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An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM2574

LM2574HV

SNVS104E –JUNE 1999–REVISED JULY 2018

LM2574x SIMPLE SWITCHER® 0.5-A Step-Down Voltage Regulator

1 Features

1• 3.3-V, 5-V, 12-V, 15-V, and Adjustable Output

Versions

• Adjustable Version Output Voltage Range: 1.23 V

to 37 V (57 V for HV version) ±4% Maximum Over

Line and Load Conditions

• Specified 0.5-A Output Current

• Wide Input Voltage Range: 40 V, up to 60 V for

HV Version

• Requires Only 4 External Components

• 52-kHz Fixed-Frequency Internal Oscillator

• TTL Shutdown Capability, Low-Power Standby

Mode

• High Efficiency

• Uses Readily Available Standard Inductors

• Thermal Shutdown and Current-Limit Protection

• Create a Custom Design Using the LM2574 With

the WEBENCH®Power Designer

2 Applications

• Simple High-Efficiency Step-Down (Buck)

Regulator

• Efficient Preregulator for Linear Regulators

• On-Card Switching Regulators

• Positive-to-Negative Converter (Buck-Boost)

3 Description

The LM2574xx series of regulators are monolithic

integrated circuits that provide all the active functions

for a step-down (buck) switching regulator, capable of

driving a 0.5-A load with excellent line and load

regulation. These devices are available in fixed output

voltages of 3.3 V, 5 V, 12 V, 15 V, and an adjustable

output version.

Requiring a minimum number of external

components, these regulators are simple to use and

include internal frequency compensation and a fixed-

frequency oscillator.

The LM2574xx series offers a high-efficiency

replacement for popular three-terminal linear

regulators. Because of its high efficiency, the copper

traces on the printed-circuit board (PCB) are normally

the only heat sinking needed.

A standard series of inductors optimized for use with

the LM2574 are available from several different

manufacturers. This feature greatly simplifies the

design of switch-mode power supplies.

Other features include a specified ±4% tolerance on

output voltage within specified input voltages and

output load conditions, and ±10% on the oscillator

frequency. External shutdown is included, featuring

50-μA (typical) standby current. The output switch

includes cycle-by-cycle current limiting, as well as

thermal shutdown for full protection under fault

conditions.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

LM2574, LM2574HV SOIC (14) 8.992 mm × 7.498 mm

PDIP (8) 6.35 mm × 9.81 mm

(1) For all available packages, see the orderable addendum at

the end of the data sheet.

Typical Application (Fixed Output Voltage Versions)

LM2574

LM2574HV

SNVS104E –JUNE 1999–REVISED JULY 2018

www.ti.com

Product Folder Links: LM2574 LM2574HV

Table of Contents

1 Features.................................................................. 1

2 Applications ........................................................... 1

3 Description............................................................. 1

4 Revision History..................................................... 2

5 Pin Configuration and Functions......................... 3

6 Specifications......................................................... 4

6.1 Absolute Maximum Ratings ...................................... 4

6.2 ESD Ratings.............................................................. 4

6.3 Recommended Operating Conditions....................... 4

6.4 Thermal Information.................................................. 4

6.5 Electrical Characteristics for All Output Voltage

Versions..................................................................... 5

6.6 Electrical Characteristics – 3.3-V Version................. 5

6.7 Electrical Characteristics – 5-V Version.................... 6

6.8 Electrical Characteristics – 12-V Version.................. 6

6.9 Electrical Characteristics – 15-V Version.................. 6

6.10 Electrical Characteristics – Adjustable Version....... 7

6.11 Typical Characteristics............................................ 8

7 Detailed Description............................................ 11

7.1 Overview................................................................. 11

7.2 Functional Block Diagram....................................... 11

7.3 Feature Description................................................. 11

7.4 Device Functional Modes........................................ 13

8 Application and Implementation ........................ 14

8.1 Application Information............................................ 14

8.2 Typical Applications ................................................ 19

9 Power Supply Recommendations...................... 26

10 Layout................................................................... 26

10.1 Layout Guidelines ................................................. 26

10.2 Layout Example .................................................... 27

10.3 Grounding ............................................................. 27

10.4 Thermal Considerations........................................ 27

11 Device and Documentation Support................. 29

11.1 Device Support...................................................... 29

11.2 Documentation Support ........................................ 31

11.3 Receiving Notification of Documentation Updates 31

11.4 Community Resources.......................................... 31

11.5 Trademarks........................................................... 31

11.6 Electrostatic Discharge Caution............................ 31

11.7 Glossary................................................................ 31

12 Mechanical, Packaging, and Orderable

Information........................................................... 31

4 Revision History

Changes from Revision D (April 2016) to Revision E Page

• Added links for WEBENCH ................................................................................................................................................... 1

• maximum supply voltage in Abs Max Ratings from "4.5" to "45" to correct typo................................................................... 4

Changes from Revision C (April 2013) to Revision D Page

• Added Device Information table, ESD Ratings table, Feature Description section, Device Functional Modes,

Application and Implementation section, Power Supply Recommendations section, Layout section, Device and

Documentation Support section, and Mechanical, Packaging, and Orderable Information section ..................................... 1

• Changed RθJA value in SOIC column to 77.1 ........................................................................................................................ 4

• Split test conditions row of the Electrical Characteristics table to include TJ= 25°C and TJ< 25°C MIN, TYP, and

MAX values............................................................................................................................................................................. 5

• Split test conditions in ILrow to rearrange the MIN, TYP, and MAX values ......................................................................... 5

Changes from Revision B (November 2004) to Revision C Page

• Changed layout of National Data Sheet to TI format ............................................................................................................. 1

1NC 14 NC

2NC 13 NC

3FB 12 OUTPUT

4SIG_GND 11 NC

5ON/OFF 10 VIN

6PWR_GND 9 NC

7NC 8 NC

1FB 8 NC

2SIG_GND 7 OUTPUT

3ON/OFF 6 NC

4PWR_GND 5 VIN

LM2574

LM2574HV

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SNVS104E –JUNE 1999–REVISED JULY 2018

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5 Pin Configuration and Functions

P Package

8-Pin PDIP

Top View NPA Package

14-Pin SOIC

Top View

Pin Functions

PIN I/O DESCRIPTION

NAME PDIP SOIC

FB 1 3 I Feedback sense input pin. Connect to the midpoint of feedback divider to set

VOUT for ADJ version or connect this pin directly to the output capacitor for a

fixed output version.

NC 8, 6 1, 2, 7, 8, 9,

11, 13, 14 — No internal connection, but must be soldered to PCB for best heat transfer.

ON/OFF 3 5 I Enable input to the voltage regulator. High = OFF and low = ON. Connect to

GND to enable the voltage regulator. Do not leave this pin float.

OUTPUT 7 12 O Emitter pin of the power transistor. This is a switching node. Attached this pin

to an inductor and the cathode of the external diode.

PWR_GND 4 6 — Power ground pins. Connect to system ground and SIF GND, ground pins of

CIN and COUT. Path to CIN must be as short as possible.

SIG_GND 2 4 — Signal ground pin. Ground reference for internal references and logic. Connect

to system ground.

VIN 5 10 I Supply input pin to collector pin of high-side transistor. Connect to power

supply and input bypass capacitors CIN. Path from VIN pin to high frequency

bypass CIN and PWR GND must be as short as possible.

