Texas Instruments LM3409HV, User Manual

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I
LED
(
A
)
V
SW
(
V
)
140
120
100
80
60
40
20
0
-20
I
LED
200 ns/DIV
0.0
V
SW
0.1
0.2
I
L
ED
(
A
)
V
SW
(
V
)
140
120
100
80
60
40
20
0
-20
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
I
LED
400 ns/DIV
V
SW
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Alternate Designs
Figure 10. Analog dimming minimum (V
ADJ
= 0V) Figure 11. Analog dimming maximum (V
ADJ
open)
9 Alternate Designs
Alternate designs with the LM3409HV evaluation board are possible with very few changes to the existing
hardware. The evaluation board FETs and diodes are already rated higher than necessary for design
flexibility. The input UVLO can remain the same and the input capacitance is sufficient for most designs,
though the input voltage ripple will change. Other designs can evaluated by changing R6, R9, L1, and C8.
The table below gives the main specifications for five different designs and the corresponding values for
R6, R9, L1 and C8. The RMS current rating of L1 should be at least 50% higher than the specified I
LED
.
Designs 3 and 5 are optimized for best analog dimming range, while designs 1, 2, and 4 are optimized for
best PWM dimming range. These are just examples, however any combination of specifications can be
achieved by following the Design Procedure in the LM3409/3409HV/3409Q/3409QHV PFET Buck
Controller for High Power LED Drivers (
SNVS602 data sheet.
Table 2. Alternate Designs
Specification / Design 1 Design 2 Design 3 Design 4 Design 5
Component
Dimming Method PWM PWM Analog PWM Analog
V
IN
24V 36V 48V 65V 75V
V
O
14V 24V 35V 56V 42V
f
SW
500 kHz 450 kHz 300 kHz 350 kHz 300 kHz
I
LED
1A 700 mA 2A 3A 1.5A
Δ i
LED
450 mA 250 mA 70 mA 1A 80 mA
R6 15.4 k Ω 25.5 k Ω 46.4 k Ω 24.9 k Ω 95.3 k Ω
R9 0.2 Ω 0.3 Ω 0.12 Ω 0.07 Ω 0.15 Ω
L1 22 µH 68 µH 150 µH 15 µH 330 µH
C8 None None 2.2 µF None 2.2 µF
13 SNVA390D – May 2009 – Revised May 2013 AN-1953 LM3409HV Evaluation Board
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