TLC59108F_15 Datasheet, PDF (26/37 Pages) Texas Instruments – 8-Bit FM+ I2C Bus LED Driver

TLC59108F
SLDS162B – MARCH 2009 – REVISED DECEMBER 2015
9.2 Typical Application
This application example provides guidance on how to set the LED current using the TLC59108F.
V_LED
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3.3V or 5V
R_SET
SCL
SDA
RESET
Microcontroller
SCL
SDA
RESET
A0-A3
VDD
OUT7
OUT6
OUT5
TLC59108F
OUT1
OUT0
GND
Figure 23. Typical Application
9.2.1 Design Requirements
For this design example, use the following as the input parameters listed in Table 11.
Table 11. Design Parameters
DESIGN PARAMETERS
V_LED
Supply voltage that
powers LED
V_F
Forward voltage across
the LED
I_LED
Current flowing through
the LED
R_ON
Resistance across open-
drain output
EXAMPLE VALUE
5V
3V
6 mA
1.5 Ω
9.2.2 Detailed Design Procedure
In the LED current path, there are three voltage drops that must be considered:
• Drop across the series resistor (V_RSET)
• Drop across the LED (V_F)
• Drop across the open-drain output channel (V_O)
The drop across the LED is defined above as V_F = 3 V. The drop across the open-drain output is calculated as
R_ON × I_LED (1.5 × 0.006 = 0.009 V). The remaining voltage must be across the series resistor:
5 V = 3 V + 0.009 V + V_RSET
(3)
V_RSET = 1.991 V
(4)
After calculating V_RSET, we can calculate R_SET using Equation 5, Equation 6, and Equation 7 :
V_RSET = I_LED × R_SET
(5)
1.991 V = 0.006 mA × R_SET
(6)
R_SET = 332 Ω
(7)
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