TLC5952 Datasheet, PDF (18/33 Pages) Texas Instruments – 24-Channel, Constant-Current LED Driver with Global Brightness Control and LED Open-Short Detection

TLC5952
SBVS129 – MAY 2009........................................................................................................................................................................................................ www.ti.com
GLOBAL BRIGHTNESS CONTROL (BC) FUNCTION: SINK CURRENT CONTROL
The TLC5952 is able to adjust the output current of each of the three color groups OUTR0-OUTR7,
OUTG0-OUTG7, and OUTB0-OUTB7. This function is called global brightness control (BC). The BC function
allows users to adjust the global brightness of LEDs connected to the three output groups (OUTR0-OUTR7,
OUTG0-OUTG7, and OUTB0-OUTB7). All color group output currents can be adjusted in 128 steps from 0% to
100% of the maximum output current, I_OLCMax. The brightness control data are entered into the TLC5952 via the
serial interface. When the BC data change, the output current also changes immediately. When the IC is
powered on, the data in the common shift register and the control data latch are not set to any default values.
Therefore, BC data must be written to the control data latch before turning on the constant-current output.
Equation 2 determines the output sink current for each color group. Table 2 summarizes the BC data versus
current ratio and set current value.
BCR/G/B
I_OUT (mA) = I_OLCMax (mA) ´
127d
(2)
Where:
I_OLCMax = the maximum channel current for each channel determined by R_IREF
BCR/G/B = the global brightness control value in the control data latch for each output color group
BC DATA
(Binary)
000 0000
000 0001
000 0010
—
111 1101
111 1110
111 1111
Table 2. BC Data versus Current Ratio and Set Current Value
BC DATA
(Decimal)
0
1
2
—
125
126
127
BC DATA
(Hex)
00
01
02
—
7D
7E
7F
RATIO OF OUTPUT
CURRENT TO
I_OLCMax
(mA, Typical)
0
0.8
1.6
—
98.4
99.2
100.0
I_OUT, mA
(I_OLCMax = 35 mA,
Typical)
0
0.28
0.55
—
34.45
34.72
35.00
I_OUT, mA
(I_OLCMax = 2 mA,
Typical)
0
0.02
0.03
—
1.97
1.98
2.00
CONSTANT-CURRENT OUTPUT ON/OFF CONTROL
When BLANK is low, each output is controlled by the data in the output on/off data latch. When data
corresponding to an output are equal to '1', the output turns on; when the data corresponding to an output are
equal to '0', the output turns off. When BLANK is high, all outputs are forced off.
When the IC is powered on, the data in the output on/off data latch are not set to any default values. Therefore,
on/off data must be written to the output on/off data latch before turning on the constant-current output and
pulling BLANK low.
If there are any OUTRn/Bn/Bn outputs not connected to an LED, including open for short-to-ground failures, the
on/off data corresponding to the unconnected output should be set to '0' before the LED is turned on. Otherwise,
the V_CC supply current (I_CC) increases while the LEDs are on. A truth table for the on/off control data is shown in
Table 3.
Table 3. On/Off Control Data Truth Table
ON/OFF CONTROL DATA
0
1
CONSTANT-CURRENT OUTPUT
STATUS
Off
On
18
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