NSC LM2674N-5.0, LM2674N-3.3, LM2674N-12, LM2674MX-ADJ, LM2674MX-5.0 Datasheet

...

September 1998

LM2674

SIMPLE SWITCHER® Power Converter High Efficiency

500 mA Step-Down Voltage Regulator

General Description

The LM2674 series of regulators are monolithic integrated circuits built with a LMDMOS process. These regulators provide all the active functions for a step-down (buck) switching regulator, capable of driving a 500 mA load current with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5.0V, 12V, and an adjustable output version.

Requiring a minimum number of external components, these regulators are simple to use and include patented internal frequency compensation (Patent Nos. 5,382,918 and 5,514,947) and a fixed frequency oscillator.

The LM2674 series operates at a switching frequency of 260 kHz, thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. Because of its very high efficiency (>90%), the copper traces on the printed circuit board are the only heat sinking needed.

A family of standard inductors for use with the LM2674 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies using these advanced ICs. Also included in the datasheet are selector guides for diodes and capacitors designed to work in switch-mode power supplies.

Other features include a guaranteed ±1.5% tolerance on output voltage within specified input voltages and output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring typically 50 µA stand-by current. The output switch includes current limiting, as well as thermal shutdown for full protection under fault conditions.

To simplify the LM2674 buck regulator design procedure, there exists computer design software, LM267X Made Simple.

Features

nEfficiency up to 96%

nAvailable in SO-8 and 8-pin DIP packages

nComputer Design Software LM267X Made Simple

nSimple and easy to design with

nRequires only 5 external components

nUses readily available standard inductors

n3.3V, 5.0V, 12V, and adjustable output versions

nAdjustable version output voltage range: 1.21V to 37V

n±1.5% max output voltage tolerance over line and load conditions

nGuaranteed 500mA output load current

n0.25Ω DMOS Output Switch

nWide input voltage range: 8V to 40V

n260 kHz fixed frequency internal oscillator

nTTL shutdown capability, low power standby mode

nThermal shutdown and current limit protection

Typical Applications

nSimple High Efficiency (>90%) Step-Down (Buck) Regulator

nEfficient Pre-Regulator for Linear Regulators

nPositive-to-Negative Converter

Typical Application

DS100041-1

SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.

Windows® is a registered trademark of Microsoft Corporation.

Voltage Down-Step mA 500 Efficiency High Converter Power SWITCHER SIMPLE LM2674

Regulator

© 1999 National Semiconductor Corporation

DS100041

www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Supply Voltage

45V

 

 

 

−0.1V VSH 6V

ON/OFF

Pin Voltage

Switch Voltage to Ground

−1V

Boost Pin Voltage

VSW + 8V

Feedback Pin Voltage

−0.3V VFB 14V

ESD Susceptibility

 

Human Body Model (Note 2)

2 kV

Power Dissipation

Internally Limited

Storage Temperature Range

−65ÊC to +150ÊC

Lead Temperature

 

M Package

 

Vapor Phase (60s)

+215ÊC

Infrared (15s)

+220ÊC

N Package (Soldering, 10s)

+260ÊC

Maximum Junction Temperature

+150ÊC

Operating Ratings

Supply Voltage

6.5V to 40V

Junction Temperature Range

−40ÊC TJ +125ÊC

Electrical Characteristics Specifications with standard type face are for TJ = 25ÊC, and those with bold type face apply over full Operating Temperature Range.

LM2674-3.3

Symbol

Parameter

Conditions

Typical

Min

Max

Units

 

 

 

(Note 4)

(Note 5)

(Note 5)

 

 

 

 

 

 

 

 

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

 

 

 

 

 

 

 

 

 

 

 

VOUT

Output Voltage

VIN = 8V to 40V, ILOAD = 20 mA to 500 mA

3.3

3.251/3.201

3.350/3.399

V

VOUT

Output Voltage

VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA

3.3

3.251/3.201

3.350/3.399

V

η

Efficiency

VIN = 12V, ILOAD = 500 mA

86

 

 

%

LM2674-5.0

Symbol

Parameter

Conditions

Typical

Min

Max

Units

 

 

 

(Note 4)

