LM2678
SIMPLE SWITCHER

High Efficiency 5A Step-Down

Voltage Regulator

General Description

The LM2678 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 characteris-
tics. 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 adjust-
able 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 in-
ductors for use with the LM2678 are available from several
manufacturers to greatly simplify the design process.

The LM2678 series also has built in thermal shutdown, cur-
rent limiting and an ON/OFF control input that can power
down the regulator to a low 50µA quiescent current standby
condition. The output voltage is guaranteed to a

2% toler-

ance. The clock frequency is controlled to within a

11% tol-

erance.

Features

Efficiency up to 92%

Simple and easy to design with (using off-the-shelf
external components)

120 m

DMOS output switch

3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions

50µA standby current when switched OFF

2%maximum output tolerance over full line and load

conditions

Wide input voltage range: 8V to 40V

260 KHz fixed frequency internal oscillator

-40 to +125°C operating junction temperature range

Applications

Simple to design, high efficiency (

90%) step-down

switching regulators

Efficient system pre-regulator for linear voltage
regulators

Battery chargers

Typical Application

SIMPLE SWITCHER

is a registered trademark of National Semiconductor Corporation.

DS100886-3

March 2000

LM2678

SIMPLE

SWITCHER

High

Efficiency

Step-Down

oltage

Regulator

DS100886

www.national.com

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

ON/OFF Pin Voltage

-0.1V to 6V

Switch Voltage to Ground

-1V to V

Boost Pin Voltage

+ 8V

Feedback Pin Voltage

-0.3V to 14V

Power Dissipation

Internally Limited

ESD (Note 2)

2 kV

Storage Temperature Range

-65°C to 150°C

Soldering Temperature

Wave

4 sec, 260°C

Infrared

10 sec, 240°C

Vapor Phase

75 sec, 219°C

Operating Ratings

Supply Voltage

8V to 40V

Junction Temperature Range (T

)

-40°C to 125°C

Electrical Characteristics

Limits appearing in bold type face apply over the entire junction temperature

range of operation, -40°C to 125°C. Specifications appearing in normal type apply for T

= T

= 25°C.

LM2678-3.3

Symbol

Parameter

Conditions

Typical

Min

Max

Units

(Note 3)

(Note 4)

OUT

Output Voltage

= 8V to 40V, 100mA

OUT

3.3

3.234/3.201

3.366/3.399

Efficiency

= 12V, I

LOAD

= 5A

LM2678-5.0

Symbol

Parameter

Conditions

Typical

Min

Max

Units

(Note 3)

(Note 4)

OUT

Output Voltage

= 8V to 40V, 100mA

OUT

5.0

4.900/4.850

5.100/5.150

Efficiency

= 12V, I

LOAD

= 5A

LM2678-12

Symbol

Parameter

Conditions

Typical

Min

Max

Units

(Note 3)

(Note 4)

OUT

Output Voltage

= 15V to 40V, 100mA

OUT

11.76/11.64

12.24/12.36

Efficiency

= 24V, I

LOAD

= 5A

LM2678-ADJ

Symbol

Parameter

Conditions

Typ

Min

Max

Units

(Note 3)

(Note 4)

Feedback
Voltage

= 8V to 40V, 100mA

OUT

Programmed for 5V

1.21

1.186/1.174

1.234/1.246

Efficiency

= 12V, I

LOAD

= 5A

LM2678

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All Output Voltage Versions
Electrical Characteristics

Limits appearing in bold type face apply over the entire junction temperature range of operation, -40°C to 125°C.
Specifications appearing in normal type apply for T

= T

= 25°C. Unless otherwise specified V

=12V for the 3.3V, 5V and

Adjustable versions and V

=24V for the 12V version.