LM2574

LM2574HV

SNVS104E –JUNE 1999–REVISED JULY 2018

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(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended

Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)

MIN MAX UNIT

Maximum supply voltage LM2574 45 V

LM2574HV 63

ON/OFF pin input voltage –0.3 VIN V

Output voltage to ground, steady-state –1 V

Power dissipation Internally limited

Lead temperature, soldering (10 s) 260 °C

Maximum junction temperature 150 °C

Storage temperature, Tstg –65 150 °C

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

6.2 ESD Ratings VALUE UNIT

V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted) MIN NOM MAX UNIT

Supply voltage LM2574 40 V

LM2574HV 60

TJTemperature –40 125 °C

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application

report.

(2) The package thermal impedance is calculated in accordance with JESD 51-7.

(3) Thermal resistances were simulated on a 4-layer, JEDEC board.

6.4 Thermal Information

THERMAL METRIC(1)(2) LM2574, LM2574HV

UNITP (PDIP) NPA (SOIC)

8 PINS 14 PINS

RθJA Junction-to-ambient thermal resistance(3) 60.4 77.1 °C/W

RθJC(top) Junction-to-case (top) thermal resistance(3) 59.9 29.2 °C/W

RθJB Junction-to-board thermal resistance(3) 37.9 33.3 °C/W

ψJT Junction-to-top characterization parameter 17.1 2 °C/W

ψJB Junction-to-board characterization parameter 37.7 32.8 °C/W

RθJC(bot) Junction-to-case (bottom) thermal resistance(3) — — °C/W

LM2574

LM2574HV

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(1) All limits specified at room temperature TYP and MAX. All room temperature limits are 100% production tested. All limits at temperature

extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate

Average Outgoing Quality Level.

(2) The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload which causes the regulated

output voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average power

dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2% (see Figure 6).

(3) Output pin sourcing current. No diode, inductor or capacitor connected to output pin.

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

(5) Feedback pin removed from output and connected to 12 V for the adjustable, 3.3-V, and 5-V versions, and 25 V for the 12-V and 15-V

versions, to force the output transistor OFF.

(6) VIN = 40 V (60 V for high voltage version).

6.5 Electrical Characteristics for All Output Voltage Versions

TJ= 25°C, and MIN and MAX apply over full operating temperature range. VIN = 12 V for the 3.3-V, 5-V, and adjustable

version, VIN = 25 V for the 12-V version, and VIN = 30 V for the 15-V version, ILOAD = 100 mA (unless otherwise noted).

PARAMETER TEST CONDITIONS MIN(1) TYP MAX(1) UNIT

IbFeedback bias current Adjustable version

only, VOUT = 5 V TJ= 25°C 50 100 nA

–40°C < TJ< 125°C 500

fOOscillator frequency See(2) TJ= 25°C 47 52 58 kHz

–40°C < TJ< 125°C 42 63

VSAT Saturation voltage IOUT = 0.5 A(3) TJ= 25°C 0.9 1.2 V

–40°C < TJ< 125°C 1.4

DC Maximum duty cycle (ON) See(4) 93% 98%

ICL Current limit Peak current(2)(3) 0.7 1 1.6 A

0.65 1.8

ILCurrent output leakage Output = 0 V 2 mA

Output = –1 V(5)(6) 7.5 30

IQQuiescent current See(5) 5 10 mA

ISTBY Standby quiescent current ON/OFF pin = 5 V (OFF) 50 200 μA

ON/OFF CONTROL (SEE Figure 27)

VIH ON/OFF pin logic input level VOUT = 0 V TJ= 25°C 2.2 1.4 V

–40°C < TJ< 125°C 2.4

VIL VOUT = Nominal output

voltage TJ= 25°C 1.2 1 V

–40°C < TJ< 125°C 0.8

IHON/OFF pin input current ON/OFF pin = 5 V (OFF) 12 30 μA

IIL ON/OFF pin = 0 V (ON) 0 10 μA

(1) Test Circuit in Figure 22 and Figure 27.

(2) All limits specified at room temperature and at temperature extremes . All room temperature limits are 100% production tested. All limits

at temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to

calculate Average Outgoing Quality Level.

6.6 Electrical Characteristics – 3.3-V Version

TJ= 25°C, and all MIN and MAX apply over full operating temperature range (unless otherwise noted).

PARAMETER(1) TEST CONDITIONS MIN(2) TYP MAX(2) UNIT

VOUT Output voltage

VIN = 12 V, ILOAD = 100 mA 3.234 3.3 3.366

LM2574, 4.75 V ≤VIN ≤40 V,

0.1 A ≤ILOAD ≤0.5 A TJ= 25°C 3.168 3.3 3.432

−40°C ≤TJ≤125°C 3.135 3.465

LM2574HV, 4.75 V ≤VIN ≤60 V,

0.1 A ≤ILOAD ≤0.5 A TJ= 25°C 3.168 3.3 3.45

−40°C ≤TJ≤125°C 3.135 3.482

ηEfficiency VIN = 12 V, ILOAD = 0.5 A 72%

LM2574

LM2574HV

SNVS104E –JUNE 1999–REVISED JULY 2018

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Product Folder Links: LM2574 LM2574HV

(1) Test circuit in Figure 22 and Figure 27.

(2) All limits specified at room temperature TYP and MAX. All room temperature limits are 100% production tested. All limits at temperature

extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate

Average Outgoing Quality Level.

6.7 Electrical Characteristics – 5-V Version

TJ= 25°C, and all MIN and MAX apply over full operating temperature range (unless otherwise noted).

PARAMETER(1) TEST CONDITIONS MIN TYP(2) MAX(2) UNIT

VOUT Output voltage

VIN = 12 V, ILOAD = 100 mA 4.9 5 5.1

LM2574, 7 V ≤VIN ≤40 V,

0.1 A ≤ILOAD ≤0.5 A TJ= 25°C 4.8 5 5.2

−40°C ≤TJ≤125°C 4.75 5.25

LM2574HV, 7 V ≤VIN ≤60 V,

0.1 A ≤ILOAD ≤0.5 A TJ= 25°C 4.8 5 5.225

−40°C ≤TJ≤125°C 4.75 5.275

ηEfficiency VIN = 12 V, ILOAD = 0.5 A 77%

(1) Test circuit in Figure 22 and Figure 27.

(2) All limits specified at room temperature TYP and MAX. All room temperature limits are 100% production tested. All limits at temperature

extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate

Average Outgoing Quality Level.

6.8 Electrical Characteristics – 12-V Version

TJ= 25°C, and all MIN and MAX apply over full operating temperature range (unless otherwise noted).

PARAMETER(1) CONDITIONS MIN TYP(2) MAX(2) UNIT

VOUT Output voltage

VIN = 25 V, ILOAD = 100 mA 11.76 12 12.24

LM2574, 15 V ≤VIN ≤40 V,

0.1 A ≤ILOAD ≤0.5 A TJ= 25°C 11.52 12 12.48

−40°C ≤TJ≤125°C 11.4 12.6

LM2574HV, 15 V ≤VIN ≤60 V,

0.1 A ≤ILOAD ≤0.5 A TJ= 25°C 11.52 12 12.54

−40°C ≤TJ≤125°C 11.4 12.66

ηEfficiency VIN = 15 V, ILOAD = 0.5 A 88%

(1) Test circuit in Figure 22 and Figure 27.

