LM2679
SIMPLE SWITCHER
5A Step-Down Voltage Regulator
with Adjustable Current Limit
General Description
The LM2679 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 5A
loads with excellent line and load regulation characteristics.
High efficiency (
>
90%) is obtained through the use of a low
ON-resistance DMOS power switch. The series consists of
fixed output voltages of 3.3V, 5V and 12V and an adjustable
output version.
The SIMPLE SWITCHER concept provides for a complete
design using a minimum number of external components. A
high fixed frequency oscillator (260KHz) allows the use of
physically smaller sized components. A family of standard
inductors for use with the LM2679 are available from several
manufacturers to greatly simplify the design process.
Other features include the ability to reduce the input surge
current at power-ON by adding a softstart timing capacitor to
gradually turn on the regulator. The LM2679 series also has
built in thermal shutdown and resistor programmable current
limit of the power MOSFET switch to protect the device and
load circuitry under fault conditions. The output voltage is
guaranteed to a
2% tolerance. The clock frequency is
controlled to within a
11% tolerance.
Features
n
Efficiency up to 92%
n
Simple and easy to design with (using off-the-shelf
external components)
n
Resistor programmable peak current limit over a range
of 3A to 7A.
n
120 m
DMOS output switch
n
3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
n
2%maximum output tolerance over full line and load
conditions
n
Wide input voltage range: 8V to 40V
n
260 KHz fixed frequency internal oscillator
n
Softstart capability
n
-40 to +125C operating junction temperature range
Applications
n
Simple to design, high efficiency (
>
90%) step-down
switching regulators
n
Efficient system pre-regulator for linear voltage
regulators
n
Battery chargers
Typical Application
10084703
SIMPLE SWITCHER
is a registered trademark of National Semiconductor Corporation.
April 2003
LM2679
SIMPLE
SWITCHER
5A
Step-Down
V
oltage
Regulator
with
Adjustable
Current
Limit
2003 National Semiconductor Corporation
DS100847
www.national.com
Connection Diagrams and Ordering Information
TO-263 Package
Top View
TO-220 Package
Top View
10084701
Order Number
LM2679S-3.3, LM2679S-5.0,
LM2679S-12 or LM2679S-ADJ
See NSC Package Number TS7B
10084702
Order Number
LM2679T-3.3, LM2679T-5.0,
LM2679T-12 or LM2679T-ADJ
See NSC Package Number TA07B
Top View
10084735
LLP-14
See NS package Number LDC14A
Ordering Information for LLP Package
Output Voltage
Order Information
Package Marking
Supplied As
12
LM2679LD-12
S0000VB
250 Units on Tape and Reel
12
LM2679LDX-12
S0000VB
2500 Units on Tape and Reel
3.3
LM2679LD-3.3
S0000TB
250 Units on Tape and Reel
3.3
LM2679LDX-3.3
S0000TB
2500 Units on Tape and Reel
5.0
LM2679LD-5.0
S0000UB
250 Units on Tape and Reel
5.0
LM2679LDX-5.0
S0000UB
2500 Units on Tape and Reel
ADJ
LM2679LD-ADJ
S0000XB
250 Units on Tape and Reel
ADJ
LM2679LDX-ADJ
S0000XB
2500 Units on Tape and Reel
LM2679
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2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Supply Voltage
45V
Softstart Pin Voltage
-0.1V to 6V
Switch Voltage to Ground
-1V to V
IN
Boost Pin Voltage
V
SW
+ 8V
Feedback Pin Voltage
-0.3V to 14V
Power Dissipation
Internally Limited
ESD (Note 2)
2 kV
Storage Temperature Range
-65C to 150C
Soldering Temperature
Wave
4 sec, 260C
Infrared
10 sec, 240C
Vapor Phase
75 sec, 219C
Operating Ratings
Supply Voltage
8V to 40V
Junction Temperature Range (T
J
)
-40C to 125C
Electrical Characteristics
Limits appearing in bold type face apply over the entire junction temperature
range of operation, -40C to 125C. Specifications appearing in normal type apply for T
A
= T
J
= 25C. R
ADJ
= 5.6K
LM2679-3.3
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
OUT
Output Voltage
V
IN
= 8V to 40V, 100mA
I
OUT
5A
3.3
3.234/3.201
3.366/3.399
V
Efficiency
V
IN
= 12V, I
LOAD
= 5A
82
%
LM2679-5.0
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
OUT
Output Voltage
V
IN
= 8V to 40V, 100mA
I
OUT
5A
5.0
4.900/4.850
5.100/5.150
V
Efficiency
V
IN
= 12V, I
LOAD
= 5A
84
%
LM2679-12
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
OUT
Output Voltage
V
IN
= 15V to 40V, 100mA
I
OUT
5A
12
11.76/11.64
12.24/12.36
V
Efficiency
V
IN
= 24V, I
LOAD
= 5A
92
%
LM2679-ADJ
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
FB
Feedback
Voltage
V
IN
= 8V to 40V, 100mA
I
OUT
5A
V
OUT
Programmed for 5V
1.21
1.186/1.174
1.234/1.246
V
Efficiency
V
IN
= 12V, I
LOAD
= 5A
84
%
LM2679
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3
All Output Voltage Versions
Electrical Characteristics
Limits appearing in bold type face apply over the entire junction temperature range of operation, -40C to 125C. Specifica-
tions appearing in normal type apply for T
A
= T
J
= 25C. Unless otherwise specified V
IN
=12V for the 3.3V, 5V and Adjustable
versions and V
IN
=24V for the 12V version.
