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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
•
•
The LM2677 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 5-A loads with excellent line
and load regulation characteristics. High efficiency
(>90%) is obtained through the use of a low onresistance DMOS power switch. The series consists
of fixed output voltages of 3.3-V, 5-V, and 12-V and
an adjustable output version.
1
•
•
•
•
•
•
•
•
Efficiency up to 92%
Simple and Easy to Design Using Off-the-Shelf
External Components
100-mΩ DMOS Output Switch
3.3-V, 5-V, and 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
External Sync Clock Capability (280 kHz to
400 kHz)
260-kHz Fixed Frequency Internal Oscillator
−40°C to 125°C Operating Junction Temperature
Range
The SIMPLE SWITCHER® concept provides for a
complete design using a minimum number of external
components. The switching clock frequency can be
provided by an internal fixed frequency oscillator
(260 kHz) or from an externally provided clock in the
range of 280 kHz to 400 kHz, which allows the use of
physically smaller-sized components. A family of
standard inductors for use with the LM2677 are
available from several manufacturers to greatly
simplify the design process. The external Sync clock
provides direct and precise control of the output ripple
frequency for consistent filtering or frequency
spectrum positioning.
2 Applications
•
•
•
•
Simple to Design, High Efficiency (> 90%) StepDown Switching Regulators
Efficient System Preregulator for Linear Voltage
Regulators
Battery Chargers
Communications and Radio Equipment Regulator
With Synchronized Clock Frequency
The LM2677 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.
Device Information(1)
PART NUMBER
LM2677
PACKAGE
BODY SIZE (NOM)
TO-263 (7)
10.16 mm × 8.69 mm
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
LM2677 - 5.0
8V to 40V
L
0.47 PF
+
+
Voltage
+
Ground
3 x 15 PF/50V
1 k:
Optional External
Sync Clock
(280 kHz to 400 kHz)
Output
Switch
Output
22 PH
6TQ045S
5V/5A
2 x 180 PF, 16V
100 pF
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
2
3
4
5
6
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
4
4
4
5
5
5
6
6
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics – 3.3 V ..............................
Electrical Characteristics – 5 V .................................
Electrical Characteristics – 12 V ...............................
Electrical Characteristics – Adjustable......................
Electrical Characteristics – All Output Voltage
Versions .....................................................................
6.10 Typical Characteristics ............................................
7
6
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 Application .................................................. 16
9 Power Supply Recommendations...................... 25
10 Layout................................................................... 25
10.1 Layout Guidelines ................................................. 25
10.2 Layout Example .................................................... 26
11 Device and Documentation Support ................. 27
11.1
11.2
11.3
11.4
11.5
11.6
Documentation Support ........................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
27
27
27
27
27
27
12 Mechanical, Packaging, and Orderable
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
2
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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
Not to scale
Thermal
Pad
7
ON/OFF
6
FB
5
SYNC
4
GND
3
CB
2
VIN
1
VSW
1
2
3
4
5
6
7
VSW
VIN
CB
GND
SYNC
FB
ON/OFF
Not to scale
NHM Package
14-Pin VSON
Top View
NC
1
14
VSW
VIN
2
13
VSW
VIN
3
12
VSW
CB
4
11
NC
NC
5
10
NC
SYNC
6
9
GND
FB
7
8
ON/OFF
DAP
Not to scale
Pin Functions
PIN
NAME
I/O
DESCRIPTION
TO-263, TO-220
VSON
CB
3
4
I
Boot-strap capacitor connection for high-side driver. Connect a high quality
100-nF capacitor from CB to VSW pin.
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.
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.
NC
—
1, 5, 10, 11
—
No connect pins
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.
SYNC
5
6
I
This input allows control of the switching clock frequency. If left open-circuited
the regulator is switched at the internal oscillator frequency, typically
260 kHz.
VIN
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.
VSW
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.
