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PDF LM2621MMX Data sheet ( Hoja de datos )
| Número de pieza | LM2621MMX | |
| Descripción | Low Input Voltage/ Step-Up DC-DC Converter | |
| Fabricantes | National Semiconductor | |
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February 2000
LM2621
Low Input Voltage, Step-Up DC-DC Converter
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 con-
verts 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 capaci-
tors. Because of the unique constant-duty-cycle gated oscil-
lator 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 pack-
age 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
© 2000 National Semiconductor Corporation DS100934
DS100934-12
www.national.com
1 page  
Typical Performance Characteristics (Continued)
Peak Inductor Current vs
Load Current
Maximum Load Current vs
Input Voltage
DS100934-10
Detailed Description
OPERATING PRINCIPLE
The LM2621 is designed to provide step-up DC-DC voltage
regulation in battery-powered and low-input voltage sys-
tems. It combines a step-up switching regulator, N-channel
power MOSFET, built-in current limit, thermal limit, and volt-
age reference in a single 8-pin MSOP package . The switch-
ing DC-DC regulator boosts an input voltage between 1.2V
and 14V to a regulated output voltage between 1.24V and
14V. The LM2621 starts from a low 1.1V input and remains
operational down to 0.65V.
DS100934-11
This device is optimized for use in cellular phones and other
applications requiring a small size, low profile, as well as low
quiescent current for maximum battery life during stand-by
and shutdown. A high-efficiency gated-oscillator topology of-
fers an output of up to 1A.
Additional features include a built-in peak switch current
limit, and thermal protection circuitry.
FIGURE 1. Functional Diagram
DS100934-14
GATED OSCILLATOR CONTROL SCHEME
A unique gated oscillator control scheme enables the
LM2621 to have an ultra-low quiescent current and provides
a high efficiency over a wide load range. The switching fre-
quency of the internal oscillator is programmable using an
external resistor and can be set between 300 kHz and 2
MHz.
5 www.national.com
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| PDF Descargar | [ Datasheet LM2621MMX.PDF ] | |
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