TLC5904 Datasheet, PDF (19/27 Pages) Texas Instruments – LED DRIVER

PRINCIPLES OF OPERATION
TLC5904
LED DRIVER
SLLS391 – NOVEMBER 1999
noise reduction
concurrent switching noise reduction
The concurrent switching noise has a potential to occur when multiple outputs turn on or off at the same time.
To prevent this noise, the device has delay output terminals such as XGSOUT and BOUT for GSCLK (gray scale
clock) and BLANK (blanking signal) respectively. By connecting these outputs to the GSCLK and BLANK
terminals of next stage IC, it allows differences in the switching time between ICs. When GSCLK is output to
GSOUT through the device, duty will be changed between input and output, and the number of stages to be
connected will be limited depending on frequency.
output slope
When the output current is 80 mA, the time to change constant current output to turnon and turnoff is
approximately 150 ns and 250 ns respectively. This allows reduced concurrent switching noise when multiple
outputs turn on or off at the same time.
delay between constant current output
The constant current output has a delay time of approximately 30 ns between outputs. This means
approximately 450 ns delay time exists between OUT0 and OUT15. This time differences by delay allows
reduced concurrent switching noise as well as the output slope previously described. This delay time has the
same value at the 8 bits or 16 bits operation mode.
power supply
The followings should be taken into consideration:
1) VCCLOG, VCCANA, and VCCLED should be supplied by a single power supply to minimize voltage
differences between these terminals.
2) The bypass capacitor should be located between the power supply and GND to eliminate the variation of
power supply voltage.
GND
Although GNDLOG, GNDANA, and GNDLED are internally tied together, these terminals should be externally
connected to reduce noise influence.
thermal pad
The thermal pad should be connected to GND to eliminate the noise influence when it is connected to the bottom
side of IC chip. Also, the desired thermal effect will be obtained by connecting this pad to the PCB pattern with
better thermal conductivity.
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