(2) All limits specified at room temperature TYP and MAX. All room temperature limits are 100% production tested. All limits at temperature

extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate

Average Outgoing Quality Level.

6.9 Electrical Characteristics – 15-V Version

TJ= 25°C, and all MIN and MAX apply over full operating temperature range (unless otherwise noted).

PARAMETER(1) TEST CONDITIONS MIN TYP(2) MAX(2) UNIT

VOUT Output voltage

VIN = 30 V, ILOAD = 100 mA 14.7 15 15.3

LM2574, 18 V ≤VIN ≤40 V,

0.1A ≤ILOAD ≤0.5 A TJ= 25°C 14.4 15 15.6

−40°C ≤TJ≤125°C 14.25 15.75

LM2574HV, 18 V ≤VIN ≤60 V,

0.1 A ≤ILOAD ≤0.5 A TJ= 25°C 14.4 15 15.68

−40°C ≤TJ≤125°C 14.25 15.83

ηEfficiency VIN = 18 V, ILOAD = 0.5 A 88%

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(1) Test circuit in Figure 22 and Figure 27.

(2) All limits specified at room temperature TYP and MAX. All room temperature limits are 100% production tested. All limits at temperature

extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate

Average Outgoing Quality Level.

6.10 Electrical Characteristics – Adjustable Version

TJ= 25°C, and all MIN and MAX apply over full operating temperature range. VIN = 12 V, ILOAD = 100 mA (unless otherwise

noted).

PARAMETER(1) TEST CONDITIONS MIN TYP(2) MAX(2) UNIT

VFB Feedback voltage

VIN = 12 V, ILOAD = 100 mA 1.217 1.23 1.243

LM2574, 7 V ≤VIN ≤40 V,

0.1 A ≤ILOAD ≤0.5 A,

VOUT programmed for 5 V

TJ= 25°C 1.193 1.23 1.267

−40°C ≤TJ≤125°C 1.18 1.28

LM2574HV, 7 V ≤VIN ≤60 V,

0.1 A ≤ILOAD ≤0.5 A,

VOUT programmed for 5 V

TJ= 25°C 1.193 1.23 1.273

−40°C ≤TJ≤125°C 1.18 1.286

ηEfficiency VIN = 12 V, VOUT = 5 V, ILOAD = 0.5 A 77%

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6.11 Typical Characteristics

See Figure 27.

Figure 1. Normalized Output Voltage Figure 2. Line Regulation

Figure 3. Dropout Voltage Figure 4. Current Limit

Figure 5. Supply Current Figure 6. Standby Quiescent Current

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Typical Characteristics (continued)

See Figure 27.

Figure 7. Oscillator Frequency Figure 8. Switch Saturation Voltage

Figure 9. Efficiency Figure 10. Minimum Operating Voltage

Figure 11. Supply Current vs Duty Cycle Figure 12. Feedback Voltage vs Duty Cycle

LM2574

LM2574HV

SNVS104E –JUNE 1999–REVISED JULY 2018

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Typical Characteristics (continued)

See Figure 27.

Figure 13. Feedback Pin Current Figure 14. Junction-to-Ambient Thermal Resistance

Unregulated

DC Input

CIN

Feedback 1

VIN Internal

Regulator ON / OFF

Signal

GND

±+

1.23 V

BAND ± GAP

REFRENCE Reset Thermal

Shutdown Current

Limit

52 kHz

OSCILLATOR

Compatator

Fixed Gain

Error Amp

ON / OFF

0.5 Amp

Switch

DRIVER

Pwr Gnd

Output +COUT

VOUT

LM2574

LM2574HV

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7 Detailed Description

7.1 Overview

The LM2574 SIMPLE SWITCHER®regulator is an easy-to-use, non-synchronous, step-down DC-DC converter

with a wide input voltage range from 40 V to up to 60 V for a HV version. It is capable of delivering up to 0.5-A

DC load current with excellent line and load regulation. These devices are available in fixed output voltages of

3.3 V, 5 V, 12 V, 15 V, and an adjustable output version. The family requires few external components and the

pin arrangement was designed for simple, optimum PCB layout.

7.2 Functional Block Diagram

Note: Pin numbers are for the 8-pin PDIP package

R1 = 1 k

3.3 V, R2 = 1.7 k

5 V, R2 = 3.1 k

12 V, R2 = 8.84 k

15 V, R2 = 11.3 k

For adjustable version,

R1 = Open, R2 = 0 Ω

7.3 Feature Description

7.3.1 Current Limit

The LM2574 device has current limiting to prevent the switch current from exceeding safe values during an

accidental overload on the output. This value (ICL) can be found in Electrical Characteristics for All Output

Voltage Versions.

7.3.2 Undervoltage Lockout

In some applications, it is desirable to keep the regulator off until the input voltage reaches a certain threshold.

An undervoltage lockout circuit which accomplishes this task is shown in Figure 15 while Figure 16 shows the

same circuit applied to a buck-boost configuration. These circuits keep the regulator off until the input voltage

reaches a predetermined level in Equation 1.

VTH ≈VZ1 + 2 VBE (1)

LM2574

LM2574HV

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Feature Description (continued)

Note: Complete circuit not shown (see Figure 20).

Note: Pin numbers are for 8-pin PDIP package.

Figure 15. Undervoltage Lockout for Buck Circuit

Note: Complete circuit not shown (see Figure 20).

Note: Pin numbers are for 8-pin PDIP package.

Figure 16. Undervoltage Lockout for Buck-Boost Circuit

7.3.3 Delayed Start-Up

The ON/OFF pin can be used to provide a delayed start-up feature as shown in Figure 17. With an input voltage

of 20 V and for the part values shown, the circuit provides approximately 10 ms of delay time before the circuit

begins switching. Increasing the RC time constant can provide longer delay times. But excessively large RC time

constants can cause problems with input voltages that are high in 60-Hz or 120-Hz ripple, by coupling the ripple

into the ON/OFF pin.

7.3.4 Adjustable Output, Low-Ripple Power Supply

A 500-mA power supply that features an adjustable output voltage is shown in Figure 18. An additional L-C filter

that reduces the output ripple by a factor of 10 or more is included in this circuit.

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Feature Description (continued)

Note: Complete circuit not shown.

Note: Pin numbers are for 8-pin PDIP package.

Figure 17. Delayed Start-Up

Note: Pin numbers are for 8-pin PDIP package.

Figure 18. 1.2-V to 55-V Adjustable 500-mA Power Supply With Low-Output Ripple

7.4 Device Functional Modes

7.4.1 Shutdown Mode

The ON/OFF pin provides electrical ON and OFF control for the LM2574. When the voltage of this pin is higher

than 1.4 V, the device is shutdown mode. The typical standby current in this mode is 50 μA.

7.4.2 Active Mode

When the voltage of the ON/OFF pin is below 1.2 V, the device starts switching and the output voltage rises until

it reaches a normal regulation voltage.

OUT

OUT IN

T V V

ON OUT

t V

T V

LOAD

1.2 I

´ ´

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LM2574HV

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

8.1.1 Input Capacitor (CIN)

To maintain stability, the regulator input pin must be bypassed with at least a 22-μF electrolytic capacitor. The

leads of the capacitor must be kept short, and located near the regulator.

