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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.

LM2676

SNVS031L –APRIL 2000–REVISED JUNE 2020

LM2676 SIMPLE SWITCHER

High Efficiency 3-A Step-Down Voltage Regulator

1 Features

1•New product available: LMR33630 36-V, 3-A, 400-

kHz synchronous converter

• Efficiency up to 94%

• Simple and easy to design with (using off-the-shelf

external components)

• 150-mΩDMOS output switch

• 3.3-V, 5-V, 12-V Fixed output and adjustable

(1.2 V to 37 V) versions

• 50-µA Standby current when switched OFF

• ±2% Maximum output tolerance over full line and

load conditions

• Wide input voltage range: 8 V to 40 V

• 260-KHz Fixed frequency internal oscillator

• –40 to 125°C Operating junction temperature

range

2 Applications

•Communication module

•Electricity meter

•Calling button operating panel

•Motor drives

3 Description

The LM2676 series of regulators are monolithic

integrated circuits which provide all of the active

functions for a step-down (buck) switching regulator

capable of driving up to 3-A loads with excellent line

and load regulation characteristics. High efficiency

(>90%) is obtained through the use of a low ON-

resistance DMOS power switch. The series consists

of fixed output voltages of 3.3-V, 5-V, and 12-V and

an adjustable output version.

The SIMPLE SWITCHER®concept provides for a

complete design using a minimum number of external

components. A high fixed frequency oscillator

(260 kHz) allows the use of physically smaller sized

components. A family of standard inductors for use

with the LM2676 are available from several

manufacturers to greatly simplify the design process.

The LM2676 series also has built-in thermal

shutdown, current limiting and an ON/OFF control

input that can power down the regulator to a low

50‑µA quiescent current standby condition. The

output voltage is ensured to a ±2% tolerance. The

clock frequency is controlled to within a ±11%

tolerance.

The new product, LMR33630, offers reduced BOM

cost, higher efficiency, and an 85% reduction in

solution size among many other features. See the

Device Comparison Table to compare specs. Start a

WEBENCH Design with LMR33630.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

LM2676 TO-263 (7) 10.10 mm × 8.89 mm

TO-220 (7) 14.986 mm × 10.16 mm

VSON (14) 6.00 mm × 5.00 mm

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

the end of the data sheet.

Typical Application

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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.................................................. 5

6.5 Electrical Characteristics: LM2676 – 3.3 V............... 5

6.6 Electrical Characteristics: LM2676 – 5 V.................. 5

6.7 Electrical Characteristics: LM2676 – 12 B................ 6

6.8 Electrical Characteristics: LM2676 – Adjustable....... 6

6.9 Electrical Characteristics – All Output Voltage

Versions..................................................................... 6

6.10 Typical Characteristics............................................ 7

7 Detailed Description............................................ 10

7.1 Overview................................................................. 10

7.2 Functional Block Diagram....................................... 10

7.3 Feature Description................................................. 10

7.4 Device Functional Modes........................................ 11

8 Application and Implementation ........................ 12

8.1 Application Information............................................ 12

8.2 Typical Applications ................................................ 15

9 Power Supply Recommendations...................... 27

10 Layout................................................................... 27

10.1 Layout Guidelines ................................................. 27

10.2 Layout Example .................................................... 29

11 Device and Documentation Support ................. 30

11.1 Documentation Support ........................................ 30

11.2 Receiving Notification of Documentation Updates 30

11.3 Support Resources ............................................... 30

11.4 Trademarks........................................................... 30

11.5 Electrostatic Discharge Caution............................ 30

11.6 Glossary................................................................ 30

12 Mechanical, Packaging, and Orderable

Information........................................................... 30

12.1 DAP (VSON Package).......................................... 30

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision K (June 2016) to Revision L Page

• Added information about the LMR33630 ............................................................................................................................... 1

Changes from Revision J (April 2013) to Revision K Page

• Added 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

• Removed all references to Computer Design Software LM267X Made Simple (Version 6.0).............................................. 1

Changes from Revision I (April 2013) to Revision J Page

• Changed layout of National Data Sheet to TI format ........................................................................................................... 26

Not to scale

DAP

1NC 14 Switch_output

2Input 13 Switch_output

3Input 12 Switch_output

4CB 11 NC

5NC 10 NC

6NC 9 GND

7FB 8 ON/OFF

Not to scale

1Switch_output

2Input

3CB

4GND

5NC

6FB

7ON/OFF

1 Switch_output

2 Input

3 CB

4 GND

5 NC

6 FB

7 ON/OFF

Not to scale

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5 Pin Configuration and Functions

KTW Package

7-Pin TO-263

Top View NDZ Package

7-Pin TO-220

Top View

NHM Package

14-Pin VSON

Top View

DAP connect to pin 9

Pin Functions

PIN I/O DESCRIPTION

NAME TO-263,

TO-220 VSON

Switch

output 1 12, 13, 14 O Source pin of the internal high-side FET. This is a switching node. Attached this pin to an

inductor and the cathode of the external diode.

