TLC5943_17 Datasheet, PDF (25/40 Pages) Texas Instruments – 16-Channel, 16-Bit PWM LED Driver with 7-Bit Global Brightness Control

TLC5943
www.ti.com
SBVS101 – DECEMBER 2007
Brightness Control (BC) Shift Register and Data Latch
The Brightness Control (BC) data shift register and the first latch are each 8 bits long; the second latch is 7 bits
long. The lower 7 bits in the latch are used to adjust the constant current value for all channels of the constant
current driver. The MSB of the first latch is used for the auto repeat mode setting. Table 5 shows the ratio of
setting the current value against the maximum current value for each BC data point. Figure 29 shows the shift
register and latch configuration for BC data. Figure 12 shows the timing for writing data.
The driver constant current value is controlled by the data in the second BC data latch. BC data can be set into
the latch at the rising edge of XLAT with BCSEL = high after writing the data into the BC Shift Register by SIN
and SCLK with BCSEL = high. A BCSEL level change occurs during SCLK = low and after 100 ns from the rising
edge of XLAT. When powered up, the data in the BC Shift Register and latches are not set to any default value.
Therefore, brightness data must be written to the BC latch before turning on the constant current output.
BC Data (Dec)
0
1
2
3
---
125
126
127
Table 5. BC Data vs Current Ratio
BC Data (Lower 7 Bits; Hex)
0
1
2
3
---
7D
7E
7F
Ratio of Setting Current Value Against MAX Value (%)
0
0.8
1.6
2.4
---
98.4
99.2
100
SOUT
MSB
7
Auto-Repeat
1 = Repeat
6
BC Data
for Bit 6
5
BC Data
for Bit 5
4
BC Data
for Bit 4
3
BC Data
for Bit 3
2
BC Data
for Bit 2
1
BC Data
for Bit 1
LSB
0
BC Data
for Bit 0
Brightness/Auto Repeat Control Shift Register (8 Bits)
Shift
Data
SIN with
BCSEL = high
Shift ^{SCLK with}
Clock ^{BCSEL = high}
MSB
7
Auto-Repeat
1 = Repeat
6
BC Data
for Bit 6
5
BC Data
for Bit 5
4
BC Data
for Bit 4
3
BC Data
for Bit 3
2
BC Data
for Bit 2
1
BC Data
for Bit 1
LSB
0
BC Data
for Bit 0
Brightness/Auto Repeat Control Data Latch 1 (8 Bits)
Latch
Signal
XLAT rising edge with
BCSEL = high
MSB
6
BC Data
for Bit 6
5
BC Data
for Bit 5
4
BC Data
for Bit 4
3
BC Data
for Bit 3
2
BC Data
for Bit 2
1
BC Data
for Bit 1
LSB
0
BC Data
for Bit 0
Brightness Control Data Latch 2 (7 Bits)
1 Bit
7 Bits
Latch
Signal
65,536th GSCLK when
Auto Repeat is enabled
or BLANK with BCSEL = high
To PWM Control Block
To Constant Current Driver
Figure 29. Brightness Control Shift Register and Latch Configuration
Copyright © 2007, Texas Instruments Incorporated
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