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SNVS077J – MAY 2004 – REVISED JUNE 2016
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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
45
V
–0.1
6
V
–1
VIN
V
VSW + 8
V
14
V
Input supply voltage
ON/OFF pin voltage
Switch voltage to ground (3)
Boost pin voltage
Feedback pin voltage
–0.3
Power dissipation
Internally limited
Soldering temperature
Wave (4 s)
260
Infrared (10 s)
240
Vapor phase (75 s)
219
Storage temperature, Tstg
(1)
(2)
(3)
–65
°C
150
°C
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.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
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
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (2)
VALUE
UNIT
±2000
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
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
Supply voltage
TJ
4
Junction temperature
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MAX
UNIT
8
40
V
–40
125
°C
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6.4 Thermal Information
LM2677
THERMAL METRIC (1)
KTW (TO-263)
NDZ (TO-220)
NHM (VSON)
7 PINS
7 PINS
14 PINS
See (2)
56
—
—
(3)
35
—
—
See (4)
26
—
—
See (5)
—
65
—
(6)
—
45
—
See (7)
—
—
55
See (8)
—
—
29
See
RθJA
Junction-to-ambient thermal resistance
See
UNIT
°C/W
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)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
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.
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.
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.
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.
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.
Junction to ambient thermal resistance for the 14-pin VSON mounted on a PC board copper area equal to the die attach paddle.
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
VOUT
Output voltage
VIN = 8 V to 40 V, 100 mA ≤ IOUT ≤ 5 A
η
Efficiency
VIN = 12 V, ILOAD = 5 A
(1)
(2)
MIN (1)
TEST CONDITIONS
TJ = 25°C
3.234
TJ = –40°C to 125°C
3.201
TYP (2)
MAX (1)
3.3
3.366
3.399
UNIT
V
82%
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).
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
VOUT
Output voltage
VIN = 8 V to 40 V, 100 mA ≤ IOUT ≤ 5 A
η
Efficiency
VIN = 12 V, ILOAD = 5 A
(1)
(2)
MIN (1)
TEST CONDITIONS
TJ = 25°C
TJ = –40°C to 125°C
4.9
TYP (2)
MAX (1)
5
4.85
5.1
5.15
UNIT
V
84%
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).
Typical values are determined with TA = TJ = 25°C and represent the most likely norm.
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SNVS077J – MAY 2004 – REVISED JUNE 2016
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6.7 Electrical Characteristics – 12 V
TJ = 25°C, sync pin open circuited (unless otherwise noted)
PARAMETER
VOUT
Output voltage
VIN = 15 V to 40 V, 100 mA ≤ IOUT ≤ 5 A
η
Efficiency
VIN = 24 V, ILOAD = 5 A
(1)
(2)
MIN (1)
TEST CONDITIONS
TJ = 25°C
11.76
TJ = –40°C to 125°C
11.64
TYP (2)
MAX (1)
12
UNIT
12.24
12.36
V
92%
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).
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
VFB
Feedback voltage
VIN = 8 V to 40 V, 100 mA ≤ IOUT ≤ 5 A,
VOUT programmed for 5 V
η
Efficiency
VIN = 12 V, ILOAD = 5 A
(1)
(2)
MIN (1)
TEST CONDITIONS
TJ = 25°C
1.186
TJ = –40°C to 125°C
1.174
TYP (2)
MAX (1)
1.21
UNIT
1.234
1.246
V
84%
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).