(Note 5)

(Note 5)

 

 

 

 

 

 

 

 

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

 

 

 

 

 

 

 

 

 

 

 

VOUT

Output Voltage

VIN = 8V to 40V, ILOAD = 20 mA to 500 mA

5.0

4.925/4.850

5.075/5.150

V

VOUT

Output Voltage

VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA

5.0

4.925/4.850

5.075/5.150

V

η

Efficiency

VIN = 12V, ILOAD = 500 mA

90

 

 

%

LM2674-12

Symbol

Parameter

Conditions

Typical

Min

Max

Units

 

 

 

(Note 4)

(Note 5)

(Note 5)

 

 

 

 

 

 

 

 

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

 

 

 

 

 

 

 

 

 

 

 

VOUT

Output Voltage

VIN = 15V to 40V, ILOAD = 20 mA to 500 mA

12

11.82/11.64

12.18/12.36

V

η

Efficiency

VIN = 24V, ILOAD = 500 mA

94

 

 

%

LM2674-ADJ

Symbol

Parameter

Conditions

Typ

Min

Max

Units

 

 

 

(Note 4)

(Note 5)

(Note 5)

 

 

 

 

 

 

 

 

SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3)

 

 

 

 

 

 

 

 

 

 

 

VFB

Feedback

VIN = 8V to 40V, ILOAD = 20 mA to 500 mA

 

 

 

 

 

Voltage

VOUT Programmed for 5V

1.210

1.192/1.174

1.228/1.246

V

 

 

(see Circuit of Figure 3)

 

 

 

 

 

 

 

 

 

 

 

VFB

Feedback

VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA

 

 

 

 

 

Voltage

VOUT Programmed for 5V

1.210

1.192/1.174

1.228/1.246

V

 

 

(see Circuit of Figure 3)

 

 

 

 

 

 

 

 

 

 

 

η

Efficiency

VIN = 12V, ILOAD = 500 mA

90

 

 

%

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2

All Output Voltage Versions

Electrical Characteristics

Specifications with standard type face are for TJ = 25ÊC, and those with bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable versions and VIN = 24V for the 12V version, and ILOAD = 100 mA.

Symbol

 

Parameters

 

 

 

Conditions

Typ

Min

Max

Units

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DEVICE PARAMETERS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IQ

Quiescent Current

VFEEDBACK = 8V

2.5

 

3.6

mA

 

 

 

 

For 3.3V, 5.0V, and ADJ Versions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VFEEDBACK = 15V

2.5

 

 

mA

 

 

 

 

For 12V Versions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ISTBY

Standby Quiescent

 

 

Pin = 0V

 

 

 

 

ON/OFF

50

 

100/150

µA

 

Current

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ICL

Current Limit

 

 

 

 

 

 

 

0.8

0.62/0.575

1.2/1.25

A

IL

Output Leakage Current

 

 

Pin = 0V

 

 

 

 

VIN = 40V, ON/OFF

1

 

25

µA

 

 

 

 

VSWITCH = 0V

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VSWITCH = −1V, ON/OFF

Pin = 0V

6

 

15

mA

RDS(ON)

Switch On-Resistance

ISWITCH = 500 mA

0.25

 

0.40/0.60

Ω

fO

Oscillator Frequency

Measured at Switch Pin

260

225

275

kHz

D

Maximum Duty Cycle

 

 

 

 

 

 

 

95

 

 

%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Minimum Duty Cycle

 

 

 

 

 

 

 

0

 

 

%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IBIAS

Feedback Bias

VFEEDBACK = 1.3V

85

 

 

nA

 

Current

ADJ Version Only

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VS/D

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ON/OFF

Pin

 

 

 

 

 

 

 

1.4

0.8

2.0

V

 

Voltage Thesholds

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IS/D

 

 

 

 

 

 

 

 

 

 

ON/OFF

Pin Current

ON/OFF Pin = 0V

20

7

37

µA

θJA

Thermal Resistance

N Package, Junction to Ambient (Note 6)

95

 

 

ÊC/W

 

 

 

 

M Package, Junction to Ambient (Note 6)

105

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 3: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator performance. When the LM2674 is used as shown in Figures 2, 3 test circuits, system performance will be as specified by the system parameters section of the Electrical Characteristics.