Input 2 2, 3 I Supply input pin to collector pin of high-side FET. Connect to power supply and input

bypass capacitors CIN. Path from VIN pin to high frequency bypass CIN and GND must be

as short as possible.

CB 3 4 I Boot-strap capacitor connection for high-side driver. Connect a high-quality 100-nF

capacitor from CB to VSW Pin.

GND 4 9 — Power ground pins. Connect to system ground. Ground pins of CIN and COUT. Path to CIN

must be as short as possible.

FB 6 7 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.

ON/OFF 7 8 I Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin high or float

to enable the regulator.

NC 5 1, 5, 6, 10, 11 — No connect pins

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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.

(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and

specifications.

(3) The absolute maximum specification of the Switch Voltage to Ground applies to DC voltage. An extended negative voltage limit of –10 V

applies to a pulse of up to 20 ns, –6 V of 60 ns and –3 V of up to 100 ns.

6 Specifications

6.1 Absolute Maximum Ratings

see (1)(2)

MIN MAX UNIT

Input supply voltage 45 V

Soft-start pin voltage –0.1 6 V

Switch voltage to ground(3) –1 VIN V

Boost pin voltage VSW + 8 V

Feedback pin voltage –0.3 14 V

Power dissipation Internally Limited

Soldering temperature Wave, 4 s 260 °CInfrared, 10 s 240

Vapor phase, 75 s 219

Storage temperature, Tstg –65 150 °C

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

(2) ESD was applied using the human-body model, a 100-pF capacitor discharged through a 1.5-kΩresistor into each pin.

6.2 ESD Ratings VALUE UNIT

V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(2) ±2000 V

6.3 Recommended Operating Conditions MIN MAX UNIT

Supply voltage 8 40 V

Junction temperature (TJ) –40 125 °C

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

report, SPRA953.

(2) Junction to ambient thermal resistance (no external heat sink) for the 7-lead TO-220 package mounted vertically, with 0.5 in leads in a

socket, or on a PCB with minimum copper area.

(3) Junction to ambient thermal resistance (no external heat sink) for the 7-lead TO-220 package mounted vertically, with 0.5 in leads

soldered to a PCB containing approximately 4 square inches of (1 oz) copper area surrounding the leads.

(4) Junction to ambient thermal resistance for the 7-lead DDPAK mounted horizontally against a PCB area of 0.136 square inches (the

same size as the DDPAK package) of 1 oz (0.0014 in thick) copper.

(5) Junction to ambient thermal resistance for the 7-lead DDPAK mounted horizontally against a PCB area of 0.4896 square inches (3.6

times the area of the DDPAK package) of 1 oz (0.0014 in thick) copper.

(6) Junction to ambient thermal resistance for the 7-lead DDPAK mounted horizontally against a PCB copper area of 1.0064 square inches

(7.4 times the area of the DDPAK 3 package) of 1 oz (0.0014 in thick) copper. Additional copper area will reduce thermal resistance

further.

(7) Junction to ambient thermal resistance for the 14-lead VSON mounted on a PCB copper area equal to the die attach paddle.

(8) Junction to ambient thermal resistance for the 14-lead VSON mounted on a PCB copper area using 12 vias to a second layer of copper

equal to die attach paddle. Additional copper area will reduce thermal resistance further. For layout recommendations, see the AN-1187

Leadless Leadfram Package (LLP) application report.

6.4 Thermal Information

THERMAL METRIC(1) LM2678

UNITNDZ (TO-220) KTW (TO-263) NHM (VSON)

7 PINS 7 PINS 14 PINS

RθJA Junction-to-ambient thermal

resistance

See (2) 65 — —

°C/W

See (3) 45 — —

See (4) — 56 —

See (5) — 35 —

See (6) — 26 —

See (7) — — 55

See (8) — — 29

RθJC(top) Junction-to-case (top) thermal resistance 2 2 — °C/W

(1) All room temperature limits are 100% tested during production with TA= TJ= 25°C. All limits at temperature extremes are specified

through correlation using standard Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level

(AOQL).

