LM5039_1 Datasheet, PDF (1/14 Pages) National Semiconductor (TI) – Input Operating Range: 36V to 75V Output Voltage: 3.3V

LM5039 Evaluation Board
National Semiconductor
Application Note 2025
Ajay Hari
February 17, 2010
Introduction
The LM5039 evaluation board is designed to provide the de-
sign engineer with a fully functional power converter based
on the half-bridge topology to evaluate the LM5039 controller.
The evaluation board is provided in an industry standard
quarter brick footprint. The performance of the evaluation
board is as follows:
• Input Operating Range: 36V to 75V
• Output Voltage: 3.3V
• Measured Efficiency: 89% @ 30A, 92% @ 15A
• Frequency of Operation: 400 kHz
• Board Size: 2.28 x 1.45x 0.5 inches
• Load Regulation: 0.2%
• Line Regulation 0.1%
• Line UVLO (31V/30V on/off)
• Constant Current Limit
The printed circuit board consists of 6 layers, 2 ounce copper
outer layers, and 3 ounce copper inner layers on FR4 mate-
rial, with a total thickness of 0.062 inches. The unit is designed
for continuous operation at rated load at <40°C and a mini-
mum airflow of 200 CFM.
Theory of Operation
Power converters based on the half-bridge topology offer
high-efficiency and good power handling capability up to
500W. A simplified half bridge circuit is illustrated below. The
capacitors C1 and C2, which form one-half of the bridge, are
arranged in series such that the mid-point is at half the input
voltage. The other half of the bridge is formed by the switches
Q1 and Q2. Switches Q1 and Q2 are turned on alternatively
with a pulse-width determined by the input and output volt-
ages and the transformer turns ratio. Each switch, when
turned on, applies one-half the input voltage to the primary of
the transformer. The resulting secondary voltage is then rec-
tified and filtered with an LC filter to provide a smoothened
output voltage. In half-bridge topology, the primary switches
are turned on alternatively energizing the windings in such a
way that the flux swings back and forth in the first and the third
quadrants of the B-H curve. The use of two quadrants allows
better utilization of the core resulting in a smaller core volume
compared to the single-ended topologies such as a forward
converter.
Simplified Half-Bridge Circuit
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