LM2744EVAL National Semiconductor, LM2744EVAL Datasheet

LM2744EVAL

Manufacturer Part Number

LM2744EVAL

Description

BOARD EVALUATION LM2744

Manufacturer

National Semiconductor

Series

PowerWise®r

Datasheets

1.LM2744MTCXNOPB.pdf (24 pages)

2.LM2744EVAL.pdf (7 pages)

Specifications of LM2744EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

1.2V

Current - Output

3.5A

Voltage - Input

1.8 ~ 5.5V

Regulator Topology

Buck

Frequency - Switching

1MHz

Board Type

Fully Populated

Utilized Ic / Part

LM2744

Lead Free Status / RoHS Status

Not applicable / Not applicable

Power - Output

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LM2744 Evaluation Board

Introduction

This application notes describes the LM2743 printed circuit

board (PCB) design and provides an example typical appli-

cation circuit. The demo board allows component design

flexibility in order to demonstrate the versatility of the

LM2744 IC.

The demo board contains a voltage-mode, high-speed syn-

chronous buck regulator controller with an external adjust-

able reference voltage between 0.5V and 1.5V. The demo

board design incorporates the LM4140 high precision low

noise reference IC providing 1.0V to the reference pin

to 6V (V

supply rails (V

frequency, adjustable from 50 kHz to 1 MHz with one exter-

nal resistor.

The demo board design regulates to an output voltage of

1.2V at 3.5A with a switching frequency of 1MHz. Note, the

demo board is optimized for a 1MHz, 14V input voltage

compensation design; if another switching frequency and

input voltage is desired, please consult the LM2744 data

sheet for control loop compensation procedures. For addi-

tional design modifications refer to the Design Consideration

section of the LM2744 data sheet.

Additional Footprints

A Schottky diode footprint (D1) is available in parallel to the

low side MOSFET. This component can improve efficiency,

due to the lower forward drop than the low side MOSFET

body diode conducting during the anti-shoot through period.

Select a Schottky diode that maintains a forward drop

around 0.4 to 0.6V at the maximum load current (consult the

I-V curve). In addition select the reverse breakdown voltage

to have sufficient margin above the maximum input voltage.

Footprint C13 is available for a multilayer ceramic capacitor

(MLCC) connected as close as possible to the source of the

low side MOSFET and drain of the high side MOSFET. This

will provide low supply impedance to the high speed switch

currents, thus minimizing the input supply noise. For ex-

ample; a MLCC is used (C13) in combination with aluminum

REF

). Though the control sections of the IC are rated for 3

), the driver sections are designed to accept input

) as high as 14V. It operates at a fixed-

AN201343

National Semiconductor

Application Note 1357

Ricardo Capetillo

October 2005

electrolytic input filter capacitors, placed in designators C12

and C14, because MLCC have lower impedance than elec-

trolytics. If MLCCs are used in designators C12 and C14

component C13 is not necessary.

The PCB is designed on two layers with 1oz. copper on a

62mil FR4 laminate.

Guidelines for Additional Options

When using a DC power supply to set a reference voltage

the DC power supply. A good starting point is 10µF, but may

need to be varied depending on the magnitude of the DC

power supply noise (any make of capacitor will do as long as

the capacitance is maintained within the operating tempera-

ture range). Remove R10 and place a zero ohm jumper in

designator R12 .

Designators R12 and R13 are provided for DDR SDRAM

(double data rate synchronous dynamic random access

memory) active termination design. Set V

supply voltage by using designators R12 and R13 as a

voltage divider. Remove resistors R7, R10 and capacitor

C21, and connect the DDR supply voltage rail to terminal

sink or source current in excess of 3A – a load transient

response applied to the output of Figure 2 is provided in

Figure 3.

Do not exceed 5.6V on the VCC pin of the demo board. The

board layout connects together both the input voltage of the

LM4140-1.0 (pin 2) and the control section of the LM2744

(VCC). The maximum DC supply voltage for the control

section of the LM2744 is 6V, while 5.6V is the maximum

rating for any input pin of the LM4140. If the design requires

the control section of the LM2744 to be 6V, a shunt zener

reference may be placed at designator location (D3) to main-

tain the input voltage of the LM4140 between 1.8V and 5.5V.

The cathode of the zener is connected to the input of the

LM4140 and the anode to GND. The resistance of R10 must

be selected to supply the appropriate amount of biasing

current into the zener and the LM4140 (refer to the Electrical

Characteristic table of the LM4140 data sheet).

DCS

REF

, refer to Figure 2. The modified circuit in Figure 1 can

), connect a capacitor (C20) from V

DCS

REF

to half the DDR

to GND to filter

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Related parts for LM2744EVAL

LM2744EVAL Summary of contents

Page 1

... MOSFET and drain of the high side MOSFET. This will provide low supply impedance to the high speed switch currents, thus minimizing the input supply noise. For ex- ample; a MLCC is used (C13) in combination with aluminum © 2005 National Semiconductor Corporation National Semiconductor Application Note 1357 Ricardo Capetillo ...

Page 2

Typical Application Circuit The typical application circuit in figure 1 provides the com- ponent designators used on the demo board. www.national.com FIGURE 1. Typical Application FIGURE 2. DDR SDRAM Termination Supply 2 20134301 20134302 ...

Page 3

Performance Characteristics Load Transient Response ± FIGURE 3. 3A Load Transient Response Applied to circuit in Figure 3.3V and OUT coupled and 5A/ DIV ...

Page 4

Performance Characteristics Switch Node Voltage and Output Ripple Voltage FIGURE 1.2V, OUT 1MHz. LOAD SW 20 MHz Bandwidth Limit FIGURE ...

Page 5

... Schottky Diode, SOD-123 Inductor 1µH, 5.3Arms, 10.2mΩ Dual N-MOSFET 20V, 24mΩ DS FIGURE 9. Complete Demo Board Schematic 5 Part Number National Semiconductor National Semiconductor Murata GRM216R61E105KA12B Vishay VJ0805Y123KXX Vishay VJ0805Y122KXX Vishay VJ0805A150KAA Vishay VJ0805Y104KXX Vishay VJ0805Y182KXX AVX 12103D106MAT AVX 12103D106MAT Sanyo 6TPD470 ...

Page 6

PCB Layout Diagram(s) www.national.com FIGURE 10. Top Layer and Top Overlay FIGURE 11. Bottom Layer 6 20134310 20134311 ...

Page 7

... 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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