Symbol
Parameter
Conditions
Typ
Min
Max
Units
DEVICE PARAMETERS
I
Q
Quiescent
Current
V
FEEDBACK
= 8V
4.2
6
mA
For 3.3V, 5.0V, and ADJ Versions
V
FEEDBACK
= 15V
For 12V Versions
V
ADJ
Current Limit
Adjust Voltage
1.21
1.181/1.169
1.229/1.246
V
I
CL
Current Limit
R
ADJ
= 5.6K
, (Note 5)
6.3
5.5/5.3
7.6/8.1
A
I
L
Output Leakage
Current
V
IN
= 40V, Softstart Pin = 0V
V
SWITCH
= 0V
V
SWITCH
= -1V
1.0
6
1.5
15
mA
mA
R
DS(ON)
Switch
On-Resistance
I
SWITCH
= 5A
0.12
0.14/0.225
f
O
Oscillator
Frequency
Measured at Switch Pin
260
225
280
kHz
D
Duty Cycle
Maximum Duty Cycle
91
%
Minimum Duty Cycle
0
%
I
BIAS
Feedback Bias
Current
V
FEEDBACK
= 1.3V
ADJ Version Only
85
nA
V
SFST
Softstart
Threshold
Voltage
0.63
0.53
0.74
V
I
SFST
Softstart Pin
Current
Softstart Pin = 0V
3.7
6.9
A
JA
Thermal
Resistance
T Package, Junction to Ambient
65
(Note 6)
JA
T Package, Junction to Ambient
45
(Note 7)
JC
T Package, Junction to Case
2
JA
S Package, Junction to Ambient
56
C/W
(Note 8)
JA
S Package, Junction to Ambient
35
(Note 9)
JA
S Package, Junction to Ambient
26
(Note 10)
JC
S Package, Junction to Case
2
++
JA
LD Package, Junction to Ambient
55
C/W
(Note 11)
JA
LD Package, Junction to Ambient
29
(Note 12)
LM2679
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4
All Output Voltage Versions
Electrical Characteristics
(Continued)
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings indicate conditions under which of the device is
guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test condition, see the electrical
Characteristics tables.
Note 2: ESD was applied using the human-body model, a 100pF capacitor discharged through a 1.5 k
resistor into each pin.
Note 3: Typical values are determined with T
A
= T
J
= 25C and represent the most likely norm.
Note 4: All limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%
tested during production with T
A
= T
J
= 25C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC)
methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Note 5: The peak switch current limit is determined by the following relationship: I
CL
=37,125/ R
ADJ
.
Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with
1
/
2
inch leads in a socket, or on a PC
board with minimum copper area.
Note 7: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with
1
/
2
inch leads soldered to a PC board
containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.
Note 8: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.136 square inches (the same size as the
TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Note 9: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.4896 square inches (3.6 times the area
of the TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Note 10: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board copper area of 1.0064 square inches (7.4 times
the area of the TO-263 package) of 1 oz. (0.0014 in. thick) copper. Additional copper area will reduce thermal resistance further. See the thermal model in Switchers
Made Simple
software.
Note 11: Junction to ambient thermal resistance for the 14-lead LLP mounted on a PC board copper area equal to the die attach paddle.
Note 12: Junction to ambient thermal resistance for the 14-lead LLP mounted on a PC board copper area using 12 vias to a second layer of copper equal to die
attach paddle. Additional copper area will reduce thermal resistance further. For layout recommendations, refer to Application Note AN-1187.
LM2679
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5
Typical Performance Characteristics
Normalized
Output Voltage
Line Regulation
10084704
10084705
Efficiency vs Input Voltage
Efficiency vs I
LOAD
10084706
10084707
Switch Current Limit
Operating Quiescent Current
10084708
10084709
LM2679
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6
Typical Performance Characteristics
(Continued)
Switching Frequency
Feedback Pin Bias Current
10084712
10084713
Continuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
= 5V, I
LOAD
= 5A
L = 10 H, C
OUT
= 400 F, C
OUT
ESR = 13 m
Discontinuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
= 5V, I
LOAD
= 500 mA
L = 10 H, C
OUT
= 400 F, C
OUT
ESR = 13 m
10084715
A: V
SW
Pin Voltage, 10 V/div.
B: Inductor Current, 2 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
Horizontal Time Base: 1 s/div
10084716
A: V
SW
Pin Voltage, 10 V/div.