(2) Typical values are determined with TA= TJ= 25°C and represent the most likely norm.

6.5 Electrical Characteristics: LM2676 – 3.3 V

Specifications apply for TA= TJ= 25°C unless otherwise noted. RADJ = 5.6 kΩ.

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

VOUT Output voltage VIN = 8 V to 40 V,

100 mA ≤IOUT ≤5 A

3.234 3.3 3.366 V

over the entire junction temperature

range of operation –40°C to 125°C 3.201 3.399

ηEfficiency VIN = 12 V, ILOAD = 5 A 86%

(1) All room temperature limits are 100% tested during production with TA= TJ= 25°C. All limits at temperature extremes are specified

through correlation using standard Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level

(AOQL).

(2) Typical values are determined with TA= TJ= 25°C and represent the most likely norm.

6.6 Electrical Characteristics: LM2676 – 5 V

Specifications apply for TA= TJ= 25°C unless otherwise noted. RADJ = 5.6 kΩ.

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

VOUT Output voltage VIN = 8 V to 40 V,

100 mA ≤IOUT ≤5 A

4.9 5 5.1 V

over the entire junction temperature

range of operation –40°C to 125°C 4.85 5.15

ηEfficiency VIN = 12 V, ILOAD = 5 A 88%

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(1) All room temperature limits are 100% tested during production with TA= TJ= 25°C. All limits at temperature extremes are specified

through correlation using standard Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level

(AOQL).

(2) Typical values are determined with TA= TJ= 25°C and represent the most likely norm.

6.7 Electrical Characteristics: LM2676 – 12 B

Specifications apply for TA= TJ= 25°C unless otherwise noted. RADJ = 5.6 kΩ.

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

VOUT Output voltage VIN = 15 V to 40 V,

100 mA ≤IOUT ≤5 A

11.76 12 12.24 V

over the entire junction temperature

range of operation –40°C to 125°C 11.64 12.36

ηEfficiency VIN = 24 V, ILOAD = 5 A 94%

(1) All room temperature limits are 100% tested during production with TA= TJ= 25°C. All limits at temperature extremes are specified

through correlation using standard Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level

(AOQL).

(2) Typical values are determined with TA= TJ= 25°C and represent the most likely norm.

6.8 Electrical Characteristics: LM2676 – Adjustable

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

VFB Feedback voltage VIN = 8 V to 40 V,

100 mA ≤IOUT ≤5 A,

VOUT programmed for 5 V

1.186 1.21 1.234 V

over the entire junction temperature

range of operation –40°C to 125°C 1.174 1.246

ηEfficiency VIN = 12 V, ILOAD = 5 A 88%

6.9 Electrical Characteristics – All Output Voltage Versions

Specifications are for TA= TJ= 25°C unless otherwise specified. Unless otherwise specified VIN = 12 V for the 3.3-V, 5-V, and

Adjustable versions and VIN = 24 V for the 12-V version.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

DEVICE PARAMETERS

IQQuiescent current VFEEDBACK = 8 V for 3.3-V, 5-V, and ADJ versions,

VFEEDBACK = 15 V for 12-V versions 4.2 6 mA

ISTBY Standby quiescent

current ON/OFF pin = 0 V 50 100 µA

over the entire junction temperature

range of operation –40°C to 125°C 150

ICL Current limit 3.8 4.5 5.25 A

over the entire junction temperature range of operation

–40°C to 125°C 3.6 5.4

ILOutput leakage

current VIN = 40 V,

soft-start pin = 0 V VSWITCH = 0V 200 µA

VSWITCH = –1V 16 15 mA

RDS(ON) Switch ON-resistance ISWITCH = 5 A 0.15 0.17

over the entire junction temperature

range of operation –40°C to 125°C 0.29

fOOscillator frequency Measured at

switch pin

260 kHz

over the entire junction temperature

range of operation –40°C to 125°C 225 280

D Duty cycle Maximum duty cycle 91%

Minimum duty cycle 0%

IBIAS Feedback bias

current VFEEDBACK = 1.3 V

ADJ version only 85 nA

VON/OFF ON/OFF threshold

voltage

1.4 V

over the entire junction temperature range of operation

–40°C to 125°C 0.8 2

ION/OFF ON/OFF input current ON/OFF pin = 0 V 20 µA

over the entire junction temperature

range of operation –40°C to 125°C 45

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6.10 Typical Characteristics

