LM3661_05 Datasheet, PDF (1/17 Pages) National Semiconductor (TI) – 450mA Subminiature, Micropower Step-Down DC-DC Converter for Ultra Low-Voltage Circuits

May 2005
LM3661
450mA Subminiature, Micropower Step-Down DC-DC
Converter for Ultra Low-Voltage Circuits
General Description
The LM3661 step-down DC-DC converter is optimized for
powering ultra-low voltage circuits from a single Lithium-Ion
cell. The device provides two pin-selectable output voltages.
See ordering information for a list of voltage options avail-
able . This allows adjustment for DSP or CPU voltage op-
tions, as well as dynamic output voltage switching for re-
duced power consumption. Internal synchronous
rectification provides high efficiency (92% typ. at 1.35V_OUT).
The LM3661 offers superior features and performance for
mobile phones and similar portable applications. Pin-
selectable PWM and Linear modes provide improved system
control for maximizing battery life. During full-load, fixed
frequency PWM operation reduces interference in RF and
data acquisition applications by minimizing noise harmonics
at sensitive IF and sampling frequencies. The SYNC/MODE
input allows synchronization of the switching frequency in a
range of below 500 kHz to 750 kHz to prevent noise from
intermodulation with system frequencies. Linear operation
reduces quiescent current to 29 µA (typ.) during system
standby for extended battery life, while supplying up to
15 mA. Shutdown turns the device off and reduces battery
consumption to 0.5 µA (typ.). This device offers a selectable
over Current Limit to protect a variety of inductors.
The LM3661 is available in a 10 pin micro SMD package.
This packaging uses National’s chip-scale micro SMD tech-
nology and offers the smallest possible size. A high (600
kHz) switching frequency allows use of tiny surface-mount
components; only three are required — an inductor and two
ceramic capacitors.
n ±3% output voltage precision in PWM mode
n Miniature 10-pin micro SMD package
n Only three tiny surface-mount external components
required
n Uses small ceramic capacitors
n 8 mV typ. PWM output voltage ripple
n Internal synchronous rectification for high efficiency
(92% at 2.7 V_IN, 1.35 V_OUT)
n 29 µA typ. quiescent current (Linear mode)
n 0.5 µA typ. shutdown current
n SYNC/MODE input for frequency synchronization from
500 kHz to 750 kHz
n Current and Thermal overload protection
n High gain control loop with internal compensation
n Up to 450mA I_OUT capability for LM3661-1.35/1.4
n Up to TBDmA I_OUT capability for LM3661-1.25
Applications
n Mobile phones
n Hand-Held radios
n Personal Digital Assistants
n Palm-top PC’s and Pocket PC’s
n Portable Instruments
n Battery Powered Device
Features
n Operates from a single Li-ION cell
n Pin selectable output voltages
n Pin selectable Inductor Current Limit
Typical Application Circuit
© 2005 National Semiconductor Corporation DS200988
20098802
www.national.com