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LM2672
SNVS136L – SEPTEMBER 1998 – REVISED JUNE 2016
LM2672 SIMPLE SWITCHER® Power Converter High Efficiency 1-A Step-Down Voltage
Regulator with Features
1 Features
3 Description
•
•
•
•
•
The LM2672 series of regulators are monolithic
integrated DC-DC converter built with a LMDMOS
process. These regulators provide all the active
functions for a step-down (buck) switching regulator,
capable of driving a 1-A load current with excellent
line and load regulation. These devices are available
in fixed output voltages of 3.3 V, 5 V, 12 V, and an
adjustable output version.
1
•
•
•
•
•
•
•
Efficiency up to 96%
Available in 8-Pin SOIC and PDIP Packages
Requires only 5 External Components
3.3-V, 5-V, 12-V, and Adjustable Output Versions
Adjustable Version Output Voltage Range: 1.21 V
to 37 V
±1.5% Maximum Output Voltage Tolerance Over
Line and Load Conditions
Specified 1-A Output Load Current
Wide Input Voltage Range: 8 V to 40 V
260-kHz Fixed Frequency Internal Oscillator
TTL Shutdown Capability, Low Power Standby
Mode
Soft-Start and Frequency Synchronization
Thermal Shutdown and Current Limit Protection
2 Applications
•
•
Simple High Efficiency (>90%) Step-Down (Buck)
Regulator
Efficient Preregulator for Linear Regulators
Requiring a minimum number of external
components, these regulators are simple to use and
include patented internal frequency compensation,
fixed frequency oscillator, external shutdown, softstart, and frequency synchronization.
The LM2672 series operates at a switching frequency
of 260 kHz, thus allowing smaller sized filter
components than what is required with lower
frequency switching regulators. Because of its very
high efficiency (>90%), the copper traces on the
printed-circuit board are the only heat sinking
required.
Device Information(1)
PART NUMBER
LM2672
PACKAGE
BODY SIZE (NOM)
SOIC (8)
5.00 mm × 6.20 mm
PDIP (8)
10.16 mm × 6.60 mm
WSON (16)
5.00 mm × 5.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application
Copyright © 2016, Texas Instruments Incorporated
Fixed output voltage versions
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.
LM2672
SNVS136L – SEPTEMBER 1998 – REVISED JUNE 2016
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Description (continued).........................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
4
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
4
4
4
4
5
5
5
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 .....................................................................
7.10 Typical Characteristics ............................................
7.11 Typical Characteristics – Fixed Output Voltage
Versions .....................................................................
8
9
6
7
9
Parameter Measurement Information ................ 10
Detailed Description ............................................ 11
9.1
9.2
9.3
9.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
11
11
11
12
10 Application and Implementation........................ 13
10.1 Application Information.......................................... 13
10.2 Typical Applications .............................................. 14
11 Power Supply Recommendations ..................... 25
12 Layout................................................................... 25
12.1 Layout Guidelines ................................................. 25
12.2 Layout Examples................................................... 25
13 Device and Documentation Support ................. 27
13.1
13.2
13.3
13.4
13.5
13.6
Documentation Support ........................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
27
27
27
27
27
27
14 Mechanical, Packaging, and Orderable
Information ........................................................... 27
14.1 DAP (WSON Package) ......................................... 27
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision K (April 2013) to Revision L
Page
•
Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section .................................................................................................. 1
•
Removed all references to Computer Design Software LM267X Made Simple (Version 6.0).............................................. 1
Changes from Revision J (April 2013) to Revision K
•
2
Page
Changed layout of National Data Sheet to TI format ............................................................................................................. 1
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5 Description (continued)
A family of standard inductors for use with the LM2672 are available from several different manufacturers. This
feature greatly simplifies the design of switch-mode power supplies using these advanced ICs. Also included in
the datasheet are selector guides for diodes and capacitors designed to work in switch-mode power supplies.
Other features include ±1.5%-tolerance on output voltage within specified input voltages and output load
conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring typically 50 μA standby current. The output switch includes current limiting, as well as thermal shutdown for full protection under fault
conditions.
6 Pin Configuration and Functions
D or P Package
8-Pin SOIC or PDIP
Top View
NHN Package
16-Pin WSON
Top View
CB
1
8
VSW
CB
1
16
VSW
SS
2
7
VIN
NC
2
15
VSW
SYNC
3
6
GND
NC
3
14
VIN
SS
4
13
NC
FB
4
5
ON/OFF
Not to scale
DAP
NC
5
12
GND
SYNC
6
11
GND
NC
7
10
NC
FB
8
9
ON/OFF
Not to scale
Pin Functions
PIN
NAME
I/O
DESCRIPTION
SOIC, PDIP
WSON
CB
1
1
I
Boot-strap capacitor connection for high-side driver. Connect a high quality
100-nF capacitor from CB to VSW Pin.
FB
4
8
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
6
11, 12
—
Power ground pins. Connect to system ground. Ground pins of CIN and COUT.
Path to CIN must be as short as possible.
NC
—
2, 3, 5,
7, 10, 13
—
No connection pins.
ON/OFF
5
9
I
Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin
high or float to enable the regulator.
SS
2
4
I
Soft-start capacitor pin. Connect a capacitor from this pin to GND to control
the output voltage ramp. If the feature not desired, the pin can be left floating.
SYNC
3
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
7
14
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
8
15, 16
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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7 Specifications
7.1 Absolute Maximum Ratings
over recommended operating junction temperature range of –40°C to 125°C (unless otherwise noted) (1)
MIN
Supply voltage
ON/OFF pin voltage, VSH
–0.1
UNIT
45
V
6
V
–1
V
VSW + 8
V
14
V
Switch voltage to ground
Boost pin voltage
MAX
Feedback pin voltage, VFB
–0.3
Power dissipation
Internally limited
D package
Lead temperature
Vapor phase (60s)
215
Infrared (15s)
220
P package (soldering, 10s)
Maximum junction temperature, TJ
Storage temperature, Tstg
(1)
°C
260
–65
150
°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.