B: Inductor Current, 1 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
Horizontal Time Base: 1 s//iv
Load Transient Response for Continuous Mode
V
IN
= 20V, V
OUT
= 5V
L = 10 H, C
OUT
= 400 F, C
OUT
ESR = 13 m
Load Transient Response for Discontinuous Mode
V
IN
= 20V, V
OUT
= 5V,
L = 10 H, C
OUT
= 400 F, C
OUT
ESR = 13 m
10084717
A: Output Voltage, 100 mV//div, AC-Coupled.
B: Load Current: 500 mA to 5A Load Pulse
Horizontal Time Base: 100 s/div
10084718
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 200 mA to 3A Load Pulse
Horizontal Time Base: 200 s/div
LM2679
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7
Block Diagram
10084714
* Active Inductor Patent Number 5,514,947
Active Capacitor Patent Number 5,382,918
LM2679
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8
Application Hints
The LM2679 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 5A, and highly
efficient operation.
The LM2679 is part of the SIMPLE SWITCHER family of
power converters. A complete design uses a minimum num-
ber of external components, which have been pre-
determined from a variety of manufacturers. Using either this
data sheet or a design software program called LM267X
Made Simple (version 2.0) a complete switching power
supply can be designed quickly. The software is provided
free of charge and can be downloaded from National Semi-
conductor's Internet site located at http://www.national.com.
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 260KHz
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).
INPUT
The input voltage for the power supply is connected to pin 2.
In addition to providing energy to the load the input voltage
also provides bias for the internal circuitry of the LM2679.
For guaranteed performance the input voltage must be in the
range of 8V to 40V. For best performance of the power
supply the input pin should always be bypassed with an input
capacitor located close to pin 2.
C BOOST
A capacitor must be connected from pin 3 to the switch
output, pin 1. This capacitor boosts the gate drive to the
internal MOSFET above Vin to fully turn it ON. This mini-
mizes conduction losses in the power switch to maintain high
efficiency. The recommended value for C Boost is 0.01F.
GROUND
This is the ground reference connection for all components
in the power supply. In fast-switching, high-current applica-
tions such as those implemented with the LM2679, it is
recommended that a broad ground plane be used to mini-
mize signal coupling throughout the circuit
CURRENT ADJUST
A key feature of the LM2679 is the ability to tailor the peak
switch current limit to a level required by a particular appli-
cation. This alleviates the need to use external components
that must be physically sized to accommodate current levels
(under shorted output conditions for example) that may be
much higher than the normal circuit operating current re-
quirements.
A resistor connected from pin 5 to ground establishes a
current (I
(pin 5)
= 1.2V / R
ADJ
) that sets the peak current
through the power switch. The maximum switch current is
fixed at a level of 37,125 / R
ADJ
.
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 (3.3V, 5V and 12V
outputs), a direct wire connection to the output is all that is
required as internal gain setting resistors are provided inside
the LM2679. 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.
SOFTSTART
A capacitor connected from pin 7 to ground allows for a slow
turn-on of the switching regulator. The capacitor sets a time
delay to gradually increase the duty cycle of the internal
power switch. This can significantly reduce the amount of
surge current required from the input supply during an abrupt
application of the input voltage. If softstart is not required this
pin should be left open circuited.
DAP (LLP PACKAGE)
The Die Attach Pad (DAP) can and should be connected to
PCB Ground plane/island. For CAD and assembly guide-
lines
refer
to
Application
Note
AN-1187
at
http://
power.national.com.
LM2679
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9
Application Hints
(Continued)
DESIGN CONSIDERATIONS
Power supply design using the LM2679 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 LM2679. A simple design
procedure using nomographs and component tables pro-
vided in this data sheet leads to a working design with very
little effort. Alternatively, the design software, LM267X Made
Simple (version 6.0), can also be used to provide instant
component selection, circuit performance calculations for
evaluation, a bill of materials component list and a circuit
schematic.
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 compari-
son of component specifications, equivalent devices from
other manufacturers could be substituted for use in an ap-
plication.
Important considerations for each external component and
an explanation of how the nomographs and selection tables
were developed follows.
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 re-
quired for a given set of operating conditions. The nomo-
graphs 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
10084723
FIGURE 1. Basic circuit for fixed output voltage applications.
10084724
FIGURE 2. Basic circuit for adjustable output voltage applications
LM2679
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10
Application Hints
(Continued)
maximum ripple current of 30% of the maximum load cur-
rent. 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 charac-
teristics.
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, will have 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.
OUTPUT CAPACITOR
The output capacitor acts to smooth the dc output voltage
and also provides energy storage. Selection of an output
capacitor, with an associated equivalent series resistance
(ESR), impacts both the amount of output ripple voltage and
stability of the control loop.
The output ripple voltage of the power supply is the product
of the capacitor ESR and the inductor ripple current. The
capacitor types recommended in the tables were selected
for having low ESR ratings.
