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POWER DISSIPATION CALCULATION

P

=

V

x I

+

D

CC

CC

V

x I

OUT

MAX

x

DCn

63

x d

PWM

x N

(

(

)

)

(2)

OPERATING MODES

SETTING DOT CORRECTION

I

OUTn +

Imax

DCn

63

(3)

TLC5940

SLVS515A – DECEMBER 2004 – REVISED AUGUST 2005

The device power dissipation needs to be below the power dissipation rate of the device package to ensure

where:

N: number of OUTn driving LED at the same time

The TLC5940 has different operating modes depending on the signals VPRG and DCPRG. Table 3 shows the

available operating modes. The TLC5940 GS operating mode (see Figure 11) and shift register values are not

defined after power up. One solution to solve this is to set dot correction data after TLC5940 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 TLC5940 is in GS PWM mode.

Table 3. TLC5940 Operating Modes Truth Table

SIGNAL

INPUT SHIFT REGISTER

MODE

DC VALUE

DCPRG

VCPRG

L

EEPROM

GND

192 bit

Grayscale PWM Mode

H

DC Register

L

EEPROM

96 bit

Dot Correction Data Input Mode

H

DC Register

L

EEPROM

X

EEPROM Programming Mode

H

Write dc register value to EEPROM

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

determines the output current for each output n:

where:

DCn = the programmed dot correction value for output n (DCn = 0 to 63).

n = 0 to 15

Dot correction data are entered for all channels at the same time. The complete dot correction data format

consists of 16 x 6-bit words, which forms a 96-bit wide serial data packet. The channel data is put one after

another. All data is clocked in with MSB first. Figure 7 shows the DC data format.

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