National Semiconductor LM2670 Technical data

February 29, 2008

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

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 step­down (buck) switching regulator capable of driving up to 3A
loads with excellent line and load regulation characteristics.
High efficiency (>90%) is obtained through the use of a low
ON-resistance DMOS power switch. The series consists of
fixed output voltages of 3.3V, 5V and 12V and an adjustable
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 internal fixed
frequency oscillator (260KHz) or from an externally provided
clock in the range of 280KHz to 400Khz which allows the use
of physically smaller sized components. A family of standard
inductors for use with the LM2670 are available 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, cur­rent 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% toler­ance.

Typical Application

Features

Efficiency up to 94%

■

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

■

external components)
150 mΩ DMOS output switch

■

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

■

37V ) versions

50μA standby current when switched OFF

■

±2%maximum output tolerance over full line and load

■

conditions
Wide input voltage range: 8V to 40V

■

External Sync clock capability (280KHz to 400KHz)

■

260 KHz fixed frequency internal oscillator

■

−40 to +125°C operating junction temperature range

■

Applications

Simple to design, high efficiency (>90%) step-down

■

switching regulators
Efficient system pre-regulator for linear voltage regulators

■

Battery chargers

■

Communications and radio equipment regulator with

■

synchronized clock frequency

10094203

SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation

© 2008 National Semiconductor Corporation 100942 www.national.com

Connection Diagrams and Ordering Information

LM2670

TO-263 Package

Top View

Order Number

LM2670S-3.3, LM2670S-5.0,

LM2670S-12 or LM2670S-ADJ

See NSC Package Number TS7B

10094201

Top View

TO-220 Package

Top View

Order Number

LM2670T-3.3, LM2670T-5.0,

LM2670T-12 or LM2670T-ADJ

See NSC Package Number TA07B

10094202

See NS package Number SRC14A

LLP-14

10094241

Ordering Information for LLP Package

Output Voltage Order Information Package Marking Supplied As

12 LM2670SD-12 S0002LB 250 Units on Tape and Reel

12 LM2670SDX-12 S0002LB 2500 Units on Tape and Reel

3.3 LM2670SD-3.3 S0002NB 250 Units on Tape and Reel

3.3 LM2670SDX-3.3 S0002NB 2500 Units on Tape and Reel

5.0 LM2670SD-5.0 S0002PB 250 Units on Tape and Reel

5.0 LM2670SDX-5.0 S0002PB 2500 Units on Tape and Reel

ADJ LM2670SD-ADJ S0002RB 250 Units on Tape and Reel

ADJ LM2670SDX-ADJ S0002RB 2500 Units on Tape and Reel

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LM2670

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 (Note 12) −1V to V

Boost Pin Voltage VSW + 8V

Feedback Pin Voltage −0.3V to 14V
Power Dissipation Internally Limited

IN

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 (TJ)

−40°C to 125°C

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 TA = TJ = 25°C. Sync pin open circuited.

LM2670-3.3

Symbol Parameter Conditions Typical Min Max Units

V

OUT

η

Output Voltage

Efficiency VIN = 12V, I

VIN = 8V to 40V, 100mA ≤ I

LOAD

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

≤ 3A

OUT

= 3A 86 %

3.3 3.234/3.201 3.366/3.399 V

LM2670-5.0

Symbol Parameter Conditions Typical Min Max Units

V

OUT

η

Output Voltage

Efficiency VIN = 12V, I

VIN = 8V to 40V, 100mA ≤ I

LOAD

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

≤ 3A

OUT

= 3A 88 %

5.0 4.900/4.850 5.100/5.150 V

LM2670-12

Symbol Parameter Conditions Typical Min Max Units

V

OUT

η

Output Voltage

Efficiency VIN = 24V, I

VIN = 15V to 40V, 100mA ≤ I

LOAD

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

≤ 3A

OUT

= 3A 94 %

12 11.76/11.64 12.24/12.36 V

LM2670-ADJ

Symbol Parameter Conditions Typ Min Max Units

V

FB

η

Feedback Voltage

Efficiency VIN = 12V, I

VIN = 8V to 40V, 100mA ≤ I
V

Programmed for 5V

OUT

LOAD

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

≤ 3A

OUT

= 3A 88 %

1.21 1.186/1.174 1.234/1.246 V

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All Output Voltage Versions Electrical Characteristics

LM2670

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 TA = TJ = 25°C. Unless otherwise specified VIN=12V for the 3.3V, 5V and Ad­justable versions and VIN=24V for the 12V version, Sync pin open circuited..

