LM3671
2MHz , 600mA Step-Down DC-DC Converter in SOT23-5
General Description
The LM3671 step-down DC-DC converter is optimized for
powering ultra-low voltage circuits from a single Li-Ion cell or
3 cell NiMH/NiCd batteries. It provides up to 600mA load
current, over an input voltage range from 2.8V to 5.5V. There
are several different fixed voltage output options available as
well as an adjustable output voltage version.
The device offers superior features and performance for
mobile phones and similar portable applications with com-
plex power management systems. Automatic intelligent
switching between PWM low-noise and PFM low-current
mode offers improved system control. During full-power op-
eration, a fixed-frequency 2 MHz (typ). PWM mode drives
loads from
70 mA to 600 mA max. Hysteretic PFM mode
extends the battery life through reduction of the quiescent
current to 16 A (typ) at light loads and system standby.
Internal synchronous rectification provides high efficiency. In
shutdown mode (Enable pin pulled low) the device turns off
and reduces battery consumption to 0.01 A (typ).
The LM3671 is available in a SOT23-5 package with Pb and
No Pb (Lead free) versions. A high switching frequency - 2
MHz (typ) - allows use of tiny surface-mount components.
Only three external surface-mount components, an inductor
and two ceramic capacitors, are required.
Features
n
16 A typical quiescent current
n
600 mA maximum load capability
n
2 MHz PWM fixed switching frequency (typ)
n
Automatic PFM/PWM mode switching
n
Available in fixed output voltages and adjustable version
n
SOT23-5 package
n
Internal synchronous rectification for high efficiency
n
Internal soft start
n
0.01 A typical shutdown current
n
Operates from a single Li-Ion cell or 3 cell NiMH/NiCd
batteries
n
Only three tiny surface-mount external components
required (one inductor, two ceramic capacitors)
n
Current overload and Thermal shutdown protection
Applications
n
Mobile phones
n
PDAs
n
MP3 players
n
W-LAN
n
Portable instruments
n
Digital still cameras
n
Portable Hard disk drives
Typical Application Circuits
20108401
FIGURE 1. Typical Application Circuit
November 2004
LM3671
2MHz
,
600mA
Step-Down
DC-DC
Converter
in
SOT23-5
2004 National Semiconductor Corporation
DS201084
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Typical Application Circuits
(Continued)
Connection Diagram and Package Mark Information
Pin Description
Pin #
Name
Description
1
V
IN
Power supply input. Connect to the input filter capacitor (Figure 1).
2
GND
Ground pin.
3
EN
Enable pin. The device is in shutdown mode when voltage to this pin is
<
0.4V and
enabled when
>
1.0V. Do not leave this pin floating.
4
FB
Feedback analog input. Connect directly to the output filter capacitor for fixed voltage
versions. For adjustable version external resistor dividers are required. The internal
resistor dividers are disabled for the adjustable version.
5
SW
Switching node connection to the internal PFET switch and NFET synchronous
rectifier.
20108431
FIGURE 2. Typical Application Circuit for ADJ version
SOT23-5 Package
NS Package Number MF05A
20108402
Note: The actual physical placement of the package marking will vary from part to part.
