TLC5942_16 Datasheet, PDF (22/29 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 7-Bit Dot Correction

TLC5942
Not Recommended for New Designs
SBVS096B – OCTOBER 2007 – REVISED OCTOBER 2007
www.ti.com
Thermal Shutdown and Thermal Error Flag
The Thermal Shutdown (TSD) function turns off all of the constant current outputs on the IC when the junction
temperature (T_J) exceeds the threshold (T_TEF = +162°C, typ) and sets the thermal error flag (TEF) to '1'. All
outputs are latched off when TEF is set to '1' and remain off until the next grayscale cycle after the junction
temperature drops below (T_(TEF) – T_(HYS)). TEF is set to '0' once the junction temperature drops below (T_(TEF) –
T_(HYS)), but the outputs do not turn on until the first GSSCLK after BLANK goes low while TEF is set to '0'.
BLANK
GSSCLK
1234
4094 4096
4093 4095
123
IC Junction
Temperature (T_J)
T_J < T_(TEF) (Normal Temperature)
T_J ³ T_(TEF)
(High Temp)
T_J < T_(TEF) - T_(HYS) (Normal Temperature)
'1'
TEF
(Internal)
'0'
'0'
OUTn
OFF
ON
If T_J ³ T_(TEF) at this time,
then OUTn is not turned on.
Figure 26. TEF/TSD Timing
T_J ³ T_(TEF)
(High Temp)
'1'
Noise Reduction
Large surge currents may flow through the IC and the board on which the device is mounted if all 16 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 TLC5942 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 9. Both turn-on and turn-off are delayed.
POWER DISSIPATION CALCULATION
The device power dissipation must be below the power dissipation rate of the device package illustrated in
Figure 13 to ensure correct operation. Equation 4 calculates the power dissipation of the device:
DCn
P_D = (V_CC ´ I_CC) + V_OUT ´ I_MAX ´ N ´ _127d ´ d_PWM
(4)
Where:
V_CC = device supply voltage
I_CC = device supply current
V_OUT = OUTn voltage when driving LED current
I_MAX = LED current adjusted by R_(IREF) resistor
DCn = maximum dot correction value for OUTn (decimal)
N = number of OUTn driving LED at the same time
d_PWM = duty ratio defined by BLANK pin or GS PWM value
22
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