Symbol Parameter Conditions Typ Min Max Units

DEVICE PARAMETERS

I

Q

I

STBY

I

CL

I

L

R

DS(ON)

f

O

D Duty Cycle Maximum Duty Cycle 91 %

I

BIAS

V

ON/OFF

I

ON/OFF

F

SYNC

V

SYNC

θ

JA

(Note 5)

θ

JA

(Note 6)

θ

JC

θ

JA

(Note 7)

θ

JA

(Note 8)

θ

JA

(Note 9)

θ

JC

θ

JA

(Note 10)

θ

JA

Quiescent Current V

FEEDBACK

= 8V

4.2

6 mA

For 3.3V, 5.0V, and ADJ Versions

V

FEEDBACK

= 15V

For 12V Versions

Standby Quiescent
Current

Current Limit

Output Leakage
Current

Switch On­Resistance

Oscillator
Frequency

ON/OFF Pin = 0V

VIN = 40V, ON/OFF Pin = 0V
V

= 0V

SWITCH

V

= −1V

SWITCH

I

= 3A

SWITCH

Measured at Switch Pin

50 100/150

4.5 3.8/3.6 5.25/5.4 A

16

0.15

200

15

0.17/0.29

260 225 280 kHz

Minimum Duty Cycle 0 %

Feedback Bias
Current

ON/OFF
Threshold Voltage

ON/OFF Input
Current

Synchronization
Frequency

SYNC Threshold
Voltage

Thermal

V

FEEDBACK

ADJ Version Only

ON/OFF Input = 0V

V

SYNC

= 1.3V

(Pin 5)=3.5V, 50% Duty Cycle

85

nA

1.4 0.8 2.0 V

20

400

1.4

45

T Package, Junction to Ambient 65

Resistance

T Package, Junction to Ambient 45

T Package, Junction to Case 2

S Package, Junction to Ambient 56

S Package, Junction to Ambient 35

S Package, Junction to Ambient 26

S Package, Junction to Case 2 ++

SD Package, Junction to Ambient 55

SD Package, Junction to Ambient 29

(Note 11)

μA

μA

mA

Ω

μA

KHz

V

°C/W

°C/W

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
Characteristics tables.

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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 TA = TJ = 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 TA = TJ = 25°C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC)
methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

Note 5: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with ½ inch leads in a socket, or on a
PC board with minimum copper area.

Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with ½ inch leads soldered to a PC
board containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.

Note 7: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.136 square inches (the same size as
the TO-263 package) of 1 oz. (0.0014 in. thick) copper.

Note 8: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.4896 square inches (3.6 times the area
of the TO-263 package) of 1 oz. (0.0014 in. thick) copper.

Note 9: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board copper area of 1.0064 square inches (7.4 times
the area of the TO-263 package) of 1 oz. (0.0014 in. thick) copper. Additional copper area will reduce thermal resistance further. See the thermal model in Switchers
Made Simple® software.

Note 10: Junction to ambient thermal resistance for the 14-lead LLP mounted on a PC board copper area equal to the die attach paddle.

Note 11: Junction to ambient thermal resistance for the 14-lead LLP mounted on a PC board copper area using 12 vias to a second layer of copper equal to die

attach paddle. Additional copper area will reduce thermal resistance further. For layout recommendations, refer to Application Note AN-1187.

Note 12: The absolute maximum specification of the 'Switch Voltage to Ground' applies to DC voltage. An extended negative voltage limit of -8V applies to a
pulse of up to 20 ns, -6V of 60 ns and -3V of up to 100 ns.

LM2670

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Typical Performance Characteristics

LM2670

Normalized

Output Voltage

Efficiency vs Input Voltage

10094209

Line Regulation

Efficiency vs I

10094210

LOAD

Switch Current Limit

10094211

10094204

10094212

Operating Quiescent Current

10094205

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LM2670

Standby Quiescent Current

10094240

ON/OFF Pin Current (Sourcing)

ON/OFF Threshold Voltage

10094213

Switching Frequency

Feedback Pin Bias Current

10094214

10094216

10094215

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Typical Performance Characteristics

LM2670

Continuous Mode Switching Waveforms

VIN = 20V, V

L = 33 μH, C

A: VSW Pin Voltage, 10 V/div.

B: Inductor Current, 1 A/div

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

= 200 μF, C

OUT

Horizontal Time Base: 1 μs/div

Load Transient Response for Continuous Mode

VIN = 20V, V

L = 33 μH, C

= 200 μF, C

OUT

OUT

= 5V, I

OUT

= 3A

LOAD

ESR = 26 mΩ

OUT

10094217

= 5V

ESR = 26 mΩ

OUT

Discontinuous Mode Switching Waveforms

VIN = 20V, V

L = 10 μH, C

A: VSW Pin Voltage, 10 V/div.

B: Inductor Current, 1 A/div

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

OUT

= 400 μF, C

OUT

= 5V, I

= 500 mA

LOAD

ESR = 13 mΩ

OUT

10094218

Horizontal Time Base: 1 μs//iv

Load Transient Response for Discontinuous Mode

L = 10 μH, C

VIN = 20V, V

= 400 μF, C

OUT

OUT

= 5V,

OUT

ESR = 13 mΩ

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

10094219

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

Horizontal Time Base: 100 μs/div

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

10094220

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

Horizontal Time Base: 200 μs/div