FIGURE 3. Top View
LM3671
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Ordering Information
Voltage Option
Order Number
Spec
Package Marking
Supplied As
ADJ*
LM3671MF-ADJ
NOPB
SBTB
1000 units, Tape-and-Reel
LM3671MFX-ADJ
NOPB
3000 units, Tape-and-Reel
LM3671MF-ADJ
1000 units, Tape-and-Reel
LM3671MFX-ADJ
3000 units, Tape-and-Reel
1.2*
LM3671MF-1.2
NOPB
SBPB
1000 units, Tape-and-Reel
LM3671MFX-1.2
NOPB
3000 units, Tape-and-Reel
LM3671MF-1.2
1000 units, Tape-and-Reel
LM3671MFX-1.2
3000 units, Tape-and-Reel
1.25*
LM3671MF-1.25
NOPB
SDRB
1000 units, Tape-and-Reel
LM3671MFX-1.25
NOPB
3000 units, Tape-and-Reel
LM3671MF-1.25
1000 units, Tape-and-Reel
LM3671MFX-1.25
3000 units, Tape-and-Reel
1.375
LM3671MF-1.375
NOPB
SEDB
1000 units, Tape-and-Reel
LM3671MFX-1.375
NOPB
3000 units, Tape-and-Reel
LM3671MF-1.375
1000 units, Tape-and-Reel
LM3671MFX-1.375
3000 units, Tape-and-Reel
1.5
LM3671MF-1.5
NOPB
SBRB
1000 units, Tape-and-Reel
LM3671MFX-1.5
NOPB
3000 units, Tape-and-Reel
LM3671MF-1.5
1000 units, Tape-and-Reel
LM3671MFX-1.5
3000 units, Tape-and-Reel
1.6
LM3671MF-1.6
NOPB
SDUB
1000 units, Tape-and-Reel
LM3671MFX-1.6
NOPB
3000 units, Tape-and-Reel
LM3671MF-1.6
1000 units, Tape-and-Reel
LM3671MFX-1.6
3000 units, Tape-and-Reel
1.8
LM3671MF-1.8
NOPB
SBSB
1000 units, Tape-and-Reel
LM3671MFX-1.8
NOPB
3000 units, Tape-and-Reel
LM3671MF-1.8
1000 units, Tape-and-Reel
LM3671MFX-1.8
3000 units, Tape-and-Reel
1.875
LM3671MF-1.875
NOPB
SDVB
1000 units, Tape-and-Reel
LM3671MFX-1.875
NOPB
3000 units, Tape-and-Reel
LM3671MF-1.875
1000 units, Tape-and-Reel
LM3671MFX-1.875
3000 units, Tape-and-Reel
* ADJ, 1.2 and 1.25V to be released soon.Samples available now.
LM3671
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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.
V
IN
Pin: Voltage to GND
-0.2V to 6.0V
FB, SW, EN Pin:
(GND-0.2V) to
(V
IN
+ 0.2V)
Continuous Power Dissipation
(Note 3)
Internally Limited
Junction Temperature (T
J-MAX
)
+125C
Storage Temperature Range
-65C to +150C
Maximum Lead Temperature
(Soldering, 10 sec.)
260C
ESD Rating (Note 4)
Human Body Model:
V
IN
,GND,SW,FB
2.0 kV
Human Body Model: EN
500V
Machine Model: All Pins
200V
Operating Ratings
(Notes 1, 2)
Input Voltage Range
2.8V to 5.5V
Recommended Load Current
0mA to 600 mA
Junction Temperature (T
J
) Range
-25C to +125C
Ambient Temperature (T
A
) Range (Note 5)
-25C to +85C
Thermal Properties
Junction-to-Ambient
Thermal Resistance (
JA
)
(SOT23-5) (Note 6)
250C/W
Electrical Characteristics
(Notes 2, 9, 10) Limits in standard typeface are for T
J
= 25C. Limits in boldface
type apply over the full operating junction temperature range (-25C
T
J
+125C). Unless otherwise noted, specifications
apply to the LM3671 Typical Application Circuit (Figure. 1) with V
IN
= EN = 3.6V, V
OUT
= 1.5V
Symbol
Parameter
Condition
Min
Typ
Max
Units
V
IN
Input Voltage Range
(Note 11)
2.8
5.5
V
V
OUT
Output Voltage
I
O
= 0 mA
-2
+4
%
I
O
= 100 mA
-4
+4
%
Line Regulation
2.8V
V
IN
5.5V
I
O
= 10 mA
0.045
%/V
Load Regulation
100 mA
I
O
300 mA
V
IN
= 3.6V
0.0031
%/mA
V
REF
Internal Reference Voltage
(Note 7)
0.5
V
I
SHDN
Shutdown Supply Current
EN = 0V
0.01
1
A
I
Q_PFM
DC Bias Current into V
IN
No load, device is not switching (FB
forced higher than programmed output
voltage)
16
35
A
R
DSON (P)
Pin-Pin Resistance for PFET
V
IN
= V
GS
= 3.6V
380
500
m
R
DSON (N)
Pin-Pin Resistance for NFET
V
IN
= V
GS
= 3.6V
250
400
m
I
LIM
Switch Peak Current Limit
Open Loop (Note 8)
830
1020
1150
mA
V
IH
Logic High Input
1.0
V
V
IL
Logic Low Input
0.4
V
I
EN
Enable (EN) Input Current
0.01
1
A
F
OSC
Internal Oscillator Frequency
PWM Mode
1.6
2
2.6
MHz
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of
the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the
Electrical Characteristics tables.