In addition, both surface mount tantalum capacitors and
through-hole aluminum electrolytic capacitors are offered as
solutions.
Impacting frequency stability of the overall control loop, 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 fre-
quency response effects together with the internal frequency
compensation circuitry of the LM2679 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 260KHz switching frequency of the
LM2679, the output capacitor is selected to provide a unity
gain bandwidth of 40KHz 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 capaci-
tance to reduce the closed loop unity gain bandwidth (to less
than 40KHz). When parallel combinations of capacitors are
required it has been assumed that each capacitor is the
exact same part type.
The RMS current and working voltage (WV) ratings of the
output capacitor are also important considerations. In a typi-
cal 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 should be greater than 1.3 times the maxi-
mum 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 tempera-
ture is important.
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
should be rated to handle this. Paralleling multiple capacitors
proportionally increases the current rating of the total capaci-
tance. The voltage rating should also be selected to be 1.3
times the maximum input voltage. Depending on the unregu-
lated input power source, under light load conditions the
maximum input voltage could be significantly higher than
normal operation and should be considered when selecting
an input capacitor.
The input capacitor should be placed very close to the input
pin of the LM2679. 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 (0.1F to 0.47F)
ceramic type capacitor in parallel with the input capacitor to
prevent or minimize any ringing.
CATCH DIODE
When the power switch in the LM2679 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 -1V so a low voltage drop
(particularly at high current levels) Schottky diode is recom-
mended. Total efficiency of the entire power supply is signifi-
cantly 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 will be reversed biased
by the input voltage. The reverse voltage rating of the diode
should be at least 1.3 times greater than the maximum input
voltage.
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 it is recommended to use a
0.01F/50V ceramic capacitor.
R
ADJ
, ADJUSTABLE CURRENT LIMIT
A key feature of the LM2679 is the ability to control the peak
switch current. Without this feature the peak switch current
would be internally set to 7A or higher to accommodate 5A
load current designs. This requires that both the inductor
LM2679
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11
Application Hints
(Continued)
(which could saturate with excessively high currents) and the
catch diode be able to safely handle up to 7A which would be
conducted under load fault conditions.
If an application only requires a load current of 3A or 4A the
peak switch current can be set to a limit just over the maxi-
mum load current with the addition of a single programming
resistor. This allows the use of less powerful and more cost
effective inductors and diodes.
The peak switch current is equal to a factor of 37,125 divided
by R
ADJ
. A resistance of 5.6K
sets the current limit to
typically 6.3A and an R
ADJ
of 8.25K
reduces the maximum
current to approximately 4.4A. For predictable control of the
current limit it is recommended to keep the peak switch
current greater than 3A. For lower current applications a 3A
switching regulator with adjustable current limit, the LM2673,
is available.
When the power switch reaches the current limit threshold it
is immediately turned OFF and the internal switching fre-
quency is reduced. This extends the OFF time of the switch
to prevent a steady state high current condition. As the
switch current falls below the current limit threshold, the
switch will turn back ON. If a load fault continues, the switch
will again exceed the threshold and switch back OFF. This
will result in a low duty cycle pulsing of the power switch to
minimize the overall fault condition power dissipation.
Css SOFTSTART CAPACITOR
This optional capacitor controls the rate at which the LM2679
starts up at power on. The capacitor is charged linearly by an
internal current source. This voltage ramp gradually in-
creases the duty cycle of the power switch until it reaches
the normal operating duty cycle defined primarily by the ratio
of the output voltage to the input voltage. The softstart
turn-on time is programmable by the selection of Css.
The formula for selecting a softstart capacitor is:
Where:
I
SST
= Softstart Current, 3.7A typical
t
SS
= Softstart time, from design requirements
V
SST
= Softstart Threshold Voltage, 0.63V typical
V
OUT
= Output Voltage, from design requirements
V
SCHOTTKY
= Schottky Diode Voltage Drop, typically 0.5V
V
IN
= Maximum Input Voltage, from design requirements
If this feature is not desired, leave the Softstart pin (pin 7)
open circuited
SIMPLE DESIGN PROCEDURE
Using the nomographs and tables in this data sheet (or use
the available design software at http://www.national.com) a
complete step-down regulator can be designed in a few
simple steps.
Step 1: Define the power supply operating conditions:
Required output voltage
Maximum DC input voltage
Maximum output load current
Step 2: Set the output voltage by selecting a fixed output
LM2679 (3.3V, 5V or 12V applications) or determine the
required feedback resistors for use with the adjustable
LM2679-ADJ
Step 3: Determine the inductor required by using one of the
four nomographs, Figure 3 through Figure 6. Table 1 pro-
vides a specific manufacturer and part number for the induc-
tor.
Step 4: Using Table 3 (fixed output voltage) or Table 6
(adjustable output voltage), determine the output capaci-
tance required for stable operation. Table 2 provides the
specific capacitor type from the manufacturer of choice.
