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LM2677
SNVS077J – MAY 2004 – REVISED JUNE 2016

LM2677 SIMPLE SWITCHER® High Efficiency 5-A Step-Down Voltage Regulator with Sync
1 Features 3 Description
•
1 Efficiency up to 92% The LM2677 series of regulators are monolithic
integrated circuits which provide all of the active
• Simple and Easy to Design Using Off-the-Shelf functions for a step-down (buck) switching regulator
External Components capable of driving up to 5-A loads with excellent line
• 100-mΩ DMOS Output Switch and load regulation characteristics. High efficiency
• 3.3-V, 5-V, and 12-V Fixed Output and Adjustable (>90%) is obtained through the use of a low on-
(1.2 V to 37 V) Versions resistance DMOS power switch. The series consists
of fixed output voltages of 3.3-V, 5-V, and 12-V and
• 50-μA Standby Current When Switched OFF an adjustable output version.
• ±2% Maximum Output Tolerance Over Full Line
The SIMPLE SWITCHER® concept provides for a
and Load Conditions
complete design using a minimum number of external
• Wide Input Voltage Range: 8 V to 40 V components. The switching clock frequency can be
• External Sync Clock Capability (280 kHz to provided by an internal fixed frequency oscillator
400 kHz) (260 kHz) or from an externally provided clock in the
• 260-kHz Fixed Frequency Internal Oscillator range of 280 kHz to 400 kHz, which allows the use of
physically smaller-sized components. A family of
• −40°C to 125°C Operating Junction Temperature standard inductors for use with the LM2677 are
Range available from several manufacturers to greatly
simplify the design process. The external Sync clock
2 Applications provides direct and precise control of the output ripple
frequency for consistent filtering or frequency
• Simple to Design, High Efficiency (> 90%) Step-
spectrum positioning.
Down Switching Regulators
• Efficient System Preregulator for Linear Voltage The LM2677 series also has built-in thermal
Regulators shutdown, current-limiting, and an ON/OFF control
input that can power down the regulator to a low
• Battery Chargers 50-μA quiescent-current standby condition. The
• Communications and Radio Equipment Regulator output voltage is ensured to a ±2% tolerance.
With Synchronized Clock Frequency
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
TO-263 (7) 10.16 mm × 8.69 mm
LM2677 TO-220 (7) 10.16 mm × 8.94 mm
VSON (14) 6.10 mm × 5.10 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.

Typical Application
Feedback

0.01 PF

Input VIN
Voltage Boost
8V to 40V
LM2677 - 5.0 L
0.47 PF Output
+ + + Voltage
Switch
22 PH 5V/5A
3 x 15 PF/50V Ground Output

1 k: 6TQ045S 2 x 180 PF, 16V

Optional External
100 pF
Sync Clock
(280 kHz to 400 kHz)
Copyright © 2016, Texas Instruments Incorporated
1

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.
LM2677
SNVS077J – MAY 2004 – REVISED JUNE 2016 www.ti.com

Table of Contents
1 Features .................................................................. 1 7.2 Functional Block Diagram ....................................... 10
2 Applications ........................................................... 1 7.3 Feature Description................................................. 10
3 Description ............................................................. 1 7.4 Device Functional Modes........................................ 11
4 Revision History..................................................... 2 8 Application and Implementation ........................ 12
8.1 Application Information............................................ 12
5 Pin Configuration and Functions ......................... 3
8.2 Typical Application .................................................. 16
6 Specifications......................................................... 4
6.1 Absolute Maximum Ratings ...................................... 4 9 Power Supply Recommendations...................... 25
6.2 ESD Ratings.............................................................. 4 10 Layout................................................................... 25
6.3 Recommended Operating Conditions....................... 4 10.1 Layout Guidelines ................................................. 25
6.4 Thermal Information .................................................. 5 10.2 Layout Example .................................................... 26
6.5 Electrical Characteristics – 3.3 V .............................. 5 11 Device and Documentation Support ................. 27
6.6 Electrical Characteristics – 5 V ................................. 5 11.1 Documentation Support ........................................ 27
6.7 Electrical Characteristics – 12 V ............................... 6 11.2 Receiving Notification of Documentation Updates 27
6.8 Electrical Characteristics – Adjustable...................... 6 11.3 Community Resources.......................................... 27
6.9 Electrical Characteristics – All Output Voltage 11.4 Trademarks ........................................................... 27
Versions ..................................................................... 6 11.5 Electrostatic Discharge Caution ............................ 27
6.10 Typical Characteristics ............................................ 7 11.6 Glossary ................................................................ 27
7 Detailed Description ............................................ 10 12 Mechanical, Packaging, and Orderable
7.1 Overview ................................................................. 10 Information ........................................................... 27

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

Changes from Revision I (June 2012) to Revision J 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
• Deleted Manufacturers' Contact Numbers tables................................................................................................................. 18

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5 Pin Configuration and Functions