If the operating temperature range includes temperatures below −25°C, the input capacitor value may need to be

larger. With most electrolytic capacitors, the capacitance value decreases and the ESR increases with lower

temperatures and age. Paralleling a ceramic or solid tantalum capacitor increases the regulator stability at cold

temperatures. For maximum capacitor operating lifetime, the RMS ripple current rating of the capacitor must be

greater than Equation 2.

where

• for a buck regulator

• for a buck-boost regulator (2)

8.1.2 Inductor Selection

All switching regulators have two basic modes of operation: continuous and discontinuous. The difference

between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a

period of time in the normal switching cycle. Each mode has distinctively different operating characteristics,

which can affect the regulator performance and requirements.

The LM2574 (or any of the SIMPLE SWITCHER family) can be used for both continuous and discontinuous

modes of operation.

In many cases the preferred mode of operation is in the continuous mode. It offers better load regulation, lower

peak switch, inductor, and diode currents, and can have lower output ripple voltage. But it does require relatively

large inductor values to keep the inductor current flowing continuously, especially at low output load currents.

To simplify the inductor selection process, an inductor selection guide (nomograph) was designed. This guide

assumes continuous mode operation, and selects an inductor that allows a peak-to-peak inductor ripple current

(ΔIIND) to be a certain percentage of the maximum design load current. In the LM2574 SIMPLE SWITCHER, the

peak-to-peak inductor ripple current percentage (of load current) is allowed to change as different design load

currents are selected. By allowing the percentage of inductor ripple current to increase for lower current

applications, the inductor size and value can be kept relatively low.

8.1.3 Inductor Ripple Current

When the switcher is operating in the continuous mode, the inductor current waveform ranges from a triangular

to a sawtooth type of waveform (depending on the input voltage). For a given input voltage and output voltage,

the peak-to-peak amplitude of this inductor current waveform remains constant. As the load current rises or falls,

the entire sawtooth current waveform also rises or falls. The average DC value of this waveform is equal to the

DC load current (in the buck regulator configuration).

IND

I212 106 mA

2 2

= = =

IND

LOAD

I212

I 0.4 A 506 mA

2 2

æ ö æ ö

= + = + =

ç ÷ ç ÷

è ø

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Application Information (continued)

If the load current drops to a low enough level, the bottom of the sawtooth current waveform reaches zero, and

the switcher changes to a discontinuous mode of operation. This is a perfectly acceptable mode of operation.

Any buck switching regulator (no matter how large the inductor value is) is forced to run discontinuous if the load

current is light enough.

The curve shown in Figure 19 illustrates how the peak-to-peak inductor ripple current (ΔIIND) is allowed to change

as different maximum load currents are selected, and also how it changes as the operating point varies from the

upper border to the lower border within an inductance region (see Inductor Selection).

Figure 19. Inductor Ripple Current (ΔiIND) Range

Consider the following example:

VOUT =5Vat0.4A

VIN = 10-V minimum up to 20-V maximum

The selection guide in Figure 24 shows that for a 0.4-A load current, and an input voltage range between 10 V

and 20 V, the inductance region selected by the guide is 330 μH. This value of inductance allows a peak-to-peak

inductor ripple current (ΔIIND) to flow that is a percentage of the maximum load current. For this inductor value,

the ΔIIND also varies depending on the input voltage. As the input voltage increases to 20 V, it approaches the

upper border of the inductance region, and the inductor ripple current increases. Referring to the curve in

Figure 19, it can be seen that at the 0.4-A load current level, and operating near the upper border of the 330-μH

inductance region, the ΔIIND is 53% of 0.4 A, or 212 mAp-p.

This ΔIIND is important because from this number the peak inductor current rating can be determined, the

minimum load current required before the circuit goes to discontinuous operation, and also, knowing the ESR of

the output capacitor, the output ripple voltage can be calculated, or conversely, measuring the output ripple

voltage and knowing the ΔIIND, the ESR can be calculated.

From the previous example, the peak-to-peak inductor ripple current (ΔIIND) = 212 mAp-p. When the ΔIND value is

known, the following three formulas can be used to calculate additional information about the switching regulator

circuit:

1. Peak inductor or peak switch current in Equation 3.

(3)

2. Minimum load current before the circuit becomes discontinuous in Equation 4.

(4)

3. Output ripple voltage = (ΔIIND) × (ESR of COUT)

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Application Information (continued)

The selection guide chooses inductor values suitable for continuous mode operation, but if the inductor value

chosen is prohibitively high, the designer should investigate the possibility of discontinuous operation.

Inductors are available in different styles such as pot core, toroid, E-frame, bobbin core, and so forth, as well as

different core materials, such as ferrites and powdered iron. The least expensive, the bobbin core type, consists

of wire wrapped on a ferrite rod core. This type of construction makes for an inexpensive inductor, but because

the magnetic flux is not completely contained within the core, it generates more electro-magnetic interference

(EMI). This EMl can cause problems in sensitive circuits, or can give incorrect scope readings because of

induced voltages in the scope probe.

The inductors listed in the selection chart include powdered iron toroid for Pulse Engineering, and ferrite bobbin

core for Renco.

An inductor must not be operated beyond its maximum rated current because it may saturate. When an inductor

begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC

resistance of the winding). This can cause the inductor current to rise very rapidly and affects the energy storage

capabilities of the inductor and could cause inductor overheating. Different inductor types have different

saturation characteristics, and consider this when selecting an inductor. The inductor manufacturers' data sheets

include current and energy limits to avoid inductor saturation.

8.1.4 Output Capacitor

An output capacitor is required to filter the output voltage and is needed for loop stability. The capacitor must be

located near the LM2574 using short PCB traces. Standard aluminum electrolytics are usually adequate, but low

ESR types are recommended for low output ripple voltage and good stability. The ESR of a capacitor depends

on many factors, some which are: the value, the voltage rating, physical size, and the type of construction. In

general, low-value or low-voltage (less than 12 V) electrolytic capacitors usually have higher ESR numbers.

The amount of output ripple voltage is primarily a function of the equivalent series resistance (ESR ) of the output

capacitor and the amplitude of the inductor ripple current, ΔIIND (see Inductor Ripple Current (ΔiIND)).

The lower capacitor values (100 μF to 330 μF) allows typically 50 mV to 150 mV of output ripple voltage, while

larger-value capacitors reduce the ripple to approximately 20 mV to 50 mV (as seen in Equation 5).

Output Ripple Voltage = (ΔIIND) (ESR of COUT) (5)

To further reduce the output ripple voltage, several standard electrolytic capacitors may be paralleled, or a

higher-grade capacitor may be used. Such capacitors are often called high-frequency, low-inductance, or low-

ESR. These reduce the output ripple to 10 mV or 20 mV. However, when operating in the continuous mode,

reducing the ESR below 0.03 Ωcan cause instability in the regulator.

Tantalum capacitors can have a very low ESR, and must be carefully evaluated if it is the only output capacitor.

Because of their good low temperature characteristics, a tantalum can be used in parallel with aluminum

electrolytics, with the tantalum making up 10% or 20% of the total capacitance.

The ripple current rating of the capacitor at 52 kHz must be at least 50% higher than the peak-to-peak inductor

ripple current.

8.1.5 Catch Diode

Buck regulators require a diode to provide a return path for the inductor current when the switch is off. This diode

must be located close to the LM2574 using short leads and short printed-circuit traces.

Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best efficiency,

especially in low output voltage switching regulators (less than 5 V). fast-recovery, high-efficiency, or ultra-fast

recovery diodes are also suitable, but some types with an abrupt turnoff characteristic may cause instability and

EMI problems. A fast-recovery diode with soft recovery characteristics is a better choice. Standard 60-Hz diodes

(for example, 1N4001 or 1N5400, and so forth) are also not suitable. See Table 1 for Schottky and soft fast-

recovery diode selection guide.

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Table 1. Diode Selection Guide

VR1-A DIODES

SCHOTTKY FAST RECOVERY

20 V 1N5817

SR102

MBR120P

30 V

1N5818

SR103

11DQ03

MBR130P

10JQ030

The following diodes are all rated to 100 V

11DF1

10JF1

MUR110

HER102

40 V

1N5819

SR104

11DQ04

11JQ04

MBR140P

50 V MBR150

SR105

11DQ05

11JQ05

60 V MBR160

SR106

11DQ06

11JQ06

90 V 11DQ09

8.1.6 Output Voltage Ripple and Transients

The output voltage of a switching power supply contains a sawtooth ripple voltage at the switcher frequency,

typically about 1% of the output voltage, and may also contain short voltage spikes at the peaks of the sawtooth

waveform.

The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of the output

capacitor (see Inductor Selection).

The voltage spikes are present because of the fast switching action of the output switch, and the parasitic

inductance of the output filter capacitor. To minimize these voltage spikes, special low inductance capacitors can

be used, and their lead lengths must be kept short. Wiring inductance, stray capacitance, as well as the scope

probe used to evaluate these transients, all contribute to the amplitude of these spikes.

An additional small LC filter (20 μH and 100 μF) can be added to the output (as shown in Figure 18) to further

reduce the amount of output ripple and transients. A 10 × reduction in output ripple voltage and transients is

possible with this filter.

8.1.7 Feedback Connection

The LM2574 (fixed voltage versions) feedback pin must be wired to the output voltage point of the switching

power supply. When using the adjustable version, physically locate both output voltage programming resistors

near the LM2574 to avoid picking up unwanted noise. Avoid using resistors greater than 100 kΩbecause of the

increased chance of noise pickup.

8.1.8 ON/OFF Input

For normal operation, the ON/OFF pin must be grounded or driven with a low-level TTL voltage (typically less

than 1.6 V). To put the regulator into standby mode, drive this pin with a high-level TTL or CMOS signal. The

ON/OFF pin can be safely pulled up to +VIN without a resistor in series with it. The ON/OFF pin must not be left

open.

( )

LOAD IN OUT IN OUT

IN IN OUT 1 OSC

I V V V V 1

V V V 2 L f

´ + ´

» + ´

+ ´ ´

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8.1.9 Additional Applications

8.1.9.1 Inverting Regulator

Figure 20 shows a LM2574-12 in a buck-boost configuration to generate a negative 12-V output from a positive

input voltage. This circuit bootstraps the ground pin of the regulator to the negative output voltage, then by

grounding the feedback pin, the regulator senses the inverted output voltage and regulates it to −12 V.

Note: Pin numbers are for the 8-pin PDIP package.

Figure 20. Inverting Buck-Boost Develops, 12 V

For an input voltage of 8 V or more, the maximum available output current in this configuration is approximately

100 mA. At lighter loads, the minimum input voltage required drops to approximately 4.7 V.

The switch currents in this buck-boost configuration are higher than in the standard buck-mode design, thus

lowering the available output current. Also, the start-up input current of the buck-boost converter is higher than

the standard buck-mode regulator, and this may overload an input power source with a current limit less than

0.6 A. Using a delayed turnon or an undervoltage lockout circuit (described in Negative Boost Regulator) would

allow the input voltage to rise to a high enough level before the switcher would be allowed to turn on.

Because of the structural differences between the buck and the buck-boost regulator topologies, the design

procedure can not be used to select the inductor or the output capacitor. The recommended range of inductor

values for the buck-boost design is between 68 μH and 220 μH, and the output capacitor values must be larger

than what is normally required for buck designs. Low-input voltages or high-output currents require a large value

output capacitor (in the thousands of micro Farads).

The peak inductor current, which is the same as the peak switch current, can be calculated from Equation 6.

where

• fosc = 52 kHz. Under normal continuous inductor current operating conditions,

• the minimum VIN represents the worst case. Select an inductor that is rated for the peak current anticipated. (6)

Also, the maximum voltage appearing across the regulator is the absolute sum of the input and output voltage.

For a −12-V output, the maximum input voltage for the LM2574 is 28 V, or 48 V for the LM2574HV.

8.1.9.2 Negative Boost Regulator

Another variation on the buck-boost topology is the negative boost configuration. The circuit in Figure 21 accepts

an input voltage ranging from −5 V to −12 V and provides a regulated −12-V output. Input voltages greater than

−12 V causes the output to rise greater than −12 V, but does not damage the regulator.

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Note: Pin numbers are for 8-pin PDIP package.

Figure 21. Negative Boost

Because of the boosting function of this type of regulator, the switch current is relatively high, especially at low

input voltages. Output load current limitations are a result of the maximum current rating of the switch. Also,

boost regulators can not provide current-limiting load protection in the event of a shorted load, so some other

means (such as a fuse) may be necessary.

8.2 Typical Applications

8.2.1 Fixed Output Voltage Applications

CIN: 22 μF, 75 V

Aluminum electrolytic

COUT: 220 μF, 25 V

Aluminum electrolytic

D1: Schottky, 11DQ06

L1: 330 μH, 52627

(for 5 V in, 3.3 V out, use

100 μH, RL-1284-100)

R1: 2k, 0.1%

R2: 6.12k, 0.1%

Figure 22. Fixed Output Voltage Versions

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Typical Applications (continued)

8.2.1.1 Design Requirements

The design requirements for the fixed output voltage application is provided in Table 2.

Table 2. Design Parameters

PARAMETER EXAMPLE VALUE

Regulated output voltage (3.3 V, 5 V, 12 V, or 15 V), VOUT 5 V

Maximum input voltage, VIN(Max) 15 V

Maximum load current, ILOAD(Max) 0.4 A

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Custom Design With WEBENCH® Tools

Click here to create a custom design using the LM2574 device with the WEBENCH® Power Designer.

1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.

2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

• Run electrical simulations to see important waveforms and circuit performance

• Run thermal simulations to understand board thermal performance

• Export customized schematic and layout into popular CAD formats

• Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

8.2.1.2.2 Inductor Selection (L1)

Select the correct Inductor value selection guide from Figure 23,Figure 24,Figure 25,orFigure 26 (output

voltages of 3.3 V, 5 V, 12 V, or 15 V respectively).

From the inductor value selection guide, identify the inductance region intersected by VIN(Max) and ILOAD(Max).

The inductance area intersected by the 15-V line and 0.4-A line is 330.

Select an appropriate inductor from Table 3. Part numbers are listed for three inductor manufacturers. The

inductor chosen must be rated for operation at the LM2574 switching frequency (52 kHz) and for a current rating

of 1.5 × ILOAD. For additional inductor information, see Inductor Selection. The required inductor value is 330 μH.

From Table 3, choose Pulse Engineering PE-52627, Renco RL-1284-330, or NPI NP5920/5921.

