Low-Noise Synchronous PWM Step-Down DC/DC Converter
l Greater than 95% efficiency.
l Guaranteed output current of 800mA.
l 100% duty cycle in dropout.
l Fixed 500 KHz or adjustable frequency sy-
chronous PWM operation.
l Very low quiescent current of 35µA (typ.).
l Adjustable output voltage from 0.75V to VIN,
ranging from 2.5V to 5.5V.
l Accurate reference: 0.75V (±1.2%).
l Synchronizable external switching frequency
up to 1MHz.
l Small 8-Pin MSOP package.
l WLAN cards
l Cellular phones.
l CPU I/O supplies.
l Cordless phones.
l Notebook chipset supplies.
l Battery-operated devices (3 or 1 Li-Ion/NiMH/
n TYPICAL APPLICATION CIRCUIT
The SS6550 is a low-noise pulse-width-
modulated (PWM) DC/DC step-down converter,
which can power logic circuits and transmitters in
small wireless systems such as communicating
PDAs, cellular phones and handy-terminals.
The device features an internal synchronous rec-
tifier for high conversion efficiency. Excellent
noise characteristics and fixed-frequency opera-
tion provide easy post-filtering. The SS6550
is ideally suited for Li-Ion battery applications. It
is also suitable for +3V or +5V fixed input appli-
cations. The device operates in one of the follow-
ing four modes. Forced PWM mode operates at a
fixed frequency regardless of the load. Synchro-
nizable PWM mode allows the synchronization of
an external switching frequency and minimizes
harmonics. PWM/PFM Mode extends battery life
by switching to a PFM pulse-skipping mode un-
der light loads. Shutdown mode places the de-
vice in standby, reducing supply current to under
The SS6550 can deliver over 800mA of out-
put current. The output voltage can be adjusted
from 0.75V to VIN with the input range of +2.5V
to +5.5V. Other features of the SS6550 include
low quiescent current, low dropout voltage, and a
±1.2% accuracy 0.75V reference. It is avail-
able in a space-saving 8-pin MSOP package.
VIN= 2.5V to 5.5V
3 SYNC/ 6
VOUT = 1.8V
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