Symbol

Parameter

Conditions

Typ

Min

Max

Units

DEVICE PARAMETERS

Quiescent
Current

FEEDBACK

= 8V

4.2

For 3.3V, 5.0V, and ADJ Versions

FEEDBACK

= 15V

For 12V Versions

STBY

Standby
Quiescent
Current

ON/OFF Pin = 0V

100/150

µA

Current Limit

6.1/5.75

8.3/8.75

Output
Leakage
Current

= 40V, ON/OFF Pin = 0V

SWITCH

= 0V

SWITCH

= -1V

1
6

200

µA

DS(ON)

Switch
On-Resistance

SWITCH

= 5A

0.12

0.14/0.225

Oscillator
Frequency

Measured at Switch Pin

260

225

280

kHz

Duty Cycle

Maximum Duty Cycle

Minimum Duty Cycle

BIAS

Feedback Bias
Current

FEEDBACK

= 1.3V

ADJ Version Only

ON/OFF

ON/OFF
Threshold
Voltage

1.4

0.8

2.0

ON/OFF

ON/OFF Input
Current

ON/OFF Input = 0V

µA

Thermal
Resistance

T Package, Junction to Ambient

(Note 5)

T Package, Junction to Ambient

(Note 6)

T Package, Junction to Case

S Package, Junction to Ambient

°C/W

(Note 7)

S Package, Junction to Ambient

(Note 8)

S Package, Junction to Ambient

(Note 9)

S Package, Junction to Case

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 Char-
acteristics 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

= T

= 25°C 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

= T

= 25°C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC) meth-

ods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

Note 5: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with

inch leads in a socket, or on a PC

board with minimum copper area.

Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with

inch leads soldered to a PC board

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

LM2678

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Typical Performance Characteristics

Continuous Mode Switching Waveforms

= 20V, V

OUT

= 5V, I

LOAD

= 5A

L = 10 µH, C

OUT

= 400 µF, C

OUT

ESR = 13 m

DS100886-17

A: V

Pin Voltage, 10 V/div.

B: Inductor Current, 2 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled

Horizontal Time Base: 1 µs/div

Discontinuous Mode Switching Waveforms

= 20V, V

OUT

= 5V, I

LOAD

= 500 mA

L = 10 µH, C

OUT

= 400 µF, C

OUT

ESR = 13 m

DS100886-18

A: V

Pin Voltage, 10 V/div.

B: Inductor Current, 1 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled

Horizontal Time Base: 1 µs//iv

Load Transient Response for Continuous Mode

= 20V, V

OUT

= 5V

L = 10 µH, C

OUT

= 400 µF, C

OUT

ESR = 13 m

DS100886-19

A: Output Voltage, 100 mV//div, AC-Coupled.
B: Load Current: 500 mA to 5A Load Pulse

Horizontal Time Base: 100 µs/div

Load Transient Response for Discontinuous Mode

= 20V, V

OUT

= 5V,

L = 10 µH, C

OUT

= 400 µF, C

OUT

ESR = 13 m

DS100886-20

A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 200 mA to 3A Load Pulse

Horizontal Time Base: 200 µs/div

LM2678

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Application Hints

The LM2678 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 ef-
ficient operation.

The LM2678 is part of the

SIMPLE SWITCHER family of

power converters. A complete design uses a minimum num-
ber

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 sup-
ply can be designed quickly. The software is provided free of
charge and can be downloaded from National Semiconduc-
tor's Internet site located at http://www.national.com.

PIN 1 - Switch Output

This is the output of a power MOSFET switch connected di-
rectly 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 oscil-
lator. 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 volt-
age. The voltage on pin 1 switches between Vin (switch ON)
and below ground by the voltage drop of the external Schot-
tky diode (switch OFF).

PIN 2 - Input

The input voltage for the power supply is connected to pin 2.
In addition to providing energy to the load the input voltage
also provides bias for the internal circuitry of the LM2678.
For guaranteed performance the input voltage must be in the
range of 8V to 40V. For best performance of the power sup-
ply the input pin should always be bypassed with an input ca-
pacitor located close to pin 2.

PIN 3 - C Boost

A capacitor must be connected from pin 3 to the switch out-
put, pin 1. This capacitor boosts the gate drive to the internal
MOSFET above Vin to fully turn it ON. This minimizes con-
duction losses in the power switch to maintain high effi-
ciency. The recommended value for C Boost is 0.01µF.