KTW Package
7-Pin TO-263 NDZ Package
Top View 7-Pin TO-220
Top View
Not to scale

7 ON/OFF
6 FB
Thermal
5 SYNC
Pad
4 GND
3 CB
2 VIN
1 VSW

Not to scale
1

7
VSW

VIN

CB

GND

SYNC

FB

ON/OFF

NHM Package
14-Pin VSON
Top View

NC 1 14 VSW

VIN 2 13 VSW

VIN 3 12 VSW

CB 4 DAP 11 NC

NC 5 10 NC

SYNC 6 9 GND

FB 7 8 ON/OFF

Not to scale

Pin Functions
PIN
I/O DESCRIPTION
NAME TO-263, TO-220 VSON
Boot-strap capacitor connection for high-side driver. Connect a high quality
CB 3 4 I
100-nF capacitor from CB to VSW pin.
Feedback sense input pin. Connect to the midpoint of feedback divider to set
FB 6 7 I VOUT for ADJ version or connect this pin directly to the output capacitor for a
fixed output version.
Power ground pins. Connect to system ground. Ground pins of CIN and COUT.
GND 4 9 —
Path to CIN must be as short as possible.
NC — 1, 5, 10, 11 — No connect pins
Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin
ON/OFF 7 8 I
high or float to enable the regulator.
This input allows control of the switching clock frequency. If left open-circuited
SYNC 5 6 I the regulator is switched at the internal oscillator frequency, typically
260 kHz.
Supply input pin to collector pin of high side FET. Connect to power supply and
VIN 2 2, 3 I input bypass capacitors CIN. Path from VIN pin to high frequency bypass CIN
and GND must be as short as possible.
Source pin of the internal High Side FET. This is a switching node. Attached this
VSW 1 12, 13, 14 O
pin to an inductor and the cathode of the external diode.

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6 Specifications
6.1 Absolute Maximum Ratings
over recommended operating junction temperature range of –40°C to 125°C (unless otherwise noted) (1) (2)
MIN MAX UNIT
Input supply voltage 45 V
ON/OFF 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
Wave (4 s) 260
Soldering temperature Infrared (10 s) 240 °C
Vapor phase (75 s) 219
Storage temperature, Tstg –65 150 °C

(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 switch voltage to ground specification 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.

6.2 ESD Ratings

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

(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-kΩ resistor into each pin.

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)
MIN MAX UNIT
Supply voltage 8 40 V
TJ Junction temperature –40 125 °C

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6.4 Thermal Information

LM2677
THERMAL METRIC (1) KTW (TO-263) NDZ (TO-220) NHM (VSON) UNIT
7 PINS 7 PINS 14 PINS
See (2) 56 — —
(3)
See 35 — —
See (4) 26 — —
RθJA Junction-to-ambient thermal resistance See (5) — 65 — °C/W
(6)
See — 45 —
See (7) — — 55
See (8) — — 29
RθJC(top) Junction-to-case (top) thermal resistance 2 2 — °C/W
RθJB Junction-to-board thermal resistance — — — °C/W
ψJT Junction-to-top characterization parameter — — — °C/W
ψJB Junction-to-board characterization parameter — — — °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance — — — °C/W

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
(2) Junction to ambient thermal resistance for the 7-pin DDPAK/TO-263 mounted horizontally against a PC board area of 0.136 square
inches (the same size as the DDPAK/TO-263 package) of 1 oz. (0.0014 in. thick) copper.
(3) Junction to ambient thermal resistance for the 7-pin DDPAK/TO-263 mounted horizontally against a PC board area of 0.4896 square
inches (3.6 times the area of the DDPAK/TO-263 package) of 1 oz. (0.0014 in. thick) copper.
(4) Junction to ambient thermal resistance for the 7-pin DDPAK/TO-263 mounted horizontally against a PC board copper area of 1.0064
square inches (7.4 times the area of the DDPAK/TO-263 package) of 1 oz. (0.0014 in. thick) copper. Additional copper area reduces
thermal resistance further.
(5) Junction to ambient thermal resistance (no external heat sink) for the 7-pin TO-220 package mounted vertically, with ½ inch leads in a
socket, or on a PC board with minimum copper area.
(6) Junction to ambient thermal resistance (no external heat sink) for the 7-pin TO-220 package mounted vertically, with ½ inch leads
soldered to a PC board containing approximately 4 square inches of (1 oz.) copper area surrounding the pins.
(7) Junction to ambient thermal resistance for the 14-pin VSON mounted on a PC board copper area equal to the die attach paddle.
(8) Junction to ambient thermal resistance for the 14-lead VSON mounted on a PC board copper area using 12 vias to a second layer of
copper equal to die attach paddle. Additional copper area reduces thermal resistance further. For layout recommendations, refer to
Application Note, AN-1187 Leadless Leadframe Package (LLP).

6.5 Electrical Characteristics – 3.3 V

TJ = 25°C, sync pin open circuited (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
TJ = 25°C 3.234 3.3 3.366
VOUT Output voltage VIN = 8 V to 40 V, 100 mA ≤ IOUT ≤ 5 A V
TJ = –40°C to 125°C 3.201 3.399
η Efficiency VIN = 12 V, ILOAD = 5 A 82%

(1) All limits are ensured at room temperature and at temperature extremes. All room temperature limits are 100% tested during production
with TA = TJ = 25°C. All limits at temperature extremes are ensured through correlation using standard 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 – 5 V

TJ = 25°C, sync pin open circuited (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
TJ = 25°C 4.9 5 5.1
VOUT Output voltage VIN = 8 V to 40 V, 100 mA ≤ IOUT ≤ 5 A V
TJ = –40°C to 125°C 4.85 5.15
η Efficiency VIN = 12 V, ILOAD = 5 A 84%

(1) All limits are ensured at room temperature and at temperature extremes. All room temperature limits are 100% tested during production
with TA = TJ = 25°C. All limits at temperature extremes are ensured through correlation using standard 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.

