TLC59291_15 Datasheet, PDF (25/45 Pages) Texas Instruments – TLC59291 8/16-Channel, Constant Current LED Driver with 7-bit Brightness Control Low Quiescent Current and Full Self Diagnosis for LED Lamp

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TLC59291
SLVSA96 – SEPTEMBER 2015
8.3.2 Global Brightness Control (BC) Function
The TLC59291 has the ability to adjust the output current of all constant current outputs simultaneously. This
function is called global brightness control (BC). The global BC for all outputs (OUT0 to OUT15) can be set with
a 7-bit word. The global BC adjusts all output currents in 128 steps from 0% to 100%. where 100% corresponds
to the maximum output current set by R_IREF. Equation 2 calculates the actual output current. BC data can be set
via the serial interface.
I_O(LCn) (mA )
=
I_O(LC
max)^(mA
127d
)
x
BC
Where:
I_O(LCmax) = the maximum constant-current value for each output determined by R_IREF.
BC = the global brightness control value in the control data latch (0h to 127d)
(2)
Table 2 shows the BC data versus the constant-current ratio against I_O(LCmax).
BINARY
000 0000
000 0001
000 0010
∙∙∙
111 1101
111 1110
111 1111
Table 2. BC Data versus Constant-Current Ratio Against I_O(LCmax)
BC DATA
DECIMAL
0
HEX
00
RATIO OF OUTPUT
CURRENT TO I_O(LCmax)
(%)
0
I_O(LC)
(mA, I_O(LCmax)= 40mA,
typ)
0
I_O(LC)
(mA, I_O(LCmax)= 1mA, typ)
0
1
01
0.8
0.31
0.01
2
02
1.6
0.63
0.02
∙∙∙
∙∙∙
∙∙∙
∙∙∙
∙∙∙
125
7D
98.4
39.4
0.98
126
7E
99.2
39.7
0.99
127
7F
100.0
40.0
1.00
8.3.3 Thermal Shutdown (TSD) and Thermal Error Flag (TEF)
The thermal shutdown (TSD) function turns off all constant-current outputs when the junction temperature (T_J)
exceeds the threshold (T_TEF = 165°C, typical) and sets all LOD data bit to ‘1’. When the junction temperature
drops below (T_TEF – T_HYST), the output control starts. The TEF is remains ‘1’ until LAT is input even if low
temperature. Figure 6 shows a timing diagram and Table 3 shows a truth table for TEF.
8.3.4 Pre-Thermal Warning (PTW)
The PTW function indicates that the IC junction temperature is high. The PTW is set and all LSD data bit are set
to “1” while the IC junction temperature exceeds the temperature threshold (T_PTW = 138 °C, typical). Then OUTn
are not forced off. When the PTW is set, the IC temperature should be reduced by lowering the power dissipated
in the driver to avoid a forced shutdown by the thermal shutdown circuit. This reduction can be accomplished by
lowering the values of the BC data. When the IC junction temperature decreases below the temperature of T_PTW,
PTW is reset. Figure 6 shows a timing diagram and Table 3 shows a truth table for PTW.
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