LM25037EVAL National Semiconductor, LM25037EVAL Datasheet

LM25037EVAL

Manufacturer Part Number

LM25037EVAL

Description

BOARD EVAL FOR LM25037

Manufacturer

National Semiconductor

Series

PowerWise®r

Datasheets

1.LM25037MTNOPB.pdf (24 pages)

2.LM25037EVAL.pdf (12 pages)

Specifications of LM25037EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Isolated

Voltage - Output

Current - Output

10A

Voltage - Input

16 ~ 32V

Regulator Topology

Buck

Frequency - Switching

250kHz

Board Type

Fully Populated

Utilized Ic / Part

LM25037

Silicon Manufacturer

National

Silicon Core Number

LM25037

Kit Application Type

Power Management - Voltage Regulator

Application Sub Type

PWM Controllers

Kit Contents

Board

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Power - Output

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LM25037 Evaluation Board

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:

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 de-

signed for continuous operation at rated load at <40°C and a

minimum airflow of 200 CFM.

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

one half of the power transformer’s primary. Where, V

the drain to source voltage across the MOSFET when turned

ON.

ds(on)

300666

", is applied across

Typical Push-Pull Circuit

ds(on)

National Semiconductor

Application Note 1861

Ajay Hari

December 18, 2008

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 volt-

age 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.

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 config-

ured for current mode control. Current mode control inher-

ently 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 in-

creasing reliability and efficiency. The evaluation board can

be synchronized to an external clock with a recommended

frequency range of 275 kHz to 500 kHz.

www.national.com

30066601

Related parts for LM25037EVAL

LM25037EVAL Summary of contents

Page 1

... When either MOSFET is turned on, a voltage equal to "Vin-V one half of the power transformer’s primary. Where, V the drain to source voltage across the MOSFET when turned ON. © 2008 National Semiconductor Corporation National Semiconductor Application Note 1861 Ajay Hari December 18, 2008 ...

Page 2

Powering and Loading Considerations When applying power to the LM25037 evaluation board cer- tain precautions should be followed. A misconnection can damage the assembly. PROPER CONNECTIONS When operated at low input voltages the evaluation board can draw ...

Page 3

Performance Characteristics Once the circuit is powered up and running normally, the out- put voltage is regulated to 5.0V, with the accuracy determined by feedback resistors and bandgap reference voltage inside the IC. When the load current is varied from ...

Page 4

Figure 4 shows the transient response for a load of change from 5A to 10A. The upper trace shows minimal output volt- age droop and overshoot during the sudden change in output current shown by the lower trace. Conditions: Input ...

Page 5

5 www.national.com ...

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PCB Layout www.national.com Bottom Layer Bottom Layer Silk Screen 6 30066610 30066611 ...

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Mid Layer-1 Mid Layer-2 7 30066612 30066613 www.national.com ...

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Top Layer Top Layer Silk Screen 8 30066614 30066615 ...

Page 9

Part Value Package C1, C2, 4.7 µF C1210 C3 C4 1500 pF C0603 C5 0.1 µF C0805 C6 1.0 µF C0603 C7, C20 0.1 µF C0603 C8 2200 pF C0603 C9 0.68 µF C0805 C10 220 pF C0603 C11 10,000 ...

Page 10

Part Value Package R7 499 R0603 R8 4.22k R0603 R9 4.02k R0603 R10 12.1k R0603 R11 NU R0603 R12, 10.0 R0805 R13 R14 0.027 R0830 R15 10.0 R0603 R16, 10.0 R2010 R17 R18 10.0 R1206 R19 NU R0805 U1 National ...

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11 www.national.com ...

Page 12

... For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers www.national.com/amplifiers Audio www.national.com/audio Clock and Timing www.national.com/timing Data Converters www.national.com/adc Interface www.national.com/interface LVDS www.national.com/lvds Power Management www.national.com/power Switching Regulators www.national.com/switchers LDOs www.national.com/ldo LED Lighting www ...

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