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LM3670 Miniature Step-Down DC-DC Converter for Ultra Low Voltage Circuits
January 2006
LM3670
Miniature Step-Down DC-DC Converter for Ultra Low
Voltage Circuits
General Description
The LM3670 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 350 mA load
current, over an input voltage range from 2.5V to 5.5V. There
are several different fixed voltage output options available as
well as an adjustable output voltage version (see ordering
information).
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 1 MHz (typ). PWM mode drives
loads from
∼70
mA to 350 mA max, with up to 95% efficiency.
Hysteretic PFM mode extends the battery life through reduc-
tion of the quiescent current to 15 µA (typ) during light
current loads and system standby. Internal synchronous rec-
tification provides high efficiency (90 to 95% typ. at loads
between 1 mA and 100 mA). In shutdown mode (Enable pin
pulled low) the device turns off and reduces battery con-
sumption to 0.1 µA (typ.).
The LM3670 is available in a SOT23-5 package. A high
switching frequency - 1 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
V
OUT
= Adj (0.7V min), 1.2, 1.5, 1.6, 1.8, 1.875, 2.5,
3.3V
n
2.5V
≤
V
IN
≤
5.5V
n
15 µA typical quiescent current
n
350 mA maximum load capability
n
1 MHz PWM fixed switching frequency (typ.)
n
Automatic PFM/PWM mode switching
n
Available in fixed output voltages as well as an
adjustable version
n
SOT23-5 package
n
Low drop out operation - 100% duty cycle mode
n
Internal synchronous rectification for high efficiency
n
Internal soft start
n
0.1 µA 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 protection
Applications
n
n
n
n
n
n
Mobile phones
HandHeld
PDAs
Palm-top PCs
Portable Instruments
Battery Powered Devices
Typical Application
20075801
FIGURE 1. Fixed Output Voltage - Typical Application Circuit
© 2006 National Semiconductor Corporation
DS200758
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LM3670
Typical Application
(Continued)
20075830
FIGURE 2. Adjustable Output Voltage - Typical Application Circuit
Connection Diagram and Package Mark Information
SOT23-5 Package
NS Package Number MF05A
20075802
Note:
The actual physical placement of the package marking will vary from part to part.
FIGURE 3. Top View
Pin Descriptions
Pin #
1
2
3
4
5
Name
V
IN
GND
EN
FB
SW
Description
Power supply input. Connect to the input filter capacitor (Figure
1).
Ground pin.
Enable input.
Feedback analog input. Connect to the output filter capacitor (Figure
1).
Switching node connection to the internal PFET switch and NFET synchronous
rectifier. Connect to an inductor with a saturation current rating that exceeds the
750 mA max. Switch Peak Current Limit specification.
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2
LM3670
Ordering Information
Voltage Option
(V)
3.3
Order Number
(Level 95)
LM3670MF-3.3
LM3670MFX-3.3
LM3670MF-3.3
LM3670MFX-3.3
2.5
LM3670MF-2.5
LM3670MFX-2.5
LM3670MF-2.5
LM3670MFX-2.5
1.875
LM3670MF-1.875
LM3670MFX-1.875
LM3670MF-1.875
LM3670MFX-1.875
1.8
LM3670MF-1.8
LM3670MFX-1.8
LM3670MF-1.8
LM3670MFX-1.8
1.6
LM3670MF-1.6
LM3670MFX-1.6
LM3670MF-1.6
LM3670MFX-1.6
1.5
LM3670MF-1.5
LM3670MFX-1.5
LM3670MF-1.5
LM3670MFX-1.5
1.2
LM3670MF-1.2
LM3670MFX-1.2
LM3670MF-1.2
LM3670MFX-1.2
Adjustable
LM3670MF-ADJ
LM3670MFX-ADJ
LM3670MF-ADJ
LM3670MFX-ADJ
NOPB
NOPB
SDFB
NOPB
NOPB
SCZB
NOPB
NOPB
S82B
NOPB
NOPB
SDBB
NOPB
NOPB
SDCB
NOPB
NOPB
SEFB
NOPB
NOPB
SDDB
SPEC
NOPB
NOPB
Package Marking
SDEB
Supplied As
(#/reel)
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
1000
3000
3
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LM3670
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
EN Pin: Voltage to GND
FB, SW Pin:
Junction Temperature (T
J-MAX
)
Storage Temperature Range
Maximum Lead Temperature
(Soldering, 10 sec.)
