Datasheet

ILD4035
350 mA Step Down LED Driver
Basic Application Information
Data Sheet 16 Revision 2.0, 2011-08-17
6 Basic Application Information
This section covers the basic information required for calculating the parameters for a certain LED application.
For detailed application information please check the Application Note AN215 (Driving 1 W LEDs with ILD4035)
or visit our web site http://www.infineon.com/led.appnotes
6.1 Setting the average LED current
The average output current for the LEDs is set by the external sense resistor R
sense
. To calculate the value of this
resistor a first approximation can be calculated using Equation (2).
V
sense
is dependent on the supply voltage V
S
and the number of LEDs in series.
(2)
Example calculation 1
V
S
= 12 V, 100 µH, V
fLED
= 3 V, 3 LEDs in series
→
V
sense
= 114 mV
I
LED
= 375 mA
→
R
sense
= 303 mΩ
Example calculation 2
V
S
= 24 V, 100 µH, V
fLED
= 3 V, 6 LEDs in series
→
V
sense
= 106 mV
I
LED
= 350 mA
→
R
sense
= 303 mΩ
An easy way to achieve these resistor values is to connect standard resistors in parallel
6.2 Dimming of the LEDs
Analog voltage dimming
The voltage level of the EN/PWM pin can be used for analog dimming of the LED current. To achieve a linear
change in LED current versus control voltage the recommended voltage range at the EN/PWM pin is 1 V to 2 V.
The maximum achievable LED current is defined by resistor
R
sense
. The maximum LED current will be achieved for
V
EN
≥ 2.5 V. Below 0.4 V the ILD4035 is set to standby mode and the output is switched off. The typical dimming
performance is shown in below figures.
LED
sense
sense
I
V
R =