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6.7 Electrical Characteristics – 12 V

TJ = 25°C, sync pin open circuited (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
TJ = 25°C 11.76 12 12.24
VOUT Output voltage VIN = 15 V to 40 V, 100 mA ≤ IOUT ≤ 5 A V
TJ = –40°C to 125°C 11.64 12.36
η Efficiency VIN = 24 V, ILOAD = 5 A 92%

(1) All limits are ensured at room temperature and at temperature extremes. All room temperature limits are 100% tested during production
with TA = TJ = 25°C. All limits at temperature extremes are ensured through correlation using standard 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 – Adjustable

TJ = 25°C, sync pin open circuited (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
VIN = 8 V to 40 V, 100 mA ≤ IOUT ≤ 5 A, TJ = 25°C 1.186 1.21 1.234
VFB Feedback voltage V
VOUT programmed for 5 V TJ = –40°C to 125°C 1.174 1.246
η Efficiency VIN = 12 V, ILOAD = 5 A 84%

(1) All limits are ensured at room temperature and at temperature extremes. All room temperature limits are 100% tested during production
with TA = TJ = 25°C. All limits at temperature extremes are ensured through correlation using standard 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.

6.9 Electrical Characteristics – All Output Voltage Versions

TJ = 25°C, VIN= 12 V for the 3.3-V, 5-V, and Adjustable versions, VIN = 24 V for the 12-V version, sync pin open circuited
(unless otherwise noted)
PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
VFEEDBACK = 8 V for 3.3-V, 5-V, and adjustable
IQ Quiescent current 4.2 6 mA
versions, VFEEDBACK = 15 V for 12-V versions
TJ = 25°C 50 100
ISTBY Standby quiescent current ON/OFF pin = 0 V μA
TJ = –40°C to 125°C 150
TJ = 25°C 6.1 7 8.3
ICL Current limit A
TJ = –40°C to 125°C 5.75 8.75
VIN = 40 V, ON/OFF pin = 0 V 1 200
μA
IL Output leakage current VSWITCH = 0 V 15
VSWITCH = –1 V 6 mA
TJ = 25°C 0.12 0.14
RDS(ON) Switch on-resistance ISWITCH = 5 A Ω
TJ = –40°C to 125°C 0.225
TJ = 25°C 260
fO Oscillator frequency Measured at switch pin kHz
TJ = –40°C to 125°C 225 280
Maximum duty cycle 91%
D Duty cycle
Minimum duty cycle 0%
IBIAS Feedback bias current VFEEDBACK = 1.3 V, ADJ version only 85 nA
TJ = 25°C 1.4
VON/OFF ON/OFF threshold voltage V
TJ = –40°C to 125°C 0.8 2
TJ = 25°C 20
ION/OFF ON/OFF input current ON/OFF input = 0 V μA
TJ = –40°C to 125°C 45
FSYNC Synchronization frequency VSYNC(pin 5) = 3.5 V, 50% duty cycle 400 kHz
VSYNC SYNC threshold voltage 1.4 V

(1) All limits are ensured at room temperature and at temperature extremes. All room temperature limits are 100% tested during production
with TA = TJ = 25°C. All limits at temperature extremes are ensured through correlation using standard 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.

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6.10 Typical Characteristics

Figure 1. Normalized Output Voltage Figure 2. Line Regulation

Figure 3. Efficiency vs Input Voltage Figure 4. Efficiency vs 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

VSW pin voltage, 10 V/div VIN = 20 V, VOUT = 5 V,

Inductor current, 2 A/div ILOAD = 5 A, L = 10 μH,
Output ripple voltage, COUT = 400 μF,
20 mV/div AC-coupled COUTESR = 13 mΩ

Figure 11. Feedback Pin Bias Current Figure 12. Continuous Mode Switching Waveforms,
Horizontal Time Base: 1 μs/div

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Typical Characteristics (continued)

VSW pin voltage, 10 V/div VIN = 20 V, VOUT = 5 V, Output voltage, VIN = 20 V, VOUT = 5 V,
ILOAD = 500 mA, 100 mV//div,
Inductor current, 1 A/div L = 10 μH,
L = 10 μH, AC-coupled
Output ripple voltage, COUT = 400 μF, Load current: 500 mA COUT = 400 μF,
20 mV/div AC-coupled COUTESR = 13 mΩ to 5-A load pulse COUTESR = 13 mΩ

Figure 13. Discontinuous Mode Switching Waveforms, Figure 14. Load Transient Response for Continuous Mode,
Horizontal Time Base: 1 μs//iv Horizontal Time Base: 100 μs/div

Output voltage, 100 mV//div, VIN = 20 V, VOUT = 5 V,

AC-coupled L = 10 μH,
Load current: 200 mA COUT = 400 μF,
to 5-A load pulse COUTESR = 13 mΩ

Figure 15. Load Transient Response for Discontinuous Mode, Horizontal Time Base: 200 μs/div

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7 Detailed Description

7.1 Overview
The LM2677 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 5 A,
and highly efficient operation.
The LM2677 is part of the SIMPLE SWITCHER family of power converters. A complete design uses a minimum
number of external components, which have been predetermined from a variety of manufacturers.

