TLC5951 Datasheet, PDF (22/46 Pages) Texas Instruments – 24-Channel, 12-Bit PWM LED Driver with 7-Bit Dot Correction and 3-Group, 8-Bit Global Brightness Control

TLC5951
SBVS127B – MARCH 2009 – REVISED DECEMBER 2009
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GLOBAL BRIGHTNESS CONTROL (BC) FUNCTION
The TLC5951 has the capability to adjust the output current of each color group simultaneously. This function is
called global brightness control (BC). The global brightness control for each of the three color groups,
(OUTR0-OUTR7, OUTG0-OUTG7, and OUTB0-OUTB7), is programmed with a separate 8-bit word. The BC of
each group is adjusted with 256 steps from 0% to 100%. 0% corresponds to 0 mA. 100% corresponds to the
maximum output current programmed by R_IREF and each output DC value. Note that even though the BC value
for all color groups are identical, the output currents can be different if the DC values are different. Equation 2
and Equation 3 calculate the actual output current as a function of R_IREF, DC adjustment range, and brightness
control value. BC data are programmed into the TLC5951 via the serial interface.
When the IC is powered on, the BC data in the 216-bit common shift register and data latch contain random
data. Therefore, BC data must be written to the BC latch before turning the constant-current output on.
Additionally, XBLNK should be low when the device turns on to prevent the outputs from turning on before the
proper grayscale values can be written. All constant-current outputs are off when XBLNK is low.
Equation 2 determines the output sink current for each color group when the dot correction high adjustment
range is chosen.
I_OUT (mA) =
1
3
I_OLCMax (mA) +
2
3
I_OLCMax (mA) ´
DC
127
BC
´
255
(2)
Equation 3 determines the output sink current for each color group when the dot correction low adjustment range
is chosen.
I_OUT (mA) =
2
3
I_OLCMax (mA) ´
DC
127
BC
´
255
(3)
Where:
I_OLCMax = the maximum channel current for each channel determined by R_IREF
DC = the decimal dot correction value for the output. This value ranges between 0 and 127.
BC = the decimal brightness control value for the output color group. This value ranges between 0 and 255.
DC DATA
(Binary)
000 0000
000 0001
000 0010
—
111 1101
111 1110
111 1111
Table 3. Output Current versus DC Data and I_OLCMax with
Dot Correction High Adjustment Range (BC Data = FFh)
DC DATA
(Decimal)
0
1
2
—
125
126
127
DC DATA
(Hex)
00
01
02
—
7D
7E
7F
BC DATA
(Hex)
FF
FF
FF
—
FF
FF
FF
PERCENTAGE
OF I_OLCMax (%)
33.3
33.9
34.4
—
99.0
99.5
100.0
I_OUT, mA
(I_OLCMax = 40 mA)
13.33
13.54
13.75
—
39.58
39.79
40.00
I_OUT, mA
(I_OLCMax = 2 mA)
0.67
0.68
0.69
—
1.98
1.99
2.00
22
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