LM2574-5.0YN - MICREL SEMICONDUCTOR

July 2005 1 M9999-072805

LM2574 Micrel, Inc.

LM2574

52kHz Simple 0.5A Buck Regulator

General Description

The LM2574 family is a series of easy to use ﬁxed and ad-

justable switching voltage regulators. The LM2574 contains

all of the active circuitry necessary to construct a stepdown

(buck) switching regulator and requires a minimum of external

components.

The LM2574 is available in 3.3V and 5V ﬁxed output ver-

sions, or an adjustable version with an output voltage range

of 1.23V to 37V. Output voltage is guaranteed to ±4% for

speciﬁed input and load conditions.

The LM2574 can supply 0.5A while maintaining excellent

line and load regulation. The output switch includes cycle-

by-cycle current limiting, as well as thermal shutdown for full

protection under fault conditions.

An external shutdown connection selects operating or standby

modes. Standby current is less than 200µA.

Heat sinks are generally unnecessary due the regulator’s

high efﬁciency. Adequate heat transfer is usually provided

by soldering all package pins to a printed circuit board.

The LM2574 includes internal frequency compensation and

an internal 52kHz ﬁxed frequency oscillator guaranteed to

±10% of the frequency.

Circuits constructed around the LM2574 use a standard

series of inductors which are available from several different

manufacturers.

All support documentation can be found on Micrel’s web site

at www.micrel.com.

Typical Application

VIN

PWR

GND SIG

GND ON/

OFF

OUT

LM2574

CIN

22µF

40V MAX

UNREGULATED

DC IN

REGULATED

OUTPUT

0.5A

11DQ05 COUT

220µF

330µH

Figure 1. Fixed Output Regulator Circuit

Features

• 3.3V, 5V, 12V, and adjustable output versions

• Adjustable version output 1.23V to 37V ±4% max. over

line and load conditions.

• Guaranteed 0.5A output current

• Wide input voltage, up to 40V

• Thermal shutdown and current limit protection

• Requires only 4 external components.

• Shutdown capability (standby mode)

• Low power standby mode < 200µA Typical

• High-efﬁciency

• 52kHz ﬁxed frequency internal oscillator

• Uses standard inductors

Applications

• Simple high-efﬁciency step-down (buck) regulator

• Efﬁcient pre-regulator for linear regulators

• On-card switching regulators

• Positive to negative converter (buck-boost)

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

LM2574 Micrel, Inc.

M9999-072805 2 July 2005

Pin Conﬁguration

FB 1

SIG GND 2

ON/OFF 3

PWR GND 4

8 NC

7 OUTPUT

6 NC

5 VIN

8-Pin DIP (N)

Ordering Information

Part Number Junction

Temp. Range

Package

Standard Pb-Free

LM2574BN LM2574YN –40ºC to +85ºC 8-pin Plastic DIP

LM2574-3.3BN LM2574-3.3YN –40ºC to +85ºC 8-pin Plastic DIP

LM2574-5.0BN LM2574-5.0YN –40ºC to +85ºC 8-pin Plastic DIP

July 2005 3 M9999-072805

LM2574 Micrel, Inc.

Absolute Maximum Ratings(1)

Maximum Supply Voltage

LM2574 ...................................................................... 45V

OFF Pin Input Voltage ................................ –0.3V ≤ V ≤ VIN

Output Voltage to Ground (Steady State) ...................... –1V

Power Dissipation ..................................... Internally Limited

Storage Temperature Range (TS) ............. –65°C to +150°C

Minimum ESD Rating

C = 100pF, R = 1.5kΩ ................................................ 2kV

FB Pin ........................................................................ 1kV

Lead Temperature (soldering, 10 sec.) ...................... 260°C

Operating Ratings(1)

Supply Voltage

LM2574 ...................................................................... 40V

Temperature Range

LM2574 ...........................................–40°C ≤ TJ ≤ +125°C

Maximum Junction Temperature (TJ .......................... 150°C

Electrical Characteristics(2)

Speciﬁcations with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range.

Unless otherwise speciﬁed, VIN = 12V, and ILOAD = 100mA.

