LM2676EP
Enhanced Plastic SIMPLE SWITCHER®High Efficiency
3A Step-Down Voltage Regulator
General Description
The LM2676EP series of regulators are monolithic inte-
grated circuits which provide all of the active functions for a
step-down (buck) switching regulator capable of driving up to
3A 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
inductors for use with the LM2676EP are available from
several manufacturers to greatly simplify the design process.
The LM2676EP series also has built in thermal shutdown,
current 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%
tolerance.
ENHANCED PLASTIC
Extended Temperature Performance of −40 to +125˚C
Baseline Control - Single Fab & Assembly Site
Process Change Notification (PCN)
Qualification & Reliability Data
Solder (PbSn) Lead Finish is standard
Enhanced Diminishing Manufacturing Sources (DMS)
Support
Features
nEfficiency up to 94%
nSimple and easy to design with (using off-the-shelf
external components)
n150 mDMOS output switch
n3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
n50µA standby current when switched OFF
n±2%maximum output tolerance over full line and load
conditions
nWide input voltage range: 8V to 40V
n260 KHz fixed frequency internal oscillator
Applications
nSimple to design, high efficiency (>90%) step-down
switching regulators
nEfficient system pre-regulator for linear voltage
regulators
nSelected Military Applications
nSelected Avionics Applications
Ordering Information
PART NUMBER VID PART NUMBER NS PACKAGE NUMBER (Note 3)
LM2676S-5.0EP V62/04631-01 TS7B
(Notes 1, 2) TBD TBD
Note 1: For the following (Enhanced Plastic) versions, check for availability: LM2676SD-12EP, LM2676SD-3.3EP, LM2676SD-5.0EP, LM2676SD-
ADJEP, LM2676SDX-12EP, LM2676SDX-3.3EP, LM2676SDX5.0EP, LM2676SDX-ADJEP, LM2676T-12EP, LM2676T-3.3EP, LM2676T-5.0EP, LM2676T-
ADJEP, LM2676S-12EP, LM2676S-3.3EP, LM2676S-ADJEP, LM2676SX-12EP, LM2676SX-3.3EP, LM2676SX-5.0EP, LM2676SX-ADJEP. Parts listed with
an "X" are provided in Tape & Reel and parts without an "X" are in Rails.
Note 2: FOR ADDITIONAL ORDERING AND PRODUCT INFORMATION, PLEASE VISIT THE ENHANCED PLASTIC WEB SITE AT: www.national.com/
mil
Note 3: Refer to package details under Physical Dimensions
SIMPLE SWITCHER®is a registered trademark of National Semiconductor Corporation.
May 2004
LM2676EP Enhanced PlasticSIMPLE SWITCHER
®
High Efficiency 3A Step-Down Voltage
Regulator
© 2004 National Semiconductor Corporation DS200996 www.national.com
Typical Application
20099603
Connection Diagrams
TO-263 Package
Top View
20099601
See NSC Package Number TS7B
TO-220 Package
Top View
20099602
See NSC Package Number TA07B
Top View
20099641
LLP-14
See NS package Number SRC14A
LM2676EP Enhanced Plastic
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Absolute Maximum Ratings (Note 4)
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
IN
Boost Pin Voltage V
SW
+8V
Feedback Pin Voltage −0.3V to 14V
Power Dissipation Internally Limited
ESD (Note 5) 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
J
) −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
A
=T
J
= 25˚C.