Figure 1. Normalized Output Voltage Figure 2. Line Regulation

Figure 3. Efficiency versus Input Voltage Figure 4. Efficiency versus ILOAD

Figure 5. Switch Current Limit Figure 6. Operating Quiescent Current

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Typical Characteristics (continued)

Figure 7. Standby Quiescent Current Figure 8. ON/OFF Threshold Voltage

Figure 9. ON/OFF Pin Current (Sourcing) Figure 10. Switching Frequency

Figure 11. Feedback Pin Bias Current

Continuous Mode Switching Waveforms VIN = 20 V, VOUT = 5 V,

ILOAD = 3 A L = 33 µH, COUT = 200 µF, COUTESR = 26 mΩ

A: VSW Pin Voltage, 10 V/div.

B: Inductor Current, 1 A/div

C: Output Ripple Voltage, 20 mV/div AC-Coupled

Figure 12. Horizontal Time Base: 1 µs/div

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Typical Characteristics (continued)

Discontinuous Mode Switching Waveforms VIN = 20 V,

VOUT = 5 V, ILOAD = 500 mA L = 10 µH, COUT = 400 µF,

COUTESR = 13 mΩ

A: VSW Pin Voltage, 10 V/div.

B: Inductor Current, 1 A/div

C: Output Ripple Voltage, 20 mV/div AC-Coupled

Figure 13. Horizontal Time Base: 1 µs/div

Load Transient Response for Continuous Mode VIN = 20 V,

VOUT = 5 V L = 33 µH, COUT = 200 µF,

COUTESR = 26 mΩ

A: Output Voltage, 100 mV//div, AC-Coupled.

B: Load Current: 500-mA to 3-A Load Pulse

Figure 14. Horizontal Time Base: 100 µs/div

Load Transient Response for Discontinuous Mode VIN = 20 V, VOUT = 5 V, L = 10 µH, COUT = 400 µF, COUTESR = 13 mΩ

A: Output Voltage, 100 mV/div, AC-Coupled

B: Load Current: 200-mA to 3-A Load Pulse

Figure 15. Horizontal Time Base: 200 µs/div

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7 Detailed Description

7.1 Overview

The LM2676 provides all of the active functions required for a step-down (buck) switching regulator. The internal

power switch is a DMOS-power MOSFET to provide power supply designs with high current capability, up to 3 A,

and highly efficient operation.

The design support WEBENCH can also be used to provide instant component selection, circuit performance

calculations for evaluation, a bill of materials component list, and a circuit schematic for LM2676.

7.2 Functional Block Diagram

* Active Inductor Patent Number 5,514,947

† Active Capacitor Patent Number 5,382,918

7.3 Feature Description

7.3.1 Switch Output

This is the output of a power MOSFET switch connected directly to the input voltage. The switch provides energy

to an inductor, an output capacitor, and the load circuitry under control of an internal pulse-width-modulator

(PWM). The PWM controller is internally clocked by a fixed 260-kHz oscillator. In a standard step-down

application, the duty cycle (Time ON/Time OFF) of the power switch is proportional to the ratio of the power

supply output voltage to the input voltage. The voltage on pin 1 switches between VIN (switch ON) and below

ground by the voltage drop of the external Schottky diode (switch OFF).

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Feature Description (continued)

7.3.2 Input

The input voltage for the power supply is connected to pin 2. In addition to providing energy to the load, the input

voltage also provides bias for the internal circuitry of the LM2676. For ensured performance, the input voltage

must be in the range of 8 V to 40 V. For best performance of the power supply, the input pin must always be

bypassed with an input capacitor located close to pin 2.

7.3.3 C Boost

A capacitor must be connected from pin 3 to the switch output, pin 1. This capacitor boosts the gate drive to the

internal MOSFET above VIN to fully turn it ON. This minimizes conduction losses in the power switch to maintain

high efficiency. The recommended value for C Boost is 0.01 µF.

7.3.4 Ground

This is the ground reference connection for all components in the power supply. In fast-switching, high-current

applications such as those implemented with the LM2676, TI recommends that a broad ground plane be used to

minimize signal coupling throughout the circuit.

7.3.5 Feedback

This is the input to a two-stage high gain amplifier, which drives the PWM controller. It is necessary to connect

pin 6 to the actual output of the power supply to set the DC output voltage. For the fixed output devices (3.3-V, 5-

V, and 12-V outputs), a direct wire connection to the output is all that is required as internal gain setting resistors

are provided inside the LM2676. For the adjustable output version, two external resistors are required to set the

DC output voltage. For stable operation of the power supply, it is important to prevent coupling of any inductor

flux to the feedback input.

