點晶科技股份有限公司
點晶科技股份有限公司
點晶科技股份有限公司
點晶科技股份有限公司
SILICON TOUCH TECHNOLOGY INC.
ST2226A
ST2226A
Version
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：
：
：A.010
Page
：
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：10
2) LED Emitting Time and Current
ST2226A adjusts the LED luminance using PWM (pulse width modulation) technique.
The luminance data (DV) has a resolution of 10 bits (1024steps) and can be set
independently for each LED. The relationship between Iout, luminance data, and emitting
time is shown in Figure 2.
Current
Iout
Time
DV x TGCLK
“LED Emitting” command issued
1024 x TGCLK
2 x GCLK
Figure 2. PWM Current Output
3) Phase Relationship of DCLK and GCLK
Matching ST2226A’s GCLK and DCLK is an important step in the system design. If
there is a certain length of delay between the rising edge of DCLK and of GCLK, the
command “LED Emitting“& “LED Disable” will not be correctly recognized, which will then
cause the display data loss. It is safe to keep both of GCLK and DCLK rising at the same
time, so that the frequencies of DCLK and GCLK have an integer multiple relationship.
For the design which has a fixed, corresponding clock phase relationship between
GCLK & DCLK, e.g. the display controller is built by FPGAs, this clock phase problem is
unlikely to happen. However, if it dose happen, try to control the clock phase, e.g. invert
GCLK, to solve this problem. On the contrary, for the design which can not control the
clock phase, e.g. the display controller is built by microprocessors, the following sequential
modification on “Emitting” & “Disable” commands is preferred to be employed in the
design:
1.
Gate GCLK.
2.
Issue “Emitting” or “Disable” command.
3.
Let go of GCLK.
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