RT7257G
Function Block Diagram
VIN
Internal
Regulator
Shutdown
V
A
V
CC
Comparator
1.2V
+
-
Oscillator
Foldback
Control
0.4V
+
-
UV
Comparator
Current Sense
Amplifier
Slope Comp
+
-
R
SENSE
V
A
BOOT
S
+
R
-
Current
Comparator
Q
Q
110m
Ω
EN
5kΩ
Lockout
Comparator
-
2.5V +
V
CC
6µA
SW
90m
Ω
GND
SS
0.8V
+
+EA
-
FB
COMP
Operation
Shutdown Comparator
Activate internal regulator once EN input level is larger
than the target level. Force IC to enter shutdown mode
when the EN input level is lower than 0.4V.
Internal Regulator
Provide internal power for logic control and switch gate
drivers.
Lockout Comparator
Activate the current comparator, release lock-out logic,
and enable the switches as EN input level is larger than
lockout voltage. Otherwise, the switches still locks out.
Oscillator
The oscillator provides internal clock and controls the
converter's switching frequency.
Foldback Control
Dynamically adjust the internal clock. It provides a slower
frequency as a lower FB voltage.
UV Comparator
As FB voltage is lower than the UV voltage, it will activate
a UV protect scheme.
Error Amplifier
The output voltage COMP of the error amplifier is adjusted
comparing FB signal with the internal reference voltage
and SS signal.
Current Sense Amplifier
R
SENSE
detects the peak current of the high side switch.
This signal is amplified by the current sense amplifier and
added with a slope compensation signal. Then, It controls
the switches by comparing this signal with the COMP
voltage.
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7257G-01
September 2012
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