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
MIN (1)
TEST CONDITIONS
IQ
Quiescent current
VFEEDBACK = 8 V for 3.3-V, 5-V, and adjustable
versions, VFEEDBACK = 15 V for 12-V versions
ISTBY
Standby quiescent current
ON/OFF pin = 0 V
ICL
Current limit
IL
Output leakage current
TJ = 25°C
TJ = 25°C
7
8.3
8.75
1
200
15
6
TJ = 25°C
ISWITCH = 5 A
fO
Oscillator frequency
Measured at switch pin
D
Duty cycle
IBIAS
Feedback bias current
0.12
TJ = –40°C to 125°C
260
TJ = –40°C to 125°C
225
280
Maximum duty cycle
91%
Minimum duty cycle
0%
VFEEDBACK = 1.3 V, ADJ version only
85
TJ = 25°C
1.4
TJ = –40°C to 125°C
0.8
TJ = 25°C
ON/OFF input current
ON/OFF input = 0 V
FSYNC
Synchronization frequency
VSYNC(pin 5) = 3.5 V, 50% duty cycle
VSYNC
SYNC threshold voltage
μA
A
μA
Ω
kHz
nA
2
20
TJ = –40°C to 125°C
mA
mA
0.14
0.225
TJ = 25°C
ION/OFF
6
100
VSWITCH = 0 V
RDS(ON) Switch on-resistance
(2)
50
5.75
VSWITCH = –1 V
(1)
6
150
6.1
TJ = –40°C to 125°C
MAX (1) UNIT
4.2
TJ = –40°C to 125°C
VIN = 40 V, ON/OFF pin = 0 V
VON/OFF ON/OFF threshold voltage
TYP (2)
45
V
μA
400
kHz
1.4
V
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).
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
Inductor current, 2 A/div
Output ripple voltage,
20 mV/div AC-coupled
Figure 11. Feedback Pin Bias Current
8
VIN = 20 V, VOUT = 5 V,
ILOAD = 5 A, L = 10 μH,
COUT = 400 μF,
COUTESR = 13 mΩ
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
Inductor current, 1 A/div
Output ripple voltage,
20 mV/div AC-coupled
VIN = 20 V, VOUT = 5 V,
ILOAD = 500 mA,
L = 10 μH,
COUT = 400 μF,
COUTESR = 13 mΩ
Figure 13. Discontinuous Mode Switching Waveforms,
Horizontal Time Base: 1 μs//iv
Output voltage, 100 mV//div,
AC-coupled
Load current: 200 mA
to 5-A load pulse
Output voltage,
100 mV//div,
AC-coupled
Load current: 500 mA
to 5-A load pulse
VIN = 20 V, VOUT = 5 V,
L = 10 μH,
COUT = 400 μF,
COUTESR = 13 mΩ
Figure 14. Load Transient Response for Continuous Mode,
Horizontal Time Base: 100 μs/div
VIN = 20 V, VOUT = 5 V,
L = 10 μH,
COUT = 400 μF,
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
Compensation
Bias
Generator
1.21 V
Reference
5 V Internal
Regulator
Start
Up
Bias
1.21 V
5V
Enable
SYNC
50 k
11 V
260 kHz
Oscillator
VRAMP
Freq. Shift
Current
Limit
ON/OFF
RSENSE
3.2 V
0.6 V
Thermal
Shutdown
FEEDBACK
3.3 V, R2 = 4.32 k
5 V, R2 = 7.83 k
12 V, R2 = 22.3 k
ADJ, R2 = 0 Ÿ
R1 is OPEN
3A
Switch
Reset
CBOOTSTRAP
R2
+
GM 1
±
2k
R1 = 2.5 k
10 k
20 mH*
+
±
GM 2
+
±
15 k
Control
Logic
Driver
PWM
Comparator
Enable
10 Q)‚
VSWITCH
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).
