TLC5910 Datasheet, PDF (17/30 Pages) Texas Instruments – LED DRIVER

TLC5910
LED DRIVER
PRINCIPLES OF OPERATION
SLLS392 – NOVEMBER 1999
output current adjustment on each constant current output – LED brightness adjustment
By using the 6 bits of the dot correction latch, the output current on each constant current output can be adjusted
to 64 steps. 1 step of 0.8% current ratio between 100% and 50.8% when the set output current is 100% by an
external resistor at 111111h of the latched value and the lower 6 bits of the brightness control register. By using
this function, the brightness deviation due to LED brightness variation can be minimized. When DCENA is pulled
low, the output current is set to 100% without dot correction.
Table 4. Relative Current Ratio By Constant Current Output
CODE
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{MSB 000000 LSB}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _.
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _.
.
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _.
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ₁₁₁₁₁₀
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _111111†
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ^†DCENA is low.
CURRENT RATIO (%)
50.8
.
.
.
.
99.2
100
IOLC=40 (mA)
20.3
.
.
.
.
39.7
40
clock edge selection
The high speed clock signal is delayed due to the duty ratio change through multiple stages of an IC or through
the module stages shown in Figure 6.
IN
A
OUT
IN
A
A’
OUT
OUT’
IN
A
OUT
IN’
A’
OUT
a) Propagate through multiple stages buffer
with slow falling edge
b) Insert inverter between buffers
Figure 6. Clock Edge Selection
As shown in Figure 6 a), if the falling at the internal buffer is behind the rising, the clock will disappear as multiple
cascade connections are made. To resolve this problem, the duty ratio can be held unchanged using the
connection as shown in Figure 6 b) if the valid clock edge can be selected (arrow in Figure 6). Note that the clock
delay is not avoided even in this case.
The device incorporates the clock edge selection function for each DCLK and GSCLK. By using this function,
the falling edge or rising edge for the valid edge can be selected depending on the status of DPOL and GSPOL.
Thus the degradation for the duty ratio can be reduced. The relation between each signals is shown in
Table 5.
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