NSC LM2673T-ADJ, LM2673T-12, LM2673SX-ADJ, LM2673SX-3.3, LM2673SX-12 Datasheet

April 2000

LM2673

SIMPLE SWITCHER® 3A Step-Down Voltage Regulator with Adjustable Current Limit

General Description

The LM2673 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 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. A high fixed frequency oscillator (260KHz) allows the use of physically smaller sized components. A family of standard inductors for use with the LM2673 are available from several manufacturers to greatly simplify the design process.

Other features include the ability to reduce the input surge current at power-ON by adding a softstart timing capacitor to gradually turn on the regulator. The LM2673 series also has built in thermal shutdown and resistor programmable current limit of the power MOSFET switch to protect the device and load circuitry under fault conditions. The output voltage is guaranteed to a ±2% tolerance. The clock frequency is controlled to within a ±11% tolerance.

Features

nEfficiency up to 94%

nSimple and easy to design with (using off-the-shelf external components)

nResistor programmable peak current limit over a range of 2A to 5A.

n150 mΩ DMOS output switch

n3.3V, 5V and 12V fixed output and adjustable (1.2V to 37V ) versions

n±2%maximum output tolerance over full line and load conditions

nWide input voltage range: 8V to 40V

n260 KHz fixed frequency internal oscillator

nSoftstart capability

n−40 to +125ÊC operating junction temperature range

Applications

nSimple to design, high efficiency (>90%) step-down switching regulators

nEfficient system pre-regulator for linear voltage regulators

nBattery chargers

Typical Application

DS100913-3

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

Limit Current Adjustable with Regulator Voltage Down-Step 3A SWITCHER SIMPLE LM2673

© 2000 National Semiconductor Corporation

DS100913

www.national.com

LM2673

Connection Diagram and Ordering Information

TO-263 Package

Top View

DS100913-1

Order Number

LM2673S-3.3, LM2673S-5.0,

LM2673S-12 or LM2673S-ADJ

See NSC Package Number TS7B

TO-220 Package

Top View

DS100913-2

Order Number

LM2673T-3.3, LM2673T-5.0,

LM2673T-12 or LM2673T-ADJ

See NSC Package Number TA07B

www.national.com

2

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
Softstart Pin Voltage	−0.1V to 6V
Switch Voltage to Ground	−1V to V IN
Boost Pin Voltage	VSW + 8V
Feedback Pin Voltage	−0.3V to 14V
Power Dissipation	Internally Limited
ESD (Note 2)	2 kV

Storage Temperature Range	−65ÊC to 150ÊC
Soldering Temperature
Wave	4 sec, 260ÊC
Infrared	10 sec, 240ÊC
Vapor Phase	75 sec, 219ÊC

Operating Ratings

Supply Voltage	8V to 40V
Junction Temperature Range (TJ)	−40ÊC to 125ÊC

Electrical Characteristics Limits appearing in bold type face apply over the entire junction temperature range of operation, −40ÊC to 125ÊC. Specifications appearing in normal type apply for T A = TJ = 25ÊC. RADJ = 8.2KΩ

LM2673-3.3

Symbol	Parameter	Conditions	Typical	Min	Max	Units
			(Note 3)	(Note 4)	(Note 4)
VOUT	Output Voltage	VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A	3.3	3.234/3.201	3.366/3.399	V
η	Efficiency	VIN = 12V, ILOAD = 3A	86			%

LM2673-5.0

Symbol	Parameter	Conditions	Typical	Min	Max	Units
			(Note 3)	(Note 4)	(Note 4)
VOUT	Output Voltage	VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A	5.0	4.900/4.850	5.100/5.150	V
η	Efficiency	VIN = 12V, ILOAD = 3A	88			%

LM2673-12

Symbol	Parameter	Conditions	Typical	Min	Max	Units
			(Note 3)	(Note 4)	(Note 4)
VOUT	Output Voltage	VIN = 15V to 40V, 100mA ≤ IOUT ≤ 3A	12	11.76/11.64	12.24/12.36	V
η	Efficiency	VIN = 24V, ILOAD = 3A	94			%

LM2673-ADJ

Symbol	Parameter	Conditions	Typ	Min	Max	Units
			(Note 3)	(Note 4)	(Note 4)
VFB	Feedback	VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A	1.21	1.186/1.174	1.234/1.246	V
	Voltage	VOUT Programmed for 5V
η	Efficiency	VIN = 12V, ILOAD = 3A	88			%

LM2673

3	www.national.com

LM2673

All Output Voltage Versions

Electrical Characteristics

Limits appearing in bold type face apply over the entire junction temperature range of operation, −40ÊC to 125ÊC. Specifications appearing in normal type apply for TA = TJ = 25ÊC. Unless otherwise specified, RADJ = 8.2KΩ, VIN=12V for the 3.3V, 5V and Adjustable versions and VIN=24V for the 12V version.

