LM3673 Datasheet PDF - National Semiconductor


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LM3673
National Semiconductor

Part Number LM3673
Description step-down DC-DC converter
Page 20 Pages

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November 2006
LM3673
2MHz, 350mA Step-Down DC-DC Converter
General Description
The LM3673 step-down DC-DC converter is optimized for
powering low voltage circuits from a single Li-Ion cell battery
and input voltage rails from 2.7V to 5.5V. It provides up to
350mA load current, over the entire input voltage range.
There are several different fixed voltage output options avail-
able as well as an adjustable output voltage version ranging
from 1.1V to 3.3V.
The device offers superior features and performance for mo-
bile phones and similar portable systems. The LM3673 uses
intelligent automatic switching between PWM and PFM for
better efficiency. During PWM mode, the device operates at
a fixed-frequency of 2 MHz (typ). Hysteretic PFM mode ex-
tends the battery life by reducing the quiescent current to 16
µA (typ) during light load and standby operation. Internal syn-
chronous rectification provides high efficiency during PWM
mode operation. In shutdown mode, the device turns off and
reduces battery consumption to 0.01 µA (typ).
The LM3673 is available in a tiny 5-bump MicroSMD package
in leaded (PB) and lead-free (NO PB) versions. A high switch-
ing frequency of 2 MHz (typ) allows the use of three tiny
surface-mount components, an inductor and two ceramic ca-
pacitors.
Features
16 µA typical quiescent current
350 mA maximum load capability
2 MHz PWM fixed switching frequency (typ)
Automatic PFM/PWM mode switching
Available in fixed and adjustable output voltages
5-bump MicroSMD package
Internal synchronous rectification for high efficiency
Internal soft start
0.01 µA typical shutdown current
Operates from a single Li-Ion cell battery
Only three tiny surface-mount external components
required (one inductor, two ceramic capacitors)
Current overload and Thermal shutdown protection
Applications
Mobile phones
PDAs
MP3 players
W-LAN
Portable instruments
Digital still cameras
Portable Hard disk drives
Typical Application Circuits
FIGURE 1. Typical Application Circuit
20183301
© 2006 National Semiconductor Corporation 201833
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20183331
FIGURE 2. Typical Application Circuit for ADJ version
Connection Diagram and Package Mark Information
20183344
FIGURE 3. 5-Bump MicroSMD Package NS Package Number TLA05CBA
Pin Descriptions (5-Bump MicroSMD)
Pin #
A1
A3
C1
C3
B2
Name
VIN
GND
EN
FB
SW
Description
Power supply input. Connect to the input filter capacitor (Figure 1).
Ground pin.
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.
Feedback analog input. Connect directly to the output filter capacitor for fixed voltage
versions. For adjustable version external resistor dividers are required (Figure 2). The
internal resistor dividers are disabled for the adjustable version.
Switching node connection to the internal PFET switch and NFET synchronous rectifier.
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Ordering Information (5-Bump MicroSMD)
Voltage Option
Order Number
ADJ LM3673TL-ADJ
LM3673TLX-ADJ
LM3673TL-ADJ
LM3673TLX-ADJ
1.2 LM3673TL-1.2
LM3673TLX-1.2
LM3673TL-1.2
LM3673TLX-1.2
1.5 LM3673TL-1.5
LM3673TLX-1.5
LM3673TL-1.5
LM3673TLX-1.5
1.8 LM3673TL-1.8
LM3673TLX-1.8
LM3673TL-1.8
LM3673TLX-1.8
1.875
LM3673TL-1.875
LM3673TLX-1.875
LM3673TL-1.875
LM3673TLX-1.875
Spec
NOPB
NOPB
PB
PB
NOPB
NOPB
PB
PB
NOPB
NOPB
PB
PB
NOPB
NOPB
PB
PB
NOPB
NOPB
PB
PB
Package Marking
R
1
H
F
2
Supplied As
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reell
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
250 units, Tape-and-Reel
3000 units, Tape-and-Reel
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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.
VIN Pin: Voltage to GND
FB, SW, EN Pin:
Continuous Power Dissipation
(Note 3)
Junction Temperature (TJ-MAX)
Storage Temperature Range
Maximum Lead Temperature
(Soldering, 10 sec.)
ESD Rating (Note 4)
−0.2V to 6.0V
(GND−0.2V) to
(VIN + 0.2V)
Internally Limited
+125°C
−65°C to +150°C
260°C
Human Body Model
Machine Model
2 KV
200V
Operating Ratings (Notes 1, 2)
Input Voltage Range (Note 10)
Recommended Load Current
Junction Temperature (TJ) Range
Ambient Temperature (TA) Range (Note
5)
2.7V to 5.5V
0mA to 350 mA
−30°C to +125°C
−30°C to +85°C
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA) (MicroSMD)
for 4 layer board (Note 6)
85°C/W
Electrical Characteristics (Notes 2, 8, 9) Limits in standard typeface are for TJ = 25°C. Limits in boldface type
apply over the full operating ambient temperature range (−30°C TA +85°C). Unless otherwise noted, specifications apply to
the LM3673TL with VIN = EN = 3.6V
Symbol
Parameter
Condition
Min Typ Max Units
VIN
VFB
VREF
ISHDN
IQ
Input Voltage
Feedback Voltage (Fixed / ADJ) TL
Line Regulation
Load Regulation
Internal Reference Voltage
Shutdown Supply Current
DC Bias Current into VIN
(Note 10)
PWM mode (Note 11)
2.7V VIN 5.5V
IO = 20 mA
150 mA IO 350 mA
VIN= 3.6V
2.7
-2.5
EN = 0V
No load, device is not switching (FB
forced higher than programmed
output voltage)
0.025
0.0015
0.5
0.01
16
5.5 V
+2.5 %
%/V
%/mA
V
1 µA
35 µA
RDSON (P)
RDSON (N)
ILIM
VIH
VIL
IEN
FOSC
Pin-Pin Resistance for PFET
Pin-Pin Resistance for NFET
Switch Peak Current Limit
Logic High Input
Logic Low Input
Enable (EN) Input Current
Internal Oscillator Frequency
VIN= VGS= 3.6V
VIN= VGS= 3.6V
Open Loop (Note 7)
PWM Mode (Note 11)
350 450 m
150 250 m
590 750 855 mA
1.0 V
0.4 V
0.01 1 µA
1.6 2 2.6 MHz
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device 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 TJ= 150°C (typ.) and disengages at
TJ= 130°C (typ.).
Note 4: The Human body model is a 100 pF capacitor discharged through a 1.5 kresistor 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 (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX), the maximum power dissipation of the device in
the application (PD-MAX) and the junction to ambient thermal resistance of the package (θJA) in the application, as given by the following equation:TA-MAX= TJ-MAX
− (θJAx PD-MAX). Refer to Dissipation rating table for PD-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. Specified value of 85 °C/W for µSMD is based on a 4 layer, 4" x 3", 2/1/1/2 oz. Cu board as per
JEDEC standards is used.
Note 7: 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 8: 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 9: The parameters in the electrical characteristic table are tested at VIN= 3.6V unless otherwise specified. For performance over the input voltage range
refer to datasheet curves.
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