Symbol Parameter Condition Min Typ Max Units

System Parameters, Adjustable Regulators(3), Test Circuit Figure 2

VOUT Feedback Voltage VIN = 12V, ILOAD = 0.1A, VOUT = 5V 1.217 1.230 1.243 V

VOUT Feedback Voltage 0.1A ≤ ILOAD ≤ 0.5A, 7V≤ VIN ≤ 40V, 1.193 1.230 1.267 V

(LM2574) VOUT = 5V 1.180 1.280 V

η Efﬁciency VIN = 12V, ILOAD = 0.1A, VOUT = 5V 78 %

System Parameters, 3.3V Regulators(3), Test Circuit Figure 3

VOUT Output Voltage VIN = 12V, ILOAD = 0.1A, VOUT = 3.3V 3.234 3.3 3.366 V

VOUT Output Voltage 0.1A ≤ ILOAD ≤ 0.5A, 4.75V ≤ VIN ≤ 40V, 3.168 3.3 3.432 V

(LM2574-3.3) VOUT = 3.3V 3.135 3.465 V

η Efﬁciency VIN = 12V, ILOAD = 0.1A 73 %

System Parameters, 5V Regulators(3), Test Circuit Figure 3

VOUT Output Voltage VIN = 12V, ILOAD = 0.1A, VOUT = 5V 4.900 5.0 5.100 V

VOUT Output Voltage 0.1A ≤ ILOAD ≤ 0.5A, 7V≤ VIN ≤ 40V, 4.800 5.0 5.200 V

(LM2574-5.0) VOUT = 5V 4.750 5.250 V

η Efﬁciency VIN = 12V, ILOAD = 0.1A, VOUT = 5V 78 %

Notes:

1. “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. “Operating Ratings” indicate for which the device is

intended to be functional, but do not guarantee speciﬁc performance limits. For guaranteed speciﬁcations and test conditions, see “Electrical Charac-

teristics.”

2. All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%

production tested. All limits at temperature extremes are guaranteed via testing.

3. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.

When the LM2574 is used as shown in Figure 1 test circuit, system performance will be shown in system parameters section of “Electrical Charac-

teristics.”

LM2574 Micrel, Inc.

M9999-072805 4 July 2005

Electrical Characteristics

Symbol Parameter Condition Min Typ Max Units

Device Parameters, Adjustable Regulator

IB Feedback Bias Current VOUT = 5V 50 100 nA

500 nA

Device Parameters, Fixed and Adjustable Regulators

fo Oscillator Frequency Note 8 47 52 58 kHz

42 63 kHz

VSAT Saturation Voltage IOUT = 0.5A(4) 0.8 1.2 V

1.4 V

DC Max Duty Cycle (ON) Note 5 93 98 %

ICL Current Limit Peak Current, tON ≤ 3µs(4) 0.7 1.0 1.6 A

0.65 1.8

IL Output Leakage Current VIN, Note 6, Output = 0V 2 mA

Note 6, Output = –1V 7.5 30

IQ Quiescent Current Note 6 5 10 mA

ISTBY Standby Quiescent Current ON/OFF Pin = 5V (OFF) 50 200 µA

θJA Thermal Resistance N Package, Junction to Ambient(7) 85 °C/W

On/Off Control, Fixed and Adjustable Regulators Test Circuit Figures 2, 3

VIH ON/OFF Input Level VOUT = 0V 2.2 1.4 V

2.4 V

VIL ON/OFF Input Level VOUT = 5V 1.2 1.0 V

0.8 V

IIH ON/OFF Logic Current ON/OFF = 5V (OFF) 4 30 µA

IIL ON/OFF Logic Current ON/OFF = 0V (ON) 0.01 10 µA

Notes:

4. Output (pin 2) sourcing current. No diode, inductor, or capacitor connected to input.

5. Feedback (pin 4) removed from output and connected to 0V.

6. Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF.

7. Junction-to-ambient thermal resistance with approximately 1 square inches of PC board copper surrounding the leads.

Test Circuit

VIN

PWR

GND SIG

GND ON/

OFF

OUT

LM2574

(adjustable)

CIN

22µF

11DQ06 COUT

220µF

330µH

3.09k

Figure 2. Adjustable Regulator Test Circuit

VIN

P W R

GND SIG

GND ON/

OFF

OUT

LM2574–

3.3, 5, 12

CIN

22µF

11DQ06 COUT

220µF

330µH

Figure 3. Fixed Regulator Test Circuit

July 2005 5 M9999-072805

LM2574 Micrel, Inc.