7.3.6 ON/OFF

This input provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any

voltage less than 0.8 V completely turns OFF the regulator. The current drain from the input supply when OFF is

only 50 µA. Pin 7 has an internal pullup current source of approximately 20 µA and a protection clamp Zener

diode of 7 V to ground. When electrically driving the ON/OFF pin, the high voltage level for the ON condition

must not exceed the 6-V absolute maximum limit. When ON/OFF control is not required, pin 7 must be left open

circuited.

7.4 Device Functional Modes

7.4.1 Shutdown Mode

The ON/OFF pin provides electrical ON and OFF control for the LM2676. When the voltage of this pin is lower

than 1.4 V, the device is shutdown mode. The typical standby current in this mode is 45 µA.

7.4.2 Active Mode

When the voltage of the ON/OFF pin is higher than 1.4 V, the device starts switching and the output voltage rises

until it reaches a normal regulation voltage.

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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 Design Considerations

Power supply design using the LM2676 is greatly simplified by using recommended external components. A wide

range of inductors, capacitors, and Schottky diodes from several manufacturers have been evaluated for use in

designs that cover the full range of capabilities (input voltage, output voltage, and load current) of the LM2676. A

simple design procedure using nomographs and component tables provided in this data sheet leads to a working

design with very little effort.

The individual components from the various manufacturers called out for use are still just a small sample of the

vast array of components available in the industry. While these components are recommended, they are not

exclusively the only components for use in a design. After a close comparison of component specifications,

equivalent devices from other manufacturers can be substituted for use in an application.

The following sections include important considerations for each external component and an explanation of how

the nomographs and selection tables were developed.

8.1.2 Inductor

The inductor is the key component in a switching regulator. For efficiency, the inductor stores energy during the

switch ON time and then transfers energy to the load while the switch is OFF.

Nomographs are used to select the inductance value required for a given set of operating conditions. The

nomographs assume that the circuit is operating in continuous mode (the current flowing through the inductor

never falls to zero). The magnitude of inductance is selected to maintain a maximum ripple current of 30% of the

maximum load current. If the ripple current exceeds this 30% limit, the next larger value is selected.

The inductors offered have been specifically manufactured to provide proper operation under all operating

conditions of input and output voltage and load current. Several part types are offered for a given amount of

inductance. Both surface mount and through-hole devices are available. The inductors from each of the three

manufacturers have unique characteristics:

• Renco:

– Ferrite stick core inductors

– Typically has the lowest cost

– Can withstand ripple and transient peak currents above the rated value

– Have an external magnetic field, which can generate EMI

• Pulse Engineering:

– Powered iron toroid core inductors

– Can withstand higher than rated currents

– Since they are toroid inductors, they have low EMI.

• Coilcraft:

– Ferrite drum core inductors

– Are the smallest physical size inductors

– Are only available as surface mount components

– Generate EMI, but less than stick inductors

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Application Information (continued)

8.1.3 Output Capacitor

The output capacitor acts to smooth the DC output voltage and also provides energy storage. Selection of an

output capacitor, with an associated equivalent series resistance (ESR), impacts both the amount of output ripple

voltage and stability of the control loop.

The output ripple voltage of the power supply is the product of the capacitor ESR and the inductor ripple current.

The capacitor types recommended in the tables were selected for having low ESR ratings.

In addition, both surface mount tantalum capacitors and through-hole aluminum electrolytic capacitors are offered

as solutions.

Impacting frequency stability of the overall control loop and the output capacitance, in conjunction with the

inductor, creates a double pole inside the feedback loop. In addition, the capacitance and the ESR value create a

zero. These frequency response effects together, with the internal frequency compensation circuitry of the

LM2676, modify the gain and phase shift of the closed-loop system.

As a general rule for stable switching regulator circuits, it is desired to have the unity gain bandwidth of the circuit

to be limited to no more than one-sixth of the controller switching frequency. With the fixed 260-kHz switching

frequency of the LM2676, the output capacitor is selected to provide a unity gain bandwidth of 40 kHz

(maximum). Each recommended capacitor value has been chosen to achieve this result.

