Introduction to LED process technology--Application of LED display driver chips

As a high-tech product, LED displays have attracted great attention from people because of their unique advantages. It combines light and electricity through computer control to form an intelligent large screen, which has been widely used in many fields. The pixels of the LED display are composed of LED light emitting diodes, which are arranged in a dot matrix form to form an LED array, which in turn constitutes an LED screen. Through different LED driving methods, various display effects can be presented. Therefore, the quality of the driver chip directly affects the display quality of the LED display.

LED driver chips can be divided into general chips and dedicated chips.
LED 驱动芯片可分为通用芯片和专用芯片。Universal chips are usually used in low-end products of LED displays, such as indoor single and two-color screens. The most commonly used general purpose chip is the 74HC595, which has 8-bit latch, serial-parallel shift register and three-state output functions. Each channel can output a maximum current of 35 mA (non-constant current). Such chips are generally produced by IC manufacturers.
2. Main parameters and development status of dedicated chips
The dedicated chip has basic characteristics such as large output current and constant current, and is suitable for applications requiring high current and high image quality, such as outdoor full-color screens, indoor full-color screens, etc. Its key performance parameters include maximum output current, number of constant current source output circuits, current output error (bit-to-chip and bit-to-chip), and data shift clock.

1. Maximum output current: At present, the maximum output current of mainstream constant current source chips is mostly defined as the maximum output current of a single circuit, which is generally around 90 mA.
2. Constant current output channel: The number of constant current source output channels has two specifications: 8-bit (8-way constant sources) and 16-bit (16-way constant sources). The 16-bit source dominates the mainstream. Its advantage lies in reducing the chip size and facilitating LED driver board (PCB) wiring, especially suitable for LED driver boards with small dot spacing.
3. Current output error: The current output error is divided into inter-bit current error and inter-chip current error. The smaller the error, the better the uniformity of the display.
4. Data shift clock: The data shift clock determines the transmission speed of display data and is a key indicator that affects the update rate of the display screen.

在 LED 上游外延片、芯片生产上，美国、日本、欧盟仍占据技术优势，中国台湾地区则成为全球重要的 LED 生产基地。Although China's LED epitaxial wafer and chip production technology lags behind the international advanced level, the huge domestic application demand provides huge development opportunities for LED downstream manufacturers. Although different chip solutions are used to drive LED displays, their functions are different and the characteristics of the driving solutions are also different.
3. Introduction and comparison of several drive solutions

1. TLC5941 driver chip: TLC5941 chip has the characteristics of dot correction, high gray level (PWM control), etc. All internal data registers, gray level registers, dot correction registers and error status information are accessed through the serial interface. The maximum serial clock frequency is 30 MHz, the inter-chip current error is generally within 6%, the inter-bit current error is generally within 4%, and the maximum output current per channel is 80 mA.
2. MBI5028 driver chip: MBI5028 is an LED screen driver chip with programmable current gain function. It has a built-in serial-parallel shift register and output latch. It adopts PrecisionDrive technology. The maximum serial clock frequency is 25 MHz. The inter-chip current error is generally within 6%, the inter-bit current error is generally within 3%, and the maximum output current is 90 mA.
3. ST2221C driver chip: ST2221C is an LED screen driver chip with built-in serial-parallel shift register unit, output latch unit and current output control unit. It has excellent electrical characteristics. The maximum serial clock frequency is 25 MHz. The inter-chip current error is generally within 10%, the inter-bit current error is generally within 6%, and the maximum output current is 120 mA.

四、存在的问题

1. Power consumption and heating problems: Due to the large output current, the power consumption and heating problems of LED display chips have always been the main factors restricting their development, especially in the driving method of handheld LED displays.
2. Application cost issue: A mainstream 16-bit steady-state current LED display driver chip can only drive 16-channel LED devices, which makes the material cost high.

Judging from the product structure of these LED driver chip manufacturers, the current mainstream chips are mainly divided into three grades.
从这几家 LED 驱动芯片制造商的产品结构来看，目前主流芯片主要分为 3 个档次。The first gear is a chip with gray scale mechanism, the second gear is a chip with output open circuit detection (LOD), temperature overheating protection (TSD), and brightness adjustment functions, and the third gear is a constant current source chip without any additional functions.