RT5771A
Functional Block Diagram
EN
EN
PGOOD
PGOOD
OSC
Slope
Com
ISEN
VIN
V
REF
0.6V
EA
Output
Clamp
OC
Limit
FB
Int-SS
Control
Logic
0.54V
PGOOD
POR
0.2V
UV
OTP
Driver
SW
NISEN
Current Limit
GND
VCC
Operation
The RT5771A is a synchronous low voltage Buck Converter
that can support the input voltage range from 2.7V to 5.5V
and the output current can be up to 3A. The RT5771A
uses a constant frequency, current mode architecture. In
normal operation, the high-side P-MOSFET is turned on
when the Switch Controller is set by the oscillator (OSC)
and is turned off when the current comparator resets the
switch controller. High-side MOSFET peak current is
measured by internal R
SENSE
. The Current Signal is where
Slope Compensator works together with sensing voltage
of R
SENSE
. The error amplifier EA adjusts COMP voltage
by comparing the feedback signal (V
FB
) from the output
voltage with the internal 0.6V reference. When the load
current increases, it causes a drop in the feedback voltage
relative to the reference, the COMP voltage then rises to
allow higher inductor current to match the load current.
UV Comparator
If the feedback voltage (V
FB
) is lower than threshold voltage
0.2V, the UV Comparator's output will go high and the
Switch Controller will turn off the high-side MOSFET.
Oscillator (OSC)
The internal oscillator runs at nominal frequency 1MHz.
PGOOD Comparator
When the feedback voltage (V
FB
) is higher than threshold
voltage 0.54V, the PGOOD open drain output will be high
impedance.
Enable
There is an internal pull down 500kΩ resistor at EN pin.
When the EN pin is higher than 1.6V, the converter will be
turned on. The EN pin can be connected to VIN through a
100kΩ resistor for automatic startup.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build the soft-start ramp voltage. The V
FB
voltage will
track the internal ramp voltage during soft-start interval.
The typical soft-start time is 700μs.
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5771A-02 June 2019
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
