TLC59208F Datasheet, PDF (26/37 Pages) Texas Instruments – 8-BIT FM+ I2C BUS LED DRIVER

TLC59208F
SCLS715A – MARCH 2009 – REVISED NOVEMBER 2015
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10.2.2 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
(1)
V_RSET = 1.991 V
(2)
After calculating V_RSET, we can calculate R_SET:
V_RSET = I_LED × R_SET
(3)
1.991 V = 0.006 mA × R_SET
(4)
R_SET = 332 Ω
(5)
10.2.3 Application Curve
The following graph shows the typical LED Current as a function of R_SET and V_F. The graph assumes that V_LED =
5 V.
70
VF = 2 V
60
VF = 3 V
50
VF = 4 V
40
30
20
10
0
0
100 200 300 400 500 600 700
R_SET (Ÿ)
C001
Figure 21. LED Current vs R_SET
11 Power Supply Recommendations
TLC59208F operates from a V_CC range of 3 V to 5.5 V. The system will also require a power supply for the
LEDs. The supply voltage for the LEDs must be greater than the forward voltage of the LED plus the V_OL of the
channel.
26
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