7.2 Functional Block Diagram

VIN

Gain Bias 1.21 V 5 V Internal Start

ON/OFF
Compensation Generator Reference Regulator Up

Bias 1.21 V 5V Enable

SYNC
260 kHz Freq. Shift Current
50 k 11 V RSENSE
VRAMP Oscillator Limit
3.2 V
0.6 V
Thermal
Shutdown

CBOOTSTRAP
3A
FEEDBACK Reset
Switch
3.3 V, R2 = 4.32 k R2
5 V, R2 = 7.83 k
12 V, R2 = 22.3 k + + Control
GM 1 ± Driver
ADJ, R2 = 0 Ÿ Logic
R1 = 2.5 k ± GM 2 ±
R1 is OPEN 2k PWM
10 k +
15 k Comparator

VSWITCH
20 mH* 10 Q)‚ Enable

1.21 V

GND
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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 CBoost
A capacitor must be connected from pin 3 to the switch output, pin 1. This capacitor boosts the gate driver 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 CBoost is 0.01 μF.

7.3.3 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 LM2677, TI recommends using a broad ground plane to
minimize signal coupling throughout the circuit.

7.3.4 Sync
This input allows control of the switching clock frequency. If left open-circuited the regulator is switched at the
internal oscillator frequency, from 225 kHz to 280 kHz. An external clock can be used to force the switching
frequency and thereby control the output ripple frequency of the regulator. This capability provides for consistent
filtering of the output ripple from system to system as well as precise frequency spectrum positioning of the ripple
frequency, which is often desired in communications and radio applications. This external frequency must be
greater than the LM2677 internal oscillator frequency, which could be as high as 280 kHz, to prevent an
erroneous reset of the internal ramp oscillator and PWM control of the power switch. The ramp oscillator is reset
on the positive going edge of the sync input signal. TI recommends ac-coupling the external TTL or CMOS
compatible clock (between 0 V and a level greater than 3 V) to the sync input through a 100-pF capacitor and a
1-kΩ resistor to ground at pin 5 as shown in Figure 16.
When the SYNC function is used, current limit frequency foldback is not active. Therefore, the device may not be
fully protected against extreme output short-circuit conditions (see Additional Application Information).

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 LM2677. 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.

7.3.7 DAP (VSON Package)

The die attach pad (DAP) must be connected to PCB ground plane. For CAD and assembly guidelines, see
application note, AN-1187 Leadless Leadframe Package (LLP).

7.4 Device Functional Modes

7.4.1 Shutdown Mode
The ON/OFF pin provides electrical ON and OFF control for the LM2677. 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 20 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 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; benefits are typically lowest cost and can withstand ripple and transient peak
currents above the rated value. These inductors have an external magnetic field, which may generate EMI.
Pulse Engineering: powdered iron toroid core inductors; these also can withstand higher than rated currents and,
being toroid inductors, has low EMI.
Coilcraft: ferrite drum core inductors; these are the smallest physical-size inductors and are available only as
surface mount components. These inductors also generate EMI but less than stick inductors.

8.1.2 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 Input and Output Capacitor Codes 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, 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 LM2677
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 LM2677, 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.

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Application Information (continued)

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 may 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.

8.1.3 Input and Output Capacitor Codes

Table 1. Surface-Mount Capacitors (1)

CAPACITOR AVX TPS SERIES SPRAGUE 594D SERIES KEMET T495 SERIES
REFERENCE
CODE 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
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 — — —

(1) Assumes worst case maximum input voltage and load current for a given inductance value

Table 2. Through-Hole Capacitors (1)

CAPACITOR SANYO OS-CON SA SERIES SANYO MV-GX SERIES NICHICON PL SERIES PANASONIC HFQ SERIES
REFERENCE IRMS IRMS IRMS IRMS
CODE C (µF) WV (V) C (µF) WV (V) C (µF) WV (V) C (µF) WV (V)
(A) (A) (A) (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

(1) Assumes worst case maximum input voltage and load current for a given inductance value
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Table 2. Through-Hole Capacitors() (continued)

CAPACITOR SANYO OS-CON SA SERIES SANYO MV-GX SERIES NICHICON PL SERIES PANASONIC HFQ SERIES
REFERENCE IRMS IRMS IRMS IRMS
CODE C (µF) WV (V) C (µF) WV (V) C (µF) WV (V) C (µF) WV (V)
(A) (A) (A) (A)
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 — — —

8.1.4 Input Capacitor

Fast changing currents in high-current switching regulators place a significant dynamic load on the unregulated
power source. An input capacitor helps to provide additional current to the power supply as well as 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 could be significantly higher than normal operation and must be considered when selecting an input
capacitor.
The input capacitor must be placed very close to the input pin of the LM2677. 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 could possibly propagate to the output or other parts of the circuitry. It
may 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.

8.1.5 Catch Diode

When the power switch in the LM2677 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 TI
recommends a low voltage drop (particularly at high current levels) Schottky diode. 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 to 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 using a 0.01-μF, 50-V ceramic capacitor.