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Table 3. Inductor Selection By Manufacturer's Part Number

INDUCTOR VALUE PULSE ENG. RENCO NPI

68 μH * RL-1284-68-43 NP5915

100 μH * RL-1284-100-43 NP5916

150 μH 52625 RL-1284-150-43 NP5917

220 μH 52626 RL-1284-220-43 NP5918/5919

330 μH 52627 RL-1284-330-43 NP5920/5921

470 μH 52628 RL-1284-470-43 NP5922

680 μH 52629 RL-1283-680-43 NP5923

1000 μH 52631 RL-1283-1000-43 *

1500 μH * RL-1283-1500-43 *

2200 μH * RL-1283-2200-43 *

8.2.1.2.3 Output Capacitor Selection (COUT)

The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching

regulator loop. For stable operation and an acceptable output ripple voltage, (approximately 1% of the output

voltage) a value between 100 μF and 470 μF is recommended. COUT = 100-μF to 470-μF standard aluminum

electrolytic.

The voltage rating of the capacitor must be at least 1.5 times greater than the output voltage. For a 5-V regulator,

a rating of at least 8 V is appropriate, and a 10-V or 15-V rating is recommended. Capacitor voltage rating =

20 V.

Higher voltage electrolytic capacitors generally have lower ESR numbers, and for this reason it may be

necessary to select a capacitor rated for a higher voltage than would normally be needed.

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8.2.1.2.4 Catch Diode Selection (D1)

The catch-diode current rating must be at least 1.5 times greater than the maximum load current. Also, if the

power supply design must withstand a continuous output short, the diode must have a current rating equal to the

maximum current limit of the LM2574. The most stressful condition for this diode is an overload or shorted output

condition. For this example, a 1-A current rating is adequate.

The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Use a 20-V

1N5817 or SR102 Schottky diode, or any of the suggested fast-recovery diodes shown in Table 1.

8.2.1.2.5 Input Capacitor (CIN)

An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable

operation. A 22-μF aluminum electrolytic capacitor located near the input and ground pins provides sufficient

bypassing.

8.2.1.3 Application Curves

Figure 23. 3.3-V LM2574HV Inductor Selection Guide Figure 24. 5-V LM2574HV Inductor Selection Guide

Figure 25. 12-V LM2574HV Inductor Selection Guide Figure 26. 15-V LM2574HV Inductor Selection Guide

OUT

2 1

REF

V24 V

R R 1 1 k 1

V 1.23 V

æ ö æ ö

= ´ - = ´ -

ç ÷ ç ÷

è ø

OUT

V 1.23 1

æ ö

= ´ +

ç ÷

è ø

OUT

2 1

REF

R R 1

æ ö

= ´ -

ç ÷

è ø

OUT REF

V V 1

æ ö

= ´ +

ç ÷

è ø

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8.2.2 Adjustable Output Voltage Applications

Figure 27. Adjustable Output Voltage Version

8.2.2.1 Design Requirements

The design requirements for the fixed output voltage application is provided in Table 4.

Table 4. Design Parameters

PARAMETER EXAMPLE VALUE

Regulated output voltage, VOUT 24 V

Maximum input voltage, VIN(Max) 40 V

Maximum load current, ILOAD(Max) 0.4 A

Switching frequency, F 52 kHz

8.2.2.2 Detailed Design Procedure

8.2.2.2.1 Programming Output Voltage

Selecting R1 and R2, as shown in Figure 27.

Use Equation 7 to select the appropriate resistor values.

where

• VREF = 1.23 V (7)

R1can be between 1k and 5k as in Equation 8. For best temperature coefficient and stability with time, use 1%

metal film resistors.

(8)

For this example, use Equation 9 and Equation 10.

select

• R1 = 1k (9)

(10)

R2= 1k (19.51−1) = 18.51k, closest 1% value is 18.7k

OUT

C 13300 22.2 µF

24 1000

> ´ =

( )

( )( )

IN MAX

OUT

C 13300 µF

V L µH

³ ´ ´

( ) 24 1000

E T 40 24 185 V µs

40 52

´ = - ´ ´ = ´

( ) ( )( )

OUT

IN OUT

V1000

E T V V V µs

V F kHz

´ = - ´ ´ ´

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8.2.2.2.2 Inductor Selection (L1)

Calculate the inductor Volt × microsecond constant, E × T (V × μs), from Equation 11.

(11)

For this example, calculate E × T (V × μs) using Equation 12.

(12)

Use the E × T value from the previous formula and match it with the E × T number on the vertical axis of the

inductor value selection guide shown in Figure 32. For this example, E × T = 185 V × μs.

On the horizontal axis, select the maximum load current, ILOAD(Max) = 0.4 A.

Identify the inductance region intersected by the E × T value and the maximum load current value, and note the

inductor value for that region, inductance region = 1000.

Select an appropriate inductor from the table shown in Table 3. Part numbers are listed for three inductor

manufacturers. The inductor chosen must be rated for operation at the LM2574 switching frequency (52 kHz) and

for a current rating of 1.5 × ILOAD. For additional inductor information, see Inductor Selection.

8.2.2.2.3 Output Capacitor Selection (COUT)

The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching

regulator loop. For stable operation, the capacitor must satisfy the requirement in Equation 13.

(13)

Equation 13 yields capacitor values between 5 μF and 1000 μF that satisfies the loop requirements for stable

operation. But to achieve an acceptable output ripple voltage, (approximately 1% of the output voltage) and

transient response, the output capacitor may need to be several times larger than the above formula yields.

The voltage rating of the capacitor must be at last 1.5 times greater than the output voltage. For a 24-V regulator,

a rating of at least 35 V is recommended. Higher voltage electrolytic capacitors generally have lower ESR

numbers, and for this reasion it may be necessary to select a capacitor rate for a higher voltage than would

normally be needed.

(14)

However, for acceptable output ripple voltage select:

COUT ≥100 μF

COUT = 100 μF electrolytic capacitor

8.2.2.2.4 Catch Diode Selection (D1)

The catch-diode current rating must be at least 1.5 times greater than the maximum load current. Also, if the

power supply design must withstand a continuous output short, the diode must have a current rating equal to the

maximum current limit of the LM2574. The most stressful condition for this diode is an overload or shorted output

condition. Suitable diodes are shown in Table 1. For this example, a 1-A current rating is adequate.

The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Use a 50-V

MBR150 or 11DQ05 Schottky diode, or any of the suggested fast-recovery diodes in Table 1.

8.2.2.2.5 Input Capacitor (CIN)

An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable

operation. A 22-μF aluminum electrolytic capacitor located near the input and ground pins provides sufficient

bypassing (see Table 1).

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8.2.2.3 Application Curves

Output pin voltage, 10 V/div, Horizontal time base,

Inductor current, 0.2 A/div, 5 μs/div,

Output ripple voltage, VOUT = 5 V,

20 mV/div, 500-mA load current,

AC-coupled L = 330 Μh

Figure 28. Continuous Mode Switching Waveforms

Output pin voltage, 10 V/div, Horizontal time base,

Inductor current, 0.2 A/div, 5 μs/div,

Output ripple voltage, VOUT = 5 V,

20 mV/div, 100-mA load current,

AC-coupled L = 100 Μh

Figure 29. Discontinuous Mode Switching Waveforms

Output voltage, 50 V/div, 500 mA load,

AC-coupled, L = 330 Μh,

100-mA to 500-mA load pulse, COUT = 300 Μf,

Horizontal time base: 200 μs/div

Figure 30. Transient Response for

Continuous Mode Operation

Output voltage, 50 V/div, 250 mA load,

AC-coupled, L = 68 Μh,

50-mA to 250-mA load pulse, COUT = 470 Μf,

Horizontal time base: 200 μs/div

Figure 31. Transient Response for

Discontinuous Mode Operation

Figure 32. Adjustable LM2574HV Inductor Selection Guide

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9 Power Supply Recommendations

As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring

inductance generate voltage transients which can cause problems. For minimal inductance and ground loops, the

length of the leads indicated by heavy lines must be kept as short as possible. Single-point grounding (as

indicated) or ground plane construction must be used for best results. When using the adjustable version,

physically locate the programming resistors near the regulator, to keep the sensitive feedback wiring short.