Step 5: Determine an input capacitor from Table 4 for fixed
output voltage applications. Use Table 2 to find the specific
capacitor type. For adjustable output circuits select a capaci-
tor from Table 2 with a sufficient working voltage (WV) rating
greater than Vin max, and an rms current rating greater than
one-half the maximum load current (2 or more capacitors in
parallel may be required).
Step 6: Select a diode from Table 5. The current rating of the
diode must be greater than I load max and the Reverse
Voltage rating must be greater than Vin max.
Step 7: Include a 0.01F/50V capacitor for Cboost in the
design and then determine the value of a softstart capacitor
if desired.
Step 8: Define a value for R
ADJ
to set the peak switch
current limit to be at least 20% greater than Iout max to allow
for at least 30% inductor ripple current (
15% of Iout). For
designs that must operate over the full temperature range
the switch current limit should be set to at least 50% greater
than Iout max (1.5 x I
out
max).
FIXED OUTPUT VOLTAGE DESIGN EXAMPLE
A system logic power supply bus of 3.3V is to be generated
from a wall adapter which provides an unregulated DC volt-
age of 13V to 16V. The maximum load current is 4A. A
softstart delay time of 50mS is desired. Through-hole com-
ponents are preferred.
Step 1: Operating conditions are:
Vout = 3.3V
Vin max = 16V
Iload max = 4A
Step 2: Select an LM2679T-3.3. The output voltage will have
a tolerance of
2% at room temperature and
3% over the full operating
temperature range.
Step 3: Use the nomograph for the 3.3V device ,Figure 3.
The intersection of the 16V horizontal line (V
in
max) and the
4A vertical line (I
load
max) indicates that L46, a 15H induc-
tor, is required.
From Table 1, L46 in a through-hole component is available
from Renco with part number RL-1283-15-43.
Step 4: Use Table 3 to determine an output capacitor. With a
3.3V output and a 15H 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 2 provides the actual capacitor characteristics.
Any of the following choices will work in the circuit:
2 x 220F/10V Sanyo OS-CON (code C5)
2 x 820F/16V Sanyo MV-GX (code C5)
1 x 3900F/10V Nichicon PL (code C7)
2 x 560F/35V Panasonic HFQ (code C5)
Step 5: Use Table 4 to select an input capacitor. With 3.3V
output and 15H there are three through-hole solutions.
These capacitors provide a sufficient voltage rating and an
LM2679
www.national.com
12
Application Hints
(Continued)
rms current rating greater than 2A (1/2 I
load
max). Again
using Table 2 for specific component characteristics the
following choices are suitable:
2 x 680F/63V Sanyo MV-GX (code C13)
1 x 1200F/63V Nichicon PL (code C25)
1 x 1500F/63V Panasonic HFQ (code C16)
Step 6: From Table 5 a 5A or more Schottky diode must be
selected. For through-hole components only 40V rated di-
odes are indicated and 4 part types are suitable:
1N5825
MBR745
80SQ045
6TQ045
Step 7: A 0.01F capacitor will be used for Cboost. For the
50mS softstart delay the following parameters are to be
used:
I
SST
: 3.7A
t
SS
: 50mS
V
SST
: 0.63V
V
OUT
: 3.3V
V
SCHOTTKY
: 0.5V
V
IN
: 16V
Using Vin max ensures that the softstart delay time will be at
least the desired 50mS.
Using the formula for Css a value of 0.148F is determined
to be required. Use of a standard value 0.22F capacitor will
produce more than sufficient softstart delay.
Step 8: Determine a value for R
ADJ
to provide a peak switch
current limit of at least 4A plus 50% or 6A.
Use a value of 6.2K
.
ADJUSTABLE OUTPUT DESIGN EXAMPLE
In this example it is desired to convert the voltage from a two
battery automotive power supply (voltage range of 20V to
28V, typical in large truck applications) to the 14.8VDC alter-
nator supply typically used to power electronic equipment
from single battery 12V vehicle systems. The load current
required is 3.5A maximum. It is also desired to implement the
power supply with all surface mount components. Softstart is
not required.
Step 1: Operating conditions are:
Vout = 14.8V
Vin max = 28V
Iload max = 3.5A
Step 2: Select an LM2679S-ADJ. To set the output voltage
to 14.9V two resistors need to be chosen (R1 and R2 in
Figure 2). For the adjustable device the output voltage is set
by the following relationship:
Where V
FB
is the feedback voltage of typically 1.21V.
A recommended value to use for R1 is 1K. In this example
then R2 is determined to be:
R2 = 11.23K
The closest standard 1% tolerance value to use is 11.3K
This will set the nominal output voltage to 14.88V which is
within 0.5% of the target value.
Step 3: To use the nomograph for the adjustable device,
Figure
6,
requires
a
calculation
of
the
inductor
Volt
microsecond constant (E
T expressed in V
S) from
the following formula:
where V
SAT
is the voltage drop across the internal power
switch which is R
ds(ON)
times I
load
. In this example this would
be typically 0.12
x 3.5A or 0.42V and V
D
is the voltage drop
across the forward bisased Schottky diode, typically 0.5V.