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8.1.7 SYNC Components

When synchronizing the LM2677 with an external clock TI recommends connecting the clock to pin 5 through a
series 100-pF capacitor, and connecting a 1-kΩ resistor to ground from pin 5. This RC network creates a short
100-nS pulse on each positive edge of the clock to reset the internal ramp oscillator. The reset time of the
oscillator is approximately 300 nS.

8.1.8 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 may 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 could 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 may 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, and 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. It must be noted that even with these components, for a
device’s current limit of ICLIM, 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 over-current 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.

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8.2 Typical Application

8.2.1 Fixed Output Voltage Applications

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Figure 16. Basic Circuit For Fixed Output Voltage Applications

8.2.1.1 Design Requirements

Table 3 lists the design requirements for the adjustable output voltage application.

Table 3. Design Parameters

PARAMETER VALUE
Required output voltage, VOUT 3.3 V
Maximum DC input voltage, VIN_MAX 16 V
Maximum output load current, ILOAD_MAX 2.5 A

8.2.1.2 Detailed Design Procedure

A system logic power supply bus of 3.3 V is to be generated from a wall adapter which provides an unregulated
DC voltage of 13 V to 16 V. The maximum load current is 2.5 A. Through-hole components are preferred.
Step 1: Select an LM2677T, 3.3 V. The output voltage has a tolerance of ±2% at room temperature and ±3%
over the full operating temperature range.
Step 2: Use the nomograph for the 3.3 V device, Figure 17. The intersection of the 16-V horizontal line (Vin max)
and the 2.5-A vertical line (Iload max) indicates that L33, a 22-μH inductor, is required. From Table 4, L33 in a
through-hole component is available from Renco with part number RL-1283-22-43 or part number PE-53933 from
Pulse Engineering.

Table 4. Inductor Manufacturer Part Numbers (1)

INDUCTOR RENCO PULSE ENGINEERING COILCRAFT
INDUCTANCE CURRENT
REF. SURFACE THROUGH SURFACE
(µH) (A) THROUGH HOLE SURFACE MOUNT
# MOUNT HOLE 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 2.00 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

(1) Assumes worst case maximum input voltage and load current for a given inductance value
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Table 4. Inductor Manufacturer Part Numbers() (continued)

INDUCTOR RENCO PULSE ENGINEERING COILCRAFT
INDUCTANCE CURRENT
REF. SURFACE THROUGH SURFACE
(µH) (A) THROUGH HOLE SURFACE MOUNT
# MOUNT HOLE MOUNT
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
L46 15 5.60 RL-1283-15-43 — — P0846 DO5022P-153HC
L47 10 5.66 RL-1283-10-43 — — P0847 DO5022P-103HC
L48 47 5.61 RL-1282-47-43 — — P0848 —
L49 33 5.61 RL-1282-33-43 — — P0849 —

Step 3: Use Table 5 to determine an output capacitor. With a 3.3-V output and a 22-μH inductor there are four
through-hole output capacitor solutions with the number of same type capacitors to be paralleled and an
identifying capacitor code given. Table 1 provides the actual capacitor characteristics. Any of the following
choices works in the circuit:
• 1 × 220-μF, 10-V Sanyo OS-CON (code C5)
• 1 × 1000-μF, 35-V Sanyo MV-GX (code C10)
• 1 × 2200-μF, 10-V Nichicon PL (code C5)
• 1 × 1000-μF, 35-V Panasonic HFQ (code C7)

Table 5. Output Capacitors for Fixed Output Voltage Application (1)

SURFACE MOUNT
OUTPUT INDUCTANCE
AVX TPS SERIES SPRAGUE 594D SERIES KEMET T495 SERIES
VOLTAGE (V) (µH)
(2) (3) (2) (3)
NO. C CODE NO. C Code NO. (2) C CODE (3)
10 5 C1 5 C1 5 C2
15 4 C1 4 C1 4 C3
3.3
22 3 C2 2 C7 3 C4
33 1 C1 2 C7 3 C4
10 4 C2 4 C6 4 C4
15 3 C3 2 C7 3 C5
5 22 3 C2 2 C7 3 C4
33 2 C2 2 C3 2 C4
47 2 C2 1 C7 2 C4
10 4 C5 3 C6 5 C9
15 3 C5 2 C7 4 C9
22 2 C5 2 C6 3 C8
12 33 2 C5 1 C7 3 C8
47 2 C4 1 C6 2 C8
68 1 C5 1 C5 2 C7
100 1 C4 1 C5 1 C8

(1) Assumes worst case maximum input voltage and load current for a given inductance value
(2) No. represents the number of identical capacitor types to be connected in parallel
(3) C Code indicates the Capacitor Reference number in Table 1 for identifying the specific component from the manufacturer.

