LM3679 Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – 3MHz, 350mA Miniature Step-Down DC-DC Converter for Ultra Low Profile Applications (Height < 0.55mm)

February 5, 2008
LM3679
3MHz, 350mA Miniature Step-Down DC-DC Converter for
Ultra Low Profile Applications (Height < 0.55mm)
General Description
The LM3679 step-down DC-DC converter is optimized for
powering ultra-low voltage circuits from a single Li-Ion cell
battery and input voltage rails from 2.5V to 5.5V. It provides
up to 350mA load current, over the entire input voltage range.
The LM3679 output voltage can be configured to 1.2V, 1.5V,
or 1.8V.
The device offers superior features and performance for mo-
bile phones and similar portable applications with complex
power management systems. Automatic intelligent switching
between PWM low-noise and PFM low-current mode offers
improved system control. During PWM mode operation, the
device operates at a fixed-frequency of 3 MHz (typ). PWM
mode drives loads from ~ 80mA to 350mA max. Hysteretic
PFM mode extends the battery life by reducing the quiescent
current to 16 µA (typ) during light load and standby operation.
Internal synchronous rectification provides high efficiency. In
shutdown mode (Enable pin pulled low), the device turns off
and reduces battery consumption to 0.01 µA (typ).
The LM3679 is available in a lead-free (No PB) 5-bump micro
SMD package, 0.6mm height, and in an ultra thin 0.3mm
height UR package. Using the UR package along with specific
external components, allows for a low profile solution size with
a max height of 0.55mm. A switching frequency of 3 MHz (typ)
allows use of tiny surface-mount components. Only three ex-
ternal surface-mount components, an inductor and two ce-
ramic capacitors, are required. .
Features
■ ^{16 µA typical quiescent current}
■ ^{350 mA maximum load capability}
■ ^{3 MHz PWM fixed switching frequency (typ)}
■ ^{Automatic PFM/PWM mode switching}
■ ^{Available in 5-bump micro SMD package and UR package}
■ ^{Internal synchronous rectification for high efficiency}
■ ^{Internal soft start}
■ ^{0.01 µA typical shutdown current}
■ ^{Operates from a single Li-Ion cell battery}
■ ^{Current overload and Thermal shutdown protection}
■ ^{Three external components required for typical}
applications
■ ^{Low profile solution (0.55mm max height, includes four}
external components)
Applications
■ ^{Mobile phones}
■ ^PDAs
■ ^{MP3 players}
■ ^W-LAN
■ ^{Portable Instruments}
■ ^{Digital still cameras}
■ ^{Portable Hard disk drives}
Typical Application Circuit
Efficiency vs. Output Current
(V_OUT = 1.8V)
30016301
FIGURE 1. Typical Low Profile Application Circuit
(0.55mm max height using LM3679UR)
© 2008 National Semiconductor Corporation 300163
30016387
www.national.com