Typical Characteristics (Circuit of Figure 1)

Supply Current

INPUT VOL TA GE ( V )

20 Measured at

Grou nd Pin

TJ = 25˚C

VOUT = 5V

40 10 20 30 40 50 60

IL O AD

to 0.5A

Supply Current

vs. Duty Cycle

D U T Y C YC LE ( % )

20.0

17.5

15.0

12.5

10.0

7.5

5.0

2.5

00 20 40 60 80 100

VIN from 7V to 40V

IL O AD

= 100 mA

JU N C T I O N TEM PE R ATU R E ( ˚C )

200

150

100

-75

VIN = 12V

Standby

Quiescent Current

VIN = 40V

-50 -25 0 25 50 75 100 125150

Current Limit

JU N C T I O N TEM PE R ATU R E ( ˚C )

1.5

0.5

-75

VIN = 25V

INPUT VOL TA GE ( V )

100

Efficiency

VOUT = 12V

-50 -25 0 25 50 75 100125 150

100 mA

VOUT = 3V

0.5A

0 5 10 15 20 25 30 35 40

Minimum Operating

Voltage

JU N C T I O N TEM PE R ATU R E ( ˚C )

5.0

IL O AD

= 100 mA

Line Regulation

INPUT VOL TA GE ( V )

JU N C T I O N TEM PE R ATU R E ( ˚C )

100

-100

-75

Feedback Pin Current

-50 -25 0 25 50 75 100 125150

VOUT = 1.23V

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

-75 -50 -25 0 25 50 75 100125150

-2

-4

-6

5 10 15 20 25 30

-25

-50

-75

JU N C T I O N TEM PE R ATU R E ( ˚C )

-8

-75

Oscillator Frequency

-50 -25 0 25 50 75 100125150

-2

-4

--6 VIN = 12V

VIN = 40V

Normalized at 25˚C

Normalized toVIN = 10V

VOUT = 5V

IL O AD

= 100mA

TJ = 25

VON/OFF

= 5V

Switch

Saturation Voltage

SW I TC H C U R R EN T ( A)

1.1

-55˚C

0.9

0.7

0.5

0.3

0 0.1 0.2 0.3 0.4 0.5

25˚C

125˚C

150˚C

-40˚C

Dropout Voltage

JU N C T I O N TEM PE R ATU R E ( ˚C )

2.0

-75 -50 -25 0 25 50 75 100125150

∆VOUT = 5%

RIND = 0.2Ω

IL O AD

= 0.5A

IL O AD

= 100 mA

1.5

1.0

0.5

Normalized

Output Voltage

JU N C T I O N TEM PE R ATU R E ( ˚C )

100

-25

-50

-75

-100

-75 -50 -25 0 25 50 75 100125150

VIN = 12V

IL O AD

= 100mA

Normalized toT

J = 25 ˚C

VOUT = 5V

LM2574 Micrel, Inc.

M9999-072805 6 July 2005

Typical Performance Characteristics (continued)

Normalized

Feedback Voltage*

JU N C T I O N TEM PE R ATU R E ( ˚C )

-5

-10

-15

-20

-25

-75 -50 -25 0 25 50 75 100125150

VIN = 12V

IL O AD

= 100mA

Normalized toT

J= 25˚C

Feedback Voltage

vs Duty Cycle*

D U T Y C YC LE ( % )

-5

-10

-15

-20

IL O AD

= 100 mA

VIN = 40V

VIN = 7V

0 20 40 60 80 100

* Adjustable version only

July 2005 7 M9999-072805

LM2574 Micrel, Inc.

ON/OFF

C OM P AR AT OR

FIXED G A I N

E R R O R A M P

1/2 AMP

SWITCH

OUTPUT

DRIVER

VIN

F EED -

BACK

1.23V

BAND-GAP

REFERENCE

52 kHz

OSCILLATOR RESET THERMAL

SHUTDOWN

CURRENT

LIMIT

Note: Pin numbers are for the TO-220 package

INTERNAL

REGULATOR ON/OFF

GND

ON/OFF

C OM P AR AT OR

FIXED G A I N

E R R O R A M P

1/2 AMP

SWITCH

OUTPUT

DRIVER

VIN

F EED -

BACK

1.23V

BAND-GAP

REFERENCE

52 kHz

OSCILLATOR RESET THERMAL

SHUTDOWN

CURRENT

LIMIT

INTERNAL

REGULATOR ON/OFF

GND

3.1k

1.0k

Block Diagrams

Fixed Regulator Adjustable Regulator

LM2574 Micrel, Inc.

M9999-072805 8 July 2005

Package Information

0.380 (9.65)

0.370 (9.40) 0.135 (3.43)

0.125 (3.18)

PIN 1

DIMENSIONS:

INCH (MM)

0.018 (0.57)

0.100 (2.54)

0.013 (0.330)

0.010 (0.254)

0.300 (7.62)

0.255 (6.48)

0.245 (6.22)

0.380 (9.65)

0.320 (8.13)

0.0375 (0.952)

0.130 (3.30)

8-Pin DIP (N)

MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com

This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.

Micrel reserves the right to change circuitry and speciﬁcations at any time without notiﬁcation to the customer.

Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can

reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into

the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a signiﬁcant injury to the user. A Purchaser's

use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify

Micrel for any damages resulting from such use or sale.