7.2 ESD Ratings
V(ESD)
(1)
Electrostatic discharge
VALUE
UNIT
±2000
V
MAX
UNIT
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
TJ
Supply voltage
6.5
40
V
Operating junction temperature
–40
125
°C
7.4 Thermal Information
LM2672
THERMAL METRIC (1) (2)
D (SOIC)
P (PDIP)
WSON (NHN)
8 PINS
8 PINS
16 PINS
UNIT
RθJA
Junction-to-ambient thermal resistance
105
95
—
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
—
—
—
°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)
4
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
Thermal resistances were simulated on 4-layer JEDEC board.
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7.5 Electrical Characteristics – 3.3 V
TJ = 25°C (unless otherwise noted; see Figure 19) (1)
PARAMETER
VIN = 8 V to 40 V, ILOAD = 20 mA to 1 A
VOUT
Output voltage
Efficiency
(1)
(2)
(3)
TYP (3)
TJ = 25°C
3.251
3.3
TJ = –40°C to 125°C
3.201
TJ = 25°C
VIN = 6.5 V to 40 V,
ILOAD = 20 mA to 500 mA
η
MIN (2)
TEST CONDITIONS
TJ = –40°C to 125°C
3.35
3.3
UNIT
3.35
3.399
3.201
VIN = 12 V, ILOAD = 1 A
MAX (2)
3.35
V
3.399
86%
External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator performance. When the LM2672 is used as shown in Figure 19 test circuits, system performance is as specified by
the system parameters section of Electrical Characteristics.
All limits specified at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits
at temperature extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
7.6 Electrical Characteristics – 5 V
TJ = 25°C (unless otherwise noted; see Figure 19) (1)
PARAMETER
TEST CONDITIONS
VIN = 8 V to 40 V, ILOAD = 20 mA to 1 A
VOUT
Output voltage
Efficiency
(1)
(2)
(3)
TJ = –40°C to 125°C
TJ = 25°C
VIN = 6.5 V to 40 V,
ILOAD = 20 mA to 500 mA
η
TJ = 25°C
TJ = –40°C to 125°C
MIN (2)
TYP (3)
4.925
5
5.075
5
5.075
4.85
4.925
5.15
4.85
VIN = 12 V, ILOAD = 1 A
MAX (2) UNIT
V
5.15
90%
External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator performance. When the LM2672 is used as shown in Figure 19 test circuits, system performance is as specified by
the system parameters section of Electrical Characteristics.
All limits specified at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits
at temperature extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
7.7 Electrical Characteristics – 12 V
TJ = 25°C (unless otherwise noted; see Figure 19) (1)
PARAMETER
VOUT
Output voltage
VIN = 15 V to 40 V, ILOAD = 20 mA to 1 A
η
Efficiency
VIN = 24 V, ILOAD = 1 A
(1)
(2)
(3)
MIN (2)
TYP (3)
TJ = 25°C
11.82
12
TJ = –40°C to 125°C
11.64
TEST CONDITIONS
MAX (2) UNIT
12.18
12.36
V
94%
External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator performance. When the LM2672 is used as shown in Figure 19 test circuits, system performance is as specified by
the system parameters section of Electrical Characteristics.
All limits specified at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits
at temperature extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
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7.8 Electrical Characteristics – Adjustable
TJ = 25°C (unless otherwise noted; see Figure 19) (1)
TEST CONDITIONS
MIN (2)
TYP (3)
VIN = 8 V to 40 V, ILOAD = 20 mA to 1 A, TJ = 25°C
VOUT programmed for 5 V (see
TJ = –40°C to 125°C
Figure 19)
1.192
1.21
VIN = 6.5 V to 40 V, ILOAD = 20 mA to
TJ = 25°C
500 mA, VOUT programmed for 5 V (see
TJ = –40°C to 125°C
Figure 19)
1.192
PARAMETER
VFB
Feedback voltage
Efficiency
η
(1)
(2)
(3)
MAX (2) UNIT
1.228
1.174
1.246
1.21
1.228
1.174
V
1.246
VIN = 12 V, ILOAD = 1 A
90%
External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator performance. When the LM2672 is used as shown in Figure 19 test circuits, system performance is as specified by
the system parameters section of Electrical Characteristics.
