Datasheet LM2574BN, LM2574-5.0BWM, LM2574-5.0BN, LM2574-3.3BWM, LM2574-12BWM Datasheet (MICREL)

LM2574 Micrel

LM2574

52kHz Simple 0.5A Buck Regulator

General Description

The LM2574 family is a series of easy to use fixed and
adjustable 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, 5V, and 12V fixed output
versions, 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-by­cycle 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.

Pin Configuration

FB 1

SIG GND 2

ON/OFF 3

PWR GND 4

*1
*2

FB 3

SIG GND 4

ON/OFF 5

PWR GND 6

*7

8-pin DIP (N)

8*
7 OUTPUT
6*
5V

IN

14 *
13 *
12 OUTPUT
11 *
10 V

IN

9*
8*

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)

Ordering Information

Part Number Temp. Range Package

LM2574BN –40°C to +85°C 8-pin Plastic DIP
LM2574BWM –40°C to +85°C 14-pin Wide SOIC
LM2574-3.3BN –40°C to +85°C 8-pin Plastic DIP
LM2574-3.3BWM –40°C to +85°C 14-pin Wide SOIC
LM2574-5.0BN –40°C to +85°C 8-pin Plastic DIP
LM2574-5.0BWM –40°C to +85°C 14-pin Wide SOIC
LM2574-12BN –40°C to +85°C 8-pin Plastic DIP
LM2574-12BWM –40°C to +85°C 14-pin Wide SOIC

Typical Application

40V MAX

UNREGULATED

DC IN

C

IN

22µF

V

IN

PWR
GND

LM2574

SIG

GND

OUT

ON/

OFF

FB

330µH

11DQ05

REGULATED
OUTPUT

0.5A

C

OUT

220µF

14-pin SOIC (WM)

* NC: solder to printed circuit for

maximum heat transfer

Figure 1. Fixed Output Regulator Circuit

August 1999 1 LM2574

LM2574 Micrel

Absolute Maximum Ratings

Maximum Supply Voltage

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

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

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

Operating Ratings

Temperature Range

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

Supply Voltage

IN

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

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

Storage Temperature Range ................... –65°C to +150°C

Minimum ESD Rating

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

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

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

Maximum Junction Temperature............................... 150°C

Electrical Characteristics Specifications with standard typeface are for T

over full Operating Temperature Range. Unless otherwise specified, V

Symbol Parameter Condition Min Typ Max Units
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit

V
V

OUT
OUT

Feedback Voltage V

= 12V, I

IN

Feedback Voltage 0.1A ≤ I

LOAD

≤ 0.5A, 7V≤ VIN ≤ 40V, V

LOAD

(LM2574) 1.180 1.280 V

η Efficiency VIN = 12V, I

LOAD

SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit
V

OUT

V

OUT

η Efficiency VIN = 12V, I

Output Voltage VIN = 12V, I
Output Voltage 0.1A ≤ I

(LM2574-3.3) V

LOAD

= 3.3V 3.135 3.465 V

OUT

LOAD

≤ 0.5A, 4.75V ≤ VIN ≤ 40V, 3.168 3.3 3.432 V

LOAD

SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit
V

OUT

V

OUT

η Efficiency VIN = 12V, I

Output Voltage VIN = 12V, I
Output Voltage 0.1A ≤ I

(LM2574-5.0) V

LOAD

= 5V 4.750 5.250 V

OUT

LOAD

≤ 0.5A, 7V≤ VIN ≤ 40V, 4.800 5.0 5.200 V

LOAD

SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit
V

OUT

V

OUT

η Efficiency VIN = 25V, I

Output Voltage VIN = 25V, I
Output Voltage 0.1A ≤ I

(LM2574-12) V

LOAD

= 12V 11.400 12.600 V

OUT

LOAD

≤ 0.5A, 15V ≤ VIN ≤ 40V, 11.520 12 12.480 V

LOAD

= 12V, and I

in

Figure 2

= 0.1A, V

= 0.1A, V

= 5V 1.217 1.230 1.243 V

OUT

= 5V 78 %

OUT

Figure 3

= 0.1A, V

= 3.3V 3.234 3.3 3.366 V

OUT

= 0.1A 73 %

Figure 3

= 0.1A, V

= 0.1A, V

= 5V 4.900 5.0 5.100 V

OUT

= 5V 78 %

OUT

Figure 3

= 0.1A, V

= 12V 11.760 12 12.240 V

OUT

= 0.1A 88 %

= 25°C, and those with boldface type apply

J

= 100mA.

