TLC5944 Datasheet, PDF (15/34 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 6-Bit Dot Correction and Pre-Charge FET

TLC5944
www.ti.com ...................................................................................................................................................................................................... SBVS112 – JUNE 2008
DETAILED DESCRIPTION
Setting for the Maximum Constant Sink Current Value
On the TLC5944, the maximum constant current sink value for each channel, I_OLCMax, is determined by an
external resistor, R_IREF, and GND pins. The R_IREF resistor value is calculated with Equation 1:
R_IREF
(k )
W
=
V_IREF (V)
I_OLCMax (mA)
40.5
´
(1)
Where:
• V_IREF = the internal reference voltage on the IREF pin (typically 1.20 V)
I_OLCMax is the largest current for all outputs. Each output sinks the I_OLCMax current when it is turned on and the dot
correction is set to the maximum value of 3Fh (63d). The sink current for each output can be reduced by
lowering the respective output dot correction data.
R_IREF must be between 810 Ω (typ) and 24.3 kΩ (typ) in order to keep I_OLCMax between 2 mA and 60 mA. The
output may become unstable when I_OLCMax is set lower than 2 mA. However, output currents lower than 2 mA
can be achieved by setting I_OLCMax to 2 mA or higher, and then using dot correction to lower the output current.
Figure 17 in the Typical Characteristics and Table 1 show the characteristics of the constant sink current versus
the external resistor, R_IREF.
Table 1. Maximum Constant Current Output versus
External Resistor Value
I_OLCMax (mA, Typical)
60
55
50
45
40
35
30
25
20
15
10
5
2
R_IREF (Ω)
810
884
972
1080
1215
1389
1620
1944
2430
3240
4860
9720
24300
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): TLC5944
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