TLC5947_17 Datasheet, PDF (12/33 Pages) Texas Instruments – 24-Channel, 12-Bit PWM LED Driver With Internal Oscillator

TLC5947
SBVS114B – JULY 2008 – REVISED JANUARY 2015
8 Detailed Description
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8.1 Overview
The TLC5947 is a 24-channel, constant-current sink driver. Each channel has an individually-adjustable, 4096-
step, PWM grayscale (GS) brightness control. The GS data is input through a serial interface port.
The TLC5947 has a 30-mA current capability. The maximum current value of all channels is determined by an
external resistor.
The TLC5947 can work without external CLK signals because the device is integrated with a 4-MHz internal
oscillator.
The device has a thermal shutdown (TSD) function that turns off all output drivers at over temperature conditions.
All of the output drivers automatically restart when the temperature returns to normal conditions.
8.2 Functional Block Diagram
VCC
SIN
SCLK
XLAT
BLANK
IREF
GND
VCC
4 MHz
Internal
Oscillator
Thermal
Detection
LSB
MSB
Grayscale (12 Bits ´ 24 Channels) Data
Shift Register
0
287
288
LSB
MSB
Grayscale (12 Bits ´ 24 Channels) Data
Data Latch
0
287
288
DQ
CK
SOUT
12 Bits PWM Timing Control
24
24-Channel, Constant Current Driver
¼
OUT0 OUT1
OUT22 OUT23
8.3 Feature Description
8.3.1 Grayscale (GS) Control Function
Each constant-current sink output OUT0–OUT23 (OUTn) turns on (starts to sink constant current) at the fifth
rising edge of the grayscale internal oscillator clock after the BLANK signal transitions from high to low if the
grayscale data latched into the grayscale data latch are not zero. After turn-on, the number of rising edges of the
internal oscillator is counted by the 12-bit grayscale counter. Each OUTn output is turned off once its
corresponding grayscale data values equal the grayscale counter or the counter reaches 4096d (FFFh). The
PWM control operation is repeated as long as BLANK is low. OUTn is not turned on when BLANK is high. The
timing is shown in Figure 18. All outputs are turned off at the XLAT rising edge. After that, each output is
controlled again from the first clock of the internal oscillator for the next display period, based on the latest
grayscale data.
12
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