Functions and Functions of LED Full Color Display Driver IC

In the work of LED full-color display, the role of the driver IC is to receive display data (from the receiving card or video processor and other information sources) in accordance with the protocol, internally produce PWM and current time changes, and output and brightness gray refresh Wait for the relevant PWM current to light the LED. Peripheral ICs composed of driver ICs, logic ICs, and MOS switches work together on the display function of the LED display and determine the display effect it presents.

LED driver chips can be divided into two types: general-purpose chips and special-purpose chips.

The so-called general-purpose chip, the chip itself is not specifically designed for LEDs, but some logic chips (such as a serial 2 parallel shift register) with some logic functions of the LED display.

The special chip refers to the driving chip designed for the LED display screen according to the LED light-emitting characteristics. LED is a current characteristic device, that is, under the premise of saturation and conduction, its brightness changes with the change of current, instead of changing by adjusting the voltage across it. Therefore, one of the biggest features of special-purpose chips is to provide a constant current source. The constant current source can ensure the stable driving of the LED and eliminate the flicker of the LED, which is the prerequisite for the high-quality picture displayed on the LED display. Some special-purpose chips also add some special functions to the requirements of different industries, such as LED error detection, current gain control and current correction.

1. Evolution of driver ICs

In the 1990s, LED display applications were mainly single- and dual-color, using constant voltage driver ICs. In 1997, China’s first dedicated driver control chip 9701 for LED display screens emerged from 16 gray levels to 8192 gray levels, achieving WYSIWYG for video. Subsequently, for the light-emitting characteristics of LEDs, constant current driving has become the first choice for full-color LED display drivers, while more integrated 16-channel drivers have replaced 8-channel drivers. In the late 1990s, Toshiba of Japan, Allegro of the United States, and Ti successively introduced 16-channel LED constant current driver chips. At the beginning of the 21st century, the driver chips of Chinese Taiwanese enterprises have also been mass-produced and used. Now, in order to solve the problem of PCB layout of small-pitch LED display, some driver IC manufacturers have introduced a highly integrated 48-channel LED constant current driver chip.

2, the performance index of the driver IC

Among the performance indicators of LED display screens, the refresh rate, gray level, and image expressiveness are one of the most important indicators. This requires high consistency of current between LED display drive IC channels, high-speed communication interface speed, and constant current response speed. In the past, the three aspects of refresh rate, gray scale and utilization rate are a kind of declining relationship. To ensure that one or two of the indicators can be superior, the remaining two indicators must be appropriately sacrificed. For this reason, many LED displays are difficult to get the best of both worlds in practical applications. Either they are not refreshed enough, black lines are prone to appear under high-speed camera equipment, or gray levels are not enough. With the advancement of driver IC manufacturers’ technology, there have been some breakthroughs in the three high issues and these problems have been solved.

In the application of LED full-color display, in order to ensure the user’s eye comfort for a long time, low brightness and high gray have become a particularly important standard to test the performance of driver ICs.

3. Trends in driver ICs

Energy saving: As a green energy source, energy saving is the eternal pursuit of LED display screens, and it is also an important criterion for driving IC performance. The energy saving of the driving IC mainly includes two aspects. One is to effectively reduce the constant-current inflection point voltage, thereby reducing the traditional 5V power supply to below 3.8V operation; the other is to reduce the operating voltage and operating current of the driving IC by optimizing the IC algorithm and design. At present, some manufacturers have introduced constant current drive ICs with a low transition voltage of 0.2V, which improves the LED utilization rate by more than 15%. Using a 16% lower power supply voltage than conventional products reduces heat generation, which greatly improves the energy efficiency of LED displays. .

Integration: With the rapid decrease in pixel pitch of LED display screens, the number of packaged devices to be mounted on a unit area increases geometrically, which greatly increases the component density of the module’s driving surface. Taking P1.9 small-pitch LED as an example, a 160 * 90 module with 15 scans requires 180 constant current driver ICs, 45 row tubes, and 2 138. With so many devices, the available wiring space of the PCB becomes extremely crowded, which increases the difficulty of circuit design. At the same time, such a crowded arrangement of components can easily cause problems such as poor welding and reduce the reliability of the module. The driver IC uses less and the PCB has a larger wiring area. The demand from the application side forces the driver IC to embark on a highly integrated technical route.

At present, mainstream driver IC suppliers in the industry have all introduced high-integration 48-channel LED constant current driver ICs, integrating large-scale peripheral circuits into the driver IC’s wafers, which can reduce the complexity of the application-side PCB circuit board design. It also avoids the problems caused by the design abilities or design differences of engineers from various manufacturers.

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