The switching frequency of 260KHz 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 to be:
Using Figure 6, the intersection of 27V
S horizontally and
the 3.5A vertical line (I
load
max) indicates that L48 , a 47H
inductor, or L49, a 33H inductor could be used. Either
inductor will be suitable, but for this example selecting the
larger inductance will result in lower ripple current.
From Table 1, L48 in a surface mount component is available
from Pulse Engineering with part number P0848.
Step 4: Use Table 6 to determine an output capacitor. With a
14.8V output the 12.5 to 15V row is used and with a 47H
inductor there are three surface mount output capacitor so-
lutions. Table 2 provides the actual capacitor characteristics
based on the C Code number. Any of the following choices
can be used:
1 x 33F/20V AVX TPS (code C6)
1 x 47F/20V Sprague 594 (code C8)
1 x 47F/20V Kemet T495 (code C8)
Important Note: When using the adjustable device in low
voltage applications (less than 3V output), if the nomograph,
Figure 6, selects an inductance of 22H or less, Table 6 does
not provide an output capacitor solution. With these condi-
tions the number of output capacitors required for stable
operation becomes impractical. It is recommended to use
either a 33H or 47H inductor and the output capacitors
from Table 6.
Step 5: An input capacitor for this example will require at
least a 35V WV rating with an rms current rating of 1.75A
(1/2 Iout max). From Table 2 it can be seen that C12, a
33F/35V capacitor from Sprague, has the highest voltage/
current rating of the surface mount components and that two
of these capacitor in parallel will be adquate.
Step 6: From Table 5 a 5A or more Schottky diode must be
selected. For surface mount diodes with a margin of safety
on the voltage rating one of two diodes can be used:
LM2679
www.national.com
13
Application Hints
(Continued)
MBRD1545CT
6TQ045S
Step 7: A 0.01F capacitor will be used for Cboost.
The softstart pin will be left open circuited.
Step 8: Determine a value for R
ADJ
to provide a peak switch
current limit of at least 3.5A plus 50% or 5.25A.
Use a value of 7.15K
.
LLP PACKAGE DEVICES
The LM2679 is offered in the 14 lead LLP surface mount
package to allow for a significantly decreased footprint with
equivalent power dissipation compared to the TO-263.
The Die Attach Pad (DAP) can and should be connected to
PCB Ground plane/island. For CAD and assembly guide-
lines
refer
to
Application
Note
AN-1187
at
http://
power.national.com.
LM2679
www.national.com
14
Inductor Selection Guides
For Continuous Mode Operation
10084719
FIGURE 3. LM2679-3.3
10084720
FIGURE 4. LM2679-5.0
10084721
FIGURE 5. LM2679-12
10084722
FIGURE 6. LM2679-ADJ
LM2679
www.national.com
15
Inductor Selection Guides
For Continuous Mode Operation (Continued)
Table 1. Inductor Manufacturer Part Numbers
Inductor
Reference
Number
Inductance
(H)
Current
(A)
Renco
Pulse Engineering
Coilcraft
Through Hole
Surface
Mount
Through
Hole
Surface
Mount
Surface Mount
L23
33
1.35
RL-5471-7
RL1500-33
PE-53823
PE-53823S
DO3316-333
L24
22
1.65
RL-1283-22-43
RL1500-22
PE-53824
PE-53824S
DO3316-223
L25
15
2.00
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
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
--
Inductor Manufacturer Contact Numbers
Coilcraft
Phone
(800) 322-2645
FAX
(708) 639-1469
Coilcraft, Europe
Phone
+44 1236 730 595
FAX
+44 1236 730 627
Pulse Engineering
Phone
(619) 674-8100
FAX
(619) 674-8262
Pulse Engineering,
Phone
+353 93 24 107
Europe
FAX
+353 93 24 459
Renco Electronics
Phone
(800) 645-5828
FAX
(516) 586-5562
LM2679
www.national.com
16
Capacitor Selection Guides
Table 2. Input and Output Capacitor Codes
Capacitor
Reference
Code
Surface Mount
AVX TPS Series
Sprague 594D Series
Kemet T495 Series
C (F) WV (V)
Irms
(A)
C (F) WV (V)
Irms
(A)
C (F) 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
LM2679
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17
Capacitor Selection Guides
