LED display solution based on D7710 chip

The data of the current mainstream LED display screen is mostly based on the shift serial storage format, and the display data consists of red, green, and blue serial data, latch control signals, and a common clock signal.

The basic principle of the traditional LED display using the low-power driver chip D5026 . In the figure, the three primary colors of red, green and blue are driven by different D5026 chips respectively. Red, green and blue have independent serial data respectively. This data adopts the transmission mode of shift register, and the data is latched through their respective latch signals. The data output of each color is used to cascade the data input of the next level D5026, thereby realizing the cascade drive of D5026. The display data of red, green and blue only contains the switching state of the pixel. The different gray levels of the pixel must be realized by simulating a PWM control signal that adjusts the switching duty cycle in a unit time through a large amount of high-speed switching data. For the current setting of the LED, each D5026 is connected to an external resistor RSET for setting the driving current. By adjusting its resistance value, the output driving current of the chip can be set.

Although this traditional solution has been widely used, it also has obvious disadvantages, which are mainly manifested in three aspects: First, since the grayscale of the pixel is simulated by PWM modulation with a large amount of data, the amount of data transmitted is very large, and it is difficult to increase the refresh rate of the display. Secondly, since the multiple outputs of each chip share a current setting resistor, the consistency requirements for each group of LEDs are high, and it is difficult to achieve point-by-point correction of the display. In addition, since the three colors are driven by different chips, PCB wiring is difficult to achieve, and it is impossible to achieve unified light drive on a display with a small dot pitch.

In response to the above problems of traditional LED display screens, Shanghai Debei Electronic Technology Co., Ltd. has designed a new solution that can effectively solve the problems encountered by traditional solutions.

D7710 is a single RGB LED driver chip, which uses two-wire data transmission, built-in 3-way constant current source driver that can be set separately and a 256-level PWM control unit. Its cascaded transmission data signal has undergone phase-locked regeneration, and the maximum operating frequency can reach 25MHz. In the LED driver part, the output current of each RGB channel is adjustable from 2 to 36mA.

Since the D7710 has a built-in PWM control unit, the display data transmitted by the system only needs grayscale commands. The D7710 can generate PWM control signals by itself instead of relying on a large amount of data to maintain the current grayscale. Therefore, the system data flow can be greatly reduced, laying the foundation for a higher display refresh rate, making it easier to implement 3D screens, indoor scanning screens, and sports competition screens that require higher refresh rates. In terms of current setting, since the D7710 can set each current individually through instructions, it can fine-tune the drive current of LEDs with different performances, thereby reducing the requirements for LED consistency and making it easier to implement the algorithm for point-by-point correction of the display. In terms of signal distribution, unlike traditional solutions, a single D7710 has red, green, and blue outputs and can directly drive an RGB LED. In this way, there is no need for signal crossover between multiple chips, PCB layout and wiring will be easier, and even on high-resolution screens, the integration of light drive can be achieved, which can greatly reduce the difficulty of display process.