TLC5905 Datasheet, PDF (19/27 Pages) Texas Instruments – LED DRIVER

PRINCIPLES OF OPERATION
TLC5905
LED DRIVER
SLLS401 – NOVEMBER 1999
noise reduction
concurrent switching noise reduction
The concurrent switching noise has 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 GSCLK and BLANK terminals
of next stage IC, it allows differences in the switching time between ICs to be made. 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 output current is 80 mA, the time to change constant current output to turnon and turnoff is approximately
150 ns and 250 ns respectively. It is effective in reducing concurrent switching noise that occurrs when multiple
outputs turn 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. It means approximately
450 ns delay time exists between OUT0 and OUT15. This time difference by delay is effective for reduction of
concurrent switching noise as well as the output slope. This delay time has the same value in 8 bits or 16 bits
operation mode.
power supply
The followings should be taken into consideration.
D V_CC(LOG), V_CC(ANA) and V_CC(LED) should be supplied by a single power supply to minimize voltage
differences between these terminals.
D The bypass capacitor should be located between power the 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 since it is connected to the bottom
side of IC chip. Also, desired thermal effect will be obtained by connecting this pad to the PCB pattern with better
thermal conductivity.
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