LED drive chips divides into universal chips and special chips. Their brightness are in pace with the changes of current under the premise of saturated conduction.

Universal chips are generally used for low-end products LED displays , like indoor single or tricolor LED screens.  The most commonly used generic chip is 74HC595 which has 8 latches, the shift register and three -state output functions. Each line are available a maximum 35 mA output non- constant current.

Owing to LED is the device with current characteristic, so when under the premise of saturated conduction, its brightness will change along with the current changes but will not change with the across voltage. The most important feature of special chip is to provide constant current source output in order to ensure the stability of LED driver and eliminate LED flicker. It has the characteristics of large output current and constant current, which mainly adopt to high -definition occasions like outdoor & indoor full color LED displays.

LED driver chip key indicators:

1. Maximum output current: At present, the maximum output current of each constant-current LED driver channel is about 90mA. In the WB state, it requires every channel export the constant-current at the same time. 

2. Constant-current output channels: Constant current source output channel has 8 and 16 in two sizes. We mainly adopt 16 channels in priority because it greatly reduce the size of the chip and more convenient for PCB’s wiring, especially for small pixel pitches LED modules.

3. Accurate current output: One is a single -chip channel between the current error value The other is the output current error between different chip values. Precision is an important parameter of current output, it has great impact on the uniformity of LED display.  The greater the error , the worse display uniformity, which makes it hard to achieve WB. The current mainstream chip constant current source between the current error bit (bit to bit) is generally within ± 3% , (chip to chip) inter-chip current error within ± 6% .

4. Data shift clock: This device decides the transmission speed of display data. It is a key indicator of LED display update rate. As a big size display device, the refresh rate should be more than 85Hz to make sure stable image(without scanning flashes). Therefore, a higher data shift clock is the basic of achieving high frequency images for an LED display. The frequency of current mainstream constant current source LED driver IC shift clock is generally over 15-25 MHz.

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