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Step 4: Use Table 6 to select an input capacitor. With 3.3-V output and 22-μH there are three through-hole
solutions. These capacitors provide a sufficient voltage rating and an rms current rating greater than 1.25 A (1/2
Iload max). Again using Table 1 for specific component characteristics the following choices are suitable:
• 1 × 1000-μF, 63-V Sanyo MV-GX (code C14)
• 1 × 820-μF, 63-V Nichicon PL (code C24)
• 1 × 560-μF, 50-V Panasonic HFQ (code C13)

Table 6. Input Capacitors for Fixed Output Voltage Application (1)

SURFACE MOUNT
OUTPUT INDUCTANCE
AVX TPS SERIES (2) SPRAGUE 594D SERIES KEMET T495 SERIES
VOLTAGE (V) (µH)
(3) (4) (3) (4)
NO. C CODE NO. C CODE NO. (3) C CODE (4)
10 3 C7 2 C10 3 C9
15 * * 3 C13 4 C12
3.3
22 * * 2 C13 3 C12
33 * * 2 C13 3 C12
10 3 C4 2 C6 3 C9
15 4 C9 3 C12 4 C10
5 22 * * 3 C13 4 C12
33 * * 2 C13 3 C12
47 * * 1 C13 2 C12
10 4 C9 2 C10 4 C10
15 4 C8 2 C10 4 C10
22 4 C9 3 C12 4 C10
12 33 * * 3 C13 4 C12
47 * * 2 C13 3 C12
68 * * 2 C13 2 C12
100 * * 1 C13 2 C12

(1) Assumes worst case maximum input voltage and load current for a given inductance value
(2) * Check voltage rating of capacitors to be greater than application input voltage.
(3) No. represents the number of identical capacitor types to be connected in parallel
(4) C Code indicates the Capacitor Reference number in Table 1 for identifying the specific component from the manufacturer.

Step 5: From Table 7 a 3-A Schottky diode must be selected. For through-hole components, 20-V rated diodes
are sufficient and 2 part types are suitable, 1N5820 and SR302.

Table 7. Schottky Diode Selection Table

REVERSE SURFACE MOUNT THROUGH HOLE
VOLTAGE (V) 3A 5 A OR MORE 3A 5 A OR MORE
— 1N5820 —
20 SK32
— SR302 —
SK33 1N5821 —
30 MBRD835L
30WQ03F 31DQ03 —
SK34 MBRB1545CT 1N5822 —
30BQ040 6TQ045S MBR340 MBR745
40 30WQ04F — 31DQ04 80SQ045
MBRS340 — SR403 6TQ045
MBRD340 — — —
SK35 — MBR350 —
50 or more 30WQ05F — 31DQ05 —
— — SR305 —

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Step 6: A 0.01-μF capacitor is used for CBoost.

8.2.1.3 Application Curves

Figure 17. LM2677, 3.3 V Figure 18. LM2677, 5 V

Figure 19. LM2677, 12 V

8.2.2 Adjustable Output Voltage Applications

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Figure 20. Basic Circuit For Adjustable Output Voltage Applications

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8.2.2.1 Design Requirements

Table 8 lists the design requirements for the adjustable output voltage application.

Table 8. Design Parameters

PARAMETER VALUE
Required output voltage, VOUT 14.8 V
Maximum DC input voltage, VIN_MAX 28 V
Maximum output load current, ILOAD_MAX 2A

8.2.2.2 Detailed Design Procedure

In this example it is desired to convert the voltage from a two-battery automotive power supply (voltage range of
20 V to 28 V, typical in large truck applications) to the 14.8 VDC alternator supply typically used to power
electronic equipment from single battery 12-V vehicle systems. The load current required is 2 A maximum. It is
also desired to implement the power supply with all surface mount components.
Step 1: Select an LM2677S-ADJ to set the output voltage to 14.9 V that chooses between two required resistors
(R1 and R2 in Figure 20). For the adjustable device, the output voltage is set by Equation 1.
æ R ö
VOUT = VFB ç 1 + 2 ÷
è R1 ø
where
• VFB is the feedback voltage of typically 1.21 V (1)
A recommended value to use for R1 is 1K. In this example then R2 is determined with Equation 2.
æV ö æ 12.8 V ö
R2 = R1 ç OUT - 1÷ = 1 kW ç - 1÷
è VFB ø è 1.21 V ø (2)
R2 = 11.2 kΩ
The closest standard 1% tolerance value to use is 11.3 kΩ. This sets the nominal output voltage to 14.88 V
which is within 0.5% of the target value.
Step 2: To use the nomograph for the adjustable device, Figure 21, requires a calculation of the inductor
Volt•microsecond constant (E × T expressed in V × μS) from Equation 3.
VOUT + VD 1000
(
E ´ T = VIN(MAX ) - VOUT - VSAT ´ ) ´
VIN(MAX ) - VSAT + VD 260
(V ´ ms )

where
• VSAT is the voltage drop across the internal power switch which is Rds(ON) times Iload (3)
In this example, this would be typically 0.15 Ω × 2 A or 0.3 V and VD is the voltage drop across the forward
bisased Schottky diode, typically 0.5 V. The switching frequency of 260 kHz is the nominal value to use to
estimate the ON-time of the switch during which energy is stored in the inductor. For this example E × T is found
with Equation 4 and Equation 5.
14.8 + 0.5 1000
E ´ T = (28 - 14.8 - 0.3 ) ´ ´ (V ´ ms )
28 - 0.3 + 0.5 260 (4)
15.3
E ´ T = (12.9 V ) ´ ´ 3.85 (V ´ ms ) = 26.9 (V ´ ms )
28.2 (5)
Using Figure 21, the intersection of 27 V × μS horizontally and the 2-A vertical line (Iload max) indicates that L38 ,
a 68-μH inductor, must be used. L38 in a surface mount component is available from Pulse Engineering with part
number PE-54038S.

