Analyze the principle of LED full-color display driver IC

Infineon / Mitsubishi / Fuji / Semikron / Eupec / IXYS

Analyze the principle of LED full-color display driver IC

Posted Date: 2024-02-02

In the work of the LED full-color display, its function is to receive display data that complies with the protocol (from information sources such as receiving cards or video processors), internally produce PWM and current time changes, and output related to brightness grayscale refresh, etc. PWM current to light up 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 its display effect.

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

The so-called general-purpose chips are not specifically designed for LEDs, but some logic chips with some logical functions of LED displays (such as serial 2-parallel shift registers).

The dedicated chip refers to a driver chip designed specifically for LED display screens based on the light-emitting 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 at both ends. Therefore, one of the characteristics 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 flickering phenomenon of the LED, which is the prerequisite for the LED display screen to display high-quality images. Some special-purpose chips also add some special functions based on the requirements of different industries, such as LED error detection, current gain control, and current correction.

The evolution of driver ICs:

In the 1990s, LED display screens were mainly used in single and double colors, using constant voltage drive ICs. In 1997, the first LED display dedicated driver 9701 appeared in my country, which spanned from 16 levels of gray to 8192 levels of gray, realizing what you see is what you get in video. Subsequently, in view of the LED light-emitting characteristics, the constant current driver became the full-color LED display driver, and the more integrated 16-channel driver replaced the 8-channel driver. In the late 1990s, companies such as Toshiba in Japan and Allegro and Ti in the United States successively launched 16-channel LED constant current driver chips. At the beginning of the 21st century, driver chips from Taiwanese companies in China were also mass-produced and used. Nowadays, in order to solve the problem of PCB wiring of small-pitch LED displays, some driver IC manufacturers have launched highly integrated 48-channel LED constant current driver chips.

Performance indicators of driver IC:

Among the performance indicators of LED displays, refresh rate, gray scale and image expressiveness are one of the most important indicators. This requires high consistency of current between LED display driver IC channels, high-speed communication interface rate and constant current response speed. In the past, refresh rate, grayscale, and utilization had a trade-off relationship. To ensure that one or two of the indicators were superior, the remaining two indicators had to be appropriately sacrificed. For this reason, it is difficult for many LED displays to have the best of both worlds in practical applications. Either they are not refreshed enough, and black lines are prone to appear when photographed by high-speed camera equipment, or the gray scale is not enough, and the brightness of colors is inconsistent. With the technological advancement of driver IC manufacturers, they have made breakthroughs in the three high issues and have been able to solve these problems.

In the application of LED full-color display screens, in order to ensure the user's eye comfort for long periods of time, low brightness and high gray have become a particularly important criterion for testing the performance of the driver IC.

Driver IC trends:

1. Energy saving:

As green energy, 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, thereby reducing the traditional 5V power supply to operate below 3.8V; the other 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 a constant current driver IC with a low turning voltage of 0.2V, which can increase the LED utilization rate by more than 15%. It uses a power supply voltage that is 16% lower than conventional products to reduce heat generation and greatly improve the energy efficiency of LED displays. .

2. Integration:

As the pixel pitch of LED displays decreases rapidly, the number of packaged devices to be mounted per unit area increases geometrically, greatly increasing the component density on the module driving surface. Taking P1.9 small-pitch LED as an example, a 15-scan 160*90 module requires 180 constant current driver ICs, 45 row tubes, and 2 138s. With so many devices, the available wiring space on the PCB becomes extremely crowded, making it more difficult. At the same time, such a crowded arrangement of components can easily cause problems such as poor welding, and also reduce the reliability of the module. The driver IC requires less usage and the PCB has a larger wiring area. Demand from the application side forces the driver IC to take a highly integrated technology route.

At present, the mainstream driver IC suppliers in the industry have successively launched highly integrated 48-channel LED constant current driver ICs. Integrating large-scale peripheral circuits into the wafer of the driver IC can reduce the complexity of application-side PCB design and also This avoids problems caused by the design capabilities or design differences of engineers from various manufacturers.

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