TLC5971 Datasheet, PDF (18/37 Pages) Texas Instruments – 12-Channel 16-Bit, Enhanced Spectrum PWM, RGB LED Driver with 3.3-V Linear Regulator

TLC5971
SBVS146 – AUGUST 2010
www.ti.com
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 3 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)
(3)
Table 3 summarizes the GS data values versus the output total on-time and duty cycle. When the IC is powered
up, BLANK (bit 213) is set to '1' to force all outputs off; however, the 224-bit shift register and the 218-bit data
latch are not set to default values. Therefore, the GS data must be written to the data latch when BLANK (bit
213) is set to '0'.
GS DATA (decimal)
0
1
2
3
—
8191
8192
8193
—
16383
16384
16385
—
24575
24576
24577
—
32765
32766
32767
Table 3. Output Duty Cycle and Total On-Time versus GS Data
GS DATA (hex)
0
1
2
3
—
1FFF
2000
2001
—
3FFF
4000
4001
—
5FFF
6000
6001
—
7FFD
7FFE
7FFF
ON-TIME DUTY (%)
0
0.002
0.003
0.005
—
12.499
12.5
12.502
—
24.999
25
25.002
—
37.499
37.501
37.502
—
49.996
49.998
49.999
GS DATA (decimal)
32768
32769
32770
32771
—
40959
40960
40961
—
49149
49150
49151
—
57343
57344
57345
—
65533
65534
65535
GS DATA (hex)
8000
8001
8002
8003
—
9FFF
A000
A001
—
BFFF
C000
C001
—
DFFF
E000
E001
—
FFFD
FFFE
FFFF
ON-TIME DUTY (%)
50.001
50.002
50.004
50.005
—
62.499
62.501
62.502
—
74.997
74.998
75
—
87.5
87.501
87.503
—
99.997
99.998
100
18
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