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SILICON TOUCH TECHNOLOGY INC

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3-CHANNEL CONSTANT CURRENT LED DRIVERS

Version:A.003

Page 10

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DM412

Output Modulation Technique

In order to minimize the harmonic noise and increasing current accuracy, DM412 provides a

new LED drive technique of output modulation. It mixes traditional Pulse Width Modulation (PWM)

represented by MSB 8 bit (Bit[15:8]) with Bit Angle Modulation (BAM) represented by LSB 8 bit

(Bit[7:0]). The main benefit of BAM is to drive LED with an equivalent multiple frequencies in the

lower intensity of LED light output. Each bit of BAM binary code is effectively allocated a fixed

width of phase angles within a modulation cycle. The reference table shows the ratio defined by the

binary significance of each bit:

bit

weighted width

7

256

6

128

5

64

4

32

3

16

2

8

1

4

0

1

The relationships between BAM and PWM in the time domain can be refer to the diagram (not to

scale) below: