RT6217A/B
Functional Block Diagram
VIN
BOOT
PGOOD
VIN
VCC
Minoff
Reg
VCC
UGATE
OC
UV
Driver
Control
SW
VREF
VIBIAS
LGATE
GND
SW
GND
Ripple
Gen.
EN
EN
SW
+
Soft-
Start
Control
VIN
+
SS
FB
-
Comparator
On
SW
Time
Operation
Input Under-Voltage Lockout
The RT6217A/B is a high-efficiency, synchronous step-
down DC-DC converter that can deliver up to 3A output
current from a 4.5V to 24V input supply. The RT6217A/B
adoptsACOTTM control mode, which can reduce the output
capacitance and provide ultrafast transient responses, and
allow minimal components sizes without any additional
external compensation network.
In addition to the EN pin, the RT6217A/B also provides
enable control through the VIN pin. It features an under-
voltage lockout (UVLO) function that monitors the internal
linear regulator (VCC). If VEN rises above VENH first,
switching will still be inhibited until the VIN voltage rises
above VUVLO. It is to ensure that the internal regulator is
ready so that operation with not- fully-enhanced internal
MOSFET switches can be prevented. After the device is
powered up, if the input voltage VIN goes below the UVLO-
falling threshold voltage (VUVLO − ΔVUVLO), this switching
will be inhibited; if VIN rises above the UVLO-rising
threshold (VUVLO), the device will resume switching.
Enable Control
The RT6217A/B provides an EN pin, as an external chip
enable control, to enable or disable the device. If VEN is
held below a logic-low threshold voltage (VENH − ΔVEN) of
the enable input (EN), the converter will enter into
shutdown mode, that is, the converter is disabled and
switching is inhibited even if the VIN voltage is above VIN
under-voltage lockout threshold (VUVLO).During shutdown
mode, the supply current can be reduced to ISHDN (10μA
or below). If the EN voltage rises above the logic-high
threshold voltage (VENH) while the VIN voltage is higher
than UVLO threshold (VUVLO), the device will be turned
on, that is, switching being enabled and soft-start
sequence being initiated.
Low-Side Current-Limit Protection
The RT6217A/B features cycle-by-cycle valley-type
current-limit protection, measuring the inductor current
through the synchronous rectifier (low-side switch). The
inductor current level is determined by measuring the low-
side switch voltage between the SW pin andGND, which
is proportional to the switch current, during the low-side
on-time. For greater accuracy, temperature compensation
is added to the voltage sensing. Once the current rises
above the low-side switch valley current limit (ILIM_L), the
Copyright 2018 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS6217A/B-01 October 2018
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