AN2141 查看數據表（PDF） - STMicroelectronics

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AN2141

LED array reference design board

STMicroelectronics 

Block diagram

1

Block diagram

AN2141

The block diagram of the LED array reference design board is shown in Figure 1. The

diagram shows a universal STMicroelectronics system solution for driving an LED array. The

number of LEDs can be increased by adding additional drivers in cascade. The input voltage

is connected to the anodes of all of the HB LEDs. The input voltage value is very important

due to the power dissipation in the drivers. A detailed explanation is described in Section 3:

Reducing power dissipation on the chip. The LED cathodes are connected to ground

through constant current sinks. The value of the constant current is set by only one external

resistor. The DC-DC converter is represented by a simple linear controller (LE33 or L78L33)

and provides 3.3 V supply voltage to the microcontroller and the LED drivers. The DC-DC

SMPS (switch mode power supply), using the L5970D step-down converter, is designed to

increase the efficiency, performance and supply voltage range (5 V up to 35 V). A detailed

description of the SMPS design can be found in the L5970D device datasheet.

The control unit in this application is a microcontroller which sends data through the serial

peripheral interface (SPI) to the shift registers. The data are shifted bit by bit to the next

driver with the falling edge of the clock frequency (the maximum communication frequency

for this driver is 30 MHz).

The control panel consists of the switch and two potentiometers. The switch changes the

modes and the potentiometers allow the changing of the brightness and the text speed

(blinking speed).

Figure 1. Block diagram

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