TLC5921 Datasheet, PDF (8/14 Pages) Texas Instruments – LED DRIVER

TLC5921
LED DRIVER
SLLS390 – SEPTEMBER 1999
PRINCIPLES OF OPERATION
setting for constant output current value
The constant current value is determined by external resistor, R_(IREF) between IREF and GND. Refer constant
output current characteristics shown on Figure 5 for this external resistor value.
Note that more current flows if connect IREF to GND directly.
constant output current operation
When BLANK is low, the corresponding output is turned on if data latch value is 1, and turned off if data latch
value is 0. When BLANK is high, all outputs are forced to turn off. If there is constant current output terminal
left unconnected (includes LED disconnection), it should be lighted on after writing zero to corresponding data
latch to its output. If this operation is not done, supply current through constant current driver will increase.
shift register latch
The shift register latch is configured with 16 × 1 bits. The 1 bit for constant current output data represents ON
for constant current output if data is 1, or OFF if data is 0. The configuration of shift register latch is shown in
below.
Data Latch
XLATCH
OUT15
Data
(1 bits)
OUT14
Data
(1 bits)
OUT1
Data
(1 bits)
OUT0
Data
(1 bits)
Shift Register
SOUT
16
15
SCLK
2
1
SIN
Figure 3. Relationship Between Shift Register and Latch
SOUT output timing selection
By setting level of SOMODE, the SOUT output timing can be changed. When SOMODE is set to low, data is
clocked out to SOUT synchronized on the rising edge of SCLK, and when SOMODE is set to high, data is
clocked out to SOUT synchronized on the falling edge of SCLK. When SOMODE is set to high and shift
operation is done, the data shift error can be prevented even though SCLK signal is externally buffered in serial.
Note that the maximum data transfer rate in cascade operation is slower than that when SMODE is set to low.
TSD (thermal shutdown)
When the junction temperature exceeds the limit, TSD starts to function and turn constant current output off and
XDOWN goes low. Since XDOWN is configured with open-collector output, the outputs of multiple ICs can be
concatenated. To recover from constant current output off-state to normal operation, power supply should be
turned off and then turned on after several seconds.
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