In some cases, multiple capacitors are required either to reduce the ESR of the output capacitor, to minimize

output ripple (a ripple voltage of 1% of VOUT or less is the assumed performance condition), or to increase the

output capacitance to reduce the closed-loop unity gain bandwidth to less than 40 kHz. When parallel

combinations of capacitors are required, it has been assumed that each capacitor is the exact same part type.

The RMS current and working voltage (WV) ratings of the output capacitor are also important considerations. In a

typical step-down switching regulator, the inductor ripple current (set to be no more than 30% of the maximum

load current by the inductor selection) is the current that flows through the output capacitor. The capacitor RMS

current rating must be greater than this ripple current. The voltage rating of the output capacitor must be greater

than 1.3 times the maximum output voltage of the power supply. If operation of the system at elevated

temperatures is required, the capacitor voltage rating can be de-rated to less than the nominal room temperature

rating. Careful inspection of the manufacturer's specification for de-rating of working voltage with temperature is

important.

8.1.4 Input Capacitor

Fast changing currents in high current switching regulators place a significant dynamic load on the unregulated

power source. An input capacitor helps provide additional current to the power supply and smooth out input

voltage variations.

Like the output capacitor, the key specifications for the input capacitor are RMS current rating and working

voltage. The RMS current flowing through the input capacitor is equal to one-half of the maximum DC load

current so the capacitor must be rated to handle this. Paralleling multiple capacitors proportionally increases the

current rating of the total capacitance. The voltage rating must also be selected to be 1.3 times the maximum

input voltage. Depending on the unregulated input power source, under light load conditions, the maximum input

voltage can be significantly higher than normal operation. Consider this when selecting an input capacitor.

The input capacitor must be placed very close to the input pin of the LM2676. Due to relative high current

operation with fast transient changes, the series inductance of input connecting wires or PCB traces can create

ringing signals at the input terminal which can possibly propagate to the output or other parts of the circuitry. It

can be necessary in some designs to add a small valued (0.1 µF to 0.47 µF) ceramic type capacitor in parallel

with the input capacitor to prevent or minimize any ringing.

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Application Information (continued)

8.1.5 Catch Diode

When the power switch in the LM2676 turns OFF, the current through the inductor continues to flow. The path for

this current is through the diode connected between the switch output and ground. This forward-biased diode

clamps the switch output to a voltage less than ground. This negative voltage must be greater than –1 V so a low

voltage drop (particularly at high current levels) Schottky diode is recommended. Total efficiency of the entire

power supply is significantly impacted by the power lost in the output catch diode. The average current through

the catch diode is dependent on the switch duty cycle (D) and is equal to the load current times (1-D). Use of a

diode rated for much higher current than is required by the actual application helps minimize the voltage drop

and power loss in the diode.

During the switch ON time, the diode is reversed biased by the input voltage. The reverse voltage rating of the

diode must be at least 1.3 times greater than the maximum input voltage.

8.1.6 Boost Capacitor

The boost capacitor creates a voltage used to overdrive the gate of the internal power MOSFET. This improves

efficiency by minimizing the on-resistance of the switch and associated power loss. For all applications, TI

recommends a 0.01-µF, 50-V ceramic capacitor.

8.1.7 Additional Application Information

When the output voltage is greater than approximately 6 V and the duty cycle at minimum input voltage is greater

than approximately 50%, the designer must exercise caution in selection of the output filter components. When

an application designed to these specific operating conditions is subjected to a current limit fault condition, it can

be possible to observe a large hysteresis in the current limit. This can affect the output voltage of the device until

the load current is reduced sufficiently to allow the current limit protection circuit to reset itself.

Under current limiting conditions, the LM267x is designed to respond in the following manner:

1. At the moment when the inductor current reaches the current limit threshold, the ON-pulse is immediately

terminated. This happens for any application condition.

2. However, the current limit block is also designed to momentarily reduce the duty cycle to below 50% to avoid

subharmonic oscillations, which can cause the inductor to saturate.

3. Thereafter, once the inductor current falls below the current limit threshold, there is a small relaxation time

during which the duty cycle progressively rises back above 50% to the value required to achieve regulation.

If the output capacitance is sufficiently large, it can be possible that as the output tries to recover. The output

capacitor charging current is large enough to repeatedly re-trigger the current limit circuit before the output has

fully settled. This condition is exacerbated with higher output voltage settings because the energy requirement of

the output capacitor varies as the square of the output voltage (½ CV2), thus requiring an increased charging

current.

A simple test to determine if this condition might exist for a suspect application is to apply a short circuit across

the output of the converter, then remove the shorted output condition. In an application with properly selected

external components, the output recovers smoothly.

