點晶科技股份有限公司
SILICON TOUCH TECHNOLOGY INC.
新竹市科學園區展業一路9號7樓之1
9-7F-1, Prosperity RoadⅠ, Hsin-Chu, Taiwan, R.O.C.
DM634
Tel：886-3-5645656
Fax：886-3-5645626
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)
signal, while latch(LAT ) signal kept high level at the same time. Meanwhile the GCK external mode
can be set back to the free-running mode. Notice that when internal RESET at low level, all the shift
registers in DM634 will be cleared (Kept at Low level) and all output current will be off
immediately.
DCK
LAT
t
Normal Operation
1
2
1
2
3
DCK
LAT
DCK
LAT
1
2
3
1
2
3
4
RESET
RESET
(internal)
(internal)
t
t
Option 1 : Timing Combination to set up
external GCK mode
Option 2 : Timing Combination to set up
free-running mode
16-channel 16-bit PWM Constant Current LED Driver
Version : A.003
Page 12
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