Datasheet

ILD4035
350 mA Step Down LED Driver
Basic Application Information
Data Sheet 17 Revision 2.0, 2011-08-17
PWM Dimming
Besides the analog dimming functionality the EN/PWM pin acts as input for a pulse width modulated (PWM) signal
to control the dimming of the LED string. For PWM dimming the signal's logic high level should be at least 2.5 V
and the PWM frequency should be lower than 5 kHz. For the ILD4035/4001 demo board a dimming frequency less
than 330 Hz is recommended to maintain a maximum contrast ratio of 100:1. The achieveable contrast ratio is
shown on Figure 4 based on the measured average LED current deviating 3 dB from the linear reference. The
maximum contrast ratio depends mainly on the rise time of the inductor current and is thus dependent on supply
voltage, inductor size and LED string forward voltage.
I
LED
versus V
EN
, T
A
=25 °C I
LED
(relative) versus V
EN
, T
A
=25 °C
I
LED
versus V
EN
, 333 mΩ, 100 µH
0
0.1
0.2
0.3
0.4
1 1.5 2 2.5 3
I
LED
[A]
V
EN
[V]
303 mΩ, 100 μH
333 mΩ, 100 μH
600 mΩ, 100 μH
1200 mΩ, 220 μH
0
10
20
30
40
50
60
70
80
90
100
110
1 1.5 2 2.5 3
I
LED
[%]
V
EN
[V]
303 mΩ, 100 μH
333 mΩ, 100 μH
600 mΩ, 100 μH
1200 mΩ, 220 μH
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
1 1.5 2 2.5 3
I
LED
[A]
V
EN
[V]
-40 °C
25 °C
85 °C
105 °C