All limits specified at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits
at temperature extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
7.9 Electrical Characteristics – All Output Voltage Versions
TJ = 25°C, VIN = 12 V for the 3.3 V, 5 V, and Adjustable versions and VIN = 24V for the 12V version, and ILOAD = 100 mA
(unless otherwise noted)
PARAMETER
IQ
Quiescent current
MIN (1) TYP (2)
TEST CONDITIONS
VFEEDBACK = 8 V for 3.3 V, 5 V, and adjustable
versions
2.5
VFEEDBACK = 15 V for 12 V versions
2.5
50
Standby quiescent current
ICL
Current limit
IL
Output leakage current
RDS(ON)
Switch on-resistance
ISWITCH = 1 A
fO
Oscillator frequency
Measured at switch pin
D
Maximum duty cycle
TJ = 25°C
Minimum duty cycle
TJ = –40°C to 125°C
Feedback bias current
VFEEDBACK = 1.3 V, adjustable version only
85
TJ = 25°C
1.4
IBIAS
ON/OFF Pin = 0 V
TJ = 25°C
ISTBY
TJ = –40°C to 125°C
MAX (1) UNIT
3.6
100
150
1.25
1.55
1.2
2.1
2.2
mA
μA
A
VSWITCH = 0 V, ON/OFF Pin = 0 V, VIN = 40 V
1
25
μA
VSWITCH = −1 V, ON/OFF Pin = 0 V
6
15
mA
0.25
0.3
TJ = 25°C
TJ = –40°C to 125°C
0.5
TJ = 25°C
TJ = –40°C to 125°C
260
225
275
Ω
kHz
95%
0%
nA
VS/D
ON/OFF pin voltage
IS/D
ON/OFF pin current
ON/OFF Pin = 0 V
FSYNC
Synchronization frequency
VSYNC = 3.5 V, 50% duty cycle
400
kHz
VSYNC
Synchronization threshold voltage
1.4
V
TJ = 25°C
0.63
VSS
Soft-start voltage
ISS
Soft-start current
(1)
(2)
6
TJ = –40°C to 125°C
0.8
TJ = 25°C
TJ = –40°C to 125°C
TJ = –40°C to 125°C
20
7
37
0.53
TJ = 25°C
TJ = –40°C to 125°C
2
0.73
4.5
1.5
6.9
V
μA
V
μA
All limits specified at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits
at temperature extremes are specified through correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
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7.10 Typical Characteristics
Figure 1. Normalized Output Voltage
Figure 2. Line Regulation
Figure 3. Efficiency
Figure 4. Drain-to-Source Resistance
Figure 5. Switch Current Limit
Figure 6. Operating Quiescent Current
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Typical Characteristics (continued)
8
Figure 7. Standby Quiescent Current
Figure 8. ON/OFF Threshold Voltage
Figure 9. ON/OFF Pin Current (Sourcing)
Figure 10. Switching Frequency
Figure 11. Feedback Pin Bias Current
Figure 12. Peak Switch Current
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Typical Characteristics (continued)
Figure 13. Dropout Voltage, 3.3-V Option
Figure 14. Dropout Voltage, 5-V Option
7.11 Typical Characteristics – Fixed Output Voltage Versions
see Figure 19
VSW pin voltage, 10 V/div
Inductor current, 0.5 A/div
Output ripple voltage,
20 mV/div AC-coupled
VIN = 20 V, VOUT = 5 V,
ILOAD = 1 A, L = 47 μH,
COUT = 68 μF,
COUTESR = 50 mΩ
Figure 15. Continuous Mode Switching Waveforms,
Horizontal Time Base: 1 μs/div
Output voltage,
100 mV/div, AC-coupled
Load current: 200 mA to
1 A load pulse
VIN = 20 V, VOUT = 5 V,
ILOAD = 1 A, L = 47 μH,
COUT = 68 μF,
COUTESR = 50 mΩ
Figure 17. Load Transient Response for Continuous Mode,
Horizontal Time Base: 50 μs/div
VSW pin voltage, 10 V/div
Inductor current, 0.5 A/div
Output ripple voltage,
20 mV/div AC-coupled
VIN = 20 V, VOUT = 5 V,
ILOAD = 300 mA, L = 15 μH,
COUT = 68 μF (2×),
COUTESR = 25 mΩ
Figure 16. Discontinuous Mode Switching Waveforms,
Horizontal Time Base: 1 μs/div
Output voltage,
100 mV/div, AC-coupled
Load current: 100 mA to
300 mA load pulse
VIN = 20 V, VOUT = 5 V,
L = 47 μH,
COUT = 68 μF,
COUTESR = 50 mΩ
Figure 18. Load Transient Response for Discontinuous
Mode, Horizontal Time Base: 200 μs/div
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8 Parameter Measurement Information
Copyright © 2016, Texas Instruments Incorporated
CIN = 22-μF, 50-V Tantalum Sprague 199D Series
COUT = 47-μF, 25-V Tantalum Sprague 595D Series
D1 = 3.3-A, 50-V Schottky Rectifier, IR 30WQ05F
L1 = 68-μH Sumida #RCR110D-680L
CB = 0.01-μF, 50-V ceramic
Figure 19. Standard Test Circuits and Layout Guides,
Fixed Output Voltage Versions
10
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9 Detailed Description
9.1 Overview
The LM2672 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 1 A,
and highly efficient operation.
The LM2672 is part of the SIMPLE SWITCHER® family of power converters. A complete design uses a minimum
number of external components, which have been pre-determined from a variety of manufacturers. Using either
this data sheet or TI's WEBENCH® design tool, a complete switching power supply can be designed quickly.
Refer to LM2670 SIMPLE SWITCHER® High Efficiency 3A Step-Down Voltage Regulator with Sync for additional
application information.
9.2 Functional Block Diagram
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9.3 Feature Description
9.3.1 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 or time OFF) of the power switch is proportional to the ratio of the power
supply output voltage to the input voltage. The voltage on the VSW pin cycles 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)
9.3.2 C Boost
A capacitor must be connected from the CB pin to the VSW pin. This capacitor boosts the gate drive to the internal
MOSFET above Vin to fully turn it ON. This minimizes conduction losses in the power switch to maintain high
efficiency. The recommended value for C Boost is 0.01 μF.
9.3.3 SYNC
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. 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 LM2672 internal oscillator frequency, which could be as high as 275 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 that the external TTL or CMOS compatible clock (between 0
V and a level greater than 3 V) be AC-coupled to the SYNC pin through a 100-pF capacitor and a
1-kΩ resistor to ground.
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.
9.3.4 Feedback
This is the input to a two-stage high gain amplifier, which drives the PWM controller. Connect the FB pin directly
to the output for proper regulation. 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 LM2672.
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.
9.4 Device Functional Modes
9.4.1 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 1.4 V completely turns OFF the regulator. The current drain from the input supply when OFF is
only 50 μA. The ON/OFF input 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 this pin must
be left open.
9.4.2 Shutdown Mode
The ON/OFF pin provides electrical ON and OFF control for the LM2671. 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 50 μA.
9.4.3 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.
12
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10 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.
10.1 Application Information
The LM2672 is a step-down DC-DC regulator. It is typically used to convert a higher DC voltage to a lower DC
voltage with a maximum output current of 1 A. The following design procedure can be used to select components
for the LM2672.
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.
Note 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 overcurrent or short-circuit conditions, the
LM267X employs frequency foldback in addition to the current limit. If the cycle-by-cycle inductor current
increases above the current limit threshold (due to short circuit or inductor saturation for example) the switching
frequency is automatically reduced to protect the IC. Frequency below 100 KHz is typical for an extreme shortcircuit condition.
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10.2 Typical Applications
10.2.1 Typical Application for Fixed Output Voltage Versions
Copyright © 2016, Texas Instruments Incorporated
CIN = 22-μF, 50-V Tantalum, Sprague 199D Series
COUT = 47-μF, 25-V Tantalum, Sprague 595D Series
D1 = 3.3-A, 50-V Schottky Rectifier, IR 30WQ05F
L1 = 68-μH Sumida #RCR110D-680L
CB = 0.01-μF, 50-V Ceramic
Figure 20. Fixed Output Voltage Typical Application
10.2.1.1 Design Requirements
Table 1 lists the design requirements for the fixed output voltage application.
Table 1. Fixed Output Voltage Application Parameters
PARAMETER
VALUE
Regulated output voltage (3.3 V, 5 V, or 12 V), VOUT
5V
Maximum DC input voltage, VIN(max)
12 V
Maximum load current, ILOAD(max)
1A
10.2.1.2 Detailed Design Procedure
10.2.1.2.1 Inductor Selection (L1)
First, select the correct inductor value selection guide from Figure 23, Figure 24, or Figure 25 (output voltages of
3.3-V, 5-V, or 12-V respectively). For all other voltages, see the design procedure for the adjustable version. Use
the inductor selection guide for the 5-V version shown in Figure 24.
From the inductor value selection guide, identify the inductance region intersected by the maximum input voltage
line and the maximum load current line. Each region is identified by an inductance value and an inductor code
(LXX). From the inductor value selection guide shown in Figure 24, the inductance region intersected by the 12 V
horizontal line and the 1 A vertical line is 33 μH, and the inductor code is L23.
Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2. Each manufacturer
makes a different style of inductor to allow flexibility in meeting various design requirements. The inductance
value required is 33 μH. From Table 2, go to the L23 line and choose an inductor part number from any of the
four manufacturers shown. In most instances, both through hole and surface mount inductors are available.
14
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Table 2. Inductor Manufacturers' Part Numbers
IND.
REF.
DESG.
INDUCTANCE
(μH)
CURRENT
(A)
L4
68
L5
47
L6
SCHOTT
RENCO
PULSE ENGINEERING
COILCRAFT
THROUGH
HOLE
SURFACE
MOUNT
THROUGH
HOLE
SURFACE
MOUNT
THROUGH
HOLE
SURFACE
MOUNT
SURFACE
MOUNT
0.32
67143940
67144310
RL-1284-68-43
RL1500-68
PE-53804
PE-53804-S
DO1608-683
0.37
67148310
67148420
RL-1284-47-43
RL1500-47
PE-53805
PE-53805-S
DO1608-473
33
0.44
67148320
67148430
RL-1284-33-43
RL1500-33
PE-53806
PE-53806-S
DO1608-333
L7
22
0.52
67148330
67148440
RL-1284-22-43
RL1500-22
PE-53807
PE-53807-S
DO1608-223
L9
220
0.32
67143960
67144330
RL-5470-3
RL1500-220
PE-53809
PE-53809-S
DO3308-224
L10
150
0.39
67143970
67144340
RL-5470-4
RL1500-150
PE-53810
PE-53810-S
DO3308-154
L11
100
0.48
67143980
67144350
RL-5470-5
RL1500-100
PE-53811
PE-53811-S
DO3308-104
L12
68
0.58
67143990
67144360
RL-5470-6
RL1500-68
PE-53812
PE-53812-S
DO3308-683
L13
47
0.70
67144000
67144380
RL-5470-7
RL1500-47
PE-53813
PE-53813-S
DO3308-473
L14
33
0.83
67148340
67148450
RL-1284-33-43
RL1500-33
PE-53814
PE-53814-S
DO3308-333
L15
22
0.99
67148350
67148460
RL-1284-22-43
RL1500-22
PE-53815
PE-53815-S
DO3308-223
L18
220
0.55
67144040
67144420
RL-5471-2
RL1500-220
PE-53818
PE-53818-S
DO3316-224
L19
150
0.66
67144050
67144430
RL-5471-3
RL1500-150
PE-53819
PE-53819-S
DO3316-154
L20
100
0.82
67144060
67144440
RL-5471-4
RL1500-100
PE-53820
PE-53820-S
DO3316-104
L21
68
0.99
67144070
67144450
RL-5471-5
RL1500-68
PE-53821
PE-53821-S
DO3316-683
L22
47
1.17
67144080
67144460
RL-5471-6
—
PE-53822
PE-53822-S
DO3316-473
L23
33
1.4
67144090
67144470
RL-5471-7
—
PE-53823
PE-53823-S
DO3316-333
L24
22
1.7
67148370
67148480
RL-1283-22-43
—
PE-53824
PE-53824-S
DO3316-223
L27
220
1
67144110
67144490
RL-5471-2
—
PE-53827
PE-53827-S
DO5022P-224
L28
150
1.2
67144120
67144500
RL-5471-3
—
PE-53828
PE-53828-S
DO5022P-154
L29
100
1.47
67144130
67144510
RL-5471-4
—
PE-53829
PE-53829-S
DO5022P-104
L30
68
1.78
67144140
67144520
RL-5471-5
—
PE-53830
PE-53830-S
DO5022P-683
10.2.1.2.2 Output Capacitor Selection (COUT)
Select an output capacitor from the output capacitor table in Table 3. Using the output voltage and the
inductance value found in the inductor selection guide, step 1, locate the appropriate capacitor value and voltage
rating. Use the 5-V section in Table 3. Choose a capacitor value and voltage rating from the line that contains the
inductance value of 33 μH. The capacitance and voltage rating values corresponding to the 33 μH.
The capacitor list contains through-hole electrolytic capacitors from four different capacitor manufacturers and
surface mount tantalum capacitors from two different capacitor manufacturers.