10 Layout

10.1 Layout Guidelines

The layout is critical for the proper operation of switching power supplies. First, the ground plane area must be

sufficient for thermal dissipation purposes. Second, appropriate guidelines must be followed to reduce the effects

of switching noise. Switch mode converters are very fast switching devices. In such cases, the rapid increase of

input current combined with the parasitic trace inductance generates unwanted L di/dt noise spikes. The

magnitude of this noise tends to increase as the output current increases. This noise may turn into

electromagnetic interference (EMI) and can also cause problems in device performance. Therefore, take care in

the layout to minimize the effect of this switching noise.

The most important layout rule is to keep the AC current loops as small as possible. Figure 33 shows the current

flow in a buck converter. The top schematic shows a dotted line which represents the current flow during the top

switch ON-state. The middle schematic shows the current flow during the top switch OFF-state. The bottom

schematic shows the currents referred to as AC currents. These AC currents are the most critical because they

are changing in a very short time period. The dotted lines of the bottom schematic are the traces to keep as short

and wide as possible. This also yields a small loop area reducing the loop inductance. To avoid functional

problems due to layout, review the PCB layout example. Best results are achieved if the placement of the

LM2574 device, the bypass capacitor, the Schottky diode, RFBB, RFBT, and the inductor are placed as shown in

the example. In the layout shown, R1 = RFBB and R2 = RFBT. TI also recommends using 2-oz. copper boards

or heavier to help thermal dissipation and to reduce the parasitic inductances of board traces. See the application

note AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) for more information.

Figure 33. Buck Converter Current Flow

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10.2 Layout Example

Figure 34. LM2574 Adjustable Output Voltage Layout

10.3 Grounding

The 8-pin molded PDIP and the 14-pin SOIC package have separate power and signal ground pins. Both ground

pins must be soldered directly to wide printed-circuit board copper traces to assure low inductance connections

and good thermal properties.

10.4 Thermal Considerations

The 8-pin PDIP (P) package and the 14-pin SOIC (NPA) package are molded plastic packages with solid copper

lead frames. The copper lead frame conducts the majority of the heat from the die, through the leads, to the

printed-circuit board copper, which acts as the heat sink. For best thermal performance, wide copper traces must

be used, and all ground and unused pins must be soldered to generous amounts of printed-circuit board copper,

such as a ground plane. Large areas of copper provide the best transfer of heat (lower thermal resistance) to the

surrounding air, and even double-sided or multilayer boards provide better heat paths to the surrounding air.

Unless the power levels are small, using a socket for the 8-pin package is not recommended because of the

additional thermal resistance it introduces, and the resultant higher junction temperature.

Because of the 0.5-A current rating of the LM2574, the total package power dissipation for this switcher is quite

low, ranging from approximately 0.1 W up to 0.75 W under varying conditions. In a carefully engineered printed-

circuit board, both the P and the NPA package can easily dissipate up to 0.75 W, even at ambient temperatures

of 60°C, and still keep the maximum junction temperature less than 125°C.

A curve, Figure 14, displaying thermal resistance versus PCB area for the two packages is shown in Typical

Characteristics.

These thermal resistance numbers are approximate, and there can be many factors that affect the final thermal

resistance. Some of these factors include board size, shape, thickness, position, location, and board

temperature. Other factors are, the area of printed-circuit copper, copper thickness, trace width, multi-layer,

single- or double-sided, and the amount of solder on the board. The effectiveness of the PCB to dissipate heat

also depends on the size, number and spacing of other components on the board. Furthermore, some of these

components, such as the catch diode and inductor generate some additional heat. Also, the thermal resistance

decreases as the power level increases because of the increased air current activity at the higher power levels,

and the lower surface to air resistance coefficient at higher temperatures.

The data sheet thermal resistance curves can estimate the maximum junction temperature based on operating

conditions. ln addition, the junction temperature can be estimated in actual circuit operation by using

Equation 15.

Tj= Tcu + (θj-cu × PD) (15)

OUT

D IN S LOAD SAT

P V I I V

= ´ + ´ ´

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Thermal Considerations (continued)

With the switcher operating under worst case conditions and all other components on the board in the intended

enclosure, measure the copper temperature (Tcu ) near the IC. This can be done by temporarily soldering a small

thermocouple to the PCB copper near the IC, or by holding a small thermocouple on the PCB copper using

thermal grease for good thermal conduction.

The thermal resistance (θj-cu) for the two packages is:

θj-cu = 42°C/W for the P-8 package

θj-cu = 52°C/W for the NPA-14 package

The power dissipation (PD) for the IC could be measured, or it can be estimated by using Equation 16.

where

• ISis obtained from the typical supply current curve (adjustable version use the supply current vs duty cycle

curve) (16)

OUT OUT

IN OUT LOSS

P P

P P P

h = =

OUT

OUT IN

T V V

= =

ON OUT

t V

T V

= =

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11 Device and Documentation Support

11.1 Device Support

11.1.1 Third-Party Products Disclaimer

TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT

CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES

OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER

ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.

11.1.2 Custom Design With WEBENCH® Tools

Click here to create a custom design using the LM2574 device with the WEBENCH® Power Designer.

1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.

2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

• Run electrical simulations to see important waveforms and circuit performance

• Run thermal simulations to understand board thermal performance

• Export customized schematic and layout into popular CAD formats

• Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

11.1.3 Device Nomenclature

11.1.3.1 Buck Regulator

A switching regulator topology in which a higher voltage is converted to a lower voltage. Also known as a step-

down switching regulator.

11.1.3.2 Buck-Boost Regulator

A switching regulator topology in which a positive voltage is converted to a negative voltage without a

transformer.

11.1.3.3 Duty Cycle (D)

The ratio of the ON-time of the output switch to the oscillator period calculated with Equation 17 for buck

regulators and Equation 18 for buck-boost regulators.

(17)

(18)

11.1.3.4 Catch Diode or Current Steering Diode

This diode provides a return path for the load current when the LM2574 switch is OFF.

In terms of efficiency (η), the proportion of input power actually delivered to the load calculated with Equation 19.

(19)

LM2574

LM2574HV

SNVS104E –JUNE 1999–REVISED JULY 2018

www.ti.com

Product Folder Links: LM2574 LM2574HV

Device Support (continued)

11.1.3.5 Capacitor Equivalent Series Resistance (ESR)

The purely resistive component of a real capacitor's impedance (see Figure 35) can causes power loss resulting

in capacitor heating, which directly affects the operating lifetime of the capacitor. When used as a switching

regulator output filter, higher ESR values result in higher output ripple voltages.

Figure 35. Simple Model Of A Real Capacitor

Most standard aluminum electrolytic capacitors in the 100 μF to 1000 μF range have 0.5-Ωto 0.1-ΩESR. Higher-

grade capacitors (low-ESR,high-frequency, or low-inductance) in the 100 μF to 1000 μF range generally have

ESR of less than 0.15 Ω.

