TLC5947 Datasheet, PDF (16/27 Pages) Texas Instruments – 24-Channel, 12-Bit PWM LED Driver with

TLC5947
SBVS114A – JULY 2008 – REVISED SEPTEMBER 2008 ................................................................................................................................................. www.ti.com
GS data are transferred from the shift register to the latch by the rising edge of XLAT. When powered up, the
data in the grayscale shift register and data latch are not set to default values. Therefore, grayscale data must be
written to the GS latch before turning on the constant current output. BLANK should be at a high level when
powered on to avoid falsely turning on the constant current outputs due to random values in the latch at
power-up. All of the constant current outputs are forced off when BLANK is high. However, if the random values
turning on at power-up is not a concern in the application, BLANK can be at any level. GS can be controlled
correctly with the grayscale data writing functions, even if BLANK is connected to GND. Equation 2 determines
each output on duty.
On Duty (%) = ^GSn ´ 100
4096
(2)
where:
GSn = the programmed grayscale value for OUTn (GSn = 0 to 4095)
SIN
GS0 GS23 GS23 GS23 GS23 GS23
0A 11B 10B 9B 8B 7B
GS0 GS0 GS0 GS0
3B 2B 1B
0B
GS23 GS23 GS23 GS23 GS23 GS23
11C 10C 9C 8C 7C 6C
SCLK
XLAT
123 4 5
285 286 287 288
12 3456 7
Shift Register
Bit 0 Data (Internal)
Shift Register
Bit 1 Data (Internal)
GS0 GS23 GS23 GS23 GS23
0A 11B 10B 9B 8B
GS0 GS0 GS23 GS23 GS23
1A 0A 11B 10B 9B
GS0 GS0 GS0 GS0
3B 2B 1B 0B
GS0 GS0 GS0 GS0
4B 3B 2B 1B
GS23 GS23 GS23 GS23 GS23 GS23
11C 10C 9C 8C 7C 6C
GS0 GS23 GS23 GS23 GS23 GS23
0B 11C 10C 9C 8C 7C
Shift Register
Bit 286 Data (Internal)
Shift Register
Bit 287 Data (Internal)
GS23 GS23 GS23 GS23 GS23
10A 9A 8A 7A 6A
GS23 GS23 GS23 GS23 GS23
11A 10A 9A 8A 7A
GS0 GS0 GS23 GS23
1A 0A 11B 10B
GS0 GS0 GS23 GS23
2A 1A 0A 11B
GS23 GS23 GS23 GS23 GS23 GS23
9B 8B 7B 6B 5B 4B
GS23 GS23 GS23 GS23 GS23 GS23
10B 9B 8B 7B 6B 5B
Grayscale Latch Data
(Internal)
SOUT
Oscillator Clock
(Internal)
OUT0/4/8/12/16/20⁽¹⁾
OUT1/5/9/13/17/21⁽¹⁾
OUT2/6/10/14/18/22⁽¹⁾
OUT3/7/11/15/19/23⁽¹⁾
Previous Grayscale Latch Data
GS23 GS23 GS23 GS23 GS23
11A 10A 9A 8A 7A
4094 4096
¼ ¼ _{4093 4095 1 2 3 4}
GS0 GS0 GS0 GS0 GS23
3A 2A 1A 0A 11B
OFF
ON
ON
ON
OFF
ON
ON
OFF
ON
ON
OFF
ON
ON
Latest Grayscale Latch Data
GS23 GS23 GS23 GS23 GS23 GS23
10B 9B 8B 7B 6B 5B
4094 4096
¼ ¼ _{4093 4095 1 2 3 4 5 6 7 8}
OFF
ON
OFF
ON
OFF
ON
OFF
ON
(1) GS data = FFFh.
Figure 20. Grayscale Data Write Operation
16
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