PIN 4 - 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 LM2678, it is rec-
ommended that a broad ground plane be used to minimize
signal coupling throughout the circuit

PIN 5 - No Connection

PIN 6 - 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 out-
puts), a direct wire connection to the output is all that is re-
quired as internal gain setting resistors are provided inside
the LM2678. 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 cou-
pling of any inductor flux to the feedback input.

PIN 7 - ON/OFF

This input provides an electrical ON/OFF control of the
power supply. Connecting this pin to ground or to any volt-
age less than 0.8V will completely turn OFF the regulator.
The current drain from the input supply when OFF is only
50µA. Pin 7 has an internal pull-up current source of approxi-
mately 20µA and a protection clamp zener diode of 7V to
ground. When electrically driving the ON/OFF pin the high
voltage level for the ON condition should not exceed the 6V
absolute maximum limit. When ON/OFF control is not re-
quired pin 7 should be left open circuited.

DESIGN CONSIDERATIONS

DS100886-7

FIGURE 1. Basic circuit for fixed output voltage applications.

LM2678

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Application Hints

(Continued)

Power supply design using the LM2678 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 volt-
age and load current) of the LM2678. A simple design proce-
dure using nomographs and component tables provided in
this data sheet leads to a working design with very little ef-
fort. Alternatively, the design software,

LM267X Made

Simple (version 2.0), 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 ar-
ray 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 appli-
cation.

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
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 low-
est 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, be-
ing 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 ca-
pacitor, 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 ca-
pacitor 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 ca-
pacitance and the ESR value create a zero. These fre-
quency response effects together with the internal frequency
compensation circuitry of the LM2678 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
LM2678, the output capacitor is selected to provide a unity
gain bandwidth of 40KHz maximum. Each recommended ca-
pacitor value has been chosen to achieve this result.

DS100886-8

FIGURE 2. Basic circuit for adjustable output voltage applications

LM2678

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Application Hints

(Continued)

In some cases multiple capacitors are required either to re-
duce 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 ex-
act 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 out-
put capacitor should be greater than 1.3 times the maximum
output voltage of the power supply. If operation of the system
at elevated temperatures is required, the capacitor voltage
rating may be de-rated to less than the nominal room tem-
perature 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 LM2678. 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 out-
put or other parts of the circuitry. It may be necessary in
some designs to add a small valued (0.1µF to 0.47µF) ce-
ramic type capacitor in parallel with the input capacitor to
prevent or minimize any ringing.

CATCH DIODE

When the power switch in the LM2678 turns OFF, the current
through the inductor continues to flow. The path for this cur-
rent is through the diode connected between the switch out-
put 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 recommended. Total
efficiency of the entire power supply is significantly impacted
by the power lost in the output catch diode. The average cur-
rent 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
0.01µF/50V ceramic capacitor.

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
LM2678 (3.3V, 5V or 12V applications) or determine the re-
quired feedback resistors for use with the adjustable
LM2678-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 (ad-
justable output voltage), determine the output capacitance
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 Volt-
age rating must be greater than Vin max.

Step 7: Include a 0.01µF/50V capacitor for Cboost in the de-
sign.

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.
Through-hole components are preferred.

Step 1: Operating conditions are:

Vout = 3.3V

Vin max = 16V

Iload max = 4A

Step 2: Select an LM2678T-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

max) and the

4A vertical line (I

load

max) indicates that L46, a 15µH induc-

tor, is required.

From Table 1, L46 in a through-hole component is available
from Renco with part number RL-1283-15-43.

LM2678

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Application Hints

(Continued)

Step 4: Use Table 3 to determine an output capacitor. With a
3.3V output and a 15µH inductor there are four through-hole
output capacitor solutions with the number of same type ca-
pacitors 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 220µF/10V Sanyo OS-CON (code C5)

2 x 820µF/16V Sanyo MV-GX (code C5)

1 x 3900µF/10V Nichicon PL (code C7)

2 x 560µF/35V Panasonic HFQ (code C5)

Step 5: Use Table 4 to select an input capacitor. With 3.3V
output and 15µH there are three through-hole solutions.
These capacitors provide a sufficient voltage rating and an
rms current rating greater than 2A (1/2 I

load

max). Again us-

ing Table 2 for specific component characteristics the follow-
ing choices are suitable:

2 x 680µF/63V Sanyo MV-GX (code C13)

1 x 1200µF/63V Nichicon PL (code C25)

1 x 1500µF/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 0.01µF capacitor will be used for Cboost.

