TLC5943_17 Datasheet, PDF (15/40 Pages) Texas Instruments – 16-Channel, 16-Bit PWM LED Driver with 7-Bit Global Brightness Control

TLC5943
www.ti.com
SBVS101 – DECEMBER 2007
DETAILED DESCRIPTION
Setting for the Maximum Constant Sink Current Value
On the TLC5943, the maximum constant current sink value for each channel, I_OLCMax, is determined by an
external resistor, R_IREF, placed between the IREF and GND pins. The R_IREF resistor value is calculated with
Equation 1:
R_IREF (kW) =
V_IREF (V)
I_OLCMax (mA)
´ 41
(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
brightness control data are set to the maximum value of 7Fh (127d). The sink current for each output can be
reduced by lowering the brightness control data.
R_IREF must be between 984 Ω (typ) and 9.84 kΩ (typ) in order to keep I_OLCMax between 5 mA and 50 mA. The
output may become unstable when I_OLCMax is set lower than 5 mA. However, output currents lower than 5 mA
can be achieved by setting I_OLCMax to 5 mA or higher, and then using brightness control to lower the output
current.
Figure 14 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)
50
45
40
35
30
25
20
15
10
5
R_IREF (Ω)
984
1093
1230
1406
1640
1968
2460
3280
4920
9840
Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): TLC5943
Submit Documentation Feedback
15