National Semiconductor LM2679 Technical data
LM2679
SIMPLE SWITCHER
®
5A Step-Down Voltage Regulator
with Adjustable Current Limit
LM2679 SIMPLE SWITCHER 5A Step-Down Voltage Regulator with Adjustable Current Limit
April 2005
General Description
The LM2679 series of regulators are monolithic integrated
circuits which provide all of the active functions for a stepdown (buck) switching regulator capable of driving up to 5A
loads with excellent line and load regulation characteristics.
High efficiency (
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
controlled to within a
>
90%) is obtained through the use of a low
±
2% tolerance. The clock frequency is
±
11% tolerance.
Typical Application
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 mΩ 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 +125˚C 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
10084703
SIMPLE SWITCHER®is a registered trademark of National Semiconductor Corporation.
© 2005 National Semiconductor Corporation DS100847 www.national.com
Connection Diagrams and Ordering Information
LM2679
TO-263 Package
Top View
TO-220 Package
Top View
Order Number
LM2679S-3.3, LM2679S-5.0,
LM2679S-12 or LM2679S-ADJ
See NSC Package Number TS7B
See NS package Number SRC14A
10084701
Order Number
10084702
LM2679T-3.3, LM2679T-5.0,
LM2679T-12 or LM2679T-ADJ
See NSC Package Number TA07B
Top View
10084735
LLP-14
Ordering Information for LLP Package
Output Voltage Order Information Package Marking Supplied As
12 LM2679SD-12 S0003FB 250 Units on Tape and Reel
12 LM2679SDX-12 S0003FB 2500 Units on Tape and Reel
3.3 LM2679SD-3.3 S0003HB 250 Units on Tape and Reel
3.3 LM2679SDX-3.3 S0003HB 2500 Units on Tape and Reel
5.0 LM2679SD-5.0 S0003JB 250 Units on Tape and Reel
5.0 LM2679SDX-5.0 S0003JB 2500 Units on Tape and Reel
ADJ LM2679SD-ADJ S0003KB 250 Units on Tape and Reel
ADJ LM2679SDX-ADJ S0003KB 2500 Units on Tape and Reel
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LM2679
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
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
Softstart Pin Voltage −0.1V to 6V
Switch Voltage to Ground −1V to V
IN
Operating Ratings
Boost Pin Voltage VSW+8V
Feedback Pin Voltage −0.3V to 14V
Power Dissipation Internally Limited
Supply Voltage 8V to 40V
Junction Temperature Range (T
) −40˚C to 125˚C
J
ESD (Note 2) 2 kV
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=TJ
= 25˚C. R
ADJ
= 5.6KΩ
LM2679-3.3
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
OUT
η Efficiency V
Output Voltage VIN= 8V to 40V, 100mA ≤ I
= 12V, I
IN
=5A 82 %
LOAD
≤ 5A 3.3 3.234/3.201 3.366/3.399 V
OUT
LM2679-5.0
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
OUT
η Efficiency V
Output Voltage VIN= 8V to 40V, 100mA ≤ I
= 12V, I
IN
=5A 84 %
LOAD
≤ 5A 5.0 4.900/4.850 5.100/5.150 V
OUT
LM2679-12
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
OUT
η Efficiency V
Output Voltage VIN= 15V to 40V, 100mA ≤ I
= 24V, I
IN
=5A 92 %
LOAD
≤ 5A 12 11.76/11.64 12.24/12.36 V
OUT
LM2679-ADJ
Symbol Parameter Conditions Typ Min Max Units
(Note 3) (Note 4) (Note 4)
V
FB
η Efficiency V
Feedback
Voltage
VIN= 8V to 40V, 100mA ≤ I
Programmed for 5V
V
OUT
= 12V, I
IN
=5A 84 %
LOAD
OUT
≤ 5A
1.21 1.186/1.174 1.234/1.246 V
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All Output Voltage Versions Electrical Characteristics
LM2679
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
versions and V
=24V for the 12V version.
