TLC5940-EP Datasheet, PDF (17/33 Pages) Texas Instruments – 16-CHANNEL LED DRIVER WITH DOT CORRECTION AND GRAYSCALE PWM CONTROL

TLC5940-EP
www.ti.com
SLVSA51D – MARCH 2010 – REVISED MAY 2010
POWER DISSIPATION CALCULATION
The device power dissipation must be below the power dissipation rating of the device package to ensure correct
operation. Equation 7 calculates the power dissipation of device:
( ) ( ) ^P_D ^{= V}_CC ^{x I}_CC
+
V_OUT x I_MAX x
DCn
63
x d_PWM
xN
(7)
where:
V_CC: device supply voltage
I_CC: device supply current
V_OUT: TLC5940 OUTn voltage when driving LED current
I_MAX: LED current adjusted by R_(IREF) Resistor
DC_n: maximum dot correction value for OUTn
N: number of OUTn driving LED at the same time
d_PWM: duty cycle defined by BLANK pin or GS PWM value
OPERATING MODES
The TLC5940 has operating modes depending on the signals DCPRG and VPRG. Table 4 shows the available
operating modes. The TPS5940 GS operating mode (see Figure 12) and shift register values are not defined
after power up. One solution to solve this is to set dot correction data after TLS5940 power-up and switch back
to GS PWM mode. The other solution is to overflow the input shift register with 193 bits of dummy data and latch
it while TLS540 is in GS PWM mode. The values in the input shift register, DC register and GS register are
unknown just after power on. The DC and GS register values should be properly stored through the serial
interface before starting the operation.
SIGNAL
DCPRG VPRG
L
GND
H
L
H
V_CC
L
H
V_(VPRG)
Table 4. TLC5940 Operating Modes Truth Table
INPUT SHIFT REGISTER
MODE
192 bit
Grayscale PWM Mode
96 bit
Dot Correction Data Input Mode
X
EEPROM Programming Mode
DC VALUE
EEPROM
DC Register
EEPROM
DC Register
EEPROM
Write dc register value to EEPROM. (Default
data: 3Fh)
SETTING DOT CORRECTION
The TLC5940 has the capability to fine adjust the output current of each channel OUT0 to OUT15 independently.
This is also called dot correction. This feature is used to adjust the brightness deviations of LEDs connected to
the output channels OUT0 to OUT15. Each of the 16 channels can be programmed with a 6-bit word. The
channel output can be adjusted in 64 steps from 0% to 100% of the maximum output current I_max. Dot correction
for all channels must be entered at the same time. Equation 8 determines the output current for each output n:
IOUTn + Imax
DCn
63
(8)
where:
I_max = the maximum programmable output current for each output.
DCn = the programmed dot correction value for output n (DCn = 0 to 63).
n = 0 to 15
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): TLC5940-EP
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