Surface mount:
• 68-μF, 10-V Sprague 594D series
• 100-μF, 10-V AVX TPS series
Through hole:
• 68-μF, 10-V Sanyo OS-CON SA series
• 220-μF, 35-V Sanyo MV-GX series
• 220-μF, 35-V Nichicon PL series
• 220-μF, 35-V Panasonic HFQ series
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Table 3. Output Capacitor Table
OUTPUT CAPACITOR
OUTPUT
VOLTAGE
(V)
3.3
5
12
INDUCTANCE
(μH)
SURFACE MOUNT
THROUGH HOLE
SPRAGUE
594D SERIES
(μF/V)
AVX TPS
SERIES
(μF/V)
SANYO OS-CON
SA SERIES
(μF/V)
SANYO MV-GX
SERIES
(μF/V)
NICHICON
PL SERIES
(μF/V)
PANASONIC
HFQ SERIES
(μF/V)
22
120/6.3
100/10
100/10
330/35
330/35
330/35
33
120/6.3
100/10
68/10
220/35
220/35
220/35
47
68/10
100/10
68/10
150/35
150/35
150/35
68
120/6.3
100/10
100/10
120/35
120/35
120/35
100
120/6.3
100/10
100/10
120/35
120/35
120/35
150
120/6.3
100/10
100/10
120/35
120/35
120/35
22
100/16
100/10
100/10
330/35
330/35
330/35
33
68/10
10010
68/10
220/35
220/35
220/35
47
68/10
100/10
68/10
150/35
150/35
150/35
68
100/16
100/10
100/10
120/35
120/35
120/35
100
100/16
100/10
100/10
120/35
120/35
120/35
150
100/16
100/10
100/10
120/35
120/35
120/35
22
120/20
(2×) 68/20
68/20
330/35
330/35
330/35
33
68/25
68/20
68/20
220/35
220/35
220/35
47
47/20
68/20
47/20
150/35
150/35
150/35
68
47/20
68/20
47/20
120/35
120/35
120/35
100
47/20
68/20
47/20
120/35
120/35
120/35
150
47/20
68/20
47/20
120/35
120/35
120/35
220
47/20
68/20
47/20
120/35
120/35
120/35
10.2.1.2.3 Catch Diode Selection (D1)
In normal operation, the average current of the catch diode is the load current times the catch diode duty cycle,
1-D (D is the switch duty cycle, which is approximately the output voltage divided by the input voltage). The
largest value of the catch diode average current occurs at the maximum load current and maximum input voltage
(minimum D). For normal operation, the catch diode current rating must be at least 1.3 times greater than its
maximum average current. However, if the power supply design must withstand a continuous output short, the
diode must have a current rating equal to the maximum current limit of the LM2672. The most stressful condition
for this diode is a shorted output condition. Refer to the table shown in Table 4. In this example, a 1-A, 20-V
Schottky diode provides the best performance. If the circuit must withstand a continuous shorted output, a higher
current Schottky diode is recommended.
The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Because of their
fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency.
This Schottky diode must be placed close to the LM2672 using short leads and short printed circuit traces.
16
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Table 4. Schottky Diode Selection Table
VR
20 V
30 V
40 V
50 V
1-A DIODES
3-A DIODES
SURFACE MOUNT
THROUGH HOLE
SURFACE MOUNT
THROUGH HOLE
SK12
1N5817
SK32
1N5820
B120
SR102
—
SR302
SK13
1N5818
SK33
1N5821
B130
11DQ03
30WQ03F
31DQ03
MBRS130
SR103
—
—
SK14
1N5819
SK34
1N5822
B140
11DQ04
30BQ040
MBR340
MBRS140
SR104
30WQ04F
31DQ04
10BQ040
—
MBRS340
SR304
10MQ040
—
MBRD340
—
15MQ040
—
—
—
SK15
MBR150
SK35
MBR350
B150
11DQ05
30WQ05F
31DQ05
10BQ050
SR105
—
SR305
10.2.1.2.4 Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground to prevent large
voltage transients from appearing at the input. This capacitor must be placed close to the IC using short leads. In
addition, the RMS current rating of the input capacitor must be selected to be at least ½ the DC load current. The
capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. Figure 21
shows typical RMS current ratings for several different aluminum electrolytic capacitor values. A parallel
connection of two or more capacitors may be required to increase the total minimum RMS current rating to suit
the application requirements.
Figure 21. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)
For an aluminum electrolytic capacitor, the voltage rating must be at least 1.25 times the maximum input voltage.
Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating must be
twice the maximum input voltage. The tables in Table 5 show the recommended application voltage for AVX TPS
and Sprague 594D tantalum capacitors. It is also recommended that they be surge current tested by the
manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge
current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small
inductor in series with the input supply line.
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Table 5. Recommended Application Voltage for AVX TPS and Sprague 594D
Tantalum Chip Capacitors Derated for 85°C
RECOMMENDED APPLICATION VOLTAGE
VOLTAGE RATING
3.3
6.3
5
10
10
20
12
25
15
35
Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN
pin.
The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a
maximum input voltage of 12 V, an aluminum electrolytic capacitor with a voltage rating greater than 15 V (1.25 ×
VIN) is required. The next higher capacitor voltage rating is 16 V.
The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load
current. In this example, with a 1-A load, a capacitor with a RMS current rating of at least 500 mA is required.
The curves shown in Figure 21 can be used to select an appropriate input capacitor. From the curves, locate the
16-V line and note which capacitor values have RMS current ratings greater than 500 mA.
For a through hole design, a 330-μF, 16-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used
provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design,
electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components
NACZ series could be considered.
For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to
the capacitor surge current rating and voltage rating. In this example, checking Table 5, and the Sprague 594D
series data sheet, a Sprague 594D 15-μF, 25-V capacitor is adequate.
10.2.1.2.5 Boost Capacitor (CB)
This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a 0.01μF, 50-V ceramic capacitor.
