LM25010EVAL National Semiconductor, LM25010EVAL Datasheet

LM25010EVAL

Manufacturer Part Number

LM25010EVAL

Description

BOARD EVALUATION LM25010

Manufacturer

National Semiconductor

Datasheets

1.LM25010SDNOPB.pdf (18 pages)

2.LM25010EVAL.pdf (6 pages)

Specifications of LM25010EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

Current - Output

Voltage - Input

6 ~ 42V

Regulator Topology

Buck

Frequency - Switching

200kHz

Board Type

Fully Populated

Utilized Ic / Part

LM25010

Lead Free Status / RoHS Status

Not applicable / Not applicable

Power - Output

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LM25010 Evaluation Board

Introduction

The LM25010EVAL 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 6V - 42V.

The circuit delivers load currents to 1A, with current limit set

at )1.3A. The board is populated with all external compo-

nents except R6 and C9-C11. These components provide

options for reducing output ripple as described later in this

document.

The board’s specification are:

Theory of Operation

Refer to the evaluation board schematic in Figure 3, which

contains a simplified block diagram of the LM25010. When

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

for a time determined by R1 and V

tion:

The on-time of this evaluation board ranges from )5000 ns

at V

inversely with V

frequency. At the end of each on-time the Minimum Off-

Timer ensures the buck switch is off for at least 260 ns. In

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

off-time, the output capacitor (C7) is discharged by the load

current. When the output voltage falls sufficiently that the

voltage at FB is below 2.5V, the regulation comparator ini-

tiates a new on-time period. For stable, fixed frequency

operation, )25 mV of ripple is required at FB to switch the

regulation comparator. Refer to the LM25010 data sheet for

a more detailed block diagram, and a complete description

of the various functional blocks.

= 6V, to )650 ns at V

to maintain a nearly constant switching

= 42V. The on-time varies

according to the equa-

AN201760

FIGURE 1. Evaluation Board - Top Side

National Semiconductor

Application Note 1431

Dennis Morgan

December 2005

• Input Voltage: 6V to 42V

• Output Voltage: 5V

• Maximum load current: 1.0A

• Minimum load current: 0A

• Current Limit: 1.3A

• Measured Efficiency: 95.5% (V

• Nominal Switching Frequency: 200 kHz

• Size: 2.25 in. x 0.88 in. x 0.47 in

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 necessary.

2) The LM25010, and the diode D1 will 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) At maximum load current (1A), the wire size and length

used to connect the load becomes important. 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 OUT1 and GND terminals

of the J3 connector. Ensure the wires are adequately sized

for the intended load current. Before start-up a voltmeter

should be connected to the input terminals, and to the output

terminals. The load current should be monitored with an

= 6V, I

OUT

20176001

www.national.com

= 200 mA)

Related parts for LM25010EVAL

LM25010EVAL Summary of contents

Page 1

... LM25010 Evaluation Board Introduction The LM25010EVAL 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 1A, with current limit set at )1 ...

Page 2

Board Connection/Start-up ammeter or a current probe recommended that the input voltage be increased gradually to 6V, at which time the output voltage should be 5V. If the output voltage is correct with then ...

Page 3

... R2, 3 Resistor R4 Resistor Switching Regulator National Semiconductor LM25010MH particular application, R5 must be added to the board. Refer (Continued) to the LM25010 data sheet to determine the appropriate value for this resistor. Minimum Load Current OUT2 The LM25010 requires a minimum load current of )500 µA to ensure the boost capacitor (C6) is recharged sufficiently during each off-time ...

Page 4

FIGURE 4. Efficiency vs Load Current FIGURE 5. Efficiency FIGURE 6. Voltage Ripple OUT1 4 20176008 20176009 20176010 OUT2 ...

Page 5

PCB Layout Board Silkscreen Board Top Layer Board Bottom Layer (viewed from top) 5 20176011 20176012 20176013 www.national.com ...

Page 6

... 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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