NSC LM2670T-5.0, LM2670T-12, LM2670SX-ADJ, LM2670SX-5.0, LM2670SX-3.3 Datasheet

LM2670

SIMPLE SWITCHER

®

High Efficiency 3A Step-Down

Voltage Regulator with Sync

General Description

The LM2670 series of regulators are monolithic integrated

circuits which provide all of the active functions for a

step-down (buck) switching regulator capable of driving up to

3A loads with excellent line and load regulation characteris-

tics. High efficiency (

>

90

%

) is obtained through the use of a

low ON-resistance DMOS powerswitch. The series consists

of fixed output voltages of 3.3V, 5V and 12V and an adjust-

able output version.

The SIMPLE SWITCHER concept provides for a complete

design using a minimum number of external components.

The switching clock frequency can be provided by an inter-

nal fixed frequency oscillator (260KHz) or from an externally

provided clock in the range of 280KHz to 400Khz which al-

lows the use of physically smaller sized components.Afam-

ily of standard inductors for use with the LM2670 are avail-

able from several manufacturers to greatly simplify the

design process. The external Sync clock provides direct and

precise control of the output ripple frequency for consistent

filtering or frequency spectrum positioning.

The LM2670 series also has built in thermal shutdown, cur-

rent limiting and an ON/OFF control input that can power

down the regulator to a low 50µA quiescent current standby

condition. The output voltage is guaranteed to a

±

2

%

toler-

ance.

Features

n Efficiency up to 94

%

n Simple and easy to design with (using off-the-shelf

external components)

n 150 mΩ DMOS output switch

n 3.3V, 5V and 12V fixed output and adjustable (1.2V to

37V ) versions

n 50µA standby current when switched OFF

n

±

2

%

maximum output tolerance over full line and load

conditions

n Wide input voltage range: 8V to 40V

n External Sync clock capability (280KHz to 400KHz)

n 260 KHz fixed frequency internal oscillator

n −40 to +125˚C operating junction temperature range

Applications

n Simple to design, high efficiency (

>

90

%

) step-down

switching regulators

n Efficient system pre-regulator for linear voltage

regulators

n Battery chargers

n Communications and radio equipment regulator with

synchronized clock frequency

Typical Application

SIMPLE SWITCHER

®

is a registered trademark of National Semiconductor Corporation.

DS100942-3

August 1998

LM2670 SIMPLE SWITCHER High Efficiency 3A Step-Down Voltage Regulator with Sync

© 1999 National Semiconductor Corporation DS100942 www.national.com

Connection Diagram and Ordering Information

TO-263 Package

Top View

DS100942-1

Order Number

LM2670S-3.3, LM2670S-5.0,

LM2670S-12 or LM2670S-ADJ

See NSC Package Number TS7B

TO-220 Package

Top View

DS100942-2

Order Number

LM2670T-3.3, LM2670T-5.0,

LM2670T-12 or LM2670T-ADJ

See NSC Package Number TA07B

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Input Supply Voltage 45V

ON/OFF Pin Voltage −0.1V to 6V

Switch Voltage to Ground −1V to V

IN

Boost Pin Voltage V

SW

+8V

Feedback Pin Voltage −0.3V to 14V

Power Dissipation Internally Limited

ESD (Note 2) 2 kV

Storage Temperature Range −65˚C to 150˚C

Soldering Temperature

Wave 4 sec, 260˚C

Infrared 10 sec, 240˚C

Vapor Phase 75 sec, 219˚C

Operating Ratings

Supply Voltage 8V to 40V

Junction Temperature Range (T

J

) −40˚C to 125˚C

Thermal Resistance (θ

JA

) 30˚C/W

Thermal Resistance (θ

JC

) 2˚C/W

Electrical Characteristics Limits appearing in bold type face apply over the entire junction temperature

range of operation, −40˚C to 125˚C. Specifications appearing in normal type apply for T

A

=

T

J

=

25˚C. Sync pin open cir-

cuited.

LM2670-3.3

Symbol Parameter Conditions Typical Min Max Units

(Note 3) (Note 4) (Note 4)

V

OUT

Output Voltage V

IN

=

8V to 40V, 100mA ≤ I

OUT

≤ 3A 3.3 3.234/3.201 3.366/3.399 V

η Efficiency V

IN

=

12V, I

LOAD

=

3A 86

%

LM2670-5.0

Symbol Parameter Conditions Typical Min Max Units

(Note 3) (Note 4) (Note 4)

V

OUT

Output Voltage V

IN

=

8V to 40V, 100mA ≤ I

OUT

≤ 3A 5.0 4.900/4.850 5.100/5.150 V

η Efficiency V

IN

=

12V, I

LOAD

=

3A 88

%

LM2670-12

Symbol Parameter Conditions Typical Min Max Units

(Note 3) (Note 4) (Note 4)

V

OUT

Output Voltage V

IN

=

15V to 40V, 100mA ≤ I

OUT

≤ 3A 12 11.76/11.64 12.24/12.36 V

η Efficiency V

IN

=

24V, I

LOAD

=

3A 94

%

LM2670-ADJ

Symbol Parameter Conditions Typ Min Max Units

(Note 3) (Note 4) (Note 4)

V

FB

Feedback

Voltage

V

IN

=

8V to 40V, 100mA ≤ I

OUT

≤ 3A

V

OUT

Programmed for 5V

1.21 1.186/1.174 1.234/1.246 V

η Efficiency V

IN

=

12V, I

LOAD

=

3A 88

%

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All Output Voltage Versions

Electrical Characteristics

Limits appearing in bold type face apply over the entire junction temperature range of operation, −40˚C to 125˚C.