LM2676-3.3EP
Symbol Parameter Conditions Typical Min Max Units
(Note 6) (Note 7) (Note 7)
V
OUT
Output Voltage V
IN
= 8V to 40V, 100mA I
OUT
3A 3.3 3.234/3.201 3.366/3.399 V
ηEfficiency V
IN
= 12V, I
LOAD
=3A 86 %
LM2676-5.0EP
Symbol Parameter Conditions Typical Min Max Units
(Note 6) (Note 7) (Note 7)
V
OUT
Output Voltage V
IN
= 8V to 40V, 100mA I
OUT
3A 5.0 4.900/4.850 5.100/5.150 V
ηEfficiency V
IN
= 12V, I
LOAD
=3A 88 %
LM2676-12EP
Symbol Parameter Conditions Typical Min Max Units
(Note 6) (Note 7) (Note 7)
V
OUT
Output Voltage V
IN
= 15V to 40V, 100mA I
OUT
3A 12 11.76/11.64 12.24/12.36 V
ηEfficiency V
IN
= 24V, I
LOAD
=3A 94 %
LM2676-ADJEP
Symbol Parameter Conditions Typ Min Max Units
(Note 6) (Note 7) (Note 7)
V
FB
Feedback
Voltage
V
IN
= 8V to 40V, 100mA I
OUT
3A
V
OUT
Programmed for 5V 1.21 1.186/1.174 1.234/1.246 V
ηEfficiency V
IN
= 12V, I
LOAD
=3A 88 %
LM2676EP Enhanced Plastic
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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. Specifica-
tions appearing in normal type apply for T
A
=T
J
= 25˚C. 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
I
STBY
Standby
Quiescent
Current
ON/OFF Pin = 0V
50 100/150 µA
I
CL
Current Limit 4.5 3.8/3.6 5.25/5.4 A
I
L
Output Leakage
Current
V
IN
= 40V, ON/OFF Pin = 0V
V
SWITCH
=0V
V
SWITCH
= −1V 16
200
15
µA
mA
R
DS(ON)
Switch
On-Resistance
I
SWITCH
= 3A 0.15 0.17/0.29
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
ON/OFF
ON/OFF
Threshold
Voltage
1.4 0.8 2.0 V
I
ON/OFF
ON/OFF Input
Current
ON/OFF Input = 0V 20 45 µA
θ
JA
Thermal
Resistance
T Package, Junction to Ambient 65
(Note 8)
θ
JA
T Package, Junction to Ambient 45
(Note 9)
θ
JC
T Package, Junction to Case 2
θ
JA
S Package, Junction to Ambient 56 ˚C/W
(Note 10)
θ
JA
S Package, Junction to Ambient 35
(Note 11)
θ
JA
S Package, Junction to Ambient 26
(Note 12)
θ
JC
S Package, Junction to Case 2 ++
θ
JA
SD Package, Junction to Ambient 55
˚C/W
(Note 13)
θ
JA
SD Package, Junction to Ambient 29
(Note 14)
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All Output Voltage Versions
Electrical Characteristics (Continued)
Note 4: 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 5: ESD was applied using the human-body model, a 100pF capacitor discharged through a 1.5 kresistor into each pin.
Note 6: Typical values are determined with TA=T
J= 25˚C and represent the most likely norm.
Note 7: 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 TA=T
J= 25˚C. 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 8: 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 9: 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 10: 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 11: 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 12: 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 13: Junction to ambient thermal resistance for the 14-lead LLP mounted on a PC board copper area equal to the die attach paddle.
Note 14: 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.
LM2676EP Enhanced Plastic
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Typical Performance Characteristics
Normalized
Output Voltage Line Regulation
20099609 20099610
Efficiency vs Input Voltage Efficiency vs I
LOAD
20099611 20099612
Switch Current Limit Operating Quiescent Current
20099604 20099605
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Typical Performance Characteristics (Continued)
Standby Quiescent Current ON/OFF Threshold Voltage
20099640 20099613
ON/OFF Pin Current (Sourcing) Switching Frequency
20099614 20099615
Feedback Pin Bias Current
20099616
LM2676EP Enhanced Plastic
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Typical Performance Characteristics
Continuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
= 5V, I
LOAD
=3A
L=3H,C
OUT
= 200 µF, C
OUT
ESR=26m
Discontinuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
= 5V, I
LOAD
= 500 mA
L=1H,C
OUT
= 400 µF, C
OUT
ESR=13m
20099617
A: VSW 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/div
20099618
A: VSW 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
V
IN
= 20V, V
OUT
=5V
L=3H,C
OUT
= 200 µF, C
OUT
ESR=26m
Load Transient Response for Discontinuous Mode
V
IN
= 20V, V
OUT
= 5V,
L=1H,C
OUT
= 400 µF, C
OUT
ESR=13m
20099619
A: Output Voltage, 100 mV//div, AC-Coupled.
B: Load Current: 500 mA to 3A Load Pulse
Horizontal Time Base: 100 µs/div
20099620
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 200 mA to 3A Load Pulse
Horizontal Time Base: 200 µs/div
LM2676EP Enhanced Plastic
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Block Diagram
20099606
* Active Inductor Patent Number 5,514,947
Active Capacitor Patent Number 5,382,918
LM2676EP Enhanced Plastic
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Application Hints
The LM2676EP 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 3A, and
highly efficient operation.
The LM2676EP 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 LM2676EP.
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 0.01µF.
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 LM2676EP, it is
recommended that a broad ground plane be used to mini-
mize signal coupling throughout the circuit
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 LM2676EP. For the adjustable output version two exter-
nal 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.
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.
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.
LM2676EP Enhanced Plastic
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Application Hints (Continued)
DESIGN CONSIDERATIONS
Power supply design using the LM2676EP is greatly simpli-
fied by using recommended external components. A wide
range of inductors, capacitors and Schottky diodes from
several manufacturers have been evaluated for use in de-
signs that cover the full range of capabilities (input voltage,
output voltage and load current) of the LM2676EP. A simple
design procedure using nomographs and component tables
provided 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 calcula-
tions 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
20099607
FIGURE 1. Basic circuit for fixed output voltage applications.
