TLC5945 Datasheet, PDF (14/29 Pages) Texas Instruments – 16-CHANNEL LED DRIVER WITH DOT CORRECTION AND GRAYSCALE PWM CONTROL

TLC5945
SLVS755 – MARCH 2007
www.ti.com
POWER DISSIPATION CALCULATION
The device power dissipation needs to be below the power dissipation rate of the device package to ensure
correct operation. Equation 7 calculates the power dissipation of device:
ǒ Ǔ ǒ Ǔ PD + VCC
ICC ) VOUT
IMAX
N
DCn
63
dPWM
(7)
where:
V_CC: device supply voltage
I_CC: device supply current
V_OUT: TLC5945 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 TLC5945 has two operating modes defined by MODE as shown in Table 4. The GS and DC registers are
set to random values that are not known just after power on. The GS and DC values must be programmed
before turning on the outputs. Please note that when initially setting GS and DC data after power on, the GS
data must be set before the DC data is set. Failure to set GS data before DC data may result in the first bit of
GS data being lost. XLAT must be low when the MODE pin goes high-to-low or low-to-high to change back and
forth between GS mode and DC mode.
MODE
GND
V_CC
Table 4. TLC5945 Operating Modes Truth Table
INPUT SHIFT REGISTER
192 bit
96 bit
OPERATING MODE
Grayscale PWM Mode
Dot Correction Data Input Mode
SETTING DOT CORRECTION
The TLC5945 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. The
TEST pin must be connected to VCC to ensure proper operation of the dot correction circuitry. 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
14
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