IN
Symbol Parameter Conditions Typ Min Max Units
DEVICE PARAMETERS
I
Q
Quiescent
V
FEEDBACK
= 8V 4.2 6 mA
Current
For 3.3V, 5.0V, and ADJ Versions
V
FEEDBACK
= 15V
For 12V Versions
V
ADJ
Current Limit
Adjust Voltage
I
CL
I
L
R
DS(ON)
Current Limit R
Output Leakage
Current
Switch
= 5.6KΩ, (Note 5) 6.3 5.5/5.3 7.6/8.1 A
ADJ
VIN= 40V, Softstart Pin = 0V
V
V
I
SWITCH
=0V
SWITCH
= −1V
SWITCH
= 5A 0.12 0.14/0.225 Ω
On-Resistance
f
O
Oscillator
Measured at Switch Pin 260 225 280 kHz
Frequency
D Duty Cycle Maximum Duty Cycle 91 %
Minimum Duty Cycle 0 %
I
V
BIAS
SFST
Feedback Bias
Current
Softstart
V
FEEDBACK
= 1.3V
ADJ Version Only
Threshold
Voltage
I
SFST
Softstart Pin
Softstart Pin = 0V
Current
θ
JA
θ
JA
Thermal
Resistance
T Package, Junction to Ambient 65
(Note 6)
T Package, Junction to Ambient 45
(Note 7)
θ
JC
θ
JA
T Package, Junction to Case 2
S Package, Junction to Ambient 56 ˚C/W
(Note 8)
θ
JA
S Package, Junction to Ambient 35
(Note 9)
θ
JA
S Package, Junction to Ambient 26
(Note 10)
θ
JC
θ
JA
S Package, Junction to Case 2 ++
SD Package, Junction to Ambient 55
(Note 11)
θ
JA
SD Package, Junction to Ambient 29
(Note 12)
= 25˚C. Unless otherwise specified VIN=12V for the 3.3V, 5V and Adjustable
A=TJ
1.21 1.181/1.169 1.229/1.246 V
1.0
6
85 nA
0.63 0.53 0.74 V
3.7 6.9 µA
1.5
15
mA
mA
˚C/W
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All Output Voltage Versions
Electrical Characteristics
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 kΩ resistor into each pin.
Note 3: Typical values are determined with T
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
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
Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with
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
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
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.
®
software.
A=TJ
A=TJ
= 25˚C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC)
(Continued)
= 25˚C and represent the most likely norm.
=37,125/ R
CL
ADJ
.
1
⁄2inch leads in a socket, or on a PC
1
⁄2inch leads soldered to a PC board
LM2679
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Typical Performance Characteristics
LM2679
Normalized
Output Voltage Line Regulation
10084704
Efficiency vs Input Voltage Efficiency vs I
10084706 10084707
LOAD
Switch Current Limit Operating Quiescent Current
10084705
10084708 10084709
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Typical Performance Characteristics (Continued)
Switching Frequency Feedback Pin Bias Current
LM2679
Continuous Mode Switching Waveforms
= 20V, V
V
L=10µH,C
A: VSWPin Voltage, 10 V/div.
B: Inductor Current, 2 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
IN
OUT
= 5V, I
OUT
= 400 µF, C
=5A
LOAD
ESR=13mΩ
OUT
10084715
Horizontal Time Base: 1 µs/div
Load Transient Response for Continuous Mode
L=10µH,C
= 20V, V
V
IN
= 400 µF, C
OUT
OUT
OUT
=5V
ESR=13mΩ
10084712
10084713
Discontinuous Mode Switching Waveforms
V
= 20V, V
IN
L=10µH,C
A: VSWPin Voltage, 10 V/div.
B: Inductor Current, 1 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
OUT
= 400 µF, C
OUT
= 5V, I
= 500 mA
LOAD
ESR=13mΩ
OUT
10084716
Horizontal Time Base: 1 µs//iv
Load Transient Response for Discontinuous Mode
V
L=10µH,C
= 20V, V
IN
= 400 µF, C
OUT
OUT
= 5V,
ESR=13mΩ
OUT
A: Output Voltage, 100 mV//div, AC-Coupled.
B: Load Current: 500 mA to 5A Load Pulse
Horizontal Time Base: 100 µs/div
10084717
A: Output Voltage, 100 mV/div, AC-Coupled.
10084718
B: Load Current: 200 mA to 3A Load Pulse
Horizontal Time Base: 200 µs/div
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Block Diagram
LM2679
* Active Inductor Patent Number 5,514,947
†
Active Capacitor Patent Number 5,382,918
10084714
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