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Step 3: Use Table 9 and Table 10 to determine an output capacitor. With a 14.8-V output the 12.5-V to 15-V row
is used and with a 68-μH inductor there are three surface mount output capacitor solutions. Table 1 provides the
actual capacitor characteristics based on the C Code number. Any of the following choices can be used:
• 1 × 33-μF, 20-V AVX TPS (code C6)
• 1 × 47-μF, 20-V Sprague 594 (code C8)
• 1 × 47-μF, 20-V Kemet T495 (code C8)

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Table 9. Surface-Mount Output Capacitors

INDUCTANCE AVX TPS SERIES SPRAGUE 594D SERIES KEMET T495 SERIES
OUTPUT VOLTAGE (V)
(µH) NO. (1) C CODE (2) NO. (1) C CODE (2) NO. (1) C CODE (2)
33 (3) 7 C1 6 C2 7 C3
1.21 to 2.50
47 (3) 5 C1 4 C2 5 C3
33 (3) 4 C1 3 C2 4 C3
2.5 to 3.75
47 (3) 3 C1 2 C2 3 C3
22 4 C1 3 C2 4 C3
3.75 to 5 33 3 C1 2 C2 3 C3
47 2 C1 2 C2 2 C3
22 3 C2 1 C3 3 C4
33 2 C2 2 C3 2 C4
5 to 6.25
47 2 C2 2 C3 2 C4
68 1 C2 1 C3 1 C4
22 3 C2 1 C4 3 C4
33 2 C2 1 C3 2 C4
6.25 to 7.5
47 1 C3 1 C4 1 C6
68 1 C2 1 C3 1 C4
33 2 C5 1 C6 2 C8
47 1 C5 1 C6 2 C8
7.5 to 10
68 1 C5 1 C6 1 C8
100 1 C4 1 C5 1 C8
33 1 C5 1 C6 2 C8
47 1 C5 1 C6 2 C8
10 to 12.5
68 1 C5 1 C6 1 C8
100 1 C5 1 C6 1 C8
33 1 C6 1 C8 1 C8
47 1 C6 1 C8 1 C8
12.5 to 15
68 1 C6 1 C8 1 C8
100 1 C6 1 C8 1 C8
33 1 C8 1 C10 2 C10
47 1 C8 1 C9 2 C10
15 to 20
68 1 C8 1 C9 2 C10
100 1 C8 1 C9 1 C10
33 2 C9 2 C11 2 C11
47 1 C10 1 C12 1 C11
20 to 30
68 1 C9 1 C12 1 C11
100 1 C9 1 C12 1 C11
10 — — 4 C13 8 C12
15 — — 3 C13 5 C12
22 No values 2 C13 4 C12
30 to 37
33 available 1 C13 3 C12
47 — — 1 C13 2 C12
68 — — 1 C13 2 C12

(1) No. represents the number of identical capacitor types to be connected in parallel
(2) C Code indicates the Capacitor Reference number in Table 1 for identifying the specific component from the manufacturer.
(3) Set to a higher value for a practical design solution.

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Table 10. Through-Hole Output Capacitors

SANYO OS-CON SA SANYO MV-GX PANASONIC HFQ
OUTPUT INDUCTANC SERIES SERIES NICHICON PL SERIES SERIES
VOLTAGE (V) E (µH)
NO. (1) C CODE (2) NO. (1) C CODE (2) NO. (1) C CODE (2) NO. (1) C CODE (2)
(3)
33 2 C3 5 C1 5 C3 3 C
1.21 to 2.50
47 (3) 2 C2 4 C1 3 C3 2 C5
33 (3) 1 C3 3 C1 3 C1 2 C5
2.5 to 3.75 (3)
47 1 C2 2 C1 2 C3 1 C5
22 1 C3 3 C1 3 C1 2 C5
3.75 to 5 33 1 C2 2 C1 2 C1 1 C5
47 1 C2 2 C1 1 C3 1 C5
22 1 C5 2 C6 2 C3 2 C5
33 1 C4 1 C6 2 C1 1 C5
5 to 6.25
47 1 C4 1 C6 1 C3 1 C5
68 1 C4 1 C6 1 C1 1 C5
22 1 C5 1 C6 2 C1 1 C5
33 1 C4 1 C6 1 C3 1 C5
6.25 to 7.5
47 1 C4 1 C6 1 C1 1 C5
68 1 C4 1 C2 1 C1 1 C5
33 1 C7 1 C6 1 C14 1 C5
47 1 C7 1 C6 1 C14 1 C5
7.5 to 10
68 1 C7 1 C2 1 C14 1 C2
100 1 C7 1 C2 1 C14 1 C2
33 1 C7 1 C6 1 C14 1 C5
47 1 C7 1 C2 1 C14 1 C5
10 to 12.5
68 1 C7 1 C2 1 C9 1 C2
100 1 C7 1 C2 1 C9 1 C2
33 1 C9 1 C10 1 C15 1 C2
47 1 C9 1 C10 1 C15 1 C2
12.5 to 15
68 1 C9 1 C10 1 C15 1 C2
100 1 C9 1 C10 1 C15 1 C2
33 1 C10 1 C7 1 C15 1 C2
47 1 C10 1 C7 1 C15 1 C2
15 to 20
68 1 C10 1 C7 1 C15 1 C2
100 1 C10 1 C7 1 C15 1 C2
33 — — 1 C7 1 C16 1 C2
47 No values 1 C7 1 C16 1 C2
20 to 30
68 available 1 C7 1 C16 1 C2
100 — — 1 C7 1 C16 1 C2
10 — — 1 C12 1 C20 1 C10
15 — — 1 C11 1 C20 1 C11
22 No values 1 C11 1 C20 1 C10
30 to 37
33 available 1 C11 1 C20 1 C10
47 — — 1 C11 1 C20 1 C10
68 — — 1 C11 1 C20 1 C10

(1) No. represents the number of identical capacitor types to be connected in parallel
(2) C Code indicates the Capacitor Reference number in Table 1 for identifying the specific component from the manufacturer.
(3) Set to a higher value for a practical design solution.