Note 2: All voltages are with respect to the potential at the GND pin.
Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at T
J
= 150C (typ.) and disengages at T
J
=
130C (typ.).
Note 4: The Human body model is a 100 pF capacitor discharged through a 1.5 k
resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin. MIL-STD-883 3015.7
Note 5: In Applications where high power dissipation and/or poor package resistance is present, the maximum ambient temperature may have to be derated.
Maximum ambient temperature (T
A-MAX
) is dependent on the maximum operating junction temperature (T
J-MAX
), the maximum power dissipation of the device in
the application (P
D-MAX
) and the junction to ambient thermal resistance of the package (
JA
) in the application, as given by the following equation:T
A-MAX
= T
J-MAX
-
(
JA
x P
D-MAX
). Refer to Dissipation rating table for P
D-MAX
values at different ambient temperatures.
Note 6: Junction to ambient thermal resistance is highly application and board layout dependent. In applications where high power dissipation exists, special care
must be given to thermal dissipation issues in board design. Value specified here 250 C/W is based on measurement results using a 2 layer, 4" x 3", 2 oz Cu board
as per JEDEC standards. The (
JA
) can be as low as 140 C/W if a 4 layer, 4" x 3", 2/1/1/2 oz. Cu board as per JEDEC standards is used.
Note 7: For the ADJ version the resistor dividers should be selected such that at the desired output voltage,the voltage at the FB pin is 0.5V.
LM3671
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Electrical Characteristics
(Notes 2, 9, 10) Limits in standard typeface are for T
J
= 25C. Limits in boldface
type apply over the full operating junction temperature range (-25C
T
J
+125C). Unless otherwise noted, specifications
apply to the LM3671 Typical Application Circuit (Figure. 1) with V
IN
= EN = 3.6V, V
OUT
= 1.5V (Continued)
Note 8: Refer to datasheet curves for closed loop data and its variation with regards to supply voltage and temperature. Electrical Characteristic table reflects open
loop data (FB=0V and current drawn from SW pin ramped up until cycle by cycle current limit is activated). Closed loop current limit is the peak inductor current
measured in the application circuit by increasing output current until output voltage drops by 10%.
Note 9: Min and Max limits are guaranteed by design, test or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
Note 10: The parameters in the electrical characteristic table are tested at V
IN
= 3.6V unless otherwise specified. For performance over the input voltage range refer
to datasheet curves.
Note 11: Input voltage range for all voltage options is 2.8V to 5.5V. The voltage range recommended (Fixed Voltage parts) for ideal applications performance with
500mA or higher output current is given below.
V
IN
= 2.8V to 4.5V for V
OUT
= 1.2V, 1.25V, 1.375V, 1.5V and 1.6V.
V
IN
= 3.0V to 4.5V for V
OUT
= 1.8V and 1.875V.
Dissipation Rating Table
JA
T
A
25C
Power Rating
T
A
= 60C
Power Rating
T
A
= 85C
Power Rating
250C/W
400mW
260mW
160mW
LM3671
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