(Continued)
Table 2. Input and Output Capacitor Codes (continued)
Capacitor
Reference
Code
Through Hole
Sanyo OS-CON SA Series
Sanyo MV-GX Series
Nichicon PL Series
Panasonic HFQ Series
C (F)
WV (V)
Irms
(A)
C (F) WV (V)
Irms
(A)
C (F) WV (V)
Irms
(A)
C (F) WV (V)
Irms
(A)
C1
47
6.3
1
1000
6.3
0.8
680
10
0.8
82
35
0.4
C2
150
6.3
1.95
270
16
0.6
820
10
0.98
120
35
0.44
C3
330
6.3
2.45
470
16
0.75
1000
10
1.06
220
35
0.76
C4
100
10
1.87
560
16
0.95
1200
10
1.28
330
35
1.01
C5
220
10
2.36
820
16
1.25
2200
10
1.71
560
35
1.4
C6
33
16
0.96
1000
16
1.3
3300
10
2.18
820
35
1.62
C7
100
16
1.92
150
35
0.65
3900
10
2.36
1000
35
1.73
C8
150
16
2.28
470
35
1.3
6800
10
2.68
2200
35
2.8
C9
100
20
2.25
680
35
1.4
180
16
0.41
56
50
0.36
C10
47
25
2.09
1000
35
1.7
270
16
0.55
100
50
0.5
C11
220
63
0.76
470
16
0.77
220
50
0.92
C12
470
63
1.2
680
16
1.02
470
50
1.44
C13
680
63
1.5
820
16
1.22
560
50
1.68
C14
1000
63
1.75
1800
16
1.88
1200
50
2.22
C15
220
25
0.63
330
63
1.42
C16
220
35
0.79
1500
63
2.51
C17
560
35
1.43
C18
2200
35
2.68
C19
150
50
0.82
C20
220
50
1.04
C21
330
50
1.3
C22
100
63
0.75
C23
390
63
1.62
C24
820
63
2.22
C25
1200
63
2.51
Capacitor Manufacturer Contact Numbers
Nichicon
Phone
(847) 843-7500
FAX
(847) 843-2798
Panasonic
Phone
(714) 373-7857
FAX
(714) 373-7102
AVX
Phone
(845) 448-9411
FAX
(845) 448-1943
Sprague/Vishay
Phone
(207) 324-4140
FAX
(207) 324-7223
Sanyo
Phone
(619) 661-6322
FAX
(619) 661-1055
Kemet
Phone
(864) 963-6300
FAX
(864) 963-6521
LM2679
www.national.com
18
Capacitor Selection Guides
(Continued)
Table 3. Output Capacitors for Fixed Output Voltage Application
Output
Voltage (V)
Inductance
(H)
Surface Mount
AVX TPS Series
Sprague 594D
Series
Kemet T495 Series
No.
C Code
No.
C Code
No.
C Code
3.3
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
5
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
12
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
Output
Voltage (V)
Inductance
(H)
Through Hole
Sanyo OS-CON SA
Series
Sanyo MV-GX Series
Nichicon PL Series
Panasonic HFQ
Series
No.
C Code
No.
C Code
No.
C Code
No.
C Code
3.3
10
2
C5
2
C6
1
C8
2
C6
15
2
C5
2
C5
1
C7
2
C5
22
1
C5
1
C10
1
C5
1
C7
33
1
C5
1
C10
1
C5
1
C7
5
10
2
C4
2
C5
1
C6
2
C5
15
1
C5
1
C10
1
C5
1
C7
22
1
C5
1
C9
1
C5
1
C5
33
1
C4
1
C5
1
C4
1
C4
47
1
C4
1
C4
1
C2
2
C4
12
10
2
C7
1
C10
1
C14
2
C4
15
1
C8
1
C6
1
C17
1
C5
22
1
C7
1
C5
1
C13
1
C5
33
1
C7
1
C4
1
C12
1
C4
47
1
C7
1
C3
1
C11
1
C3
68
1
C6
1
C2
1
C10
1
C3
100
1
C6
1
C2
1
C9
1
C1
No. represents the number of identical capacitor types to be connected in parallel
C Code indicates the Capacitor Reference number in Table 2 for identifying the specific component from the manufacturer.
LM2679
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19
Capacitor Selection Guides
(Continued)
Table 4. Input Capacitors for Fixed Output Voltage Application
(Assumes worst case maximum input voltage and load current for a given inductance value)
Output
Voltage (V)
Inductance
(H)
Surface Mount
AVX TPS Series
Sprague 594D
Series
Kemet T495 Series
No.
C Code
No.
C Code
No.
C Code
3.3
10
3
C7
2
C10
3
C9
15
*
*
3
C13
4
C12
22
*
*
2
C13
3
C12
33
*
*
2
C13
3
C12
5
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
12
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
Output
Voltage (V)
Inductance
(H)
Through Hole
Sanyo OS-CON SA
Series
Sanyo MV-GX Series
Nichicon PL Series
Panasonic HFQ
Series
No.
C Code
No.
C Code
No.
C Code
No.
C Code
3.3
10
2
C9
2
C8
1
C18
1
C8
15
*
*
2
C13
1
C25
1
C16
22
*
*
1
C14
1
C24
1
C16
33
*
*
1
C14
1
C24
1
C16
5
10
2
C7
2
C8
1
C25
1
C8
15
*
*
2
C8
1
C25
1
C8
22
*
*
2
C13
1
C25
1
C16
33
*
*
1
C14
1
C23
1
C13
47
*
*
1
C12
1
C19
1
C11
12
10
2
C10
2
C8
1
C18
1
C8
15
2
C10
2
C8
1
C18
1
C8
22
*
*
2
C8
1
C18
1
C8
33
*
*
2
C12
1
C24
1
C14
47
*
*
1
C14
1
C23
1
C13
68
*
*
1
C13
1
C21
1
C15
100
*
*
1
C11
1
C22
1
C11
* 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 2 for identifying the specific component from the manufacturer.