11.1.3.6 Equivalent Series Inductance (ESL)

The pure inductance component of a capacitor is seen in Figure 35. The amount of inductance is determined to a

large extent on the capacitor's construction. In a buck regulator, this unwanted inductance causes voltage spikes

to appear on the output.

11.1.3.7 Output Ripple Voltage

The AC component of the output voltage of the switching regulator is usually dominated by the output capacitor's

ESR multiplied by the inductor's ripple current (ΔIIND). The peak-to-peak value of this sawtooth ripple current can

be determined by reading Inductor Ripple Current (ΔiIND).

11.1.3.8 Capacitor Ripple Current

The RMS value of the maximum allowable alternating current at which a capacitor can be operated continuously

at a specified temperature.

11.1.3.9 Standby Quiescent Current (ISTBY)

Supply current required by the LM2574 when in the standby mode (ON/OFF pin is driven to TTL-high voltage,

thus turning the output switch OFF).

11.1.3.10 Inductor Ripple Current (ΔiIND)

The peak-to-peak value of the inductor current waveform, typically a sawtooth waveform when the regulator is

operating in the continuous mode (vs. discontinuous mode).

11.1.3.11 Continuous and Discontinuous Mode Operation

These mode operations relate to the inductor current. In the continuous mode, the inductor current is always

flowing and never drops to zero, versus the discontinuous mode, where the inductor current drops to zero for a

period of time in the normal switching cycle.

11.1.3.12 Inductor Saturation

The condition which exists when an inductor cannot hold any more magnetic flux. When an inductor saturates,

the inductor appears less inductive and the resistive component dominates. Inductor current is then limited only

by the DC resistance of the wire and the available source current.

11.1.3.13 Operating Volt Microsecond Constant (E × Top)

The product (in VoIt × μs) of the voltage applied to the inductor and the time the voltage is applied. This E × Top

constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core,

the core area, the number of turns, and the duty cycle.

LM2574

LM2574HV

www.ti.com

SNVS104E –JUNE 1999–REVISED JULY 2018

Product Folder Links: LM2574 LM2574HV

11.2 Documentation Support

11.2.1 Related Documentation

For related documentation see the following:

AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines,SNVA054

11.3 Receiving Notification of Documentation Updates

To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper

right corner, click on Alert me to register and receive a weekly digest of any product information that has

changed. For change details, review the revision history included in any revised document.

11.4 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective

contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of

Use.

TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration

among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help

solve problems with fellow engineers.

Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and

contact information for technical support.

11.5 Trademarks

E2E is a trademark of Texas Instruments.

WEBENCH, SIMPLE SWITCHER are registered trademarks of Texas Instruments.

All other trademarks are the property of their respective owners.

11.6 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

11.7 Glossary

SLYZ022 —TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

PACKAGE OPTION ADDENDUM

www.ti.com 23-Jul-2018

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM2574HVM-12/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-12 P+

LM2574HVM-15 NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574HVM

-15 P+

LM2574HVM-15/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-15 P+

LM2574HVM-3.3/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-3.3 P+

LM2574HVM-5.0 NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574HVM

-5.0 P+

LM2574HVM-5.0/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-5.0 P+

LM2574HVM-ADJ NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574HVM

-ADJ P+

LM2574HVM-ADJ/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-ADJ P+

LM2574HVMX-12/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-12 P+

LM2574HVMX-15/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-15 P+

LM2574HVMX-3.3/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-4-260C-72 HR -40 to 125 LM2574HVM

-3.3 P+

LM2574HVMX-5.0 NRND SOIC NPA 14 1000 TBD Call TI Call TI -40 to 125 LM2574HVM

-5.0 P+

LM2574HVMX-5.0/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-5.0 P+

LM2574HVMX-ADJ/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574HVM

-ADJ P+

LM2574HVN-12/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN

-12 P+

LM2574HVN-15/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN

-15 P+

LM2574HVN-5.0/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN

-5.0 P+

PACKAGE OPTION ADDENDUM

www.ti.com 23-Jul-2018

Addendum-Page 2

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM2574HVN-ADJ/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574HVN

-ADJ P+

LM2574M-12/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574M

-12 P+

LM2574M-3.3/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574M

-3.3 P+

LM2574M-5.0 NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574M

-5.0 P+

LM2574M-5.0/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574M

-5.0 P+

LM2574M-ADJ NRND SOIC NPA 14 50 TBD Call TI Call TI -40 to 125 LM2574M

-ADJ P+

LM2574M-ADJ/NOPB ACTIVE SOIC NPA 14 50 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574M

-ADJ P+

LM2574MX-12/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574M

-12 P+

LM2574MX-3.3/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-4-260C-72 HR -40 to 125 LM2574M

-3.3 P+

LM2574MX-5.0 NRND SOIC NPA 14 1000 TBD Call TI Call TI -40 to 125 LM2574M

-5.0 P+

LM2574MX-5.0/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574M

-5.0 P+

LM2574MX-ADJ/NOPB ACTIVE SOIC NPA 14 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 LM2574M

-ADJ P+

LM2574N-12/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574N

-12 P+

LM2574N-3.3/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574N

-3.3 P+

LM2574N-5.0/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574N

-5.0 P+

LM2574N-ADJ/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2574N

-ADJ P+

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PACKAGE OPTION ADDENDUM

www.ti.com 23-Jul-2018

Addendum-Page 3

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish

value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM2574HVMX-12/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574HVMX-15/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574HVMX-3.3/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574HVMX-5.0 SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574HVMX-5.0/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574HVMX-ADJ/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574MX-12/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574MX-3.3/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574MX-5.0 SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574MX-5.0/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

LM2574MX-ADJ/NOPB SOIC NPA 14 1000 330.0 16.4 10.9 9.5 3.2 12.0 16.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 23-Jul-2018

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM2574HVMX-12/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574HVMX-15/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574HVMX-3.3/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574HVMX-5.0 SOIC NPA 14 1000 367.0 367.0 38.0

LM2574HVMX-5.0/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574HVMX-ADJ/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574MX-12/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574MX-3.3/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574MX-5.0 SOIC NPA 14 1000 367.0 367.0 38.0

LM2574MX-5.0/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

LM2574MX-ADJ/NOPB SOIC NPA 14 1000 367.0 367.0 38.0

PACKAGE MATERIALS INFORMATION

www.ti.com 23-Jul-2018

Pack Materials-Page 2

MECHANICAL DATA

NPA0014B

www.ti.com

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Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Texas Instruments:

LM2574HVM-12 LM2574HVM-12/NOPB LM2574HVM-15 LM2574HVM-15/NOPB LM2574HVM-3.3 LM2574HVM-

3.3/NOPB LM2574HVM-5.0 LM2574HVM-5.0/NOPB LM2574HVM-ADJ LM2574HVM-ADJ/NOPB LM2574HVMX-

12/NOPB LM2574HVMX-15 LM2574HVMX-15/NOPB LM2574HVMX-3.3 LM2574HVMX-3.3/NOPB LM2574HVMX-

5.0 LM2574HVMX-5.0/NOPB LM2574HVMX-ADJ LM2574HVMX-ADJ/NOPB LM2574HVN-12/NOPB LM2574HVN-

15 LM2574HVN-15/NOPB LM2574HVN-5.0/NOPB LM2574HVN-ADJ/NOPB