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SILICON TOUCH TECHNOLOGY INC

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16-channel 16-bit PWM Constant Current LED Driver

Version : A.003

Page 16

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DM634

Output Modulation Technique

DM634 provides a new LED drive technique of output modulation. It mixes traditional Pulse

Width Modulation (PWM) represented by LSB 12 bit with Sequential Split Modulation (SSM)

represented by MSB 4 bit. The main benefits of SSM are to drive LED with an equivalent higher

relationships between PWM and SSM in time domain can be refer to the diagram below (not to

scale):

Traditional PWM Width represented by Bit [11:0]

Sequential Split Modulation represented by Bit [15:12]

A complete modulation cycle

t

0

8

1

9

2

10

3

11

4

12

5

13

6

14

7

15

Bit[11:0] (PWM)

Bit[15:0]

on

off

on

off

on

off

on

off

on

off

on

off

on

off

on

off

t

65536 clocks

Bit[11:0] (PWM)

Bit[11:0] (PWM)

Bit[11:0] (PWM)

Bit[11:0] (PWM)

Bit[11:0] (PWM)

Bit[11:0] (PWM)

Bit[11:0] (PWM)

A complete modulation cycle

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

Ultra High Resolution Current Outputs

DM634 could provide 16-bit linear PWM control current outputs for each channel. There are

two advantages for system design. One is DM634 has sufficient bit resolution (65536 steps), not

only LED color information but additional data such as global brightness, dot correction, and

gamma correction can be represented by the proper algorithms. The other is to reduce a lot of clock

and data rate compared to conventional ON-OFF type LED drivers.