In recent years, with the rapid development of computer technology, LSI and special components, the 256 gray-scale full-color LED display in the country has developed rapidly, but its display is not ideal: on the one hand, LED lights. The luminous efficiency of manufacturing process affect the performance of the inherent differences, but this difference also change over time, so by a large number of LED large screen display, there will be some random dark spots or bright spots, seriously affecting the display requirements, needs line point correction to eliminate this effect, on the other hand, full-color large-screen brightness levels, even with non-linear gray-scale control technology, the performance of color in low light level capability is still poor, displayed layering Another problem is caused by the lack of brightness levels is not easy to γ correction so that the full-color LED display some color distortion.
TLC5941 driver chip TI’s latest point correction and the characteristics of high brightness level, he’s big screen driver program to a certain extent to solve the above problems, can constitute a high-performance display system.
2 TLC5941 chip
2.1 chip features
A total of 28 pins TLC5941 is a 16-channel LED Driver can drive 16 LEDs per channel maximum drive capability of 80mA, each channel can be PWM mode depending on the value of the internal brightness register 4096 brightness control The length of each channel within the brightness register 12 In addition, the flow of each channel LED driver circuit 64 control the value of the internal 6-bit dot correction register, and the maximum drive current through the chip resistor set .
64 current control LED spot brightness correction capability, the 4096 brightness adjustment to ensure even at low brightness levels, each point in the lattice up to 256 grayscale representation, which red, green and blue The full color display 16M color color skills, these two high-quality color screen display is an additional and important.
The use of programmable logic chips (or high-speed CPU) compared to traditional color large screen display system, the design focus to generate the PWM brightness control, using the TLC5941 driver chip TLC5941 complete PWM brightness control, programmable logic chips (or high-speed CPU) only need to deal with cache management, brightness and dot correction data output, the design complexity is reduced, and PWM brightness control and data serial out of nothing to do, can easily get higher frame rates, and achieved a good dynamic display.
2.2 pin functions
The TLC5941 all internal data registers, the brightness register, dot correction register and error status information through the serial interface to access the maximum efficiency of the serial clock is 30MHz.
The TLC5941 The serial interface mode is similar to 74HC595, the interface part consists of five signal lines.
Mode (mode signal): Mode = 0 is the luminance signal input mode, Mode = 1 point correction signal input mode.
SCLK (serial clock), at each rising edge of SCLK, Mode = 0 the input data and output data into and out of the internal 192 (16 channels × 12), the brightness of serial shift register, when Mode = 1 input data into and out of the internal 96 (× 6)-point correction of the 16-channel serial shift register and output data.
SOUT: Serial data output.
SIN: Serial data input.
XLAT: data latches, the rising edge of XLAT If Mode = 0, brightness serial shift register latch to the brightness control registers, random control the brightness of the PWM output, if Mode = 1 point calibration serial shift register latches point correction control register to control the current output.
In order to safeguard the reliable operation of the large color screen, TLC5941 each way LED open-circuit and over-temperature detection, the pin XERR open collector output for alarm when an error of 16 channels, regardless of which channel the error occurred, XERR will be pulled low, query the internal state of the chip, you can know which road to failure, the system all TLC5941 XERR pin can be wired together, received a high level through the pull-up resistor by monitoring this signal, the system can self-diagnosis during operation.
In addition, the TLC5941 also provide a GCLK pin, input a clock signal synchronous PWM generation.
3 Based on the TLC5941 dynamic scan driver circuit
This design object is 640 × 480 full-color display system, where only about his driving part of the entire screen consists of four sub-screen, the size range of a sub-screen to manage 640 × 120 pixels, has a separate driver circuit indoor screen-driven design using dynamic 1/8 scan driver mode.