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LM2621
Low Input Voltage, Step-Up DC-DC Converter
LM2621 Low Input Voltage, Step-Up DC-DC Converter
February 2000
General Description
The LM2621 is a high efficiency, step-up DC-DC switching
regulator for battery-powered and low input voltage systems.
It accepts an input voltage between 1.2V and 14V and converts it into a regulated output voltage. The output voltage
can be adjusted between 1.24V and 14V. It has an internal
0.17Ω N-Channel MOSFET power switch. Efficiencies up to
90% are achievable using the LM2621.
The high switching frequency (adjustable up to 2MHz) of the
LM2621 allows for tiny surface mount inductors and capacitors. Because of the unique constant-duty-cycle gated oscillator topology very high efficiencies are realized over a wide
load range. The supply current is reduced to 80µA because
of the BiCMOS process technology. In the shutdown mode,
the supply current is less than 2.5µA.
The LM2621 is available in a Mini-SO-8 package.This package uses half the board area of a standard 8-pin SO and has
a height of just 1.09 mm.
Features
n Small Mini-SO8 Package (Half the Footprint of Standard
8-Pin SO Package)
n 1.09 mm Package Height
n Up to 2 MHz Switching Frequency
n 1.2V to 14V Input Voltage
n 1.24V - 14V Adjustable Output Voltage
n Up to 1A Load Current
n 0.17 Ω Internal MOSFET
n Up to 90% Regulator Efficiency
n 80 µA Typical Operating Current
<
n
2.5µA Guaranteed Supply Current In Shutdown
Applications
n PDAs, Cellular Phones
n 2-Cell and 3-Cell Battery-Operated Equipment
n PCMCIA Cards, Memory Cards
n Flash Memory Programming
n TFT/LCD Applications
n 3.3V to 5.0V Conversion
n GPS Devices
n Two-Way Pagers
n Palmtop Computers
n Hand-Held Instruments
Typical Application Circuit
DS100934-12
© 2000 National Semiconductor Corporation DS100934 www.national.com
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Connection Diagram
LM2621
Ordering Information
Mini SO-8 (MM) Package
DS100934-18
Top View
Order Number Package Type
LM2621MMX Mini SO-8 MUA08A S06A 3000 Units on Tape and Reel
LM2621MM Mini SO-8 MUA08A S06A 1000 Units on Tape and Reel
NSC Package
Drawing
Package
Marking
Supplied As
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LM2621
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Power Dissipation (T
=25˚C)
A
500mW
(Note 2)
ESD Rating (Note 3) 2kV
Distributors for availability and specifications.
SW Pin Voltage −0.5 V to 14.5V
BOOT, V
, EN and FB Pins −0.5V to 10V
DD
FREQ Pin 100µA
θ
(Note 2) 240˚C/W
JA
T
(Note 2) 150˚C
Jmax
Storage Temperature Range −65˚C to +150˚C
Operating Conditions (Note 1)
V
Pin 2.5V to 5V
DD
FB, EN Pins 0 to V
BOOT Pin 0 to 10V
Ambient Temperature (T
) −40˚C to +85˚C
A
DD
Lead Temp. (Soldering, 5 sec) 260˚C
Electrical Characteristics
Limits in standard typeface are for TJ= 25˚C, and limits in boldface type apply over the full operating temperature range of
−40˚C to +85˚C. Unless otherwise specified: VDD=V
Symbol Parameter Condition Typ Min Max Units
V
IN_ST
Minimum Start-Up Supply
I
LOAD
Voltage (Note 4)
V
IN_OP
Minimum Operating Supply
I
LOAD
Voltage (once started)
V
FB
V
OUT_MAX
V
HYST
η Efficiency V
FB Pin Voltage 1.24 1.2028 1.2772 V
Maximum Output Voltage 14 V
Hysteresis Voltage (Note 7) 30 45 mV
IN
= 500mA
V
IN
= 200mA
D Switch Duty Cycle 70 60 80 %
I
DD
Operating Quiescent Current
FB Pin>1.3V; EN Pin at V
(Note 6)
I
SD
I
CL
R
DS_ON
Shutdown Quiescent Current
(Note 7)
VDD, BOOT and SW Pins at
5.0V; EN Pin
Switch Peak Current Limit 2.85 A
MOSFET Switch On
Resistance
Enable Section
V
EN_LO
V
EN_HI
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
outside of its rated operating conditions.
Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
bient thermal resistance), and T
given in the Absolute Maximum Ratings, whichever is lower.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. For Pin 8 (SW) the ESD rating is 1.5 kV.
Note 4: Output in regulation, V
Note 5: This is the hysteresis value of the internal comparator used for the gated-oscillator control scheme.
Note 6: This is the current into the V
Note 7: This is the total current into pins V
Note 8: When the EN pin is below V
EN Pin Voltage Low (Note 8) 0.15V
EN Pin Voltage High (Note 8) 0.7V
(ambient temperature). The maximum allowable power dissipation at any temperature is P
A
OUT=VOUT (NOMINAL
pin.
DD
EN_LO
)±5%
, BOOT, SW and FREQ.
DD
, the regulator is shut down; when it is above V
= 3.3V.
OUT
= 0mA 1.1 1.2 V
= 0mA 0.65 V
= 3.6V; V
= 2.5V; V
OUT
OUT
= 5V; I
= 3.3V; I
LOAD
LOAD
DD
87
87
80 110 µA
0.01 2.5 µA
<
200mV
0.17 Ω
DD
DD
(maximum junction temperature), θJA(junction to am-
jmax
, the regulator is operating.
EN_HI
dmax
=(T
)/ θJAor the number
jmax-TA
%
V
V
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