TLC5924_16 Datasheet, PDF (8/28 Pages) Texas Instruments – 16-CHANNEL LED DRIVER WITH DOT CORRECTION AND PRE-CHARGE FET

TLC5924
SLVS626 – JUNE 2006
PRINCIPLES OF OPERATION
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Setting Maximum Channel Current
The maximum output current per channel is set by a single external resistor, R_(IREF), which is placed between
IREF and GND. The voltage on IREF is set by an internal band gap V_(IREF) with a typical value of 1.24V. The
maximum channel current is equivalent to the current flowing through R_(IREF) multiplied by a factor of 40. The
maximum output current per channel can be calculated by Equation 1:
IMAX
+
VIREF
RIREF
40
(1)
where:
V_IREF = 1.24V typ.
R_IREF = User selected external resistor ®_IREF should not be smaller than 600 Ω)
Figure 17 shows the maximum output current, I_OLC, versus R_(IREF) . In Figure 17, R_(IREF) is the value of the
resistor between IREF terminal to ground, and I_OLC is the constant output current of OUT0,.....OUT15. A variable
power supply may be connected to the IREF pin through a resistor to change the maximum output current per
channel. The maximum output per channel is 40 times the current flowing out of the IREF pin. The maximum
current from IREF equals 1.24V/600Ω.
Setting Dot-Correction
The TLC5924 has the capability to fine adjust the current of each channel, OUT0 to OUT15 independently. This
is also called dot correction. This feature is used to adjust the brightness deviations of LED connected to the
output channels OUT0 to OUT15. Each of the 16 channels can be programmed with a 7-bit word. The channel
output can be adjusted in 128 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 2 determines the output current for each OUTn:
IOutn
+
IMAX
127
DCn
(2)
where:
I_Max = the maximum programmable current of each output
DCn = the programmed dot-correction value for output n (DCn = 0, 1, 2 ...127)
n = 0, 1, 2 ... 15
Dot correction data are entered for all channels at the same time. The complete dot correction data format
consists of 16 x 7-bit words, which forms a 112-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. The DC15.6 in Figure 7 stands
for the 6^th most significant bit for output 15.
MSB
111
105 104
LSB
7
6
0
DC 15.6
DC 15.0 DC 14.6
DC 1.0 DC 0.6
DC 0.0
DC OUT15
DC OUT14 − DC OUT1
DC OUT0
Figure 7. DC Data Format
To input data into dot correction register, MODE must be set to high. The internal input shift register is then set
to 112-bit width. After all serial data is clocked in, a high level pulse of XLAT signal connects the serial data to
the dot correction register. The dot correction registers are level-triggered latches of XLAT signal. The serial
data is latched into the dot correction registers when XLAT goes low. The data in dot correction registers is held
constant when XLAT is low. BLANK signal does not need to be high to latch in new data. Since XLAT is a
level-triggered signal when MODE is high, SCLK and SIN must not be changed while XLAT is high. (Figure 16).
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