National Semiconductor M29F040 Technical data

November 5, 2008

LM22673
3A SIMPLE SWITCHER®, Step-Down Voltage Regulator
with Adjustable Soft-Start and Current Limit

LM22673 3A SIMPLE SWITCHER®, Step-Down Voltage Regulator with Adjustable Soft-Start and

Current Limit

General Description

The LM22673 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 N-channel MOSFET. The series consists of a
fixed 5V output and an adjustable version.

The SIMPLE SWITCHER® concept provides for an easy to
use complete design using a minimum number of external
components and National’s Webench® design tool. National’s
Webench® tool includes features such as external component
calculation, electrical simulation, thermal simulation, and
Build-It boards for easy design-in. The switching clock fre­quency is provided by an internal fixed frequency oscillator
which operates at 500 kHz. The LM22673 series also has built
in thermal shutdown and current limiting. The current limit
threshold can be adjusted using an external resistor. An ad­justable soft-start feature is provided by selecting an appro­priate external soft-start capacitor.

Features

Wide input voltage range: 4.5V to 42V

■

Internally compensated voltage mode control

■

Stable with low ESR ceramic capacitors

■

120 mΩ N-channel MOSFET TO-263 THIN package

■

100 mΩ N-channel MOSFET PSOP-8 package

■

Output voltage options:

■

-ADJ (outputs as low as 1.285V)

-5.0 (output fixed to 5V)
±1.5% feedback reference accuracy

■

Switching frequency of 500kHz

■

-40°C to 125°C operating junction temperature range

■

Adjustable soft-start

■

Adjustable current limit

■

Integrated boot diode

■

Fully Webench® enabled

■

Step-down and inverting buck-boost applications

■

Package

PSOP-8 (Exposed Pad)

■

TO-263 THIN (Exposed Pad)

■

Applications

Industrial Control

■

Telecom and Datacom Systems

■

Embedded Systems

■

Automotive Telematics and Body Electronics

■

Conversions from Standard 24V, 12V and 5V Input Rails

■

Simplified Application Schematic

30076201

© 2008 National Semiconductor Corporation 300762 www.national.com

Connection Diagrams

LM22673

8-Lead Plastic PSOP-8 Package

NS Package Number MRA08B

7-Lead Plastic TO-263 THIN Package

NS Package Number TJ7A

30076240

30076202

Ordering Information

Output Voltage Order Number Package Type NSC Package Drawing Supplied As

ADJ LM22673MR-ADJ PSOP-8 Exposed Pad MRA08B 95 Units in Rails

ADJ LM22673MRE-ADJ 250 Units in Tape and Reel

ADJ LM22673MRX-ADJ 2500 Units in Tape and Reel

ADJ LM22673TJE-ADJ TO-263 THIN Exposed Pad TJ7A 250 Units in Tape and Reel

ADJ LM22673TJ-ADJ 1000 Units in Tape and Reel

5.0 LM22673MR-5.0 PSOP-8 Exposed Pad MRA08B 95 Units in Rails

5.0 LM22673MRE-5.0 250 Units in Tape and Reel

5.0 LM22673MRX-5.0 2500 Units in Tape and Reel

5.0 LM22673TJE-5.0 TO-263 THIN Exposed Pad TJ7A 250 Units in Tape and Reel

5.0 LM22673TJ-5.0 1000 Units in Tape and Reel

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Pin Descriptions

LM22673

Pin Numbers

PSOP-8

Package

1 3 BOOT Bootstrap input Provides the gate voltage for the high side NFET.

2 - NC Not Connected Pin is not electrically connected inside the chip. Pin

3 5 IADJ Current limit setting pin A resistor attached between this pin and GND can be

4 6 FB Feedback pin Inverting input to the internal voltage error amplifier.

5 7 SS Soft-Start pin An external capacitor and an internal 50 µA current

6 4 GND System ground Provide good capacitive decoupling between VIN and

7 2 VIN Source input voltage Input to the regulator. Operates from 4.5V to 42V.

8 1 SW Switch pin Attaches to the switch node.

Pin Numbers

TO-263 THIN

Package

Name Description Application Information

does function as thermal conductor.

used to set the current limit threshold. Pin can be left
floating and internal setting will be default.

source set the time constant for the rise of the error
amplifier reference. Pin can be left floating and internal
soft-start will be default.

this pin.