Note 4: Typical numbers are at 25ÊC and represent the most likely norm.

Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

Note 6: Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional copper area will lower thermal resistance further. See Application Information section in the application note accompanying this datasheet and the thermal model in LM267X Made Simple software.

3

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Connection Diagram and Ordering Information

8-Lead Package

Top View

DS100041-2

* No Connections

For Surface Mount Package

Order Number

LM2674M-3.3, LM2674M-5.0,

LM2674M-12 or LM2674M-ADJ

See NSC Package Number M08A

For DIP Package

Order Number

LM2674N-3.3, LM2674N-5.0,

LM2674N-12 or LM2674N-ADJ

See NSC Package Number N08E

Typical Performance Characteristics

Normalized

Line Regulation

Efficiency

Output Voltage

 

 

 

DS100041-4

DS100041-5

 

DS100041-3

 

Drain-to-Source

Switch Current Limit

Operating

Resistance

 

Quiescent Current

DS100041-7

DS100041-6

DS100041-8

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4

Typical Performance Characteristics (Continued)

Standby

 

 

 

 

 

 

ON/OFF Threshold

ON/OFF Pin

Quiescent Current

Voltage

Current (Sourcing)

 

DS100041-9

 

 

DS100041-10

DS100041-11

Switching Frequency

Feedback Pin

 

 

Bias Current

Peak Switch Current

DS100041-12

DS100041-13

DS100041-14

Dropout Voltage Ð 3.3V Option

Dropout Voltage Ð 5.0V Option

DS100041-15

DS100041-16

5

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NSC LM2674N-5.0, LM2674N-3.3, LM2674N-12, LM2674MX-ADJ, LM2674MX-5.0 Datasheet

Block Diagram

DS100041-17

* Active Inductor Patent Number 5,514,947

² Active Capacitor Patent Number 5,382,918

 

FIGURE 1.

Typical Performance Characteristics (Circuit of Figure 2)

Continuous Mode Switching Waveforms

Discontinuous Mode Switching Waveforms

VIN = 20V, VOUT = 5V, ILOAD = 500 mA

VIN = 20V, VOUT = 5V, ILOAD = 300 mA

L = 100 µH, C OUT = 100 µF, C OUTESR = 0.1Ω

L = 15 µH, C OUT = 68 µF (2x), C OUTESR = 25 mΩ

DS100041-18

DS100041-19

A: VSW Pin Voltage, 10 V/div.

A: VSW Pin Voltage, 10 V/div.

B: Inductor Current, 0.2 A/div

B: Inductor Current, 0.5 A/div

C: Output Ripple Voltage, 50 mV/div AC-Coupled

C: Output Ripple Voltage, 20 mV/div AC-Coupled

Horizontal Time Base: 1 µs/div

Horizontal Time Base: 1 µs/div

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6

Typical Performance Characteristics

Load Transient Response for Continuous Mode

VIN = 20V, VOUT = 5V,

L = 100 µH, C OUT = 100 µF, C OUTESR = 0.1Ω

(Circuit of Figure 2) (Continued)

Load Transient Response for Discontinuous Mode

VIN = 20V, VOUT = 5V,

L = 47 µH, C OUT = 68 µF, C OUTESR = 50 mΩ

DS100041-20

DS100041-21

A: Output Voltage, 100 mV/div, AC-Coupled.

A: Output Voltage, 100 mV/div, AC-Coupled.

B: Load Current: 100 mA to 500 mA Load Pulse

B: Load Current: 100 mA to 400 mA Load Pulse

Horizontal Time Base: 50 µs/div

Horizontal Time Base: 200 µs/div

Test Circuit and Layout Guidelines

DS100041-22

CIN - 22 µF, 50V Tantalum, Sprague ª199D Seriesº

COUT - 47 µF, 25V Tantalum, Sprague ª595D Seriesº

D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F

L1 - 68 µH Sumida #RCR110D-680L

CB - 0.01 µF, 50V Ceramic

FIGURE 2. Standard Test Circuits and Layout Guides

Fixed Output Voltage Versions

7

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