TLC5902 Datasheet, PDF (12/22 Pages) Texas Instruments – LED DRIVER

TLC5902
LED DRIVER
SLLS382 – DECEMBER 1999
PRINCIPLES OF OPERATION
constant current output selection by user (80 mA × 16 bits or 120 mA × 8 bits)
When MODE terminal is set to high, output is selected as 80 mA × 16 bits. When MODE terminal is set to low,
output is selected as 120 mA × 8 bits. By this setting, the internal shift register and latch are changed. Note that
two constant output terminals should be tied, such as OUT0 to OUT1 and OUT2 to OUT3 when 8-bit output is
selected.
MODE
H
L
80 mA x 16 bits
120 mA x 8 bits
OUTPUT
setting for constant current value
On the constant current output terminals (OUT0 to OUT15), approximately 38 times the current that flows
through the external resistor, R_(IREF) (connected between IREF and GND), can flow. The external resistor value
is calculated using the following equation.
^ I_(OUTn)(mA) 38 1.24(V)
W R_(IREF)(k )
(1)
More current flows if IREF is connected to GND directly.
shift register latch for gray scale data
The shift register latch for gray scale data is set as 8 × 8 bits configuration each at 8 bit mode, and as 16 x 8
bits configuration each at 16-bit mode. By setting RSEL to low, the shift register latch for gray scale data is
selected. Data structure shows that DIN0 corresponds to LSB, and DIN7 to MSB. This results in 2⁸ = 256 steps
gray scale. The latched data is compared to GSCLK (clock for gray scale) counts, and constant current output
continues to turn on until these values are equal.
shift register latch for brightness control
The shift register latch for brightness control is configured with 1 × 8 bits each. The data input terminal and latch
terminal are common to shift register latch for gray scale data. By setting RSEL to low, the shift register latch
for gray scale data is selected, and by setting RSEL to high, the shift register latch for brightness control is
selected. If the brightness control function is not used, BC_ENA terminal should be pulled low. Since the
brightness control latch is reset to initial value of 00011111h, it is not necessary to write data to shift register latch
for brightness control. When power is up, latch data is undetermined. Data should be written to shift register
latch when the brightness control function is used. Also, rewriting the latch value for brightness control is
inhibited when the LED is turned on.
RSEL
L
H
SHIFT REGISTER LATCH SELECTED
Shift register latch for gray scale data
Shift register latch for brightness control
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