National Semiconductor LM2678 Technical data
LM2678
SIMPLE SWITCHER
Voltage Regulator
®
High Efficiency 5A Step-Down
LM2678 SIMPLE SWITCHER High Efficiency 5A Step-Down Voltage Regulator
September 1998
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 characteristics. High efficiency (
low ON-resistance DMOS powerswitch. 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 LM2678 are available from several
manufacturers to greatly simplify the design process.
The LM2678 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
ance. The clock frequency iscontrolled to within a
erance.
>
90%) is obtained through the use of a
±
2%toler-
±
11%tol-
Typical Application
Features
n Efficiency up to 92
n Simple and easy to design with (using off-the-shelf
external components)
n 120 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
DS100886-3
SIMPLE SWITCHER®is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS100886 www.national.com
Connection Diagram and Ordering Information
TO-263 Package
Top View
Order Number
LM2678S-3.3, LM2678S-5.0,
LM2678S-12 or LM2678S-ADJ
See NSC Package Number TS7B
TO-220 Package
Top View
Order Number
LM2678T-3.3, LM2678T-5.0,
LM2678T-12 or LM2678T-ADJ
See NSC Package Number TA07B
DS100886-1
DS100886-2
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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
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
IN
Junction Temperature Range (T
Thermal Resistance (θ
Thermal Resistance (θ
JA
JC
) −40˚C to 125˚C
J
) 30˚C/W
) 2˚C/W
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.
A
J
LM2678-3.3
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
Output Voltage V
OUT
η Efficiency V
=
8V to 40V, 100mA ≤ I
IN
=
12V, I
IN
LOAD
≤ 5A 3.3 3.234/3.201 3.366/3.399 V
=
OUT
5A 82
%
LM2678-5.0
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
Output Voltage V
OUT
η Efficiency V
=
8V to 40V, 100mA ≤ I
IN
=
12V, I
IN
LOAD
≤ 5A 5.0 4.900/4.850 5.100/5.150 V
=
OUT
5A 84
%
LM2678-12
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
Output Voltage V
OUT
η Efficiency V
=
15V to 40V, 100mA ≤ I
IN
=
24V, I
IN
LOAD
≤ 5A 12 11.76/11.64 12.24/12.36 V
=
OUT
5A 92
%
LM2678-ADJ
Symbol Parameter Conditions Typ Min Max Units
(Note 3) (Note 4) (Note 4)
V
Feedback
FB
Voltage
η Efficiency V
=
V
8V to 40V, 100mA ≤ I
IN
Programmed for 5V
V
OUT
=
12V, I
IN
LOAD
≤ 5A
OUT
=
5A 84
1.21 1.186/1.174 1.234/1.246 V
%
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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
Adjustable versions and V
=
24V for the 12V version.
IN
Symbol Parameter Conditions Typ Min Max Units
DEVICE PARAMETERS
I
Q
Quiescent
Current V
FEEDBACK
=
For 3.3V, 5.0V, and ADJ Versions
V
FEEDBACK
=
For 12V Versions
I
STBY
Standby
Quiescent
ON/OFF Pin=0V
Current
I
CL
I
L
R
f
O
Current Limit 7 6.1/5.75 8.3/8.75 A
=
40V, ON/OFF Pin=0V
V
IN
=
V
SWITCH
V
SWITCH
I
SWITCH
0V
=
−1V
=
5A 0.12 0.14/0.225 Ω
Measured at Switch Pin 260 225 280 kHz
DS(ON)
Output
Leakage
Current
Switch
On-Resistance
Oscillator
Frequency
D Duty Cycle Maximum Duty Cycle 91
Minimum Duty Cycle 0
I
V
BIAS
ON/OFF
Feedback Bias
Current
ON/OFF
Threshold
V
FEEDBACK
ADJ Version Only
=
Voltage
I
ON/OFF
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
ods. All limits are used to calculateAverage Outgoing Quality Level (AOQL).
ON/OFF Input
Current
ON/OFF Input=0V
=
=
T
25˚C and represent the most likely norm.
A
J
=
=
T
25˚C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC) meth-
A
J
=
=
T
25˚C. Unless otherwise specified V
A
J
=
12V for the 3.3V, 5V and
IN
8V 4.2 6 mA
15V
50 100/150 µA
1
6
200
15
µA
mA
%
%
1.3V
85 nA
1.4 0.8 2.0 V
20 45 µA
%
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Typical Performance Characteristics
Normalized
Output Voltage
Efficiency vs I
LOAD
Standby Quiescent Current
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Line Regulation
Switch Current Limit
ON/OFF Threshold Voltage
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Efficiency vs Input Voltage
DS100886-11
Operating Quiescent Current
DS100886-5
ON/OFF Pin Current (Sourcing)
Switching Frequency
DS100886-40
DS100886-15
Feedback Pin Bias Current
DS100886-13
DS100886-16
DS100886-14
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Block Diagram
* Active Inductor Patent Number 5,514,947
†
Active Capacitor Patent Number 5,382,918
DS100886-6
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Typical Performance Characteristics
Continuous Mode Switching Waveforms
L=10 µH, C
A: VSWPin Voltage, 10 V/div.
B: Inductor Current, 2 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
OUT
=
V
20V, V
IN
OUT
=
400 µF, C
=
5V, I
=
LOAD
ESR=13 mΩ
OUT
DS100886-17
Horizontal Time Base: 1 µs/div
Load Transient Response for Continuous Mode
L=10 µH, C
V
OUT
IN
=
20V, V
=
400 µF, C
OUT
=
5V
ESR=13 mΩ
OUT
5A
Discontinuous Mode Switching Waveforms
=
V
20V, V
IN
L=10 µH, C
A: VSWPin Voltage, 10 V/div.
B: Inductor Current, 1 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
OUT
OUT
=
400 µF, C
=
5V, I
=
LOAD
ESR=13 mΩ
OUT
DS100886-18
500 mA
Horizontal Time Base: 1 µs//iv
Load Transient Response for Discontinuous Mode
L=10 µH, C
=
V
20V, V
IN
=
400 µF, C
OUT
OUT
=
5V,
ESR=13 mΩ
OUT
A: Output Voltage, 100 mV//div, AC-Coupled.
B: Load Current: 500 mA to 5A Load Pulse
Horizontal Time Base: 100 µs/div
DS100886-19
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 200 mA to 3A Load Pulse
Horizontal Time Base: 200 µs/div
DS100886-20
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