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.
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 A (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 A (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 (.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 A 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 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 protection
Applications
n
Mobile phones
n
Hand-Held Radios
n
Personal Digital Assistants
n
Palm-top PCs
n
Portable Instruments
n
Battery Powered Devices
Typical Application
20075801
FIGURE 1. 1.8V - Fixed Output Voltage - Typical Application Circuit
December 2004
LM3670
Miniature
Step-Down
DC-DC
Converter
for
Ultra
Low
V
oltage
Circuits
2004 National Semiconductor Corporation
DS200758
www.national.com
Typical Application
(Continued)
Connection Diagram and Package Mark Information
Pin Descriptions
Pin #
Name
Description
1
V
IN
Power supply input. Connect to the input filter capacitor (Figure 1).
2
GND
Ground pin.
3
EN
Enable input.
4
FB
Feedback analog input. Connect to the output filter capacitor (Figure 1).
5
SW
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.
20075830
FIGURE 2. 1.2V - Adjustable Output Voltage - Typical Application Circuit
SOT23-5 Package
NS Package Number XXXX
20075802
Note: The actual physical placement of the package marking will vary from part to part.
FIGURE 3. Top View
LM3670
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2
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
EN Pin: Voltage to GND
-0.2V to 6.0V
FB, SW Pin:
(GND-0.2V) to
(V
IN
+ 0.2V)
Junction Temperature (T
J-MAX
)
-45C to +125C
Storage Temperature Range
-45C to +150C
Maximum Lead Temperature
(Soldering, 10 sec.)
260C
ESD Rating (Note 3)
Human Body Model:
VIN,SW,FB,GND
2.0kV
EN
500V
Machine Model:
200V
Operating Ratings
(Notes 1, 2)
Input Voltage Range
2.5V to 5.5V
Recommended Load Current
0A to 350 mA
Junction Temperature (T
J
) Range
-40C to +125C
Ambient Temperature (T
A
) Range
-40C to +85C
Thermal Properties
Junction-to-Ambient
Thermal Resistance (
JA
)
(SOT23-5)
250C/W
Electrical Characteristics
Limits in standard typeface are for T
J
= 25C. Limits in boldface type apply over
the full operating junction temperature range (-40C
T
J
+125C). Unless otherwise noted V
IN
= 3.6V, V
OUT
= 1.8V,
I
O
=150mA, EN=V
IN
Symbol
Parameter
Condition
Min
Typ
Max
Units
V
IN
Input Voltage Range
2.5
5.5
V
V
OUT
Fixed Output Voltage
2.5V
V
IN
5.5V
I
O
= 10 mA
-1.5
+3.0
%
2.5V
V
IN
5.5V
0 mA
I
O
350 mA
-4.5
+3.0
%
Adjustable Output Voltage
2.5V
V
IN
5.5V
I
O
= 10 mA
-1.0
+2.5
%
2.5V
V
IN
5.5V
0 mA
I
O
350 mA
-4.0
+2.5
%
Line Regulation
2.5V
V
IN
5.5V
I
O
= 10 mA
0.26
%/V
Load Regulation
150 mA
I
O
350 mA
0.0014
%/mA
V
REF
Internal Reference Voltage
0.5
V
I
Q_SHDN
Shutdown Supply Current
T
A
=85
o
C
0.1
1
A
I
Q_PFM
DC Bias Current into V
IN
No load, device is not switching
(V
OUT
forced higher than
programmed output voltage)
15
30
A
V
UVLO
Minimum V
IN
below which
V
OUT
will be disabled
2.4
V
R
DSON (P)
Pin-Pin Resistance for PFET
V
IN
=V
GS
=3.6V
360
690
m
R
DSON (N)
Pin-Pin Resistance for NFET
V
IN
=V
GS
=3.6V
250
660
m
I
LKG (P)
P Channel Leakage Current
V
DS
=5.5V
0.1
1
A
I
LKG (N)
N Channel Leakage Current
V
DS
=5.5V
0.1
1.5
A
I
LIM
Switch Peak Current Limit
400
620
750
mA
Efficiency
(V
IN
= 3.6V, V
OUT
= 1.8V)
I
LOAD
= 1 mA
91
%
I
LOAD
= 10 mA
94
I
LOAD
= 100 mA
94
I
LOAD
= 200 mA
94
I
LOAD
= 300 mA
92
I
LOAD
= 350 mA
90
LM3670
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4
Electrical Characteristics
Limits in standard typeface are for T
J
= 25C. Limits in boldface type apply over
the full operating junction temperature range (-40C
T
J
+125C). Unless otherwise noted V
IN
= 3.6V, V
OUT
= 1.8V,
I
O
=150mA, EN=V
IN
(Continued)
Symbol
Parameter
Condition
Min
Typ
Max
Units
V
IH
Logic High Input
1.3
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
550
1000
1300
kHz
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: 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
LM3670
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