RT2657BQ
Operation
The RT2657BQ is a synchronous low voltage step-down
converter that can support the input voltage range from
2.7V to 5.5V and the output current can be up to 0.6A.
The RT2657BQ 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.
The 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 2.25MHz.
Enable Comparator
The EN pin can be connected to VIN through a 100kΩ
resistor for automatic startup.
Soft-Start (SS)
An internal current source (25nA) charges an internal
capacitor (15pF) to build the soft-start ramp voltage (V
SS
).
The V
FB
voltage will track the internal ramp voltage during
soft-start interval. The typical soft-start time is 300μs.
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS2657BQ-00 July 2014
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