Specifications appearing in normal type apply for T

A

=

T

J

=

25˚C. Unless otherwise specified V

IN

=

12V for the 3.3V, 5V and

Adjustable versions and V

IN

=

24V for the 12V version, Sync pin open circuited..

Symbol Parameter Conditions Typ Min Max Units

DEVICE PARAMETERS

I

Q

Quiescent

Current V

FEEDBACK

=

8V 4.2 6 mA

For 3.3V, 5.0V, and ADJ Versions

V

FEEDBACK

=

15V

For 12V Versions

I

STBY

Standby

Quiescent

Current

ON/OFF Pin

=

0V

50 100/150 µA

I

CL

Current Limit 4.5 3.8/3.6 5.25/5.4 A

I

L

Output

Leakage

Current

V

IN

=

40V, ON/OFF Pin

=

0V

V

SWITCH

=

0V

V

SWITCH

=

−1V

16

200

15

µA

mA

R

DS(ON)

Switch

On-Resistance

I

SWITCH

=

3A

0.15 0.17/0.29 Ω

f

O

Oscillator

Frequency

Measured at Switch Pin

260 225 280 kHz

D Duty Cycle Maximum Duty Cycle 91

%

Minimum Duty Cycle 0

%

I

BIAS

Feedback Bias

Current

V

FEEDBACK

=

1.3V

ADJ Version Only

85 nA

V

ON/OFF

ON/OFF

Threshold

Voltage

1.4 0.8 2.0 V

I

ON/OFF

ON/OFF Input

Current

ON/OFF Input

=

0V

20 45 µA

F

SYNC

Synchronization

Frequency

V

SYNC

(Pin 5)

=

3.5V, 50

%

Duty Cycle

400 KHz

V

SYNC

SYNC

Threshold

Voltage

1.4 V

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings indicate conditions under which of the device is

guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test condition, see the electrical Char-

acteristics tables.

Note 2: ESD was applied using the human-body model, a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 3: Typical values are determined with T

A

=

T

J

=

25˚C and represent the most likely norm.

Note 4: All limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100

%

tested during production with T

A

=

T

J

=

25˚C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC) meth-

ods. All limits are used to calculateAverage Outgoing Quality Level (AOQL).

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Typical Performance Characteristics

Normalized

Output Voltage

DS100942-9

Line Regulation

DS100942-10

Efficiency vs Input Voltage

DS100942-11

Efficiency vs I

LOAD

DS100942-12

Switch Current Limit

DS100942-4

Operating Quiescent Current

DS100942-5

Standby Quiescent Current

DS100942-40

ON/OFF Threshold Voltage

DS100942-13

ON/OFF Pin Current (Sourcing)

DS100942-14

Switching Frequency

DS100942-15

Feedback Pin Bias Current

DS100942-16

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Block Diagram

DS100942-6

* Active Inductor Patent Number 5,514,947

†

Active Capacitor Patent Number 5,382,918

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Typical Performance Characteristics

Continuous Mode Switching Waveforms

V

IN

=

20V, V

OUT

=

5V, I

LOAD

=

3A

L

=

33 µH, C

OUT

=

200 µF, C

OUT

ESR

=

26 mΩ

DS100942-17

A: V

SW

Pin Voltage, 10 V/div.

B: Inductor Current, 1 A/div

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

Horizontal Time Base: 1 µs/div

Discontinuous Mode Switching Waveforms

V

IN

=

20V, V

OUT

=

5V, I

LOAD

=

500 mA

L

=

10 µH, C

OUT

=

400 µF, C

OUT

ESR

=

13 mΩ

DS100942-18

A: V

SW

Pin Voltage, 10 V/div.

B: Inductor Current, 1 A/div

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

Horizontal Time Base: 1 µs//iv

Load Transient Response for Continuous Mode

V

IN

=

20V, V

OUT

=

5V

L

=

33 µH, C

OUT

=

200 µF, C

OUT

ESR

=

26 mΩ

DS100942-19

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

B: Load Current: 500 mA to 3A Load Pulse

Horizontal Time Base: 100 µs/div

Load Transient Response for Discontinuous Mode

V

IN

=

20V, V

OUT

=

5V,

L

=

10 µH, C

OUT

=

400 µF, C

OUT

ESR

=

13 mΩ

DS100942-20

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

B: Load Current: 200 mA to 3A Load Pulse

Horizontal Time Base: 200 µs/div

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