LM3409HVEVAL: 1.5A @ 42V Max, 48V in

This evaluation board showcases the LM3409HV PFET controller for a buck current regulator. It is designed to drive 12 LEDs (VO = 42V) at a maximum average LED current (ILED = 1.5A) from a DC input voltage (VIN = 48V). The switching frequency (fSW = 400 kHz) is targeted for the nominal operating point, however fSW 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 VO = VIN ideally.

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.