點晶科技股份有限公司

SILICON TOUCH TECHNOLOGY INC

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9-7F-1, Prosperity RoadⅠ, Hsin-Chu, Taiwan, R.O.C.

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16-channel 16-bit PWM Constant Current LED Driver

Version : A.003

Page 12

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DM634

Selection of Internal/External PWM Frequency

The default operation mode is the free-running PWM signal generated by internal oscillator

after power-on. Users could switch internal to external PWM frequency source by following timing

sequence. There are two alternative options could be selected. The option 1 shows three rising edges

of latch pulse ( LAT ) when the clock (DCK) kept at high level then two rising edges of clock (DCK)

pulse when the latch pulse ( LAT ) kept at high level. Then the SOMODE/GCK pin could input

external frequency to operate PWM function. The option 2 shows four rising edges of latch

pulse( LAT ) when clock(DCK) kept at high level then sending three rising edges of clock (DCK)

registers in DM634 will be cleared (Kept at Low level) and all output current will be off

immediately.

DCK

LAT

Normal Operation

t

DCK

LAT

RESET

(internal)

Option 2 : Timing Combination to set up

free-running mode

t

DCK

LAT

Option 1 : Timing Combination to set up

external GCK mode

RESET

(internal)

t

12

3

12

12

3

12

3

4