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 re-
quired is 3.5A maximum. It is also desired to implement the
power supply with all surface mount components.

Step 1: Operating conditions are:

Vout = 14.8V

Vin max = 28V

Iload max = 3.5A

Step 2: Select an LM2678S-ADJ. To set the output voltage
to 14.9V two resistors need to be chosen (R1 and R2 in

Fig-

ure 2). For the adjustable device the output voltage is set by
the following relationship:

Where V

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,

Fig-

ure

requires

calculation

the

inductor

Volt

microsecond constant (E

T expressed in V

µS) 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

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 en-
ergy is stored in the inductor.

For this example E

T is found to be:

Using

Figure 6, the intersection of 27V

µS horizontally and

the 3.5A vertical line (I

load

max) indicates that L48 , a 47µH

inductor, or L49, a 33µH inductor could be used. Either in-
ductor 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 47µH in-
ductor there are three surface mount output capacitor solu-
tions. Table 2 provides the actual capacitor characteristics
based on the C Code number. Any of the following choices
can be used:

1 x 33µF/20V AVX TPS (code C6)

1 x 47µF/20V Sprague 594 (code C8)

1 x 47µF/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 22µH or less, Table 6 does
not provide an output capacitor solution. With these condi-
tions the number of output capacitors required for stable op-
eration becomes impractical. It is recommended to use ei-
ther a 33µH or 47µH 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
33µF/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:

MBRD1545CT

6TQ045S

Step 7: A 0.01µF capacitor will be used for Cboost.

LM2678

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Application Hints

(Continued)

TABLE 1. Inductor Manufacturer Part Numbers

Inductor

Reference

Number

Inductance

(µH)

Current

(A)

Renco

Pulse Engineering

Coilcraft

Through Hole

Surface

Mount

Through

Hole

Surface

Mount

Surface Mount

L23

1.35

RL-5471-7

RL1500-33

PE-53823

PE-53823S

DO3316-333

L24

1.65

RL-1283-22-43

RL1500-22

PE-53824

PE-53824S

DO3316-223

L25

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

1.71

RL-5471-5

RL6050-68

PE-53830

PE-53830S

DO5022P-683

L31

2.06

RL-5471-6

RL6050-47

PE-53831

PE-53831S

DO5022P-473

L32

2.46

RL-5471-7

RL6050-33

PE-53932

PE-53932S

DO5022P-333

L33

3.02

RL-1283-22-43

RL6050-22

PE-53933

PE-53933S

DO5022P-223

L34

3.65

RL-1283-15-43

PE-53934

PE-53934S

DO5022P-153

L38

2.97

RL-5472-2

PE-54038

PE-54038S

L39

3.57

RL-5472-3

PE-54039

PE-54039S

L40

4.26

RL-1283-33-43

PE-54040

PE-54040S

L41

5.22

RL-1283-22-43

PE-54041

P0841

L44

3.45

RL-5473-3

PE-54044

L45

4.47

RL-1283-10-43

P0845

DO5022P-103HC

L46

5.60

RL-1283-15-43

P0846

DO5022P-153HC

L47

5.66

RL-1283-10-43

P0847

DO5022P-103HC

L48

5.61

RL-1282-47-43

P0848

L49

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

LM2678

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Application Hints

(Continued)

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 (µF)

(V)

Irms

(A)

(µF)

(V)

Irms

(A)

(µF)

(V)

Irms

(A)

(µF)

(V)

Irms

(A)

