NSC LM2676T-5.0, LM2676T-3.3, LM2676T-12, LM2676SX-5.0, LM2676SX-3.3 Datasheet
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LM2676
SIMPLE SWITCHER
®
High Efficiency 3A Step-Down
Voltage Regulator
General Description
The LM2676 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
3A loads with excellent line and load regulation characteristics. High efficiency (
>
90%) is obtained through the use of a
low ON-resistance DMOS power switch. The series consists
of fixed output voltages of 3.3V, 5V and 12V and an adjustable output version.
The SIMPLE SWITCHER concept provides for a complete
design using a minimum number of external components. A
high fixed frequency oscillator (260KHz) allows the use of
physically smaller sized components.Afamilyofstandardinductors for use with the LM2676 are available from several
manufacturers to greatly simplify the design process.
The LM2676 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%tol-
erance.
Features
n Efficiency up to 94%
n Simple and easy to design with (using off-the-shelf
external components)
n 150 mΩ DMOS output switch
n 3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
n 50µA standby current when switched OFF
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 −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
Typical Application
SIMPLE SWITCHER®is a registered trademark of National Semiconductor Corporation.
DS100914-3
April 2000
LM2676 SIMPLE SWITCHER High Efficiency 3A Step-Down Voltage Regulator
© 2000 National Semiconductor Corporation DS100914 www.national.com
Connection Diagram and Ordering Information
TO-263 Package
Top View
DS100914-1
Order Number
LM2676S-3.3, LM2676S-5.0,
LM2676S-12 or LM2676S-ADJ
See NSC Package Number TS7B
TO-220 Package
Top View
DS100914-2
Order Number
LM2676T-3.3, LM2676T-5.0,
LM2676T-12 or LM2676T-ADJ
See NSC Package Number TA07B
LM2676
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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
IN
Boost Pin Voltage VSW+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
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=TJ
= 25˚C.
LM2676-3.3
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
OUT
Output Voltage VIN= 8V to 40V, 100mA ≤ I
OUT
≤ 3A 3.3 3.234/3.201 3.366/3.399 V
η Efficiency V
IN
= 12V, I
LOAD
=3A 86 %
LM2676-5.0
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
OUT
Output Voltage VIN= 8V to 40V, 100mA ≤ I
OUT
≤ 3A 5.0 4.900/4.850 5.100/5.150 V
η Efficiency V
IN
= 12V, I
LOAD
=3A 88 %
LM2676-12
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
OUT
Output Voltage VIN= 15V to 40V, 100mA ≤ I
OUT
≤ 3A 12 11.76/11.64 12.24/12.36 V
η Efficiency V
IN
= 24V, I
LOAD
=3A 94 %
LM2676-ADJ
Symbol Parameter Conditions Typ Min Max Units
(Note 3) (Note 4) (Note 4)
V
FB
Feedback
Voltage
VIN= 8V to 40V, 100mA ≤ I
OUT
≤ 3A
V
OUT
Programmed for 5V
1.21 1.186/1.174 1.234/1.246 V
η Efficiency V
IN
= 12V, I
LOAD
=3A 88 %
LM2676
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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 TA=TJ= 25˚C. Unless otherwise specified VIN=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
1
6
200
15
µA
mA
R
DS(ON)
Switch
On-Resistance
I
SWITCH
= 3A 0.15 0.17/0.29 Ω
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 5)
θ
JA
T Package, Junction to Ambient 45
(Note 6)
θ
JC
T Package, Junction to Case 2
θ
JA
S Package, Junction to Ambient 56 ˚C/W
(Note 7)
θ
JA
S Package, Junction to Ambient 35
(Note 8)
θ
JA
S Package, Junction to Ambient 26
(Note 9)
θ
JC
S Package, Junction to Case 2 ++
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
A=TJ
= 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
A=TJ
= 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
1
⁄2inch 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
1
⁄2inch leads soldered to a PC board
containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.
LM2676
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(Continued)
Note 7: 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 8: 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 9: 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.Additionalcopper area will reduce thermal resistance further.See the thermal model in Switchers Made
Simple
®
software.
LM2676
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Typical Performance Characteristics
Normalized
Output Voltage
DS100914-9
Line Regulation
DS100914-10
Efficiency vs Input Voltage
DS100914-11
Efficiency vs I
LOAD
DS100914-12
Switch Current Limit
DS100914-4
Operating Quiescent Current
DS100914-5
Standby Quiescent Current
DS100914-40
ON/OFF Threshold Voltage
DS100914-13
ON/OFF Pin Current (Sourcing)
DS100914-14
Switching Frequency
DS100914-15
Feedback Pin Bias Current
DS100914-16
LM2676
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Block Diagram
DS100914-6
* Active Inductor Patent Number 5,514,947
†
Active Capacitor Patent Number 5,382,918
LM2676
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