rt9270 Richtek Technology Corporation, rt9270 Datasheet - Page 2

• Manufacturer Part Number: rt9270
• Description: High Performance, Noise Boost Converter
• Manufacturer: Richtek Technology Corporation

RT9270
Function Block Diagram
Operation
The RT9270 is a high efficiency step-up Boost converter
with a fixed-frequency, current-mode PWM architecture.
It performs fast transient response and low noise operation
with appropriate component selection. The output voltage
is regulated through a feedback control consisting of an
error amplifier, a summing comparator, and several control
signal generators (as shown in function block diagram).
The feedback reference voltage is 1.24V. The error
amplifier varies the COMP voltage by sensing the FB pin.
The slope compensation signal summed with the current
-sense signal will be compared with the COMP voltage
through the summing comparator to determine the current
trip point and duty cycle. When driving light loads, the
RT9270 will perform the pulse-skipping mode to prevent
overcharging the output voltage. In this mode, the
switching frequency will be reduced to perform a higher
efficiency.
Soft-Start
The RT9270 provides soft-start function. When the EN pin
is connected to high, a 4uA constant current is sourced to
charge an external capacitor. The voltage rate of rise on
the COMP pin is limited during the charging period, and
so is the peak inductor current. When the EN pin is
connected to GND, the external capacitor will be
discharged to ground for the next time soft-start.
www.richtek.com
2
COMP
FREQ
EN
FB
5uA
Oscillator
1.24V
Error
Amplifier
-
+
Compen-
sation
Slope
Preliminary
1.24
V
V
LX
IN
FB
Summing
Comparator
Protection
Current Limitation
The switch current is monitored to limit the value not to
exceed 1.9A typically. When the switch current reaches
1.9A, the output voltage will be pulled down to limit the
total output power to protect the power switch and external
components.
Shutdown
Connect the EN to GND to turn the RT9270 off and reduce
the supply current to 0.1uA. In this operation, the output
voltage is the value of VIN to subtract the forward voltage
of catch diode.
Frequency Selection
The switching frequency of RT9270 can be selected to
operate at either 670kHz or 1.3MHz. When the FREQ
pin is connected to GND for 670kHz operation, and
connected to VIN for 1.3MHz operation. FREQ is preset
to 670kHz operation for allowing the FREQ pin
unconnected.
-
+
Clock
Enable
Current
Control
Sense
Driver
Logic
and
Soft-
Start
DS9270-09 March 2007
4uA
N
VIN
SS
LX
GND