LED full-color display driver chip classification and performance parameters
The LED full-color display driver chip is an important part of the display screen. Different driving methods of the LED chip can obtain different video image display effects. Therefore, the pros and cons of the driver chip affect the display effect of the full-color LED display. play an important role.
LED driver chips are classified into the following two types:
1. General chip
It is widely used in low-end LED screen production. The most commonly used general-purpose chip is 74HC595, which has 8-bit latch, serial-parallel shift register and tri-state output function. Each channel can output a maximum current of 35 mA (not constant current).
2. Special chip
One of the biggest features of the special chip is to supply a constant current source. Since the LED is a current characteristic device, that is, under the premise of saturation conduction, its brightness changes with the change of the current size, not with the change of the voltage across it. . The constant current source can ensure the stable driving of the LED and eliminate the flashing phenomenon of the LED.
Important parameters of LED display chip:
Maximum output current:
The current mainstream constant current source chip has a maximum output current of about 90 mA. Constant current is the basic feature of special-purpose chips, and it is also the basis for obtaining high image quality. The maximum value of the constant current output by each channel at the same time (that is, the maximum constant output current) is more meaningful to the display screen, because under the condition of white balance, each channel is required to output constant current at the same time.
Current output error:
There are two types of current output errors, 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 output current error between different chips. The current output error is a very critical parameter, which has a great influence on the uniformity of the full-color display. The larger the error, the worse the uniformity of the display screen, and it is difficult to make the screen body reach the white balance.
At present, the current error between bits (bit to bit) of mainstream constant current source chips is generally within +60%, and the current error between chips (chip to chip) is within ±15%.
Constant current source output number:
There are two specifications of constant current source output: 8-channel constant source and 16-channel constant source. Now 16-bit source is the mainstream. The advantage is that the size of the LED driver chip is small, which is convenient for LED driver board (PCB) wiring. The LED driver board is more beneficial.
Data shift clock:
The data shift clock determines the transmission speed of the display data and is a key indicator that affects the update rate of the display. As a large-size display device, the display refresh rate should be above 85 Hz to ensure a stable picture (no scanning sparkle). A higher data shift clock is the basis for the display 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.