TLC5945
www.ti.com
SLVS755–MARCH 2007
POWER DISSIPATION CALCULATION
The device power dissipation needs to be below the power dissipation rate of the device package to ensure
correct operation. Equation 7ǒcaVlculates the power dissipation of device:
Ǔ
DC
n
+ ǒVCC CCǓ)
P
I
I
N
d
D
OUT
MAX
PWM
63
(7)
where:
VCC: device supply voltage
ICC: device supply current
VOUT: TLC5945 OUTn voltage when driving LED current
IMAX: LED current adjusted by R(IREF) Resistor
DCn: maximum dot correction value for OUTn
N: number of OUTn driving LED at the same time
dPWM: 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.
Table 4. TLC5945 Operating Modes Truth Table
MODE
GND
VCC
INPUT SHIFT REGISTER
OPERATING MODE
Grayscale PWM Mode
192 bit
96 bit
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 Imax. 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:
DCn
63
I
+ I
max
OUTn
where:
(8)
Imax = 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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