RT7291A/B
Functional Block Diagram
VCC
VBYP
V
IN
Soft-Start
VOUT
V
REF
V
FB
+
+
-
POR &
Reference
V
CC
Switch-Over
On-Time
One shot
Min off Time
BSTREG
V
IN
BOOT
Gate
Control
Logic
SW
V
CC
EN
V
OUT
SW
V
OC
+
-
PGND
OCP
PGOOD
Fault
Logic
120% x V
REF
-
+
OVP
-
+
90% x V
REF
POK
60% x V
REF
+
-
AGND
UVP
V
OUT
CLK
CLK
Generator
V
CC
V
CC
Regulator
LDO
Control
LDO
Switch-Over
V
OUT
VIN
ENLDO LDO
Operation
Overall
The RT7291A/B is a synchronous step-down converter
with advanced constant on-time control mode. Using the
ACOT
TM
control mode can reduce the output capacitance
and provide fast transient response. It can minimize the
component size without additional external compensation
network.
Internal VCC Regulator
The regulator provides 5V power to supply the internal
control circuit. Connecting a 2.2μF ceramic capacitor for
decoupling and stability is required.
Soft-Start
In order to prevent the converter output voltage from
overshooting during the startup period, the soft-start
function is necessary. The soft-start time is internal setting
and the duration is around 1.5ms
CLK Generator
Provide a 300kHz clock to drive external charge pump.
VCC Switch-Over
The internal regulator output will switch over to VBYP if
VBYP level is higher than 4.6V.
LDO
Built-in 5V, 100mA LDO with 1% accuracy. The LDO output
will switch over to VOUT once PGOOD goes high.
is a registered trademark of Richtek Technology Corporation.
OCP
The inductor valley current is monitored via the internal
switches in cycle-by-cycle. Once the output voltage drops
below UV threshold, the device enters latch mode.
Power Good
After soft-start is finished, the power good function will be
activated. The PGOOD pin is an open-drain output.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
DS7291A/B-03 January 2018
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