20099608
FIGURE 2. Basic circuit for adjustable output voltage applications
LM2676EP Enhanced Plastic
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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 LM2676EP 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
LM2676EP, the output capacitor is selected to provide a
unity gain bandwidth of 40KHz maximum. Each recom-
mended 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 LM2676EP. 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 (0.1µF to 0.47µF)
ceramic type capacitor in parallel with the input capacitor to
prevent or minimize any ringing.
CATCH DIODE
When the power switch in the LM2676EP 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 nega-
tive 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
0.01µF/50V ceramic capacitor.
LM2676EP Enhanced Plastic
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Application Hints (Continued)
ADDITIONAL APPLICATON INFORMATION
When the output voltage is greater than approximately 6V,
and the duty cycle at minimum input voltage is greater than
approximately 50%, the designer should exercise caution in
selection of the output filter components. When an applica-
tion designed to these specific operating conditions is sub-
jected 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 ter-
minated. 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 ca-
pacitor 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 out-
put capacitor varies as the square of the output voltage
(
1
2
CV
2
), 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 will recover smoothly.
Practical values of external components that have been
experimentally found to work well under these specific oper-
ating conditions are C
OUT
= 47µF, L = 22µH. It should be
noted that even with these components, for a device’s cur-
rent limit of I
CLIM
, the maximum load current under which the
possibility of the large current limit hysteresis can be mini-
mized is I
CLIM
/2. For example, if the input is 24V and the set
output voltage is 18V, then for a desired maximum current of
1.5A, the current limit of the chosen switcher must be con-
firmed to be at least 3A.
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
LM2676EP (3.3V, 5V or 12V applications) or determine the
required feedback resistors for use with the adjustable
LM2676−ADJEP
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 0.01µF/50V capacitor for Cboost in the
design.
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 2.5A.
Through-hole components are preferred.
Step 1: Operating conditions are:
Vout = 3.3V
Vin max = 16V
Iload max = 2.5A
Step 2: Select an LM2676T-3.3EP. 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
2.5A vertical line (I
load
max) indicates that L33, a 22µH
inductor, is required.
From Table 1, L33 in a through-hole component is available
from Renco with part number RL-1283-22-43 or part number
PE-53933 from Pulse Engineering.
Step 4: Use Table 3 to determine an output capacitor. With a
3.3V output and a 22µH 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:
1 x 220µF/10V Sanyo OS-CON (code C5)
1 x 1000µF/35V Sanyo MV-GX (code C10)
1 x 2200µF/10V Nichicon PL (code C5)
1 x 1000µF/35V Panasonic HFQ (code C7)
Step 5: Use Table 4 to select an input capacitor. With 3.3V
output and 22µH there are three through-hole solutions.
These capacitors provide a sufficient voltage rating and an
rms current rating greater than 1.25A (1/2 I
load
max). Again
using Table 2 for specific component characteristics the
following choices are suitable:
1 x 1000µF/63V Sanyo MV-GX (code C14)
1 x 820µF/63V Nichicon PL (code C24)
1 x 560µF/50V Panasonic HFQ (code C13)
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Application Hints (Continued)
Step 6: From Table5a3ASchottky diode must be selected.
For through-hole components 20V rated diodes are sufficient
and 2 part types are suitable:
1N5820
SR302
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
required is 2A 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 = 2A
Step 2: Select an LM2676S-ADJEP. To set the output volt-
age 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
Voltmicrosecond constant (ET expressed in VµS) 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 0.15x 2A or 0.3V 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 ET is found to be:
Using Figure 6, the intersection of 27VµS horizontally and
the 2A vertical line (I
load
max) indicates that L38 , a 68µH
inductor, should be used.
From Table 1, L38 in a surface mount component is available
from Pulse Engineering with part number PE-54038S.
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 68µH
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 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
operation becomes impractical. It is recommended to use
either 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 1A (1/2
Iout max). From Table 2 it can be seen that C12, a 33µF/35V
capacitor from Sprague, has the required voltage/current
rating of the surface mount components.
Step 6: From Table5a3ASchottky diode must be selected.
For surface mount diodes with a margin of safety on the
voltage rating one of five diodes can be used:
SK34
30BQ040
30WQ04F
MBRS340
MBRD340
Step 7: A 0.01µF capacitor will be used for Cboost.
LLP PACKAGE DEVICES
The LM2676EP may be offered in the 14 lead LLP surface
mount package to allow for a significantly decreased foot-
print with equivalent power dissipation compared to the TO-
263. For details on mounting and soldering specifications,
refer to Application Note AN-1187 at http://
power.national.com.
