Several solutions are introduced and compared
TLC5941 driver chips
TLC5941 chip is the latest TI Texas instruments) company, has high point correction, grey scale (PWM) control, etc. TLC5941 all internal data register, gray register, register point calibration and error status information through the serial interface to access to the largest serial clock frequency of 30 MHZ, generally within plus or minus 6%, between the current error between the current error generally within plus or minus 4%, per channel maximum output current 80 ma
TLC5941 each channel available PWM mode according to the internal gray register values for level 4096 gray scale control, the register is 12, each channel LED driver circuit from 6 loci correction control register values for level 64, and the maximum of the drive current can be set off chip resistor. Current control provides a level 64 LED point gray level correction ability, level 4096 gray-scale adjustment is to ensure the even under the low grey scale, each point in the lattice has as many as 256 level gray scale, said to all red, green and blue color can be 16 m color color expression ability, both for high quality color large screen display is especially important compared with traditional color large screen display system, concentration to produce PWM gray-scale control, programmable logic chip (or high speed CPU cache management, gray level correction and point data need to deal with the output, reduce the design complexity, and the PWM gray-scale control has nothing to do with data serial removed, can easily get high frame frequency, obtain good dynamic display effect.
In order to ensure the reliable operation of large color screen, TLC5941 provides each LED all the way open circuit (LOD and temperature detection (TSD ability, the built-in open collector output circuit, is used when something goes wrong alarm. Whichever channel has 16 channel error occurs, the built-in open collector output circuit of the output pin is pulled to the low level, by querying the chip’s internal state information, you will know that which way fails, all the TLC5941 built-in open collector output circuit in the system output pin can be together, through the pull-up resistor receives high level, by monitoring the signal, the system can be in operation in the process of self diagnosis. Meanwhile TLC5941 is suitable for the working environment is poor, the display effect is very demanding and high performance requirements on safety, such as highway LED message sign, large outdoor LED TV, etc.
MBI5028 driver chips
MBI5028 Taiwan MBI macroblock) launched a programmable current gain function of LED driver chips. Built-in string and shift register and the output latch, and adopt PrecisionDr technology to get more superior electrical properties. MBl5028 serial clock frequency is 25 MHZ, largest piece between the current error within the plus or minus 6%, generally between the current error generally within plus or minus 3%, maximum output current is 90 ma
MBI5028 built-in current gain control logic unit and a programmable current gain function of the Share – IO technology, do not need to add additional tube feet, only need to the corresponding pin input a specific sequence of signals, it can be adjusted into MBI5028 special function mode – the current model. In this mode, it can be through the system microcontroller, to write different current gain control logic unit current gain data, lock to save these data, and through the built-in digital to analog converter of sharing, to effectively control the current output. Aging due to the change of working environment and the LED screen, LED brightness will be reduced, such as at a fixed forward current, the brightness of the LED screen deviation will be smaller. Through programmable current gain PrecisionDr technology and function, can adjust the current deviation, compensate for the brightness of the LED screen, get a high quality images at the same time. PrecisionDr technology is used and Shared built-in digital to analog converter, under the same precision, by changing the way of digital code to gain relative to the output current, thus improving image quality of the LED screen.
Current technology can provide the LED display screen with current level, 256 to 1200% of the total dynamic range, provide 256 output current rating. Electrical characteristics and chip packaging, MBI5026 compatibility is better, users don’t have to change for the PCB of the same kind of chip design before, can get a Share – IO technology of current gain technology, can greatly reduce the cost of upgrade. MBI5026 is suitable for the work environment conditions are not demanding, but requires high quality LED driver solution on imaging, such as indoor large LED display and other mid-range screen. MBI5028 also applies to the upgrading of old driver chip.
ST2221C driver chips
ST2221C Taiwan SITI point crystal science and technology) company of China able to launch a LED drive chip. The built-in string and shift register unit, the output latch unit and control unit, the output current is relatively good electrical characteristics. ST2221C serial clock frequency is 25 MHZ, largest piece between the current error within the plus or minus 10%, generally between the current error generally within plus or minus 6%, maximum output current is 120 ma ST2221C contains a 16-channel constant current drive unit, can also drive a 16-way LED applicable to drive some low-end screen, such as indoor LED display information screen and so on the low end.
There is a problem
Power consumption and heat problem
Because of its high output current, power consumption and fever of LED display chip is the first factor of blocking driver chip development. Hand-held LED display that may occur in the future on the drive way, the problem would be particularly. With the progress of LED device manufacturing technology level and the decrease of the drive current, the problem will be solved step by step.
Application cost problem
A 16-bit steady-state current mainstream LED display drive chip can only drive a 16-way LED device. A resolution of 1024 x 768 led display must be used more than driving chip to achieve the desired effect, which makes the cost of materials is quite high. If the driver chip itself USES the scanning mode, a mainstream drive chip can drive multiplexed LED device at a time, will make the cost down many application.
The Trade Directory summary
From the terms of the structure of several LED drive chip manufacturers products, is currently the mainstream chip is mainly divided into three grades. The first class is a chip with gray mechanism, this kind of IC with PWM function, can according to the input data to produce gray, are more likely to form deep gray, display high quality images. Second class is to have the output open circuit detection (LOD temperature overheating protection (TSD brightness adjustment function of the chip, the chip with the additional features and more suitable for specific occasions, such as used for the variable information board, to have the function of the detection error LED chip. Third is without any additional features constant current source chip, this chip is only provided for the LED constant current source, ensure the quality of screen display is good.