Texas Instruments Evaluation Boards for LM25037 - Dual PWM Controller with Alternating Outputs LM25037EVAL/NOPB LM25037EVAL/NOPB Scheda Tecnica
Codici prodotto
LM25037EVAL/NOPB
User's Guide
SNVA352C – July 2008 – Revised May 2013
AN-1861 LM25037 Evaluation Board
1
Introduction
The LM25037 evaluation board is designed to provide the design engineer with a fully functional power
converter based on push-pull topology to evaluate the LM25037 controller. The performance of the
evaluation board is as follows:
converter based on push-pull topology to evaluate the LM25037 controller. The performance of the
evaluation board is as follows:
Input Operating Range: 16 to 32V
Output Voltage: 5.0V
Output Current: 0 to 10A
Measured Efficiency: 88% @ 10A Load and 24V Input
Frequency of Operation: 250 kHz
Board Size: 3.5x2.25x0.05 inches
Load Regulation: 2%
Line UVLO (14V rising / 11V falling)
The printed circuit board consists of 4 layers of 2 oz copper on FR4 material, with a thickness of 0.050 in.
The unit is designed for continuous operation at rated load at <40°C and a minimum airflow of 200 LFM.
The unit is designed for continuous operation at rated load at <40°C and a minimum airflow of 200 LFM.
2
Theory of Operation
Push-Pull topology consists of two MOSFETs on the primary side driven 180 degrees out of phase. When
either MOSFET is turned on, a voltage equal to "Vin-V
either MOSFET is turned on, a voltage equal to "Vin-V
ds(on)
", is applied across one half of the power
transformer’s primary. Where, V
ds(on)
is the drain to source voltage across the MOSFET when turned ON.
The center-tapped secondary of the transformer has 2 turns in each winding, resulting in a 2:1 step-down
of the voltage applied across the primary. The transformer secondary voltage is then rectified and filtered
with an LC filter to provide the output voltage.
of the voltage applied across the primary. The transformer secondary voltage is then rectified and filtered
with an LC filter to provide the output voltage.
In a push-pull topology, the primary MOSFETS are turned on alternatively energizing the windings in such
a way that the flux swings back and forth in the first and third quadrants of B-H curve. The use of two
quadrants allows better utilization of the core resulting in a smaller core volume compared to single-ended
topologies such as a forward converter.
a way that the flux swings back and forth in the first and third quadrants of B-H curve. The use of two
quadrants allows better utilization of the core resulting in a smaller core volume compared to single-ended
topologies such as a forward converter.
The feedback resistors are set so that at the desired output voltage, the voltage at the feedback pin is
equal to the internal reference voltage (1.25V). The LM25037 has been configured for current mode
control. Current mode control inherently provides line voltage feed-forward, cycle-by-cycle current limiting
and ease of loop compensation as it removes the additional pole due to output inductor. Hence, a
standard “type II” network is used for the compensation.
equal to the internal reference voltage (1.25V). The LM25037 has been configured for current mode
control. Current mode control inherently provides line voltage feed-forward, cycle-by-cycle current limiting
and ease of loop compensation as it removes the additional pole due to output inductor. Hence, a
standard “type II” network is used for the compensation.
In this particular evaluation board, the output inductor not only smoothes the output voltage waveform, but
also generates an auxiliary voltage (by means of its secondary winding). This feature reduces power
dissipation within the IC, thereby increasing reliability and efficiency. The evaluation board can be
synchronized to an external clock with a recommended frequency range of 275 kHz to 500 kHz.
also generates an auxiliary voltage (by means of its secondary winding). This feature reduces power
dissipation within the IC, thereby increasing reliability and efficiency. The evaluation board can be
synchronized to an external clock with a recommended frequency range of 275 kHz to 500 kHz.
All trademarks are the property of their respective owners.
1
SNVA352C – July 2008 – Revised May 2013
AN-1861 LM25037 Evaluation Board
Copyright © 2008–2013, Texas Instruments Incorporated