RT7263B
Function Block Diagram
VIN
VCC
EN
Regulator
Oscillator
SYNC
OC Limit
Clamp
Reference
FB
10µA
SS
Error
Amplifier
GND
30pF
+
-
Ramp
Generator
Current Sense
Amplifier
-
+
BOOT
S
Q
R
SW
PWM
Comparator
Driver
+
+
-
400k
1pF
Operation
The RT7263B is a constant frequency, current mode
synchronous step-down converter. In normal operation,
the high side N-MOSFET is turned on when the S-R latch
is set by the oscillator and is turned off when the current
comparator resets the S-R latch. 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 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. In
short circuit condition, the frequency is reduced to 150kHz
for low power consumption.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high
side gate driver.
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
Enable
The converter is turned on when the EN pin is higher than
2V. When the EN pin is lower than 0.4V, the converter will
enter shutdown mode and reduce the supply current to
be less than 1μA.
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 4ms.
UV Comparator
If the feedback voltage (V
FB
) is lower than 0.4V, the UV
Comparator will go high to turn off the high side MOSFET.
The output under voltage protection is designed to operate
in Hiccup mode. When the UV condition is removed, the
converter will resume switching.
Thermal Shutdown
The over temperature protection function will shut down
the switching operation when the junction temperature
exceeds 150°C. Once the junction temperature cools
down by approximately 30°C, the converter will
automatically resume switching.
is a registered trademark of Richtek Technology Corporation.
DS7263B-01
September 2012
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
