RT6217A/B
Functional Block Diagram
PGOOD
BOOT
VIN
VIN
Reg
VCC
Minoff
VCC
UGATE
OC
Control
Driver
LGATE
UV
GND
GND SW
SW
VIBIAS
VREF
SW
SS
Soft-
Start
Control
Ripple
Gen.
+
+
-
Comparator
EN
VIN
On
Time
SW
EN
FB
Operation
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
adopts ACOT
TM
control mode, which can reduce the output
capacitance and provide ultrafast transient responses, and
allow minimal components sizes without any additional
external compensation network.
Enable Control
The RT6217A/B provides an EN pin, as an external chip
enable control, to enable or disable the device. If V
EN
is
held below a logic-low threshold voltage (V
ENH
− ΔV
EN
) 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 (V
UVLO
). During shutdown
mode, the supply current can be reduced to I
SHDN
(10μA
or below). If the EN voltage rises above the logic-high
threshold voltage (V
ENH
) while the V
IN
voltage is higher
than UVLO threshold (V
UVLO
), the device will be turned
on, that is, switching being enabled and soft-start
sequence being initiated.
Input Under-Voltage Lockout
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 V
EN
rises above V
ENH
first,
switching will still be inhibited until the VIN voltage rises
above V
UVLO
. 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 V
IN
goes below the UVLO-
falling threshold voltage (V
UVLO
− ΔV
UVLO
), this switching
will be inhibited; if V
IN
rises above the UVLO-rising
threshold (V
UVLO
), the device will resume switching.
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 and GND, 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 (I
LIM_L
), the
is a registered trademark of Richtek Technology Corporation.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
DS6217A/B-01 October 2018
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
