TLC5926 Datasheet, PDF (15/29 Pages) Texas Instruments – 16-CHANNEL CONSTANT-CURRENT LED SINK DRIVERS

TLC5926, TLC5927
www.ti.com ....................................................................................................................................................................................................... SLVS677 – JULY 2008
APPLICATION INFORMATION
Operating Principles
Constant Current
In LED display applications, TLC5926/TLC5927 provides nearly no current variations from channel to channel
and from IC to IC. While I_OUT ≤ 50 mA, the maximum current skew between channels is less than ±6% and
between ICs is less than ±6%.
Adjusting Output Current
TLC5926/TLC5927 scales up the reference current, I_ref, set by the external resistor R_ext to sink a current, I_out, at
each output port. Users can follow the below formulas to calculate the target output current I_OUT,target in the
saturation region:
V_R-EXT = 1.26 V × VG
I_ref = V_R-EXT/R_ext, if another end of the external resistor R_ext is connected to ground.
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, and 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.
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
I_OUT,target = (1.25 V/R_ext) × 15
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 11.
140
120
100
80
40
0
0 500 1000 1500 2000 2500 3000 3500 4000
R
ext
–
W
Figure 11. Default Relationship Curve Between I_OUT,target and R_ext
Copyright © 2008, Texas Instruments Incorporated
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Product Folder Link(s): TLC5926 TLC5927