6.3

1000

6.3

0.8

680

0.8

0.4

150

6.3

1.95

270

0.6

820

0.98

120

0.44

330

6.3

2.45

470

0.75

1000

1.06

220

0.76

100

1.87

560

0.95

1200

1.28

330

1.01

220

2.36

820

1.25

2200

1.71

560

1.4

0.96

1000

1.3

3300

2.18

820

1.62

100

1.92

150

0.65

3900

2.36

1000

1.73

150

2.28

470

1.3

6800

2.68

2200

2.8

100

2.25

680

1.4

180

0.41

0.36

C10

2.09

1000

1.7

270

0.55

100

0.5

C11

220

0.76

470

0.77

220

0.92

C12

470

1.2

680

1.02

470

1.44

C13

680

1.5

820

1.22

560

1.68

C14

1000

1.75

1800

1.88

1200

2.22

C15

220

0.63

330

1.42

C16

220

0.79

1500

2.51

C17

560

1.43

C18

2200

2.68

C19

150

0.82

C20

220

1.04

C21

330

1.3

C22

100

0.75

C23

390

1.62

C24

820

2.22

C25

1200

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

LM2678

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Application Hints

(Continued)

TABLE 3. Output Capacitors for Fixed Output Voltage Application

Output

Voltage

(V)

Inductance

(µH)

Surface Mount

AVX TPS Series

Sprague 594D

Series

Kemet T495 Series

No.

C Code

No.

C Code

No.

C Code

3.3

100

Output

Voltage

(V)

Inductance

(µH)

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

C10

C14

C17

C13

C12

C11

C10

100

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.

LM2678

www.national.com

Application Hints

(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

(µH)

Surface Mount

AVX TPS Series

Sprague 594D

Series

Kemet T495 Series

No.

C Code

No.

C Code

No.

C Code

3.3

C10

C13

C12

C13

C12

C13

C12

C10

C13

C12

C13

C12

C13

C12

C10

C12

C10

C13

C12

C13

C12

C13

C12

100

C13

C12

Output

Voltage

(V)

Inductance

(µH)

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

C18

C13

C25

C16

C14

C24

C16

C14

C24

C16

C25

C13

C25

C16

C14

C23

C13

C12

C19

C11

C10

C18

C10

C18

C12

C24

C14

C23

C13

C21

C15

100

C11

C22

C11

Check voltage rating of capacitors to be greater than application input voltage.

LM2678

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Application Hints

(Continued)

TABLE 6. Output Capacitors for Adjustable Output Voltage Applications

Output Voltage

(V)

Inductance

(µH)

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

2.5 to 3.75

3.75 to 5

5 to 6.25

6.25 to 7.5

7.5 to 10

100

10 to 12.5

100

12.5 to 15

100

15 to 20

C10

100

C10

20 to 30

C11

C10

C12

C11

C12

C11

100

C12

C11

30 to 37

C13

C12

C13

C12

No Values Available

C13

C12

C13

C12

C13

C12

C13

C12

LM2678

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Application Hints

(Continued)

Output Capacitors for Adjustable Output Voltage Applications (continued)

Output Voltage

(V)

Inductance

(µH)

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

2.5 to 3.75

3.75 to 5

5 to 6.25

6.25 to 7.5

7.5 to 10

C14

100

C14

10 to 12.5

C14

100

12.5 to 15

C10

C15

C10

C15

C10

C15

100

C10

C15

15 to 20

C10

C15

C10

C15

C10

C15

100

C10

C15

20 to 30

C16

No Values

C16

Available

C16

100

C16

30 to 37

C12

C20

C10

C11

C20

C11

No Values

C11

C20

C10

Available

C11

C20

C10

C11

C20

C10

C11

C20

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.

LM2678

www.national.com

Physical Dimensions

inches (millimeters) unless otherwise noted (Continued)

LIFE SUPPORT POLICY

NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com

National Semiconductor
Europe

Fax: +49 (0) 180-530 85 86

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 69 9508 6208
English

Tel: +44 (0) 870 24 0 2171

Français Tel: +33 (0) 1 41 91 8790

National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: ap.support@nsc.com

National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507

www.national.com

TO-220 Power Package

Order Number LM2678T-3.3, LM2678T-5.0,

LM2678T-12 or LM2678T-ADJ

NS Package Number TA07B

LM2678

SIMPLE

SWITCHER

High

Efficiency

Step-Down

oltage

Regulator

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.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM2678S-5.0

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM2678S-5.0