LOAD

= 5V 1.193 1.230 1.267 V

OUT

LM2574 2 August 1999

LM2574 Micrel

Electrical Characteristics (continued)

Symbol Parameter Condition Min Typ Max Units
DEVICE PARAMETERS, ADJUSTABLE REGULATOR

I

B

DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS

f

o

V

SAT

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

CL

I

L

I

Q

I

STBY

θ

JA

ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS Test Circuit
V

IH

V

IL

I

IH

I

IL

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

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

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

Note 4 Output (pin 2) sourcing current. No diode, inductor, or capacitor connected to input.
Note 5 Feedback (pin 4) removed from output and connected to 0V.
Note 6 Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF.
Note 7 Junction to ambient thermal resistance with approximately 1 square inches of PC board copper surrounding the leads.

Feedback Bias Current V

= 5V 50 100 nA

OUT

500 nA

Oscillator Frequency Note 8 47 52 58 kHz

42 63 kHz

Saturation Voltage I

= 0.5A, Note 4 0.8 1.2 V

OUT

1.4 V

Current Limit Peak Current, tON ≤ 3µs, Note 4 0.7 1.0 1.6 A

0.65 1.8

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

Note 6, Output = –1V 7.5 30

Quiescent Current Note 6 510mA
Standby Quiescent Current ON/OFF Pin = 5V (OFF) 50 200 µA
Thermal Resistance N Package, Junction to Ambient, Note 7 85 °C/W

WM Package, Junction to Ambient, Note 7 100 °C/W

Figures 2, 3

ON/OFF Input Level V

= 0V 2.2 1.4 V

OUT

2.4 V

ON/OFF Input Level V

= 5V 1.2 1.0 V

OUT

0.8 V
ON/OFF Logic Current ON/OFF = 5V (OFF) 4 30 µA
ON/OFF Logic Current ON/OFF = 0V (ON) 0.01 10 µA

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

are 100% production tested. All limits at temperature extremes are guaranteed via testing.

the LM2574 is used as shown in
istics.

Figure 1

test circuit, system performance will be shown in system parameters section of Electrical Character-

August 1999 3 LM2574

LM2574 Micrel

Typical Performance Characteristics (Circuit of Figure 1)

Supply Current

20
18

16
14
12
10

8

SUPPLY CURRENT (mA)

6
4

I

0102030405060

Measured at

Ground Pin

TJ = 25˚C

V

to 0.5A

LOAD

INPUT VOLTAGE (V)

Current Limit

1.5

1

0.5

OUTPUT CURRENT (A)

0

-75

-50 -25 0 25 50 75 100125 150

JUNCTION TEMPERATURE (˚C)

= 5V

OUT

VIN = 25V

Supply Current
vs. Duty Cycle

20.0

17.5

15.0

12.5

10.0
I

7.5

5.0

SUPPLY CURRENT (mA)

2.5
0

0 20406080100

= 100 mA

LOAD

VIN from 7V to 40V

DUTY CYCLE (%)

Switch
Saturation Voltage

1.1

0.9

-55˚C

-40˚C

0.7
25˚C

0.5

125˚C

SATURATION VOLTAGE (V)

150˚C

0.3
0

0.1 0.2 0.3 0.4 0.5

SWITCH CURRENT (A)

Standby
Quiescent Current

200

150

100

50

STANDBY QUIESCENT CURRENT (µA)

0

-75

VIN = 40V

V

ON/OFF

VIN = 12V

-50 -25 0 25 50 75 100 125 150

JUNCTION TEMPERATURE (˚C)

Efficiency

100

95
90
85

100 mA

80
75

EFFICIENCY (%)

70
65
60

0 5 10 15 20 25 30 35 40

V

OUT

0.5A
V

INPUT VOLTAGE (V)

100 mA

OUT

= 5V

= 12V

0.5A

= 3V

Minimum Operating
Voltage

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

INPUT VOLTAGE (V)