LM2676EP Enhanced Plastic
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Inductor Selection Guides For Continu-
ous Mode Operation
20099621
FIGURE 3. LM2676-3.3EP
20099622
FIGURE 4. LM2676-5.0EP
20099623
FIGURE 5. LM2676-12EP
20099624
FIGURE 6. LM2676-ADJEP
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Inductor Selection Guides For Continuous Mode Operation (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 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
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
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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 (µF) WV (V)
Irms
(A) C (µF) WV (V)
Irms
(A) C (µF) WV (V)
Irms
(A)
C1 330 6.3 1.15 120 6.3 1.1 100 6.3 0.82
C2 100 10 1.1 220 6.3 1.4 220 6.3 1.1
C3 220 10 1.15 68 10 1.05 330 6.3 1.1
C4 47 16 0.89 150 10 1.35 100 10 1.1
C5 100 16 1.15 47 16 1 150 10 1.1
C6 33 20 0.77 100 16 1.3 220 10 1.1
C7 68 20 0.94 180 16 1.95 33 20 0.78
C8 22 25 0.77 47 20 1.15 47 20 0.94
C9 10 35 0.63 33 25 1.05 68 20 0.94
C10 22 35 0.66 68 25 1.6 10 35 0.63
C11 15 35 0.75 22 35 0.63
C12 33 35 1 4.7 50 0.66
C13 15 50 0.9
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) WV (V)
Irms
(A) C (µF) WV (V)
Irms
(A) C (µF) WV (V)
Irms
(A) C (µF) 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
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Capacitor Selection Guides (Continued)
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
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
10 4 C2 3 C1 4 C4
15 4 C2 3 C1 4 C4
22 3 C2 2 C7 3 C4
33 2 C2 2 C6 2 C4
5
10 4 C2 4 C6 4 C4
15 3 C2 2 C7 3 C4
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 C8
22 2 C5 2 C6 3 C8
33 2 C5 1 C7 2 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
(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
10 1 C3 1 C10 1 C6 2 C6
15 1 C3 1 C10 1 C6 2 C5
22 1 C5 1 C10 1 C5 1 C7
33 1 C2 1 C10 1 C13 1 C5
5
10 2 C4 1 C10 1 C6 2 C5
15 1 C5 1 C10 1 C5 1 C6
22 1 C5 1 C5 1 C5 1 C5
33 1 C4 1 C5 1 C13 1 C5
47 1 C4 1 C4 1 C13 2 C3
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Capacitor Selection Guides (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
12
10 2 C7 1 C5 1 C18 2 C5
15 1 C8 1 C5 1 C17 1 C5
22 1 C7 1 C5 1 C13 1 C5
33 1 C7 1 C3 1 C11 1 C4
47 1 C7 1 C3 1 C10 1 C3
68 1 C7 1 C2 1 C10 1 C3
100 1 C7 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.
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
10 2 C5 1 C7 2 C8
15 3 C9 1 C10 3 C10
22 * * 2 C13 3 C12
33 * * 2 C13 2 C12
5
10 2 C5 1 C7 2 C8
15 2 C5 1 C7 2 C8
22 3 C10 2 C12 3 C11
33 * * 2 C13 3 C12
47 * * 1 C13 2 C12
12
10 2 C7 2 C10 2 C7
15 2 C7 2 C10 2 C7
22 3 C10 2 C12 3 C10
33 3 C10 2 C12 3 C10
47 * * 2 C13 3 C12
68 * * 2 C13 2 C12
100 * * 1 C13 2 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
10 1 C7 2 C4 1 C5 1 C6
15 1 C10 1 C10 1 C18 1 C6
22 * * 1 C14 1 C24 1 C13
33 * * 1 C12 1 C20 1 C12
5
10 1 C7 2 C4 1 C14 1 C6
15 1 C7 2 C4 1 C14 1 C6
22 * * 1 C10 1 C18 1 C13
33 * * 1 C14 1 C23 1 C13
47 * * 1 C12 1 C20 1 C12
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Capacitor Selection Guides (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
12
10 1 C9 1 C10 1 C18 1 C6
15 1 C10 1 C10 1 C18 1 C6
22 1 C10 1 C10 1 C18 1 C6
33 * * 1 C10 1 C18 1 C6
47 * * 1 C13 1 C23 1 C13
68 * * 1 C12 1 C21 1 C12
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.
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 MBRB1545CT 1N5822
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
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 33* 7 C1 6 C2 7 C3
47* 5 C1 4 C2 5 C3
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Capacitor Selection Guides (Continued)
Table 6. Output Capacitors for Adjustable Output Voltage Applications (Continued)
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
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
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Capacitor Selection Guides (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 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.
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Physical Dimensions inches (millimeters)
unless otherwise noted
TO-263 Surface Mount Power Package
NS Package Number TS7B
TO-220 Power Package
NS Package Number TA07B
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
14-Lead LLP Package
NS Package Number SRC14A
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safety or effectiveness.
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LM2676EP Enhanced PlasticSIMPLE SWITCHER
®
High Efficiency 3A Step-Down Voltage
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.