reliability in the challenging automotive environment. Liquid crystals have the ability to change their transmissivity with applied voltage. Each sub-pixel in an active-matrix TFT-LCD display receives its bias voltage (which sets its transmissivity) through a TFT transistor that acts as a switch. A pixel is made up of three sub-pixels, one for each of the primary colors: red, green, and blue.

Figure 2 shows the main elements of the TFT-LCD display power system. A power supply (PS) block, TFT_LCD PS, powers the source and gate drivers with all of the power sequencing driven by a microcontroller. The gate drivers are supplied with the voltages VPGVDD and VDGVEE, which are used to switch on and off the TFT switches in each sub-pixel.