National Semiconductor LM22674 Technical data

LM22674 500 mA SIMPLE SWITCHER®, Step-Down Voltage Regulator with Precision Enable

October 17, 2008

General Description

The LM22674 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 500 mA 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 LM22674 series also has built in thermal shutdown, current limiting and an enable control input that can power down the regulator to a low 25 µA quiescent current standby condition.

Features

Wide input voltage range: 4.5V to 42V

■

Internally compensated voltage mode control

■

Stable with low ESR ceramic capacitors

■

200 mΩ N-channel MOSFET

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Output voltage options:

■

-ADJ (outputs as low as 1.285V)

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

■

Switching frequency of 500 kHz

■

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

■

Precision enable pin

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Integrated boot diode

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Integrated soft-start

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Fully WEBENCH® enabled

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Step-down and inverting buck-boost applications

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Package

PSOP-8 (Exposed Pad)

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Applications

Industrial Control

■

Telecom and Datacom Systems

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Embedded Systems

■

Automotive Telematics and Body Electronics

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

■

Simplified Application Schematic

30076901

Connection Diagram

LM22674

8-Lead Plastic PSOP-8 Package

NS Package Number MRA08B

30076940

Ordering Information

Output Voltage Order Number Package Type NSC Package Drawing Supplied As

ADJ LM22674MR-ADJ

ADJ LM22674MRE-ADJ 250 Units in Tape and Reel

ADJ LM22674MRX-ADJ 2500 Units in Tape and Reel

5.0 LM22674MR-5.0 95 Units in Rails

5.0 LM22674MRE-5.0 250 Units in Tape and Reel

5.0 LM22674MRX-5.0 2500 Units in Tape and Reel

PSOP-8 Exposed Pad MRA08B

95 Units in Rails

Pin Descriptions

Pins Name Description Application Information

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

2, 3 NC Not Connected Pins are not electrically connected inside the chip. Pins do function

as thermal conductor.

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

5 EN Precision enable pin When pulled low regulator turns off.

6 GND System ground Provide good capacitive decoupling between VIN and this pin

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

8 SW Switch pin Attaches to the switch node

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LM22674

Absolute Maximum Ratings (Note 1)

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

VIN to GND 43V EN Pin Voltage -0.5V to 6V 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

Electrical Characteristics Limits in standard type are for T

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

Operating Ratings (Note 1)

Supply Voltage (VIN)

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

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

4.5V to 42V

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)

LM22674-5.0

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

LM22674-ADJ

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

All Output Voltage Versions

STDBY

Quiescent Current VFB = 5V 3.4 6 mA

Standby Quiescent Current EN Pin = 0V 25 40 µA

Current Limit 0.56/0.62 0.7 0.84/0.9 A

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

VSW = -1V 0.1 3 µA

DS(ON)

OFFMIN

ONMIN

BIAS

Switch On-Resistance 0.2 0.24/0.32

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

Enable Threshold Voltage 1.3 1.6 1.9 V

Enable Input Current EN Input = 0V 6 µA

Thermal Shutdown

150 °C

Threshold

Thermal Resistance MR package, Junction to ambient

60 °C/W

temperature resistance (Note 6)

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.

LM22674

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 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.

Efficiency vs I

OUT

= 3.3V

and V

Current Limit vs Temperature

30076927

Normalized Switching Frequency vs Temperature

30076904

Normalized R

vs Temperature

DS(ON)

30076903

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30076908

LM22674

Feedback Bias Current vs Temperature

30076905

Standby Quiescent Current vs Input Voltage

Normalized Enable Threshold Voltage vs Temperature

30076910

Normalized Feedback Voltage vs Temperature

30076906

Normalized Feedback Voltage vs Input Voltage

30076909

30076907

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