10.2.1.2.6 Soft-Start Capacitor (CSS, Optional)
This capacitor controls the rate at which the device starts up. The formula for the soft-start capacitor CSS is
calculated with Equation 1.
where
•
•
•
•
•
•
ISS = Soft-start current (4.5 µA, typical)
tSS = Soft-start time (selected)
VSSTH = Soft-start threshold voltage (0.63 V, typical)
VOUT = Output voltage (selected)
VSCHOTTKY = Schottky diode voltage drop (0.4 V, typical)
VIN = Input voltage (selected)
(1)
If this feature is not desired, leave this pin open. With certain soft-start capacitor values and operating conditions,
the LM2672 can exhibit an overshoot on the output voltage during turn on. Especially when starting up into no
load or low load, the soft-start function may not be effective in preventing a larger voltage overshoot on the
output. With larger loads or lower input voltages during startup this effect is minimized. In particular, avoid using
soft-start capacitors between 0.033 µF and 1 µF.
For this application, selecting a start-up time of 10 ms and using the formula for CSS results in a value of
Equation 2.
(2)
18
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10.2.1.2.7 Frequency Synchronization (Optional)
The LM2672 (oscillator) can be synchronized to run with an external oscillator, using the sync pin (pin 3). By
doing so, the LM2672 can be operated at higher frequencies than the standard frequency of 260 kHz. This
allows for a reduction in the size of the inductor and output capacitor.
As shown in Figure 22, a signal applied to a RC filter at the sync pin causes the device to synchronize to the
frequency of that signal. For a signal with a peak-to-peak amplitude of 3 V or greater, a 1-kΩ resistor and a 100pF capacitor are suitable values. For all applications, use a 1-kΩ resistor and a 100-pF capacitor for the RC filter.
Figure 22. Synchronization on LM2672
10.2.1.3 Application Curves
Figure 23. LM2672, 3.3-V Output
Figure 24. LM2672, 5-V Output
Figure 25. LM2672, 12-V Output
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10.2.2 Typical Application for Adjustable Output Voltage Versions
Copyright © 2016, Texas Instruments Incorporated
CIN = 22-μF, 50-V Tantalum, Sprague 199D Series
COUT = 47-μF, 25-V Tantalum, Sprague 595D Series
D1 = 3.3-A, 50-V Schottky Rectifier, IR 30WQ05F
L1 = 68-μH Sumida #RCR110D-680L
R1 = 1.5-kΩ , 1%
CB = 0.01-μF, 50-V Ceramic
Figure 26. Adjustable Output Voltage Typical Application
10.2.2.1 Design Requirements
Table 6 lists the design requirements for the adjustable output voltage application.
Table 6. Adjustable Output Voltage Application Parameters
PARAMETERS
VALUE
Regulated output voltage, VOUT
20 V
Maximum input voltage, VIN(max)
28 V
Maximum load current, ILOAD(max)
1A
Switching frequency, F
Fixed at a nominal 260 kHz
10.2.2.2 Detailed Design Procedure
10.2.2.2.1 Programming Output Voltage
For this application, TI recommends selecting R1 and R2, as shown in Parameter Measurement Information.
Use Equation 3 to select the appropriate resistor values.
where
•
VREF = 1.21 V
(3)
Select a value for R1 between 240 Ω and 1.5 kΩ. The lower resistor values minimize noise pickup in the sensitive
feedback pin. For the lowest temperature coefficient and the best stability with time, use 1% metal film resistors
as in Equation 4.
(4)
20
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For this application example, select R1 to be 1 kΩ, 1%. Solve for R2 with Equation 5.
(5)
R2 = 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
R2 = 15.4 kΩ.
10.2.2.2.2 Inductor Selection (L1)
Calculate the inductor Volt × microsecond constant E × T (V × μs) with Equation 6.
where
•
•
VSAT = internal switch saturation voltage = 0.25 V
VD = diode forward voltage drop = 0.5 V
(6)
For this application example, calculate the inductor Volt × microsecond constant (E × T) with Equation 7.
(7)
Use the E × T value from the previous formula and match it with the E × T number on the vertical axis of the
inductor value selection guide in Figure 27. E × T = 21.6 (V × μs).
On the horizontal axis, select the maximum load current (ILOAD(max) = 1 A).
Identify the inductance region intersected by the E × T value and the maximum load current value. Each region is
identified by an inductance value and an inductor code (LXX). From the inductor value selection guide shown in
Figure 27, the inductance region intersected by the 21.6 (V × μs) horizontal line and the 1-A vertical line is 68 μH,
and the inductor code is L30.
Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2. For information on the
different types of inductors, see the inductor selection in the fixed output voltage design procedure. From the
table in Table 2, locate line L30, and select an inductor part number from the list of manufacturers' part numbers.
10.2.2.2.3 Output Capacitor SeIection (COUT)
Select an output capacitor from the capacitor code selection guide in Table 7. Using the inductance value found
in the inductor selection guide, step 1, locate the appropriate capacitor code corresponding to the desired output
voltage. Use the appropriate row of the capacitor code selection guide, in Table 7. For this example, use the 15
to 20 V row. The capacitor code corresponding to an inductance of 68 μH is C20.
Table 7. Capacitor Code Selection Guide
INDUCTANCE (μH)
CASE STYLE (1)
OUTPUT
VOLTAGE (V)
22
33
47
SM and TH
1.21 to 2.5
—
—
SM and TH
2.5 to 3.75
—
—
SM and TH
3.75 to 5
—
SM and TH
5 to 6.25
—
SM and TH
6.25 to 7.5
C8
C4
C7
C6
C6
C6
C6
SM and TH
7.5 to 10
C9
C10
C11
C12
C13
C13
C13
SM and TH
10 to 12.5
C14
C11
C12
C12
C13
C13
C13
SM and TH
12.5 to 15
C15
C16
C17
C17
C17
C17
C17
SM and TH
15 to 20
C18
C19
C20
C20
C20
C20
C20
SM and TH
20 to 30
C21
C22
C22
C22
C22
C22
C22
TH
30 to 37
C23
C24
C24
C25
C25
C25
C25
(1)
68
100
150
220
—
—
C1
C2
C3
—
C1
C2
C3
C3
—
C4
C5
C6
C6
C6
C4
C7
C6
C6
C6
C6
SM = surface mount, TH = through hole
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Select an appropriate capacitor value and voltage rating, using the capacitor code, from the output capacitor
selection table in Table 8. There are two solid tantalum (surface mount) capacitor manufacturers and four
electrolytic (through hole) capacitor manufacturers to choose from. TI recommends that both the manufacturers
and the manufacturer's series that are listed in the table be used. From the output capacitor selection table in
Table 8, choose a capacitor value (and voltage rating) that intersects the capacitor code(s) selected in section A,
C20 (Table 8).
