TLC5943_17 Datasheet, PDF (29/40 Pages) Texas Instruments – 16-Channel, 16-Bit PWM LED Driver with 7-Bit Global Brightness Control

TLC5943
www.ti.com
SBVS101 – DECEMBER 2007
Thermal Shutdown and Thermal Error Flag
The Thermal Shutdown (TSD) function turns off all of the constant current outputs on the IC immediately when
the junction temperature (T_J) exceeds the threshold (T_(TEF) = +162°C, typ) and sets the thermal error flag (TEF)
to '1'. The XERR pin goes low at the same time. The XERR pin level and the TEF level are kept until the first
SCLK falling edge after an XLAT falling edge of grayscale data. Then if T_J is still greater than T_(TEF), TEF
continues at '1' while XERR remains low. If T_J becomes less than T_(TEF) –T_(HYS), TEF is set to '0' and XERR
becomes Hi-Z. XERR is not forced to a Hi-Z state while BLANK is high. Therefore, the error type TEF or LOD
can be distinguished from the BLANK signal control. OUTn is turned on at the first GSCLK after the BLANK
falling edge if T_J becomes less than T_(TEF) – T_(HYS) at the BLANK rising edge.
When the IC powers on, TEF may be set and all output is forced off. Therefore, an XLAT pulse and a BLANK
rising edge should be input once to turn on the output. Figure 33 illustrates the TEF/TSD/XERR timing sequence.
BLANK
XLAT
SCLK
GSCLK
IC Junction
Temperature (T_J)
1234
T_J < T_(TEF)
TEF
(Internal)
XERR
'0'
'Hi-Z’
OFF
OUTn
ON
65,534 65,536
65,533 65,535
T_J ³ T_(TEF)
'1'
T_J < T_(TEF) - T_(HYS)
Low
('L')
OFF
Figure 33. TEF/TSD/XERR timing
123
'0'
T_J ³ T_(TEF)
POWER DISSIPATION CALCULATION
The device power dissipation must be below the power dissipation rate of the device package (illustrated in
Figure 15) to ensure correct operation. Equation 4 calculates the power dissipation of the device:
BCn
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
• BCn = maximum BC value for OUTn
• N = number of OUTn driving LED at the same time
• d_PWM = duty ratio defined by BLANK pin or GS PWM value
Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): TLC5943
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