LM2608
400mA Sub-miniature, High Efficiency, Programmable
DC-DC Converter with Linear Mode
General Description
The LM2608 step-down DC-DC converter is optimized for
powering ultra-low voltage circuits from a single Lithium-Ion
cell. It provides up to 400mA over an input voltage range of
2.8V to 5.5V. Operating from a 1.35V reference, this device
provides
pin-selectable
output
voltages
of
1.3V/1.5V
(300mA) for low voltage version or 1.5V/1.8V (400mA) for
high voltage version. This allows adjustment for DSP or CPU
voltage options, as well as dynamic output voltage switching
for reduced power consumption. Internal synchronous recti-
fication provides high efficiency.
The LM2608 offers superior features and performance for
mobile phones and similar portable applications with com-
plex power management systems. Pin-selectable PWM low-
noise and linear micropower modes offer improved system
control for maximizing battery life. During full power opera-
tion, fixed-frequency PWM mode reduces interference in RF
and data acquisition applications by minimizing noise har-
monics at sensitive IF and sampling frequencies. A SYNC
input allows synchronizing the switching frequency in a
range of 500kHz to 1MHz to avoid noise from intermodula-
tion with system frequencies. Linear operation reduces qui-
escent current to 20μA (typ) during system standby for ex-
tended battery life. It provides up to 3 mA in the linear mode.
Shutdown reduces battery consumption to 0.02μA (typ.).
The LM2608 is available in a 10 pin Micro SMD package.
This package uses National’s wafer level chip-scale Micro
SMD technology and offers the smallest possible size.Ahigh
switching frequency (600KHz) allows use of tiny surface-
mount components. Only four small external surface-mount
components, an inductor and three ceramic capacitors are
required. Pin selectable output voltage eliminates the need
for bulky external feedback resistors.
Key Specifications
n
Operates from a single LiION cell (2.8V to 5.5V)
n
Pin selectable output voltage (1.5V/1.8V or 1.3V/1.5V
versions), without external feedback resistors
n
400mA maximum load capability
n
±
1% PWM mode DC output voltage precision
(Excluding external reference tolerance)
n
5mV typ PWM mode output voltage ripple
n
20 μA typ quiescent current (Linear Mode)
n
0.02μA typ shutdown mode current
n
Internal synchronous rectification for high efficiency
(91% at 2.8V
IN
, 1.8V
OUT
)
n
600kHz PWM mode switching frequency
n
SYNC input for PWM mode frequency synchronization
from 500kHz to 1MHz
n
15% accuracy for F
OSC
and I
lim
Features
n
Sub-miniature 10-pin thin Micro SMD package
n
Only four tiny surface-mount external components
required
n
Uses small ceramic capacitors
n
Internal soft start
n
Current and Thermal shutdown protection
n
No external compensation required
Applications
n
Mobile Phones
n
Hand-Held Radios
n
Battery Powered Devices
Typical Application Circuit
20036602
December 2002
L
M
2003 National Semiconductor Corporation
DS200366
www.national.com