The capacitance and voltage rating values corresponding to the capacitor code C20 are surface mount and
through hole.
Surface mount:
• 33-μF, 25-V Sprague 594d series
• 33-μF, 25-V AVX TPS series
Through hole:
• 33-μF, 25-V Sanyo OS-CON SC series
• 120-μF, 35-V Sanyo MV-GX series
• 120-μF, 35-V Nichicon PL series
• 120-μF, 35-V Panasonic HFQ series
Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications
(especially the 100 kHz ESR) closely match the characteristics of the capacitors listed in the output capacitor
table. Refer to the capacitor manufacturers' data sheet for this information.
Table 8. Output Capacitor Selection Table
OUTPUT CAPACITOR
SURFACE MOUNT
THROUGH HOLE
CAP.
REF.
DESG.
#
SPRAGUE
594D SERIES
(μF/V)
AVX TPS
SERIES
(μF/V)
SANYO OS-CON
SA SERIES
(μF/V)
SANYO MV-GX
SERIES
(μF/V)
NICHICON
PL SERIES
(μF/V)
PANASONIC
HFQ SERIES
(μF/V)
C1
120/6.3
100/10
100/10
220/35
220/35
220/35
C2
120/6.3
100/10
100/10
150/35
150/35
150/35
C3
120/6.3
100/10
100/35
120/35
120/35
120/35
C4
68/10
100/10
68/10
220/35
220/35
220/35
C5
100/16
100/10
100/10
150/35
150/35
150/35
C6
100/16
100/10
100/10
120/35
120/35
120/35
C7
68/10
100/10
68/10
150/35
150/35
150/35
C8
100/16
100/10
100/10
330/35
330/35
330/35
C9
100/16
100/16
100/16
330/35
330/35
330/35
C10
100/16
100/16
68/16
220/35
220/35
220/35
C11
100/16
100/16
68/16
150/35
150/35
150/35
C12
100/16
100/16
68/16
120/35
120/35
120/35
C13
100/16
100/16
100/16
120/35
120/35
120/35
C14
100/16
100/16
100/16
220/35
220/35
220/35
C15
47/20
68/20
47/20
220/35
220/35
220/35
C16
47/20
68/20
47/20
150/35
150/35
150/35
C17
47/20
68/20
47/20
120/35
120/35
120/35
C18
68/25
(2×) 33/25
47/25 (1)
220/35
220/35
220/35
C19
33/25
33/25
33/25 (1)
150/35
150/35
150/35
C20
33/25
33/25
33/25 (1)
120/35
120/35
120/35
(2)
(1)
(2)
22
C21
33/35
(2×) 22/25
150/35
150/35
150/35
C22
33/35
22/35
See
See (2)
120/35
120/35
120/35
C23
See (2)
See (2)
See (2)
220/50
100/50
120/50
C24
See (2)
See (2)
See (2)
150/50
100/50
120/50
C25
See (2)
See (2)
See (2)
150/50
82/50
82/50
The SC series of Os-Con capacitors (others are SA series)
The voltage ratings of the surface mount tantalum chip and Os-Con capacitors are too low to work at these voltages.
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10.2.2.2.4 Catch Diode Selection (D1)
In normal operation, the average current of the catch diode is the load current times the catch diode duty cycle,
1-D (D is the switch duty cycle, which is approximately VOUT / VIN). The largest value of the catch diode average
current occurs at the maximum input voltage (minimum D). For normal operation, the catch diode current rating
must be at least 1.3 times greater than its maximum average current. However, if the power supply design must
withstand a continuous output short, the diode must have a current rating greater than the maximum current limit
of the LM2672. The most stressful condition for this diode is a shorted output condition. Refer to the table shown
in Table 4. Schottky diodes provide the best performance, and in this example a 1-A, 40-V Schottky diode would
be a good choice. If the circuit must withstand a continuous shorted output, a higher current (at least 2.2-A)
Schottky diode is recommended.
The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. Because of their
fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency.
The Schottky diode must be placed close to the LM2672 using short leads and short printed circuit traces.
10.2.2.2.5 Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground to prevent large
voltage transients from appearing at the input. This capacitor must be placed close to the IC using short leads. In
addition, the RMS current rating of the input capacitor must be selected to be at least ½ the DC load current. The
capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. Figure 21
shows typical RMS current ratings for several different aluminum electrolytic capacitor values. A parallel
connection of two or more capacitors may be required to increase the total minimum RMS current rating to suit
the application requirements.
For an aluminum electrolytic capacitor, the voltage rating must be at least 1.25 times the maximum input voltage.
Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating must be
twice the maximum input voltage. The tables in Table 5 show the recommended application voltage for AVX TPS
and Sprague 594D tantalum capacitors. It is also recommended that they be surge current tested by the
manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge
current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small
inductor in series with the input supply line.
Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN
pin.
The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a
maximum input voltage of 28 V, an aluminum electrolytic capacitor with a voltage rating of at least 35 V (1.25 ×
VIN) is required.
The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load
current. In this example, with a 1-A load, a capacitor with a RMS current rating of at least 500 mA is required.