1.0

0.5
0

-75 -50 -25 0 25 50 75 100125150

JUNCTION TEMPERATURE (˚C)

V

I

LOAD

OUT

Normalized
Output Voltage

100

75
50
25

0

-25

-50

-75

OUTPUT VOLTAGE CHANGE (mV)

-100

-75 -50 -25 0 25 50 75 100 125150

JUNCTION TEMPERATURE (˚C)

VIN = 12V

I

= 100mA

LOAD

Normalized to TJ = 25˚C

V

OUT

= 1.23V

= 100 mA

= 5V

Line Regulation

14

Normalized to VIN = 10V

12

V

= 5V

OUT

10

I

= 100mA

LOAD

8

TJ = 25

6
4
2
0

-2

-4

NORMALIZED FEEDBACK VOLTAGE (mV)

-6
0

51015202530

INPUT VOLTAGE (V)

Oscillator Frequency

+8
+6

+4
+2

0

-2

-4

--6

NORMALIZED FREQUENCY (%)

-8

-75

-50 -25 0 25 50 75 100125150

JUNCTION TEMPERATURE (˚C)

Normalized at 25˚C

VIN = 40V

VIN = 12V

Feedback Pin Current

100

75
50
25

0

-25

-50

-75

STANDBY QUIESCENT CURRENT (nA)

-100

-75

-50 -25 0 25 50 75 100 125150

JUNCTION TEMPERATURE (˚C)

Dropout Voltage

2.0

I

= 0.5A

LOAD

1.5

1.0

I

= 100 mA

LOAD

0.5

INPUT-OUTPUT DIFFERENTIAL (V)

0

-75 -50 -25 0 25 50 75 100125150

JUNCTION TEMPERATURE (˚C)

∆V

= 5%

OUT

R

= 0.2Ω

IND

LM2574 4 August 1999

LM2574 Micrel

Typical Performance Characteristics (continued)

C

IN

22µF

V

IN

LM2574

(adjustable)

PWR
GND

SIG

GND

Normalized
Feedback Voltage*

25
20
15
10

5
0

-5

-10

-15

-20

NORMALIZED FEEDBACK VOLTAGE (mV)

-25

-75 -50 -25 0 25 50 75 100125150

FB

OUT
ON/

OFF

Normalized to TJ = 25˚C

JUNCTION TEMPERATURE (˚C)

* Adjustable version only

330µH

11DQ06

I

LOAD

C

220µF

OUT

VIN = 12V

= 100mA

3.09k

1k

Feedback Voltage
vs Duty Cycle*

20
15
10

5
0

-5

-10

-15

FEEDBACK VOLTAGE CHANGE (mV)

-20
0 20 40 60 80 100

C

IN

22µF

Load

I

= 100 mA

LOAD

V

VIN = 7V

DUTY CYCLE (%)

V

IN

LM2574–

3.3, 5, 12

PWR

GND

IN

= 40V

SIG

GND

OUT

ON/

OFF

FB

330µH

11DQ06

C

OUT

220µF

Load

Block Diagrams

V

IN

1

FEED-

4

BACK

3.1k

+

1.0k

-

1.23V

BAND-GAP

REFERENCE

Note: Pin numbers are for the TO-220 package

Figure 3. Fixed Regulator Test CircuitFigure 2. Adjustable Regulator Test Circuit

FIXED GAIN
ERROR AMP

52 kHz

OSCILLATOR

INTERNAL

REGULATOR

COMPARATOR

+

-

RESET

THERMAL

SHUTDOWN

ON/OFF

DRIVER

CURRENT

LIMIT

1/2 AMP
SWITCH

5

FEED­BACK

1

FIXED GAIN
ERROR AMP

4

+

V

IN

ON/OFF

-

2

OUTPUT

1.23V

BAND-GAP

3

GND

REFERENCE

52 kHz

OSCILLATOR

INTERNAL

REGULATOR

COMPARATOR

+

-

RESET

THERMAL

SHUTDOWN

ON/OFF

DRIVER

CURRENT

LIMIT

Fixed Regulator Adjustable Regulator

1/2 AMP
SWITCH

ON/OFF

5

2

OUTPUT

3

GND

August 1999 5 LM2574