Practical values of external components that have been experimentally found to work well under these specific

operating conditions are COUT = 47 µF, L = 22 µH. Note that even with these components, for a current limit of

ICLIM of the device, the maximum load current under which the possibility of the large current limit hysteresis can

be minimized, is ICLIM / 2. For example, if the input is 24 V and the set output voltage is 18 V, then for a desired

maximum current of 1.5 A, the current limit of the chosen switcher must be confirmed to be at least 3 A.

Under extreme overcurrent or short-circuit conditions, the LM267x employs frequency foldback in addition to the

current limit. If the cycle-by-cycle inductor current increases above the current limit threshold (due to short circuit

or inductor saturation for example), the switching frequency is automatically reduced to protect the IC. Frequency

below 100 kHz is typical for an extreme short-circuit condition.

LM2676

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SNVS031L –APRIL 2000–REVISED JUNE 2020

Product Folder Links: LM2676

8.2 Typical Applications

8.2.1 Typical Application for All Output Voltage Versions

Figure 16. Basic Circuit for All Output Voltage Versions

8.2.1.1 Design Requirements

Select the power supply operating conditions and the maximum output current and follow below procedures to

find the external components for LM2676.

8.2.1.2 Detailed Design Procedure

A complete step-down regulator can be designed in a few simple steps using the nomographs and tables in this

data sheet (or use the available design software at www.ti.com).

Step 1: Define the power supply operating conditions:

• Required output voltage

• Maximum DC input voltage

• Maximum output load current

Step 2: Set the output voltage by selecting a fixed output LM2676 (3.3-V, 5-V or 12-V applications) or determine

the required feedback resistors for use with the adjustable LM2676-ADJ.

Step 3: Determine the inductor required by using one of the four nomographs (Figure 17 through Figure 20).

Table 3 provides a specific manufacturer and part number for the inductor.

Step 4: Using Table 5 and Table 6 (fixed output voltage) or Table 9 and Table 10 (adjustable output voltage),

determine the output capacitance required for stable operation. Table 1 and Table 2 provide the specific

capacitor type from the manufacturer of choice.

Step 5: Determine an input capacitor from Table 7 or Table 8 for fixed output voltage applications. Use Table 1

or Table 2 to find the specific capacitor type. For adjustable output circuits, select a capacitor from Table 1 or

Table 2 with a sufficient working voltage (WV) rating greater than VIN max, and an RMS current rating greater

than one-half the maximum load current (two or more capacitors in parallel can be required).

Step 6: Select a diode from Table 4. The current rating of which must be greater than ILOAD max and the reverse

voltage rating must be greater than VIN max.

Step 7: Include a 0.01-µF, 50-V capacitor for CBOOST in the design.

8.2.1.2.1 Capacitor Selection Guides

Table 1. Input and Output Capacitor Codes—Surface Mount

CAPACITOR

REFERENCE

CODE

SURFACE MOUNT

AVX TPS SERIES SPRAGUE 594D SERIES KEMET T495 SERIES

C (µF) WV (V) Irms (A) C (µF) WV (V) Irms (A) C (µF) WV (V) Irms (A)

C1 330 6.3 1.15 120 6.3 1.1 100 6.3 0.82

C2 100 10 1.1 220 6.3 1.4 220 6.3 1.1

C3 220 10 1.15 68 10 1.05 330 6.3 1.1

LM2676

SNVS031L –APRIL 2000–REVISED JUNE 2020

www.ti.com

Product Folder Links: LM2676

Typical Applications (continued)

Table 1. Input and Output Capacitor Codes—Surface Mount (continued)

CAPACITOR

REFERENCE

CODE

SURFACE MOUNT

AVX TPS SERIES SPRAGUE 594D SERIES KEMET T495 SERIES

C (µF) WV (V) Irms (A) C (µF) WV (V) Irms (A) C (µF) WV (V) Irms (A)

C4 47 16 0.89 150 10 1.35 100 10 1.1

C5 100 16 1.15 47 16 1 150 10 1.1

C6 33 20 0.77 100 16 1.3 220 10 1.1

C7 68 20 0.94 180 16 1.95 33 20 0.78

C8 22 25 0.77 47 20 1.15 47 20 0.94

C9 10 35 0.63 33 25 1.05 68 20 0.94

C10 22 35 0.66 68 25 1.6 10 35 0.63

C11 — — — 15 35 0.75 22 35 0.63

C12 — — — 33 35 1 4.7 50 0.66

C13 — — — 15 50 0.9 — — —

LM2676

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SNVS031L –APRIL 2000–REVISED JUNE 2020

