RT6242A/B
Function Block Diagram
PVCC
BOOT
EN
POR &
Reg
VBIAS
OC
UV & OV
PVCC
6µA
Ripple
Gen.
FB
V
IN
On-Time
V
REF
Min.
Off-Time
PVCC
UGATE
VIN
SW
LGATE
GND
Control
Driver
ZC
SS
+
+
-
Comparator
Comparator
0.9 V
REF
+
-
FB
PGOOD
Operation
The RT6242A/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 fast transient response. It can minimize the component
size without additional external compensation network.
Power Good
After soft-start has finished, the power good function will
be activated. The PGOOD pin is an open-drain output. If
the FB voltage is lower than 85% V
REF
, the PGOOD pin
will be pulled low.
PVCC
The regulator provides 5V power to supply the internal
control circuit. 1μF 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 adjustable
by an external capacitor.
Current Protection
The inductor current is monitored via the internal switches
cycle-by-cycle. Once the output voltage drops under UV
threshold, the RT6242A/B will enter hiccup mode.
UVLO Protection
To protect the chip from operating at insufficient supply
voltage, the UVLO is needed. When the input voltage of
VIN is lower than the UVLO falling threshold voltage, the
device will be lockout.
Thermal Shutdown
When the junction temperature exceeds the OTP
threshold value, the IC will shut down the switching
operation. Once the junction temperature cools down and
is lower than the OTP lower threshold, the converter will
autocratically resume switching.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6242A/B-05 April 2016
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