−0.2V to 6.0V
−0.2V to 6.0V
(GND−0.2V) to
(V
IN
+ 0.2V)
−45˚C to +125˚C
−45˚C to +150˚C
260˚C
ESD Rating (Note 3)
Human Body Model:
VIN, SW, FB, EN, GND
Machine Model:
2.0kV
200V
Operating Ratings
(Notes 1, 2)
Input Voltage Range
Recommended Load Current
Junction Temperature (T
J
) Range
Ambient Temperature (T
A
) Range
2.5V to 5.5V
0A to 350 mA
−40˚C to +125˚C
−40˚C to +85˚C
Thermal Properties
Junction-to-Ambient
Thermal Resistance (θ
JA
)
(SOT23-5)
250˚C/W
Electrical Characteristics
Limits in standard typeface are for T
J
= 25˚C. Limits in
boldface
type apply over
the full operating junction temperature range (−40˚C
≤
T
J
≤
+125˚C). Unless otherwise noted V
IN
= 3.6V, V
OUT
= 1.8V, I
O
=
150mA, EN = V
IN
Symbol
V
IN
V
OUT
Parameter
Input Voltage Range
Fixed Output Voltage: 1.2V
(Note 5)
2.5V
≤
V
IN
≤
5.5V
I
O
= 10 mA
2.5V
≤
V
IN
≤
5.5V
0 mA
≤
I
O
≤
150 mA
Fixed Output Voltage: 1.5V
2.5V
≤
V
IN
≤
5.5V
I
O
= 10 mA
2.5V
≤
V
IN
≤
5.5V
0 mA
≤
I
O
≤
350 mA
Fixed Output Voltage: 1.6V,
1.875V
2.5V
≤
V
IN
≤
5.5V
I
O
= 10 mA
2.5V
≤
V
IN
≤
5.5V
0 mA
≤
I
O
≤
350 mA
Fixed Output Voltage: 1.8V
2.5V
≤
V
IN
≤
5.5V
I
O
= 10 mA
2.5V
≤
V
IN
≤
5.5V
0 mA
≤
I
O
≤
350 mA
Fixed Output Voltage: 2.5V,
3.3V
3.6V
≤
V
IN
≤
5.5V
I
O
= 10 mA
3.6V
≤
V
IN
≤
5.5V
0 mA
≤
I
O
≤
350 mA
Adjustable Output Voltage
(Note 4)
2.5V
≤
V
IN
≤
5.5V
I
O
= 10 mA
2.5V
≤
V
IN
≤
5.5V
0 mA
≤
I
O
≤
150 mA
Line_reg
Load_reg
V
REF
I
Q_SHDN
Line Regulation
Load Regulation
Internal Reference Voltage
Shutdown Supply Current
T
A
=85 C
o
Condition
Min
2.5
-2.0
-4.5
-2.5
-5.0
-2.5
-5.5
-1.5
−4.5
-2.0
-6.0
-2.5
-4.0
Typ
Max
5.5
+4.0
+4.0
+4.0
+4.0
+4.0
+4.0
+3.0
+3.0
+4.0
+4.0
+4.5
+4.5
Units
V
%
%
%
%
%
%
2.5V
≤
V
IN
≤
5.5V
I
O
= 10 mA
150 mA
≤
I
O
≤
350 mA
0.26
0.0014
0.5
0.1
1
%/V
%/mA
V
µA
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