In the work of the LED full-color display, the function of the driver IC is to receive the display data (from the receiving card or the video processor and other information sources) in compliance with the agreement, and to produce the PWM and current time changes internally, and the output and brightness grayscale refresh The related PWM current is used to light the LED; the peripheral IC composed of the driver IC, logic IC and MOS switch works together on the display function of the LED display screen and determines the display effect it presents.
Full color LED display driver
1LED driver chip classification
The so-called general-purpose chip, the chip itself is not specially designed for LED, but some logic chip with some logic functions of LED display screen (such as string 2 parallel shift register). The dedicated chip refers to a driver chip designed specifically for LED display screens according to the luminous characteristics of LEDs. LED is a current characteristic device, that is, under the premise of saturated conduction, its brightness changes with the change of current, rather than by adjusting the voltage across it. Therefore, one of the biggest features of the dedicated chip is to provide a constant current source. The constant current source can ensure the stable driving of the LED and eliminate the flicker phenomenon of the LED, which is the prerequisite for the LED display to display high-quality images. Some dedicated chips also add some special functions to the requirements of different industries, such as LED error detection, current gain control and current correction.
2 Evolution of Driver IC
In the 1990s, LED display applications were dominated by single and double colors, using constant voltage drive ICs. In 1997, my country appeared the first LED display dedicated drive control chip 9701, which spanned from 16 gray levels to 8192 gray levels, realizing what you see is what you get in video. Subsequently, in view of the LED light-emitting characteristics, constant current drive became the first choice for full-color LED display drive, and at the same time, the more integrated 16-channel drive replaced the 8-channel drive. At the end of the 1990s, companies such as Toshiba of Japan, Allegro and Ti of the United States successively introduced 16-channel LED constant current driver chips. In the early 21st century, driver chips of Chinese Taiwanese enterprises were also mass-produced and used. Nowadays, in order to solve the problem of PCB wiring of small-pitch LED display screens, some driver IC manufacturers have introduced highly integrated 48-channel LED constant current driver chips.
Full color LED display driver
3 Performance indicators of the driver IC
Among the performance indicators of LED displays, refresh rate, gray level, and image expressiveness are one of the most important indicators. This requires high consistency of the current between the LED display driver IC channels, high-speed communication interface rate and constant current response speed. In the past, the refresh rate, gray scale, and utilization ratio were in a trade-off relationship. To ensure that one or two of the indicators can be more excellent, the remaining two indicators must be appropriately sacrificed. For this reason, it is difficult for many LED display screens to have the best of both worlds in practical applications. Either they are not refreshed enough, black lines are prone to appear under high-speed camera shooting, or the grayscale is not enough, and the color brightness is inconsistent. With the technological advancement of driver IC manufacturers, there have been breakthroughs in the three-high issues and have been able to solve these problems.
In the application of LED full-color display, in order to ensure the user's long-term eye comfort, low brightness and high gray have become a particularly important standard for testing the performance of driver ICs.
Energy saving: As a green energy source, energy saving is the eternal pursuit of LED displays, and it is also an important criterion for considering the performance of driver ICs. The energy saving of the driver IC mainly includes two aspects. One is to effectively reduce the constant current inflection point voltage, and then the traditional 5V power supply is reduced to below 3.8V. The second is to reduce the operating voltage and operating current of the driver IC by optimizing the IC algorithm and design. At present, some manufacturers have launched constant current driver ICs with a low 0.2V turning voltage and a 15 percent improvement in LED utilization. The use of a 16 percent lower power supply voltage than conventional products reduces heat generation and greatly improves the energy efficiency of LED displays. .
Full color LED display driver
Integration: the function and role of LED full-color display driver IC. With the rapid decline of the pixel pitch of the LED display screen, the packaged devices to be mounted on a unit area have increased geometrically, which greatly increases the component density of the module drive surface. Take the P1.9 small-pitch LED as an example, a 15-scan 16090 module requires 180 constant current drive ICs, 45 line tubes, and 2 138s. With so many devices, the wiring space available on 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 soldering, and also reduce the reliability of the module. With fewer driver ICs and a larger wiring area on the PCB, 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 successively introduced highly integrated 48-channel LED constant current driver ICs, which integrate large-scale peripheral circuits into the driver IC wafers, which can reduce the complexity of the application-side PCB circuit board design. , It also avoids the problems caused by the design ability or design differences of the engineers of each manufacturer.
