LM5025EVAL National Semiconductor, LM5025EVAL Datasheet

LM5025EVAL

Manufacturer Part Number

LM5025EVAL

Description

EVALUATION BOARD FOR LM5025

Manufacturer

National Semiconductor

Series

PowerWise®r

Datasheets

1.LM5025SDNOPB.pdf (16 pages)

2.LM5025EVAL.pdf (14 pages)

Specifications of LM5025EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

3.3V

Current - Output

30A

Voltage - Input

36 ~ 72V

Regulator Topology

Buck

Frequency - Switching

230kHz

Board Type

Fully Populated

Utilized Ic / Part

LM5025

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Power - Output

Other names

*LM5025EVAL
*LM5025EVAL/NOPB
LM5025EVAL

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LM5025A Evaluation Board

Introduction

The LM5025A evaluation board is designed to provide the

design engineer with a fully functional power converter

based on the Active Clamp Forward topology to evaluate the

LM5025A controller. The evaluation board is provided in an

industry standard half-brick footprint.

The performance of the evaluation board is as follows:

• Input range: 36V to 78V (100V peak)

• Output voltage: 3.3V

• Output current: 0 to 30A

• Measured efficiency: 90.5% at 30A, 92.5% at 15A

• Frequency of operation: 230kHz

• Board size: 2.3 x 2.4 x 0.5 inches

• Load Regulation: 1%

• Line Regulation: 0.1%

• Line UVLO, Hiccup Current Limit

The printed circuit board consists of 4 layers of 3 ounce

copper on FR4 material with a total thickness of 0.050

inches. Soldermask has been omitted from some areas to

facilitate cooling. The unit is designed for continuous opera-

tion at rated load at

CFM.

Theory of Operation

Power converters based on the Forward topology offer high

efficiency and good power handling capability in applications

up to several hundred Watts. The operation of the trans-

former in a forward topology does not inherently self-reset

each power switching cycle, a mechanism to reset the trans-

former is required. The active clamp reset mechanism is

40˚C and a minimum airflow of 200

AN201276

National Semiconductor

Application Note 1345

Robert Bell

December 2004

presently finding extensive use in medium level power con-

verters in the 50 to 200W range.

The Forward converter is derived from the Buck topology

family, employing a single modulating power switch. The

main difference between the topologies are, the Forward

topology employs a transformer to provide input / output

ground isolation and a step down or step up function.

Each cycle, the main primary switch turns on and applies the

input voltage across the primary winding, which has 12

turns. The transformer secondary has 2 turns, leading to a

6:1 step-down of the input voltage. For an output voltage of

3.3V the required duty cycle (D) of the main switch must vary

from approximately 60% (low line) to 25% (high line). The

clamp capacitor along with the reset switch reverse biases

the transformer primary each cycle when the main switch

turns off. This reverse voltage resets the transformer. The

clamp capacitor voltage is Vin / (1-D).

The secondary rectification employs self-driven synchronous

rectification to maintain high efficiency and ease of drive.

Feedback from the output is processed by an amplifier and

reference, generating an error voltage, which is coupled

back to the primary side control through an optocoupler. The

LM5025A voltage mode controller pulse width modulates the

error signal with a ramp signal derived from the input volt-

age. Deriving the ramp signal slope from the input voltage

provides line feed-forward, which improves line transient

rejection. The LM5025A also provides a controlled delay

necessary for the reset switch.

The evaluation board can be synchronized to an external

clock with a recommended frequency range of 190 to

300KHz.

www.national.com

Related parts for LM5025EVAL

LM5025EVAL Summary of contents

Page 1

... Watts. The operation of the trans- former in a forward topology does not inherently self-reset each power switching cycle, a mechanism to reset the trans- former is required. The active clamp reset mechanism is © 2004 National Semiconductor Corporation National Semiconductor Application Note 1345 Robert Bell ...

Page 2

Theory of Operation Powering and Loading Considerations When applying power to the LM5025A evaluation board certain precautions need to be followed. A failure or mis- connection can present itself in a very alarming manner. Proper Connections When operated at low ...

Page 3

Powering Up (Continued) the wattage of the load. As you remove the connection from the shutdown pin to ground, immediately check for 3.3 volts at the output. A most common occurrence, that will prove unnerving, is when the current limit ...

Page 4

Performance Characteristics TURN-ON WAVEFORMS When applying power to the LM5025A evaluation board a certain sequence of events must occur. Soft-start capacitor values and other components allow the feedback loop to stabilize without overshoot. Figure 1 shows the output volt- age ...

Page 5

Performance Characteristics (Continued) Conditions: Input Voltage = 78VDC Output Current = 25A Trace 1: Q1 drain voltage Volts/div = 20V Horizontal Resolution = 1µs/div FIGURE 5. Conditions: Input Voltage = 48VDC Output Current = 5A Synchronous rectifier, Q3 gate Volts/div ...

Page 6

www.national.com 6 ...

Page 7

Layout and Bill of Materials The Bill of Materials is shown below and includes the manu- facturer and part number. The layers of the printed circuit board are shown in top down order. View is from the top Bill of ...

Page 8

Layout and Bill of Materials Bill of Materials (Continued) DESIGNATOR QTY R9,R10 R11 1 R12,R15,R18,R26 4 R13 1 R14 1 R23,R24 2 R27 1 R28 1 R30 ...

Page 9

PCB Layouts 20127610 9 www.national.com ...

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PCB Layouts (Continued) www.national.com 20127611 10 ...

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PCB Layouts (Continued) 20127612 11 www.national.com ...

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PCB Layouts (Continued) www.national.com 20127613 12 ...

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PCB Layouts (Continued) 20127614 13 www.national.com ...

Page 14

... BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. ...

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