Symbol	Parameter	Conditions	Typ	Min	Max	Units
DEVICE PARAMETERS
IQ	Quiescent	VFEEDBACK = 8V	4.2		6	mA
	Current
		For 3.3V, 5.0V, and ADJ Versions
		VFEEDBACK = 15V
		For 12V Versions
VADJ	Current Limit		1.21	1.181/1.169	1.229/1.246	V
	Adjust Voltage
ICL	Current Limit	RADJ = 8.2KΩ, (Note 5)	4.5	3.8/3.6	5.25/5.4	A
IL	Output	VIN = 40V, Softstart Pin = 0V				mA
	Leakage	VSWITCH = 0V	1.0		1.5
						mA
	Current	VSWITCH = −1V	6		15
RDS(ON)	Switch	ISWITCH = 3A	0.15		0.17/0.29	Ω
	On-Resistance
fO	Oscillator	Measured at Switch Pin	260	225	280	kHz
	Frequency
D	Duty Cycle	Maximum Duty Cycle	91			%
		Minimum Duty Cycle	0			%
IBIAS	Feedback Bias	VFEEDBACK = 1.3V	85			nA
	Current	ADJ Version Only
VSFST	Softstart
	Threshold		0.63	0.53	0.74	V
	Voltage
ISFST	Softstart Pin	Softstart Pin = 0V	3.7		6.9	µA
	Current
θJA	Thermal	T Package, Junction to Ambient	65
	Resistance	(Note 6)
θJA		T Package, Junction to Ambient	45
		(Note 7)
θJC		T Package, Junction to Case	2
θJA		S Package, Junction to Ambient	56			ÊC/W
		(Note 8)
θJA		S Package, Junction to Ambient	35
		(Note 9)
θJA		S Package, Junction to Ambient	26
		(Note 10)
θJC		S Package, Junction to Case	2			++

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.

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 = 25ÊC 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 = 25ÊC. 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: The peak switch current limit is determined by the following relationship: ICL=37,125/ RADJ.

Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with 1¤2 inch leads in a socket, or on a PC board with minimum copper area.

Note 7: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with 1¤2 inch leads soldered to a PC board containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.

www.national.com

4

(Continued)

Note 8: 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 9: 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 10: 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.

LM2673

5	www.national.com

LM2673

Typical Performance Characteristics

Normalized	Line Regulation	Efficiency vs Input Voltage
Output Voltage

	DS100913-5	DS100913-6
	DS100913-4
Efficiency vs ILOAD	Switch Current Limit	Operating Quiescent Current

DS100913-7 DS100913-8 DS100913-9

Switching Frequency Feedback Pin Bias Current

DS100913-12

DS100913-13

www.national.com

6

Block Diagram

*Active Inductor Patent Number 5,514,947

²Active Capacitor Patent Number 5,382,918

LM2673

DS100913-14

7	www.national.com

LM2673

Typical Performance Characteristics

Continuous Mode Switching Waveforms	Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 3A	VIN = 20V, VOUT = 5V, ILOAD = 500 mA
L = 33 µH, C OUT = 200 µF, C OUTESR = 26 mΩ	L = 10 µH, C OUT = 400 µF, C OUTESR = 13 mΩ

DS100913-15

A:VSW 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

Load Transient Response for Continuous Mode

VIN = 20V, VOUT = 5V

L = 33 µH, C OUT = 200 µF, C OUTESR = 26 mΩ

DS100913-17

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

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

Horizontal Time Base: 100 µs/div

DS100913-16

A:VSW 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 Discontinuous Mode

VIN = 20V, VOUT = 5V,

L = 10 µH, C OUT = 400 µF, C OUTESR = 13 mΩ

DS100913-18

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

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

Horizontal Time Base: 200 µs/div

www.national.com

8