LM5026EVAL National Semiconductor, LM5026EVAL Datasheet

LM5026EVAL

Manufacturer Part Number

LM5026EVAL

Description

BOARD EVALUATION LM5026

Manufacturer

National Semiconductor

Series

PowerWise®r

Datasheets

1.LM5026MTNOPB.pdf (22 pages)

2.LM5026EVAL.pdf (14 pages)

Specifications of LM5026EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Isolated

Voltage - Output

3.3V

Current - Output

30A

Voltage - Input

36 ~ 78V

Regulator Topology

Buck

Frequency - Switching

230kHz

Board Type

Fully Populated

Utilized Ic / Part

LM5026

Lead Free Status / RoHS Status

Not applicable / Not applicable

Power - Output

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LM5026 Evaluation Board

Introduction

The LM5026 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

LM5026 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

• Output voltage: 3.3V

• Output current: 0 to 30A

• Measured efficiency: 90% 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

presently finding extensive use in medium level power con-

verters in the 50 to 200W range.

40˚C and a minimum airflow of 200

AN201546

National Semiconductor

Application Note 1387

Robert Bell

September 2005

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 65% (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

COMP input to the LM5026 greatly increases the achievable

loop bandwidth. The capacitance effect (and associated

pole) of the optocoupler is greatly reduced by holding the

voltage across the optocoupler constant. The LM5026 cur-

rent mode controller pulse width modulates the error signal

with a ramp signal derived from the transformer primary. A

standard “type II” (pole-zero-pole) is used as a compensa-

tion network. The LM5026 provides a controlled delay nec-

essary for the reset switch.

The evaluation board can be synchronized to an external

clock with a recommended frequency range of 230 to

300KHz.

www.national.com

Related parts for LM5026EVAL

LM5026EVAL Summary of contents

Page 1

... The active clamp reset mechanism is presently finding extensive use in medium level power con- verters in the 50 to 200W range. © 2005 National Semiconductor Corporation National Semiconductor Application Note 1387 Robert Bell September 2005 The Forward converter is derived from the Buck topology family, employing a single modulating power switch ...

Page 2

Theory of Operation Powering and Loading Considerations When applying power to the LM5026 evaluation board cer- tain precautions need to be followed. A mis-connection can damage the assembly. Proper Connections When operated at low input voltages the evaluation board can ...

Page 3

Powering Up (Continued) supply folding back and the evaluation board going into undervoltage shutdown will start an oscillation, or chatter, that may have undesirable consequences. A quick efficiency check is the best way to confirm that everything is operating properly. ...

Page 4

Performance Characteristics TURN-ON WAVEFORMS When applying power to the LM5026 evaluation board a certain sequence of events occurs. Soft-start capacitor val- ues and other components allow for a minimal output voltage for a short time until the feedback loop can ...

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 DESIGNATOR QTY ...

Page 8

Layout and Bill of Materials DESIGNATOR QTY www.national.com (Continued) TABLE 1. Bill of Materials (Continued) PART NUMBER DESCRIPTION LM5026MM CONTROLLER, NATIONAL SEMI MOCD207M OPTO-COUPLER, QT OPTO LM6132AIM OPAMP, NATIONAL SEMI LM4041CEM3-1.2 REFERENCE, ...

Page 9

PCB Layouts 20154609 9 www.national.com ...

Page 10

PCB Layouts (Continued) www.national.com 20154610 10 ...

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PCB Layouts (Continued) 20154611 11 www.national.com ...

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PCB Layouts (Continued) www.national.com 20154612 12 ...

Page 13

PCB Layouts (Continued) 20154613 13 www.national.com ...

Page 14

... BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that 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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