Product Folder Links: LM2676

Table 2. Input and Output Capacitor Codes—Through Hole

CAPACITOR

REFERENCE

CODE

THROUGH HOLE

SANYO OS-CON SA SERIES SANYO MV-GX SERIES NICHICON PL SERIES PANASONIC HFQ SERIES

C (µF) WV (V) Irms (A) C (µF) WV (V) Irms (A) C (µF) WV (V) Irms (A) C (µF) WV (V) Irms (A)

C1 47 6.3 1 1000 6.3 0.8 680 10 0.8 82 35 0.4

C2 150 6.3 1.95 270 16 0.6 820 10 0.98 120 35 0.44

C3 330 6.3 2.45 470 16 0.75 1000 10 1.06 220 35 0.76

C4 100 10 1.87 560 16 0.95 1200 10 1.28 330 35 1.01

C5 220 10 2.36 820 16 1.25 2200 10 1.71 560 35 1.4

C6 33 16 0.96 1000 16 1.3 3300 10 2.18 820 35 1.62

C7 100 16 1.92 150 35 0.65 3900 10 2.36 1000 35 1.73

C8 150 16 2.28 470 35 1.3 6800 10 2.68 2200 35 2.8

C9 100 20 2.25 680 35 1.4 180 16 0.41 56 50 0.36

C10 47 25 2.09 1000 35 1.7 270 16 0.55 100 50 0.5

C11 — — — 220 63 0.76 470 16 0.77 220 50 0.92

C12 — — — 470 63 1.2 680 16 1.02 470 50 1.44

C13 — — — 680 63 1.5 820 16 1.22 560 50 1.68

C14 — — — 1000 63 1.75 1800 16 1.88 1200 50 2.22

C15 — — — — — — 220 25 0.63 330 63 1.42

C16 — — — — — — 220 35 0.79 1500 63 2.51

C17 — — — — — — 560 35 1.43 — — —

C18 — — — — — — 2200 35 2.68 — — —

C19 — — — — — — 150 50 0.82 — — —

C20 — — — — — — 220 50 1.04 — — —

C21 — — — — — — 330 50 1.3 — — —

C22 — — — — — — 100 63 0.75 — — —

C23 — — — — — — 390 63 1.62 — — —

C24 — — — — — — 820 63 2.22 — — —

C25 — — — — — — 1200 63 2.51 — — —

8.2.1.2.2 Inductor Selection Guides

Table 3. Inductor Manufacturer Part Numbers

INDUCTOR

REFERENCE

NUMBER

INDUCTANCE

(µH) CURRENT

(A)

RENCO PULSE ENGINEERING COILCRAFT

THROUGH

HOLE SURFACE

MOUNT THROUGH

HOLE SURFACE

MOUNT SURFACE

MOUNT

L23 33 1.35 RL-5471-7 RL1500-33 PE-53823 PE-53823S DO3316-333

L24 22 1.65 RL-1283-22-43 RL1500-22 PE-53824 PE-53824S DO3316-223

L25 15 2 RL-1283-15-43 RL1500-15 PE-53825 PE-53825S DO3316-153

L29 100 1.41 RL-5471-4 RL-6050-100 PE-53829 PE-53829S DO5022P-104

L30 68 1.71 RL-5471-5 RL6050-68 PE-53830 PE-53830S DO5022P-683

L31 47 2.06 RL-5471-6 RL6050-47 PE-53831 PE-53831S DO5022P-473

L32 33 2.46 RL-5471-7 RL6050-33 PE-53932 PE-53932S DO5022P-333

L33 22 3.02 RL-1283-22-43 RL6050-22 PE-53933 PE-53933S DO5022P-223

L34 15 3.65 RL-1283-15-43 — PE-53934 PE-53934S DO5022P-153

L38 68 2.97 RL-5472-2 — PE-54038 PE-54038S —

L39 47 3.57 RL-5472-3 — PE-54039 PE-54039S —

L40 33 4.26 RL-1283-33-43 — PE-54040 PE-54040S —

L41 22 5.22 RL-1283-22-43 — PE-54041 P0841 —

L44 68 3.45 RL-5473-3 — PE-54044 — —

L45 10 4.47 RL-1283-10-43 — — P0845 DO5022P-103HC