TLC5947_17 Datasheet, PDF (14/33 Pages) Texas Instruments – 24-Channel, 12-Bit PWM LED Driver With Internal Oscillator

TLC5947
SBVS114B – JULY 2008 – REVISED JANUARY 2015
www.ti.com
Feature Description (continued)
8.3.2 Auto Display Repeat Function
This function can repeat the total display period without any timing control signal, as shown in Figure 19.
BLANK
GS Counter Value
Internal Oscillator Clock
2048
4095
2048
4095
¼
¼
¼
¼
0 0 0 0 1 2 3 2047 2049 4094 0 1 2 3 2047 2049 4094 0
4095
¼
1 2 3 0 0 0 0 0 0 1 2 4094 4096 1 2
Grayscale counter starts to count from the fifth clock _{Display period is turned on again by}
of the internal oscillator clock after BLANK goes low. _{the auto display repeat function.}
OUTn ^OFF
(GS Data = 001h) _ON
OUTn ^OFF
(GS Data = 800h) _ON
OUTn ^OFF
(GS Data = FFFh) _ON
First Display Period
(4096 Internal Clock)
Four Internal Clock Intervals After BLANK Goes Low
Second Display Period
(4096 Internal Clock)
Nth Display Period
First
Display Period
Second
Display Period
Four Internal Clock Intervals After BLANK Goes Low
Figure 19. Auto Display Repeat Operation
8.3.3 Thermal Shutdown (TSD)
The thermal shutdown (TSD) function turns off all constant-current outputs immediately when the IC junction
temperature exceeds the high temperature threshold (T_(TEF) = +162° C, typ). The outputs will remain disabled as
long as the over-temperature condition exists. The outputs are turned on again at the first clock after the IC
junction temperature falls below the temperature of T_(TEF) – T_(HYS). Figure 20 shows the TSD operation.
IC Junction Temperature (T_J)
T_J < T_(TEF) - T_(HYS)
T_J ³ T_(TEF)
T_J < T_(TEF) - T_(HYS)
T_J ³ T_(TEF)
BLANK
High
Low
Internal Oscillator Clock
1 23
4096
4095 1 2
4096
4095 1 2
4096
4095 1 2
4096
4095 1 2
4096
4095 1 2
4096
4095 1 2
OFF
OUTn
(GS Data = FFFh)
ON
OFF
OFF
ON
Figure 20. TSD Operation
8.3.4 Noise Reduction
Large surge currents may flow through the IC and the board on which the device is mounted if all 24 LED
channels 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 TLC5947 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 six channels each. The first group is OUT0, 4, 8, 12, 16, 20; the second group is OUT1, 5, 9, 13, 17,
21; the third group is OUT2, 6, 10, 14, 18, 22; and the fourth group is OUT3, 7, 11, 15, 19, 23. Each group turns
on sequentially with a small delay between groups; see Figure 3. Both turn-on and turn-off are delayed.
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