10
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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
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)
AVX TPS SERIES
SPRAGUE 594D SERIES
KEMET T495 SERIES
Assumes worst case maximum input voltage and load current for a given inductance value
Table 2. Through-Hole Capacitors (1)
CAPACITOR
REFERENCE
CODE
(1)
SANYO OS-CON SA SERIES
SANYO MV-GX SERIES
IRMS
(A)
C (µF)
NICHICON PL SERIES
WV (V)
IRMS
(A)
C (µF)
WV (V)
C (µF)
WV (V)
C1
47
6.3
1
1000
6.3
0.8
680
10
C2
150
6.3
1.95
270
16
0.6
820
10
C3
330
6.3
2.45
470
16
0.75
1000
10
C4
100
10
1.87
560
16
0.95
1200
C5
220
10
2.36
820
16
1.25
2200
C6
33
16
0.96
1000
16
1.3
C7
100
16
1.92
150
35
C8
150
16
2.28
470
35
C9
100
20
2.25
680
35
C10
47
25
2.09
1000
C11
—
—
—
220
C12
—
—
—
C13
—
—
—
C14
—
—
C15
—
—
IRMS
(A)
PANASONIC HFQ SERIES
IRMS
(A)
C (µF)
WV (V)
0.8
82
35
0.4
0.98
120
35
0.44
1.06
220
35
0.76
10
1.28
330
35
1.01
10
1.71
560
35
1.4
3300
10
2.18
820
35
1.62
0.65
3900
10
2.36
1000
35
1.73
1.3
6800
10
2.68
2200
35
2.8
1.4
180
16
0.41
56
50
0.36
35
1.7
270
16
0.55
100
50
0.5
63
0.76
470
16
0.77
220
50
0.92
470
63
1.2
680
16
1.02
470
50
1.44
680
63
1.5
820
16
1.22
560
50
1.68
—
1000
63
1.75
1800
16
1.88
1200
50
2.22
—
—
—
—
220
25
0.63
330
63
1.42
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
REFERENCE
CODE
SANYO OS-CON SA SERIES
SANYO MV-GX SERIES
NICHICON PL SERIES
C (µF)
WV (V)
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
—
—
—
C (µF)
WV (V)
IRMS
(A)
C (µF)
PANASONIC HFQ SERIES
IRMS
(A)
WV (V)
IRMS
(A)
C (µF)
WV (V)
IRMS
(A)
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
REF.
#
(1)
16
INDUCTANCE CURRENT
(µH)
(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
2.00
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
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
REF.
#
INDUCTANCE CURRENT
(µH)
(A)
RENCO
PULSE ENGINEERING
COILCRAFT
THROUGH HOLE
SURFACE
MOUNT
THROUGH
HOLE
SURFACE
MOUNT
SURFACE 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
VOLTAGE (V)
INDUCTANCE
(µH)
AVX TPS SERIES
NO.
3.3
5
12
(1)
(2)
(3)
(2)
C CODE
SPRAGUE 594D SERIES
(3)
NO.
(2)
C Code
(3)
KEMET T495 SERIES
NO. (2)
C CODE (3)
10
5
C1
5
C1
5
C2
15
4
C1
4
C1
4
C3
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
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
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
Assumes worst case maximum input voltage and load current for a given inductance value
No. represents the number of identical capacitor types to be connected in parallel
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
VOLTAGE (V)
INDUCTANCE
(µH)
AVX TPS SERIES (2)
NO.
3.3
5
12
(1)
(2)
(3)
(4)
(3)
C CODE
SPRAGUE 594D SERIES
(4)
NO.
(3)
C CODE
(4)
KEMET T495 SERIES
NO. (3)
C CODE (4)
10
3
C7
2
C10
3
C9
15
*
*
3
C13
4
C12
22
*
*
2
C13
3
C12
33
*
*
2
C13
3
C12
10
3
C4
2
C6
3
C9
15
4
C9
3
C12
4
C10
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
33
*
*
3
C13
4
C12
47
*
*
2
C13
3
C12
68
*
*
2
C13
2
C12
100
*
*
1
C13
2
C12
Assumes worst case maximum input voltage and load current for a given inductance value
* Check voltage rating of capacitors to be greater than application input voltage.
No. represents the number of identical capacitor types to be connected in parallel
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
VOLTAGE (V)
20
30
40
50 or more
18
SURFACE MOUNT
3A
SK32
SK33
30WQ03F
THROUGH HOLE
5 A OR MORE
3A
5 A OR MORE
—
1N5820
—
—
MBRD835L
SR302
—
1N5821
—
31DQ03
—
—
SK34
MBRB1545CT
1N5822
30BQ040
6TQ045S
MBR340
MBR745
30WQ04F
—
31DQ04
80SQ045
MBRS340
—
SR403
6TQ045
MBRD340
—
—
—
SK35
—
MBR350
—
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
Copyright © 2016, Texas Instruments Incorporated
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 ÷
R1 ø
è
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 1.21 V
ø
è VFB
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 ´
´
(V ´ ms )
VIN(MAX ) - VSAT + VD 260
(
)
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.