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

LM22673

please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

VIN to GND 43V
SS, IADJ Pin Voltage -0.5V to 7V
SW to GND (Note 2) -5V to V

Boot Pin Voltage VSW + 7V

FB Pin Voltage -0.5V to 7V
Power Dissipation Internally Limited
Junction Temperature 150°C

Soldering Information
Vapor Phase (75 sec.) 219°C
Infrared (10 sec.) 240°C
Wave (4 sec.) 260°C
ESD Rating (Note 3)
Human Body Model ±2 kV

IN

Storage Temperature Range -65°C to +150°C

Operating Ratings (Note 1)

Supply Voltage (VIN)

Junction Temperature Range -40°C to +125°C

4.5V to 42V

Electrical Characteristics Limits in standard type are for T

= 25°C only; limits in boldface type apply over the

J

junction temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are guaranteed through test, design, or statistical
correlation. Typical values represent the most likely parametric norm at TA = TJ = 25°C, and are provided for reference purposes
only. Unless otherwise specified: VIN = 12V.

Symbol Parameter Conditions Min

(Note 5)

Typ

(Note 4)

Max

(Note 5)

LM22673-5.0

V

FB

Feedback Voltage VIN = 8V to 42V 4.925/4.9 5.0 5.075/5.1 V

LM22673-ADJ

V

FB

Feedback Voltage VIN = 4.7V to 42V 1.266/1.259 1.285 1.304/1.311 V

All Output Voltage Versions

I

V

ADJ

I

CL

I

CLADJ

I

Q

L

Quiescent Current VFB = 5V 3.4 6 mA

Current Limit Adjust Voltage 0.65 0.8 0.9 V

Current Limit 3.4/3.35 4.2 5.3/5.5 A

Current Limit Adjust

IADJ Resistor = 56.2 kΩ

0.4 0.7 1 A

Output Leakage Current VIN = 42V, SS Pin = 0V, VSW = 0V 0.2 2 µA

VSW = -1V 0.1 3 mA

R

DS(ON)

Switch On-Resistance TO-263 THIN Package 0.12 0.16/0.22

PSOP-8 Package 0.10 0.16/0.20

T

OFFMIN

T

ONMIN

I

BIAS

I

T

f

SS

O

SD

Oscillator Frequency 400 500 600 kHz

Minimum Off-time 300 ns

Minimum On-time 100 ns

Feedback Bias Current VFB = 1.3V (ADJ Version Only) 230 nA

Soft-start Current EN Input = 0V 30 50 70 µA

Thermal Shutdown

150 °C

Threshold

θ

JA

Thermal Resistance TJ Junction to ambient temperature

22 °C/W

resistance (Note 6)

θ

JA

Thermal Resistance MR Package, Junction to ambient

60 °C/W

temperature resistance (Note 7)

Units

Ω

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Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability
and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in
the recommended Operating Ratings is not implied. The recommended Operating Ratings indicate conditions at which the device is functional and should not be
operated beyond such conditions.

Note 2: The absolute maximum specification of the ‘SW to GND’ applies to DC voltage. An extended negative voltage limit of -10V applies to a pulse of up to 50
ns.

Note 3: ESD was applied using the human body model, a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 4: Typical values represent most likely parametric norms at the conditions specified and are not guaranteed.

Note 5: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical

Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL).

Note 6: The value of θJA for the TO-263 THIN (TJ) package of 22°C/W is valid if package is mounted to 1 square inch of copper. The θJA value can range from
20 to 30°C/W depending on the amount of PCB copper dedicated to heat transfer. See application note AN-1797 for more information.

Note 7: The value of θJA for the PSOP-8 exposed pad (MR) package of 60°C/W is valid if package is mounted to 1 square inch of copper. The θJA value can
range from 42 to 115°C/W depending on the amount of PCB copper dedicated to heat transfer.

Typical Performance Characteristics Unless otherwise specified the following conditions apply: Vin =

12V, TJ = 25°C.

LM22673

Efficiency vs I

V

OUT

OUT

= 3.3V

and V

IN

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Normalized Switching Frequency vs Temperature

Current Limit vs Temperature

30076203

Feedback Bias Current vs Temperature

30076204

30076205

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