RT7271A
Function Block Diagram
PGOOD
VIN
UVLO
EN
1.4V
-
+
Shutdown
Comparator
Internal
Regulator
BOOT
UVLO
Current
Sense
0.72V
0.3V
+
- OV
Comparator Protection
Control
+
- UV
Comparator
BOOT
Driver
Control
LX
FB
0.6V
-
+ EA
+
Oscillator
HS Switch
Current
Comparator
Slope
Compensation
LS Switch
Current
Comparator
Current
Sense
GND
AGND
Soft-Start
COMP
Operation
The RT7271A is a constant frequency, current mode
synchronous step-down converter. In normal operation,
the high side N-MOSFET is turned on when the driver
control is set by the oscillator and is turned off when the
current comparator resets the driver control. While the
high side N-MOSFET is turned off, the low side N-MOSFET
is turned on to conduct the inductor current until next
cycle begins.
Error Amplifier
The error amplifier adjusts its output voltage by comparing
the feedback signal (V
FB
) with the internal 0.6V reference.
When the load current increases, it causes a drop in the
feedback voltage relative to the reference, the error
amplifier's output voltage then rises to allow higher inductor
current to match the load current.
Oscillator
The internal oscillator runs at fixed frequency 500kHz.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high
side gate driver.
Thermal Shutdown
The over temperature protection function will shut down
the switching operation when the junction temperature
exceeds 160°C. Once the junction temperature cools
down by the hysteresis, the converter will automatically
resume switching.
Enable
The converter is turned on when the EN pin is higher than
1.4V. When the EN pin is lower than 1.15V, the converter
will enter shutdown mode.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build a soft-start ramp voltage. The FB voltage will track
the internal ramp voltage during soft-start interval. The
typical soft-start time is 1.5ms.
UV Comparator
If the feedback voltage (V
FB
) is lower than 0.3V, the UV
Comparator will go high to turn off the high side MOSFET.
The output under voltage protection is designed to operate
in latch mode. When the UV condition is removed, the
controller can be reset by EN pin or VIN pin.
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7271A-00 February 2013
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
