TLC5922_14 Datasheet, PDF (7/19 Pages) Texas Instruments – LED DRIVER

TLC5922
www.ti.com
SLVS486B – SEPTEMBER 2003 – REVISED OCTOBER 2009
PRINCIPLES OF OPERATION
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 can be calculated by Equation 1:
IMAX
+
VIREF
RIREF
40
(1)
where:
V_IREF = 1.24V typ.
R_IREF = User selected external resistor (R_IREF should not be smaller than 600 Ω)
Figure 6 shows the maximum output current, I_O(LC), versus R_(IREF) . In Figure 6, R_(IREF) is the value of the resistor
between IREF terminal to ground, and I_O(LC) is the constant output current of OUT0,.....OUT15.
100 k
48.8 k
V_Outn = 1 V
DC = 127
10 k
9.76 k
4.88 k
2.44 k
1.63 k
1.22 k
1k
976 ₈₁₃
697
100
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
I_OLC − Output Current − mA
Figure 6. Reference Resistor vs Output Current
Setting Dot-Correction
The TLC5922 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. 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
Copyright © 2003–2009, Texas Instruments Incorporated
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