RT9201 pdf datasheet (PWM Step

The RT9201 is a high-efficiency pulse-width-modulated
(PWM) step-down DC-DC converter. Capable of delivering
600mA output current over a wide input voltage range
from 2.5 to 5.5V, the RT9201 is ideally suited for portable
electronic devices that are powered from 1-cell Li-ion
battery or from other power sources within the range such
as cellular phones, PDAs and handy-terminals.
Four operational modes are available: PWM, PSM, Low-
Dropout and shut-down modes. Internal synchronous
rectifier with low RDS(ON) dramatically reduces conduction
loss at PWM mode. No external Schottky diode is
required in practical application. The RT9201 automatically
turns off the synchronous rectifier while the
inductor current is low and enters discontinuous PWM
mode. This can increase efficiency at light load condition.
The RT9201 enters PSM (pulse-skipping mode) at
extremely light load condition. The equivalent switching
frequency is reduced to increase the efficiency in PSM.
The RT9201 enters Low-Dropout mode when normal
PWM cannot provide regulated output voltage by
continuously turning on the upper P-MOSFET. RT9201
enters shut-down mode and consumes less than 0.1mA
when EN pin is pulled low.
The switching ripple is easily smoothed-out by small
package filtering elements due to a fixed operation
frequency of 800kHz. This along with small VDFN package
provides small PCB area application. Other features
include soft start, 0.8V internal reference voltage with
1% accuracy, over temperature protection, and over
current protection.