Datasheet

ILD4035
350 mA Step Down LED Driver
Thermal Characteristics
Data Sheet 13 Revision 2.0, 2011-08-17
Figure 3 Safe Operating Area
Figure 3 shows the safe operating area for the respective inductance values. The safe operating area consists of
the minimum and maximum allowed average LED current and the resulting voltage overhead. The voltage
overhead
V
overhead
is the difference between the supply voltage V
S
and the sum of the LED forward voltages V
ΣfLED
.
Example calculation 1
3 LEDs in series,
V
fLED
= 3V, I
LED
= 350 mA, V
S
= 12 V
V
overhead
= V
S
- V
ΣfLED
= 12 V - 9 V = 3 V
→ any of the above coil values can be used
Example calculation 2
6 LEDs in series,
V
fLED
= 3V, I
LED
= 250 mA, V
S
= 24 V
V
overhead
= V
S
- V
ΣfLED
= 24 V - 18 V = 6 V
→ the coil values needs to be at least 68 µH
Outside the safe operating area the switching frequency, hysteretic peak current and associated power dissipation
P
tot
of ILD4035 will increase beyond the maximum ratings.
0
5
10
15
20
25
30
35
40
45
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
V
S
- V
ΣfLED
[V]
Average LED current I
LED
[A]
47 μH
68 μH
100 μH
150 μH
220 μH
330 μH