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NOTE
When using the adjustable device in low voltage applications (less than 3-V output), if the
nomograph, Figure 21, selects an inductance of 22 μH or less, Table 9 does not provide
an output capacitor solution. With these conditions the number of output capacitors
required for stable operation becomes impractical. TI recommends using either a 33-μH or
47-μH inductor and the output capacitors from Table 9.

Step 4: An input capacitor for this example requires at least a 35-V WV rating with an rms current rating of 1 A
(1/2 Iout max). From Table 1 it can be seen that C12, a 33-μF, 35-V capacitor from Sprague, has the required
voltage/current rating of the surface mount components.
Step 5: From Table 7 a 3-A Schottky diode must be selected. For surface mount diodes with a margin of safety
on the voltage rating one of five diodes can be used:
• SK34
• 30BQ040
• 30WQ04F
• MBRS340
• MBRD340
Step 6: A 0.01-μF capacitor is used for Cboost.

8.2.2.3 Application Curve

Figure 21. LM2677, Adjustable

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9 Power Supply Recommendations

Power supply design using the LM2677 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 LM2677. 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 could be substituted for use in an application.
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 LM2677. 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 placed close to pin 2.

10 Layout

10.1 Layout Guidelines

Layout is very important in switching regulator designs. Rapidly switching currents associated with wiring
inductance can generate voltage transients which can cause problems. For minimal inductance and ground
loops, the wires indicated by heavy lines (in Figure 16 and Figure 20) must be wide printed circuit traces and
must be kept as short as possible. For best results, external components must be placed as close to the switcher
IC as possible using ground plane construction or single-point grounding. If open-core inductors are used, take
special care as to the location and positioning of this type of inductor. Allowing the inductor flux to intersect
sensitive feedback, IC ground path, and C wiring can cause problems.
When using the adjustable version, take special care as to the location of the feedback resistors and the
associated wiring. Physically place both resistors near the IC, and route the wiring away from the inductor,
especially an open-core type of inductor.

10.1.1 VSON Package Devices

The LM2677 is offered in the 14-pin VSON surface mount package to allow for a significantly decreased footprint
with equivalent power dissipation compared to the TO-220 or TO-263. For details on mounting and soldering
specifications, see application note, AN-1187 Leadless Leadframe Package (LLP).

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10.2 Layout Example

Figure 22. LM2677 Sample Layout

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11 Device and Documentation Support

11.1 Documentation Support

11.1.1 Related Documentation
For related documentation see the following:
AN-1187 Leadless Leadframe Package (LLP) (SNOA401)

11.2 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.

11.3 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.

11.4 Trademarks
E2E is a trademark of Texas Instruments.
SIMPLE SWITCHER is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 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.

11.6 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.

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 MECHANICAL DATA
NHM0014A

SRC14A (Rev A)

www.ti.com
 MECHANICAL DATA
NDZ0007B

TA07B (Rev E)

www.ti.com
 MECHANICAL DATA

MPSF015 – AUGUST 2001

KTW (R-PSFM-G7) PLASTIC FLANGE-MOUNT

0.410 (10,41) 0.304 (7,72)

–A–
0.385 (9,78) 0.006 0.296 (7,52)
–B–
0.303 (7,70) 0.300 (7,62)
0.0625 (1,587) H 0.297 (7,54) 0.055 (1,40) 0.252 (6,40)
0.064 (1,63)
0.0585 (1,485) 0.045 (1,14)
0.056 (1,42)

0.370 (9,40) 0.187 (4,75)

0.330 (8,38) 0.179 (4,55)
H A
0.605 (15,37)
0.595 (15,11)
0.012 (0,305)
C 0.000 (0,00)
0.104 (2,64)
0.019 (0,48) 0.096 (2,44) H
0.017 (0,43)

0.050 (1,27) 0.026 (0,66)

C
0.034 (0,86) 0.014 (0,36)
0°~3°
C F 0.022 (0,57)
0.010 (0,25) M B AM C M

0.183 (4,65)
0.170 (4,32)

4201284/A 08/01

NOTES: A. All linear dimensions are in inches (millimeters).

B. This drawing is subject to change without notice.
C. Lead width and height dimensions apply to the
plated lead.
D. Leads are not allowed above the Datum B.
E. Stand–off height is measured from lead tip
with reference to Datum B.
F. Lead width dimension does not include dambar
protrusion. Allowable dambar protrusion shall not
cause the lead width to exceed the maximum
dimension by more than 0.003”.
G. Cross–hatch indicates exposed metal surface.
H. Falls within JEDEC MO–169 with the exception
of the dimensions indicated.

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