TLC5916-Q1_16 Datasheet, PDF (24/34 Pages) Texas Instruments – 8-Bit Constant-Current LED Sink Drivers

TLC5916-Q1, TLC5917-Q1
SLVS814A – JANUARY 2008 – REVISED MAY 2015
10 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
10.1 Application Information
10.1.1 Constant Current
In LED display applications, the TLC591x-Q1 provides nearly no current variations from channel to channel and
from IC to IC. While I_OUT ≤ 100 mA, the maximum current skew between channels is less than ±3% and between
ICs is less than ±6%.
10.1.2 Adjusting Output Current
The TLC591x-Q1 scales up the reference current, I_ref, set by the external resistor R_ext to sink a current, I_out, at
each output port. Use the following formulas to calculate the target output current
I_OUT,target in the saturation region:
(1)
I_ref = V_R-EXT/R_ext, if another end of the external resistor R_ext is connected to groundV_R-EXT = 1.26 V × VG
(2)
I_OUT,target = I_ref × 15 × 3^{CM – 1}
where
• R_ext is the resistance of the external resistor connected to the R-EXT terminal.
• V_R-EXT is the voltage of R-EXT, which is controlled by the programmable voltage gain (VG), which is defined by
the Configuration Code.
(3)
The Current Multiplier (CM) determines that the ratio I_OUT,target/I_ref is 15 or 5. After power on, the default value of
VG is 127/128 = 0.992, and the default value of CM is 1, so that the ratio I_OUT,target/I_ref = 15. Based on the default
VG and CM.
V_R-EXT = 1.26 V × 127/128 = 1.25 V
(4)
I_OUT,target = (1.25 V/R_ext) × 15
(5)
Therefore, the default current is approximately 52 mA at 360 Ω and 26 mA at 720 Ω. The default relationship
after power on between I_OUT,target and R_ext is shown in Figure 19.
140
120
100
80
40
0
0 500 1000 1500 2000 2500 3000 3500 4000
R_ext – Ω
Figure 19. Default Relationship Curve Between I_OUT,target and R_ext After Power Up
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