Classification of LED full-color display performance parameter driver chips

　　LED full-color display driver chip is an important part of the display screen. Different driving methods of LED chip can obtain different video image display effects. Therefore, the advantages and disadvantages of the driver chip play an important role in the display effect of full-color LED display screen.

　　1. LED driver chips are classified into the following two types

　　Universal chip: it is widely used in the production of low-end LED screen. The commonly used universal chip is 74HC595, which has the functions of 8-bit latch, serial parallel shift memory and tri state output. Each circuit can output 35 mA current (not constant current).

　　Special chip: one of the characteristics of the special chip is to supply a constant current source. As LED is a current characteristic device, its brightness changes with the change of current size, not with the change of voltage at its two ends, under the premise of saturated conduction. Constant current source can ensure the stable driving of LED and eliminate the flashing phenomenon of LED.

　　2. Important parameters of LED display chip

　　Maximum output current: The maximum output current of the current mainstream constant current source chip is about 90 mA. Constant current is the basic feature of ASIC, and it is also the basis for obtaining high image quality. The maximum value of constant current (i.e., the maximum constant output current) output by each channel at the same time is more meaningful for the display screen, because under the white balance condition, each channel is requested to output constant current at the same time.

　　Current output error: the current output error is divided into two types, one is the inter bit current error, that is, the error between each output of the same chip; The other is the inter chip current error, that is, the error of output current between different chips. The current output error is a very important parameter, which has a great influence on the uniformity of the full-color display screen. The greater the error, the worse the uniformity of the display screen, and it is difficult to make the screen reach white balance. At present, the bit to bit error of mainstream constant current source chips is generally within+60%, and the chip to chip current error is within ± 15%.

　　The number of constant current sources: The number of constant current sources has two specifications: 8-way constant source and 16 way constant source. At present, the 16 bit source is in the mainstream. The advantage is that the size of the LED driver chip is smaller, which is convenient for the wiring of the LED driver board (PCB), and more favorable for the LED driver board with smaller point spacing.

　　Data shift clock: The data shift clock determines the transmission speed of the displayed data and is a key indicator that affects the update rate of the display screen. As a large size display device, the display refresh rate should be above 85 Hz to ensure a stable image (no scanning flash). A high data shift clock is the basis for the display screen to obtain a high refresh rate picture. At present, the shift clock frequency of mainstream constant current source driver chips is generally above 15 MHz.

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