The curves shown in Figure 21 can be used to select an appropriate input capacitor. From the curves, locate the
35-V line and note which capacitor values have RMS current ratings greater than 500 mA.
For a through hole design, a 330-μF, 35-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used
provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design,
electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components
NACZ series could be considered.
For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to
the capacitor surge current rating and voltage rating. In this example, checking Table 5, and the Sprague 594D
series datasheet, a Sprague 594D 15-μF, 50-V capacitor is adequate.
10.2.2.2.6 Boost Capacitor (CB)
This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a
0.01-μF, 50-V ceramic capacitor. If the soft-start and frequency synchronization features are desired, see steps 6
and 7 in the fixed output design procedure.
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10.2.2.3 Application Curve
Figure 27. LM2672, Adjustable Output
24
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11 Power Supply Recommendations
The input voltage for the power supply is connected to the VIN pin. In addition to providing energy to the load the
input voltage also provides bias for the internal circuitry of the LM2672. For ensured performance, the input
voltage must be in the range of 6.5 V to 40 V. For best performance of the power supply, the VIN pin must always
be bypassed with an input capacitor placed close to this pin and GND.
12 Layout
12.1 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 19) 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.
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 LM2672, TI recommends that a broad ground plane be used to
minimize signal coupling throughout the circuit.
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 COUT 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.
12.1.1 WSON Package Devices
The LM2672 is offered in the 16-pin WSON surface mount package to allow for increased power dissipation
compared to the 8-pin SOIC and PDIP.
The Die Attach Pad (DAP) can and must be connected to PCB Ground plane/island. For CAD and assembly
guidelines, refer to AN-1187 Leadless Leadframe Package (LLP).
12.2 Layout Examples
CIN = 15-μF, 50-V, solid tantalum Sprague 594D series
COUT = 68-μF, 16-V, solid tantalum Sprague 594D series
D1 = 1-A, 40-V Schottky rectifier, surface mount
L1 = 33-μH, L23, coilcraft DO3316
CB = 0.01-μF, 50-V ceramic
Figure 28. Typical Surface Mount PC Board Layout, Fixed Output
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Layout Examples (continued)
CIN = 15-μF, 50-V, solid tantalum Sprague 594D series
COUT = 33-μF, 25-V, solid tantalum Sprague 594D series
D1 = 1-A, 40-V Schottky rectifier, surface mount
L1 = 68-μH, L30, coilcraft DO3316
CB = 0.01-μF, 50-V ceramic
R1 = 1k, 1%, R2: use formula in Detailed Design Procedure
Figure 29. Typical Surface Mount PC Board Layout, Adjustable Output
26
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13 Device and Documentation Support
13.1 Documentation Support
13.1.1 Related Documentation
For related documentation see the following:
• LM2670 SIMPLE SWITCHER® High Efficiency 3A Step-Down Voltage Regulator with Sync (SNVS036)
• AN-1187 Leadless Leadframe Package (LLP) (SNOA401)
13.2 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.
13.3 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.
13.4 Trademarks
E2E is a trademark of Texas Instruments.
SIMPLE SWITCHER, WEBENCH are registered trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
13.5 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.
13.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
14 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.
14.1 DAP (WSON Package)
The die attach pad (DAP) must be connected to the PCB ground plane. For CAD and assembly guidelines, refer
to AN-1187 Leadless Leadframe Package (LLP).
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PACKAGE OPTION ADDENDUM
www.ti.com
16-Sep-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
LM2672LD-ADJ/NOPB
ACTIVE
WSON
NHN
16
1000
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
S0004B
Samples
LM2672M-12/NOPB
ACTIVE
SOIC
D
8
95
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
M-12
Samples
LM2672M-3.3
NRND
SOIC
D
8
95
Non-RoHS
& Green
Call TI
Level-1-235C-UNLIM
-40 to 125
2672
M3.3
LM2672M-3.3/NOPB
ACTIVE
SOIC
D
8
95
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
M3.3
LM2672M-5.0
NRND
SOIC
D
8
95
Non-RoHS
& Green
Call TI
Level-1-235C-UNLIM
-40 to 125
2672
M5.0
LM2672M-5.0/NOPB
ACTIVE
SOIC
D
8
95
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
M5.0
LM2672M-ADJ
NRND
SOIC
D
8
95
Non-RoHS
& Green
Call TI
Level-1-235C-UNLIM
-40 to 125
2672
MADJ
LM2672M-ADJ/NOPB
ACTIVE
SOIC
D
8
95
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
MADJ
Samples
LM2672MX-12/NOPB
ACTIVE
SOIC
D
8
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
M-12
Samples
LM2672MX-3.3/NOPB
ACTIVE
SOIC
D
8
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
M3.3
Samples
LM2672MX-5.0
NRND
SOIC
D
8
2500
Non-RoHS
& Green
Call TI
Level-1-235C-UNLIM
-40 to 125
2672
M5.0
LM2672MX-5.0/NOPB
ACTIVE
SOIC
D
8
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
M5.0
LM2672MX-ADJ
NRND
SOIC
D
8
2500
Non-RoHS
& Green
Call TI
Level-1-235C-UNLIM
-40 to 125
2672
MADJ
LM2672MX-ADJ/NOPB
ACTIVE
SOIC
D
8
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
2672
MADJ
Samples
LM2672N-12/NOPB
ACTIVE
PDIP
P
8
40
RoHS & Green
NIPDAU
Level-1-NA-UNLIM
-40 to 125
LM2672
N-12
Samples
LM2672N-5.0/NOPB
ACTIVE
PDIP
P
8
40
RoHS & Green
NIPDAU
Level-1-NA-UNLIM
-40 to 125
LM2672
N-5.0
Samples
LM2672N-ADJ/NOPB
ACTIVE
PDIP
P
8
40
RoHS & Green
Call TI | NIPDAU
Level-1-NA-UNLIM
-40 to 125
LM2672
N-ADJ
Samples
Addendum-Page 1
Samples
Samples
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
16-Sep-2022
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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