
July 2007
LM3668
1A, High Efficiency Dual Mode Single Inductor Buck-Boost
DC/DC Converter
General Description
The LM3668 is a synchornous buck-boost DC-DC converter
optimized for powering low voltage circuits from a Li-Ion bat-
tery and input voltage rails between 2.5V and 5.5V. It has the
capability to support up to 1A output current over a output
voltage range of 2.8V/3.3V. The LM3668 regulates the output
voltage over the complete input voltage range by automati-
cally switching between buck or boost modes depending on
the input voltage.
The LM3668 has 2 N-channel MOSFETS and 2 P-channel
MOSFETS arranged in a topology that provides continuous
operation through the buck and boost operating modes.
There is a MODE pin that allows the user to choose between
an intelligent automatic PFM-PWM mode operation and
forced PWM operation. During PWM mode, a fixed-frequency
2.2MHz (typ.) is used. PWM mode drives load up to 1A. Hys-
teretic PFM mode extends the battery life through reduction
of the quiescent current to 45A (typ.) at light loads during
system standby. Internal synchronous rectification provides
high efficiency. In shutdown mode (Enable pin pulled low) the
device turns off and reduces battery consumption to 0.01A
(typ.).
The LM3668 is available in a 12-pin LLP package. A high
switching frequency of 2.2MHz (typ.) allows the use of tiny
surface-mount components including a 2.2H inductor, a
10F input capacitor, and a 22F output capacitor.
Features
■ 45A typical quiescent current
■ 1A maximum load current for V
IN = 2.8V to 5.5V
■ 800mA maximum load current for V
IN = 2.7V
■ 600mA maximum load current for V
IN = 2.5V
■ 2.2 MHz PWM fixed switching frequency (typ.)
■ Automatic PFM-PWM Mode or Forced PWM Mode
■ Wide Input Voltage Range: 2.5V to 5.5V
■ Output Voltage Range: 2.8V/3.3V
■ Internal synchronous rectification for high efficiency
■ Internal soft start: 600s Maximum start-up time
■ 0.01A typical shutdown current
■ Current overload and Thermal shutdown protection
■ Frequency Sync Pin: 1.6Mhz to 2.7MHz
Applications
■ Handset Peripherals
■ MP3 players
■ Pre-Regulation for linear regulators
■ PDAs
■ Portable Hard Disk Drives
■ WiMax Modems
Typical Applications
20191401
Typical Application Circuit
20191425
Efficiency at 3.3V Output
2007 National Semiconductor Corporation
201914
www.national.com
LM3668
1A,
High
Efficiency
Dual
Mode
Single
Inductor
Buck-Boost
DC/DC
Converter