TLC59461 Datasheet, PDF (19/33 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 6-Bit Dot Correction

TLC59461
www.ti.com............................................................................................................................................... SLVS896A – NOVEMBER 2008 – REVISED MARCH 2009
AUTO OUTPUT OFF
The TLC59461 does not implement the Auto Output Off functionality that is available in the TLC5946. This
revised architecture allows the voltage at the OUTn pins of the IC to be reduced to a voltage lower than the LED
open detection threshold V_LOD (0.3V typical) specified in the TLC5946 data sheet and continue to have OUTn
remain turned on. Reducing the voltage at OUTn minimizes the power dissipation in the IC.
THERMAL ERROR FLAG (TEF)
The TLC59461 has a thermal error flag (TEF) function to indicate an over-temperature condition. If the junction
temperature exceeds the threshold temperature, +162°C typical, TEF toggles to '1' and the XERR pin goes to a
low level. Once TEF becomes '1', it remains a '1' until the first falling edge of SCLK after XLAT goes high, as
shown in Figure 28. If the junction temperature (T_J) remains higher than the threshold temperature, TEF remains
'1', even after the first falling edge of SCLK. TEF is also shifted out of the SOUT pin; see the Status Information
Data (SID) section.
XLAT
BLANK
SCLK
GSCLK
1234
123
IC Junction
Temperature (T_J)
TEF
(Internal)
XERR
T_J < T_TEF
'0'
Hi-Z
T_J ³ T_TEF
'1'
T_J < T_TEF - T_HYS
Low
Figure 28. TEF and XERR Timing
T_J ³ T_TEF
'0'
NOISE REDUCTION
Large surge currents can flow through the IC and the board if all 16 LED channels fully turn on simultaneously at
the start of each grayscale cycle. These large current surges could introduce detrimental noise and
electromagnetic interference (EMI) into other circuits. The TLC59461 turns on the LED channels in a series
delay, to provide a current soft-start feature. The output current sinks are grouped into four groups of four
channels each. The first group is OUT0, 4, 8, 12; the second group is OUT1, 5, 9, 13; the third group is OUT2, 6,
10, 14; and the fourth group is OUT3, 7, 11, 15. Each group turns on sequentially with a small delay between
groups; see Figure 12. Both turn-on and turn-off are delayed.
OUTPUT ENABLE
When BLANK is high, all constant-current outputs turn off and the grayscale counter is reset. When BLANK is
low, all constant-current outputs are controlled by the GS PWM timing controller. If BLANK goes low and then
toggles high again in a very short time, all outputs that are programmed to turn on do so, for either the
programmed number of grayscale clocks or the length of time that the BLANK signal was low, whichever is
lower. For example, if all outputs are programmed to turn on for 1 ms, but the BLANK signal is only low for 50 ns,
all outputs turn on for 50 ns, even though some outputs will turn on after the BLANK signal has already gone
high.
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