LM25007EVAL National Semiconductor, LM25007EVAL Datasheet

LM25007EVAL

Manufacturer Part Number

LM25007EVAL

Description

BOARD EVALUATION LM25007

Manufacturer

National Semiconductor

Datasheets

1.LM25007SDNOPB.pdf (12 pages)

2.LM25007EVAL.pdf (9 pages)

Specifications of LM25007EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

Current - Output

450mA

Voltage - Input

9 ~ 42V

Regulator Topology

Buck

Frequency - Switching

306kHz

Board Type

Fully Populated

Utilized Ic / Part

LM25007

Lead Free Status / RoHS Status

Not applicable / Not applicable

Power - Output

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LM25007 Evaluation Board

Introduction

The LM25007EVAL evaluation board provides the design

engineer with a fully functional buck regulator, employing the

constant on-time (COT) operating principle. This evaluation

board provides a 5V output over an input range of 9V - 42V.

The circuit delivers load currents to 450 mA, with current limit

at )670 mA. The board is populated with all external com-

ponents except C6 and C9. These components provide op-

tions for managing the output ripple as described later in this

document.

The board’s specification are:

Theory of Operation

Refer to the evaluation board schematic in Figure 5, which

contains a simplified block diagram of the LM25007. When

the circuit is in regulation, the buck switch is on each cycle

for a time determined by R1 and the input voltage according

to the equation:

The nominal switching frequency is calculated from:

The on-time in this evaluation board ranges from )1800 ns

at Vin = 9V, to )390 ns at Vin = 42V. The on-time varies

inversely with V

frequency, which is nominally 306 kHz in this evaluation

board . At the end of each on-time the Minimum Off-Timer

ensures the buck switch is off for at least 300 ns. In normal

operation the off-time is much longer. During the off-time the

output capacitor (C2) is discharged by the load current.

When the output voltage falls sufficiently that the voltage at

FB is below 2.5V, the regulation comparator initiates a new

to maintain a nearly constant switching

AN201850

FIGURE 1. Evaluation Board - Top Side

National Semiconductor

Application Note 1453

Dennis Morgan

March 2006

• Input Voltage: 9V to 42V

• Output Voltage: 5V

• Maximum load current: 450 mA

• Minimum load current: 0 mA

• Current Limit: )670 mA

• Measured Efficiency: 92.6% (V

• Nominal Switching Frequency: 306 kHz

• Size: 1.6 in. x 1.0 in. x 0.5 in

on-time period. For stable, fixed frequency operation, )25

mVp-p of ripple is required at FB to switch the regulation

comparator. Refer to the LM25007 data sheet for a more

detailed block diagram, and a complete description of the

various functional blocks.

Board Layout and Probing

The pictorial in Figure 1 shows the placement of the circuit

components. The following should be kept in mind when the

board is powered:

1) When operating at high input voltage and high load cur-

rent, forced air flow is recommended.

2) The LM25007 may be hot to the touch when operating at

high input voltage and high load current.

3) Use CAUTION when probing the circuit at high input

voltages to prevent injury, as well as possible damage to the

circuit.

4) Ensure the wires connecting this board to the load are

sized appropriately for the load current. Ensure there is not a

significant drop in the wires between this evaluation board

and the load.

Board Connection/Start-up

The input connections are made to the J1 connector. The

load is normally connected to the V1 and GND terminals of

the J3 connector. Ensure the wires are adequately sized for

20185001

= 9V, I

OUT

www.national.com

= 150 mA)

Related parts for LM25007EVAL

LM25007EVAL Summary of contents

Page 1

... LM25007 Evaluation Board Introduction The LM25007EVAL evaluation board provides the design engineer with a fully functional buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 5V output over an input range 42V. The circuit delivers load currents to 450 mA, with current limit at )670 mA ...

Page 2

Board Connection/Start-up the intended load current. Before start-up a voltmeter should be connected to the input terminals, and to the output termi- nals. The load current should be monitored with an ammeter or a current probe recommended that ...

Page 3

Output Ripple Control B) Intermediate Ripple Level Configuration: This configu- ration generates more ripple at V OUT1 FIGURE 3. Intermediate Ripple Level Configuration Using C6 and chosen to generate ≥ OUT1 minimum ripple current ...

Page 4

Output Ripple Control D) Alternate Low Ripple Configuration: A low ripple output can be obtained by connecting the load to V circuits of options above. Since R4 degrades load regulation, this alternative may be viable for applications ...

Page 5

... Unpopulated TDK C2012X7R2A222M Unpopulated Diodes Inc. DFLS160 Power DI 123 TDK SLF7045T-101MR50 Vishay CRCW08051153F Vishay CRCW08053011F Vishay CRCW2010000Z Vishay CRCW08052003F Vishay CRCW08051213F National Semiconductor LM25007MM 5 Package Value 1210 1.0 µF, 100V 1210 22 µF, 16V 0805 0.1 µF, 100V 0805 0.01 µF, 100V ...

Page 6

Circuit Performance www.national.com 20185012 FIGURE 6. Efficiency vs Load Current 20185013 FIGURE 7. Efficiency vs Input Voltage 6 ...

Page 7

Circuit Performance (Continued) FIGURE 9. Switching Frequency vs. Load Current 20185014 FIGURE 8. Output Voltage Ripple 20185015 7 www.national.com ...

Page 8

PCB Layout www.national.com Board Silkscreen Board Top Layer 8 20185016 20185017 ...

Page 9

... 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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