INPUT VOLTAGE (V)
EF
F
IC
IEN
C
Y
(%
)
100
95
90
85
80
75
40
45
50
55
60
65
70
75
User's Guide
SNVA390D – May 2009 – Revised May 2013
AN-1953 LM3409HV Evaluation Board
1
Introduction
This evaluation board showcases the LM3409HV PFET controller for a buck current regulator. It is
designed to drive 12 LEDs (V
O
= 42V) at a maximum average LED current (I
LED
= 1.5A) from a DC input
voltage (V = 48V). The switching frequency (f
SW
= 400 kHz) is targeted for the nominal operating point,
however f
SWIN
varies across the entire operating range. The circuit can accept an input voltage of 6V-75V.
However, if the input voltage drops below the regulated LED string voltage, the converter goes into
dropout and V
O
= V
IN
ideally.
The PCB is made using 4 layers of 2 oz. copper with FR4 dieletric. The evaluation board showcases all
features of the LM3409HV including analog dimming using the IADJ pin and internal PWM dimming using
the EN pin. High frequency external parallel FET shunt PWM dimming can also be evaluated. The board
has a header (J1) with a removable jumper, which is used to select the PWM dimming method.
The evaluation board has a right angle connector (J2) which can mate with an external LED load board
allowing for the LEDs to be mounted close to the driver. This reduces potential ringing when there is no
output capacitor. Alternatively, the LED+ and LED- turrets can be used to connect the LED load.
This board can be easily modified to demonstrate other operating points as shown in
Section 9
. The
Design Procedure section of the LM3409/3409HV/3409Q/3409QHV PFET Buck Controller for High
Power LED Drivers (
SNVS602
) data sheet can be used to design for any set of specifications.
Figure 1. Efficiency with 12 Series LEDS AT 1.5A
Since the board contains a buck regulator designed for 48V input, the efficiency is very high at input
voltages near or less than 48V. The switching frequency increases as input voltage increases, yielding
lower efficiency at higher input voltages. Note that increasing the off-time resistor (R6) will increase the
efficiency at high input voltage.
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1
SNVA390D – May 2009 – Revised May 2013
AN-1953 LM3409HV Evaluation Board
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