LM2679
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20
Capacitor Selection Guides
(Continued)
Table 5. Schottky Diode Selection Table
Reverse
Voltage
(V)
Surface Mount
Through Hole
3A
5A or More
3A
5A or
More
20V
SK32
1N5820
SR302
30V
SK33
MBRD835L
1N5821
30WQ03F
31DQ03
40V
SK34
MBRD1545CT
1N5822
1N5825
30BQ040
6TQ045S
MBR340
MBR745
30WQ04F
31DQ04
80SQ045
MBRS340
SR403
6TQ045
MBRD340
50V or
More
SK35
MBR350
30WQ05F
31DQ05
SR305
Diode Manufacturer Contact Numbers
International Rectifier
Phone
(310) 322-3331
FAX
(310) 322-3332
Motorola
Phone
(800) 521-6274
FAX
(602) 244-6609
General
Semiconductor
Phone
(516) 847-3000
FAX
(516) 847-3236
Diodes, Inc.
Phone
(805) 446-4800
FAX
(805) 446-4850
LM2679
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21
Capacitor Selection Guides
(Continued)
Table 6. Output Capacitors for Adjustable Output Voltage Applications
Output Voltage
(V)
Inductance
(H)
Surface Mount
AVX TPS Series
Sprague 594D
Series
Kemet T495 Series
No.
C Code
No.
C Code
No.
C Code
1.21 to 2.50
33
*
7
C1
6
C2
7
C3
47
*
5
C1
4
C2
5
C3
2.5 to 3.75
33
*
4
C1
3
C2
4
C3
47
*
3
C1
2
C2
3
C3
3.75 to 5
22
4
C1
3
C2
4
C3
33
3
C1
2
C2
3
C3
47
2
C1
2
C2
2
C3
5 to 6.25
22
3
C2
3
C3
3
C4
33
2
C2
2
C3
2
C4
47
2
C2
2
C3
2
C4
68
1
C2
1
C3
1
C4
6.25 to 7.5
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
7.5 to 10
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
10 to 12.5
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
12.5 to 15
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
15 to 20
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
20 to 30
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
30 to 37
10
4
C13
8
C12
15
3
C13
5
C12
22
No Values Available
2
C13
4
C12
33
1
C13
3
C12
47
1
C13
2
C12
68
1
C13
2
C12
LM2679
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22
Capacitor Selection Guides
(Continued)
Table 6. Output Capacitors for Adjustable Output Voltage Applications (continued)
Output Voltage
(V)
Inductance
(H)
Through Hole
Sanyo OS-CON SA
Series
Sanyo MV-GX Series
Nichicon PL Series
Panasonic HFQ
Series
No.
C Code
No.
C Code
No.
C Code
No.
C Code
1.21 to 2.50
33
*
2
C3
5
C1
5
C3
3
C
47
*
2
C2
4
C1
3
C3
2
C5
2.5 to 3.75
33
*
1
C3
3
C1
3
C1
2
C5
47
*
1
C2
2
C1
2
C3
1
C5
3.75 to 5
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
5 to 6.25
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
6.25 to 7.5
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
7.5 to 10
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
10 to 12.5
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
12.5 to 15
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
15 to 20
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
20 to 30
33
1
C7
1
C16
1
C2
47
No Values
1
C7
1
C16
1
C2
68
Available
1
C7
1
C16
1
C2
100
1
C7
1
C16
1
C2
30 to 37
10
1
C12
1
C20
1
C10
15
1
C11
1
C20
1
C11
22
No Values
1
C11
1
C20
1
C10
33
Available
1
C11
1
C20
1
C10
47
1
C11
1
C20
1
C10
68
1
C11
1
C20
1
C10
* Set to a higher value for a practical design solution. See Applications Hints section
No. represents the number of identical capacitor types to be connected in parallel
C Code indicates the Capacitor Reference number in Table 2 for identifying the specific component from the manufacturer.
LM2679
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23
Physical Dimensions
inches (millimeters)
unless otherwise noted
TO-263 Surface Mount Power Package
Order Number LM2679S-3.3, LM2679S-5.0,
LM2679S-12 or LM2679S-ADJ
NS Package Number TS7B
LM2679
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24
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
TO-220 Power Package
Order Number LM2679T-3.3, LM2679T-5.0,
LM2679T-12 or LM2679T-ADJ
NS Package Number TA07B
LM2679
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25
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
14-Lead LLP Package
NS Package Number LDC14A
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LM2679
SIMPLE
SWITCHER
5A
Step-Down
V
oltage
Regulator
with
Adjustable
Current
Limit
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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