TLC5971_15 Datasheet, PDF (19/45 Pages) Texas Instruments – 12-Channel, 16-Bit, Enhanced Spectrum, PWM, RGB, LED Driver

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TLC5971
SBVS146D – AUGUST 2010 – REVISED DECEMBER 2015
8.5 Programming
8.5.1 Global Brightness Control (BC) Function (Sink Current Control)
The TLC5971 has the capability to adjust all output currents of each color group (OUTR0-3, OUTG0-3, and
OUTB0-3) to the same current value. This function is called global brightness (BC) control. The BC data are
seven bits long, which allows each color group output current to be adjusted in 128 steps from 0% to 100% of
the maximum output current, I_OLCMax. The BC data are set through the serial interface. When the BC data are
changed, the output current is changed immediately.
When the IC is powered on, all outputs are forced off by BLANK (bit 213). BLANK initializes in the data latch but
the data in the 224-bit shift register and the 218-bit data latch are not set to a default value, except for the
BLANK bit. Therefore, BC data must be written to the data latch when BLANK is set to 0.
Equation 7 determines each color group maximum output sink current:
BCX
I_OUT (mA) = I_OLCMax (mA) ´ _127d
Where:
I_OLCMax = the maximum channel current for each channel determined by R_IREF
BC = the global brightness control value in the data latch for the specific color group
(BCX = 0d to 127d, X = R/G/B)
(7)
Table 2 summarizes the BC data value versus the output current ratio and set current value.
BC DATA (BINARY)
000 0000
000 0001
000 0010
—
111 1101
111 1110
111 1111
Table 2. BC Data vs Current Ratio and Set Current Value
BC DATA
(DECIMAL)
0
1
2
—
125
126
127
BC DATA
(HEX)
00
01
02
—
7D
7E
7F
OUTPUT CURRENT
RATIO TO I_OLCMax
(%, TYPICAL)
0
0.8
1.6
—
98.4
99.2
100
60 mA I_OLCMax
(mA, TYPICAL)
0
0.47
0.94
—
59.06
59.53
60
2 mA I_OLCMax
(mA, TYPICAL)
0
0.02
0.03
—
1.97
1.98
2
8.5.2 Grayscale (GS) Function (PWM Control)
The TLC5971 can adjust the brightness of each output channel using the enhanced spectrum pulse width
modulation (ES-PWM) control scheme. The PWM bit length for each output is 16 bits. The use of the 16-bit
length results in 65536 brightness steps from 0% to 100% brightness.
The PWM operation for all color groups is controlled by a 16-bit grayscale (GS) counter. The GS counter
increments on each rising or falling edge of the external or internal GS reference clock that is selected by
OUTTMG (bit 217) and EXTGCK (bit 216) in the data latch. When the external GS clock is selected, the GS
counter uses the SCKI clock as the grayscale clock. The GS counter is reset to 0000h and all outputs are forced
off when BLANK (bit 213) is set to 1 in the data latch and the counter value is held at 0 while BLANK is 1, even if
the GS reference clock is toggled in between.
Equation 8 calculates each output (OUTXn) total on-time (t_{OUT_ON}):
t_{OUT_ON} (ns) = t_GSCLK (ns) ´ GSXn
Where:
t_GSCLK = one period of the selected GS reference clock
(internal clock = 100ns typical, external clock = the period of SCKI)
GSXn = the programmed GS value for OUTXn (0d to 65535d)
(8)
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