LM2651EVAL National Semiconductor, LM2651EVAL Datasheet

LM2651EVAL

Manufacturer Part Number

LM2651EVAL

Description

EVALUATION BOARD FOR LM2651

Manufacturer

National Semiconductor

Datasheets

1.LM2651MTC-3.3NOPB.pdf (11 pages)

2.LM2651EVAL.pdf (4 pages)

Specifications of LM2651EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

2.5V

Current - Output

1.5A

Voltage - Input

4 ~ 14V

Regulator Topology

Buck

Frequency - Switching

300kHz

Board Type

Fully Populated

Utilized Ic / Part

LM2651

Lead Free Status / RoHS Status

Lead free / RoHS Compliant

Power - Output

Other names

*LM2651EVAL

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LM2651_EVAL

1.5A High Efficiency

Synchronous Switching

Regulator Evaluation Board

Introduction

The LM2651 switching regulator provides high efficiency

power conversion over a 100:1 load range (1.5A to 15mA).

This feature makes the LM2651 an ideal fit in battery powered

applications.

Synchronous rectification and 75 mΩ internal switches pro-

vide up to 97% efficiency. At light loads, the LM2651 enters

a low power hysteretic or sleep mode to keep the efficiency

high. In many applications, the efficiency still exceeds 80% at

15 mA load.

A shutdown pin is available to disable the LM2651 and reduce

the supply current to 7 µA. The IC contains patented current

sensing circuitry for current mode control. This feature elimi-

nates the external current sensing required by other current

mode DC to DC converters. The IC has a 300kHz fixed fre-

quency internal oscillator. The high oscillator frequency al-

lows the use of extremely small, low profile components.

The evaluation board can be obtained by ordering part num-

ber LM2651_EVAL from your local National Semiconductor

sales office, or National's website at www.national.com.

Evaluation Board Design

The evaluation board is designed to supply 1.8V, 2.5V, 3.3V

or adjustable output voltages at 15 mA up to 1.5A. The eval-

uation board comes with a design to supply an output voltage

of 2.5V with input voltage range of 4V to 14V and output cur-

rent range of 15 mA to 1.5A. The design can easily be

modified to provide other output voltage using the equation

below to change the ratio of the feedback resistors R1 and

R2:

FIGURE 1. LM2651_EVAL Schematic for Adjustable Voltage

101237

National Semiconductor

Application Note 1147

Ifeanyi Nwachukwu

October 2007

The feedback resistors should not be made arbitrarily large

as this would create a high impedance node at the feedback

pin that is more susceptible to noise. A combined value of 50

kΩ for the two resistors is adequate.

Components were selected based on the design procedure

in the LM2651 datasheet. PCB layout is critical to reduce

noise and ensure specified performance for any power supply

design. To minimize the parasitic inductance in the loop of

input capacitors and the internal MOSFETs, connect the ca-

pacitors to V

This is important because the rapidly switching current, to-

gether with wiring inductance can generate large voltage

spikes that may cause noise problems. Locate the feedback

resistors close to the IC and keep the feedback trace as short

as possible. Do not run any feedback traces near the switch

node and keep away from the flux field of the inductor. The

schematic is shown in Figure 1. The parts list of the design is

shown in Table 1. The pictorial representations of the layout

top, bottom and silkscreen layers are shown at the end of this

application note.

When an undervoltage situation occurs, the output voltage

can be pulled below ground as the inductor current is reversed

through the synchronous FET. For applications which need

to be protected from a negative voltage, a clamping diode D2

is recommended. When used, D2 should be connected cath-

ode to V

mum of 2A is recommended.

OUT

and anode to ground. A diode rated for a mini-

and PGND pins with short and wide traces.

10123702

www.national.com

Related parts for LM2651EVAL

LM2651EVAL Summary of contents

Page 1

... The high oscillator frequency al- lows the use of extremely small, low profile components. The evaluation board can be obtained by ordering part num- ber LM2651_EVAL from your local National Semiconductor sales office, or National's website at www.national.com. Evaluation Board Design The evaluation board is designed to supply 1.8V, 2.5V, 3.3V or adjustable output voltages ...

Page 2

Ref Designator U1 L1 CIN CSS CC2 CC1 COUT CIN2 Operating the Evaluation Board SETUP The LM2651_EVAL evaluation board comes ready to be test- ed. The only setup needed is connecting the input voltage to ...

Page 3

Notes 3 www.national.com ...

Page 4

... National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. ...

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