What are the various driving schemes for LED displays?
Introduction and comparison of several drive solutions
TLC5941 driver chip
The TLC5941 chip is the latest from TI (Texas Instruments). It has features such as point correction and high gray scale (PWM control). All internal data registers, grayscale registers, point correction registers, and error status information of TLC5941 are accessed through the serial interface. The maximum serial clock frequency is 30MHz. The inter-chip current error is generally within ± 6% and the inter-bit current error is generally within ± Within 4%, the maximum output current of each channel is 80mA.
Each channel of TLC5941 can use PWM mode to perform 4096-level grayscale control according to the value of the internal grayscale register. This register is 12-bit. The LED drive circuit of each channel is controlled by 64-bit level by the value of the 6-bit dot correction register. The maximum value can be set by an off-chip resistor. 64-level current control provides the capability of LED dot grayscale correction, and 4096-level grayscale adjustment ensures that even at lower grayscale levels, each point in the dot matrix can have up to 256 grayscale representations, so The red, green and blue full-color screen can have 16M colors of color expression ability. These two points are particularly important for high-quality large-color screen display. Compared with the traditional large-color screen display system, it generates PWM for grayscale control and programmable logic. The chip (or high-speed CPU only needs to handle buffer management, grayscale and point correction data output, design complexity is reduced, and because PWM grayscale control has nothing to do with serial data shifting out, it can easily obtain a higher frame rate Good dynamic display effect.
In order to ensure the reliable operation of the large color screen, TLC5941 provides each LED open circuit (LOD and over temperature detection (TSD capability, built-in open collector output circuit for alarm when an error occurs. No matter which of the 16 channels has an error, The output pins of the built-in open-collector output circuit will be pulled to a low level. By querying the internal status information of the chip, you can know which one is faulty. The output pins of all TLC5941 built-in open-collector output circuits in the system are available. Connected together, connected to a high level through a pull-up resistor. By monitoring this signal, the system can perform self-diagnosis during operation. TLC5941 is suitable for harsh working environments, high requirements for display effects and high requirements for safety performance Occasions, such as highway LED information signs, large outdoor LED TVs, etc.
MBI5028 driver chip
MBI5028 Taiwan MBI Technology Co., Ltd. introduced an LED screen driver chip with programmable current gain function. Built-in serial-to-parallel shift register and output latch, and adopts PrecisionDr technology for better electrical characteristics. The maximum serial clock frequency of MBl5028 is 25MHz, the inter-chip current error is generally within ± 6%, the inter-bit current error is generally within ± 3%, and the maximum output current is 90mA
MBI5028 has a built-in current gain control logic unit. The programmable current gain function uses Share-IO technology. No additional pins are required. You only need to input a specific sequence signal at the corresponding pin to enter the special function mode of MBI5028- Current adjustment mode. In this mode, different current gain data can be written to the current gain control logic unit through the system microcontroller, the data can be latched, and the current output can be effectively controlled by the built-in converter shared by digital and analog. Due to changes in the working environment and aging of the LED screen, the brightness of the LED screen will decrease. For example, with a fixed forward current, the brightness deviation of the LED screen will be smaller. Through the programmable current gain function and PrecisionDr technology, the current deviation can be adjusted, the brightness of the LED screen can be compensated, and a higher quality image can be obtained at the same time. Using PrecisionDr technology and built-in digital and analog shared converters, with the same accuracy, by changing the digital code method, the relative output current is obtained, thereby improving the imaging quality of the LED screen.
Current technology can provide 256 current levels for the LED display, making it reach a total dynamic range of 1200%, providing 256 output current levels. In terms of electrical characteristics and chip packaging, MBI5026 has good compatibility. Users do not need to change the PCB board designed for the same type of chip before, they can get the current gain technology with Share-IO technology, which can greatly reduce the upgrade cost. MBI5026 is suitable for LED screen driving solutions that do not require harsh working conditions, but require high-quality imaging, such as large and medium-end indoor LED screens. At the same time MBI5028 is also suitable for upgrading the old driver chip.
ST2221C driver chip
ST2221C China Taiwan SITI Point Crystal Technology) company introduced an LED screen driver chip. Built-in serial-parallel shift register unit, output latch unit and current output control unit have excellent electrical characteristics. The maximum serial clock frequency of ST2221C is 25MHz. The inter-chip current error is generally within ± 10%. The inter-bit current error is generally within ± 6%. The maximum output current is 120mA. LED is suitable for driving of some low-end screens, such as low-end LED displays such as indoor information screens.
Problem
Power and heat issues
Due to the large output current, the power consumption and heat generation of LED display chips have been the first factors that hinder the development of driving chips. This problem will become more prominent in the driving mode of the handheld LED display that may appear in the future. With the progress of LED device manufacturing technology and the reduction of driving current, the problem will be gradually solved.
Application cost issues
A mainstream 16-bit steady-state current LED display driver chip can only drive 16 LED devices. For a 1024 × 768 LED display with multiple resolutions, multiple driver chips must be used to achieve the desired effect, which results in higher material costs. If the driving chip itself is used for scanning, a mainstream driving chip can drive multiple LED devices at one time, which will greatly reduce the application cost.
summary
From the product structure of these LED driver chip manufacturers, the mainstream chips are currently divided into 3 grades. The first grade is a chip with a grayscale mechanism. This type of chip has a PWM function inside, which can generate grayscale according to the input data, and it is easier to form deep grayscale and display high-quality images. The second grade is chips with output open-circuit detection (LOD temperature overheat protection (TSD brightness adjustment function). These chips are more suitable for specific occasions due to additional functions. For variable information boards, the chip must have a detection LED Wrong function. The third gear is a constant current source chip without any additional functions. This type of chip only provides a constant current source for the LED to ensure good screen display quality.
If you want to know more, our website has product specifications for the LED displays， you can go to ALLICDATA ELECTRONICS LIMITED to get more information