E ´ T = (28 - 14.8 - 0.3 ) ´
E ´ T = (12.9 V ) ´
14.8 + 0.5
1000
´
(V ´ ms )
28 - 0.3 + 0.5 260
15.3
´ 3.85 (V ´ ms ) = 26.9 (V ´ ms )
28.2
(4)
(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.
20
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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
OUTPUT VOLTAGE (V)
1.21 to 2.50
2.5 to 3.75
3.75 to 5
5 to 6.25
6.25 to 7.5
7.5 to 10
10 to 12.5
12.5 to 15
15 to 20
20 to 30
30 to 37
(1)
(2)
(3)
22
AVX TPS SERIES
SPRAGUE 594D SERIES
KEMET T495 SERIES
INDUCTANCE
(µH)
NO. (1)
C CODE (2)
NO. (1)
C CODE (2)
NO. (1)
C CODE (2)
33 (3)
7
C1
6
C2
7
C3
47 (3)
5
C1
4
C2
5
C3
33 (3)
4
C1
3
C2
4
C3
47 (3)
3
C1
2
C2
3
C3
22
4
C1
3
C2
4
C3
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
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
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
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
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
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
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
68
1
C9
1
C12
1
C11
100
1
C9
1
C12
1
C11
10
—
—
4
C13
8
C12
15
—
—
3
C13
5
C12
2
C13
4
C12
1
C13
3
C12
22
No values
available
33
47
—
—
1
C13
2
C12
68
—
—
1
C13
2
C12
No. represents the number of identical capacitor types to be connected in parallel
C Code indicates the Capacitor Reference number in Table 1 for identifying the specific component from the manufacturer.
Set to a higher value for a practical design solution.
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Table 10. Through-Hole Output Capacitors
OUTPUT
VOLTAGE (V)
1.21 to 2.50
2.5 to 3.75
3.75 to 5
5 to 6.25
6.25 to 7.5
7.5 to 10
10 to 12.5
12.5 to 15
15 to 20
20 to 30
30 to 37
(1)
(2)
(3)
INDUCTANC
E (µH)
SANYO OS-CON SA
SERIES
SANYO MV-GX
SERIES
NICHICON PL SERIES
PANASONIC HFQ
SERIES
NO. (1)
C CODE (2)
NO. (1)
C CODE (2)
NO. (1)
C CODE (2)
NO. (1)
(3)
2
C3
5
C1
5
C3
3
C
47 (3)
2
C2
4
C1
3
C3
2
C5
33 (3)
1
C3
3
C1
3
C1
2
C5
(3)
33
47
C CODE (2)
1
C2
2
C1
2
C3
1
C5
22
1
C3
3
C1
3
C1
2
C5
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
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
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
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
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
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
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
1
C7
1
C16
1
C2
C2
47
No values
available
1
C7
1
C16
1
100
68
—
—
1
C7
1
C16
1
C2
10
—
—
1
C12
1
C20
1
C10
15
—
—
1
C11
1
C20
1
C11
1
C11
1
C20
1
C10
1
C11
1
C20
1
C10
22
No values
available
33
47
—
—
1
C11
1
C20
1
C10
68
—
—
1
C11
1
C20
1
C10
No. represents the number of identical capacitor types to be connected in parallel
C Code indicates the Capacitor Reference number in Table 1 for identifying the specific component from the manufacturer.
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
24
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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
26
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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
NDZ0007B
TA07B (Rev E)
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MECHANICAL DATA
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BOTTOM SIDE OF PACKAGE
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