AN2141 데이터 시트보기 (PDF) - STMicroelectronics

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AN2141

LED array reference design board

STMicroelectronics 

LED array reference designs

5

LED array reference designs

AN2141

Two LED array reference designs have been developed: one with 80 LEDs using the

STP16CPS05 LED driver, and another with 32 LEDs using the STP16CP05 and

STP16CPS05 LED drivers. In the following sections these two designs and their differences

are briefly described.

5.1

80 LED array reference design

An example of the 80 LED array reference design proposal (no evaluation board is currently

available for this design) is shown in Figure 6. Its block schematic description is provided in

Section 1: Block diagram. The only simplification in this reference design is that it does not

include an SMPS DC-DC converter. Therefore the supply voltage should be in the range of

4 V to 5 V.

Figure 6. 80 LED array reference design

5.1.1

Application schematic

A detailed application schematic of this design is shown in Figure 7. Five STP16CPS05 LED

drivers with 16 outputs are controlled by the ST7Lite09 microcontroller. The microcontroller

provides the clock frequency (SCK pin), the serial data (MOSI pin), the PWM signal (PWM

pin) and the latch signal (PA0 pin). The clock frequency in this application is 633 KHz and

the PWM signal for brightness regulation is 619 Hz. Resistors R1 to R5 (one for each driver)

set the constant current for all outputs. Their value is 1.3 kΩ and they set the constant sink

current to approximately 10 mA (for more information, please refer to the STP16CP05 and

STP16CPS05 datasheets). The analog voltage values from the trimmers R6 and R8 are

measured and converted by the microcontroller’s ADC to the digital reference signal. The

microcontroller sets the PWM signal for brightness and the data time delay for text speed

control accordingly.

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