TS1518

Step-Up DC-DC Converter, White LED Driver

5/7

Version: B07

Application Information (Continue)

LED Current and Dimming Control

The LED’s current is set by a resistor connected at FB pin to GND using:

The maximum LED current set initially can be reduced by pulse width modulating the CTRL voltage from 0.4V to 1.8V.

A better approach is to adjust the feedback voltage for dimming control. Either a DC level signal or a filtered PWM

signal can be used to control the LED current as illustrated in below figures respectively. Using the above different

scheme, the LED current can be controlled from 0% to 100% to its maximum value.

Dimming Control using a DC Voltage

Dimming Control using a Filtered PWM Signal

LED

LED

R

mV

I

100

=

VDC(V)

VFB

Iout(mA)

2

0

0

1.8

2.2

0.43

1.6

9.2

1.8

1.4

19.6

3.6

1.2

31.1

6

1

43.4

8.5

0.8

63

12.3

0.6

74

14.5

0.4

86.4

16.9

0.2

96.9

19

0

102

20

Duty

Iout ( mA)

0%

20

20%

17.4

30%

15

40%

12.4

50%

10

60%

8

70%

6.4

80%

4.07

100%

0

PWM : 2V ; 1KHz ; Vin=3.6V