RT6215F
Operation
The RT6215F is a high-efficiency, synchronous step-down
DC-DC converter that can deliver up to 2Aoutput current
from a 4.5V to 24V input supply. The RT6215F adopts
ACOTTM control mode, which can reduce the output
capacitance and provide ultrafast transient responses, and
allow minimal components sizes without any additional
external compensation network.
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 on-
time one-shot will be inhibited until the inductor current
ramps down to the current limit level (ILIM_L), that is, another
on-time can only be triggered when the inductor current
goes below the low-side current limit. This function can
prevent the average output current from greatly exceeding
the guaranteed low-side current limit value. If the output
load current exceeds the available inductor current
(clamped by the above-mentioned low-side current limit),
the output capacitor needs to supply the extra current
such that the output voltage will begin to drop. If it drops
below the output under-voltage protection trip threshold,
the IC will stop switching to avoid excessive heat.
Enable Control
The RT6215F 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 (VENL) 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 10μAor below (ISHDN). 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.
Output Under-Voltage Protection
The RT6215F includes output under-voltage protection
(UVP) against over-load or short-circuited condition by
constantly monitoring the feedback voltage VFB. If VFB
drops below the under-voltage protection trip threshold
(typically 50% of the internal reference voltage), the UV
comparator will go high to turn off both the internal high-
side and low-side MOSFET switches.
Input Under-Voltage Lockout
In addition to the EN pin, the RT6215F 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
Hiccup Mode
If the output under-voltage condition continues for a period
of time, the RT6215F will enter output under-voltage
protection with hiccup mode. During hiccup mode, the IC
will shut down for tHICCUP_OFF (5.7ms), and then attempt
to recover automatically for tHICCUP_ON (2.1ms). Upon
completion of the soft-start sequence, if the fault condition
is removed, the converter will resume normal operation;
otherwise, such cycle for auto-recovery will be repeated
until the fault condition is cleared. Hiccup mode allows
the circuit to operate safely with low input current and
power dissipation, and then resume normal operation as
soon as the over-load or short-circuit condition is removed.
will still be inhibited until the VIN voltage rises above VUVLO
.
It is to ensure that the internal regulator is ready so that
operation without 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.
Low-Side Current Limit Protection
The RT6215F 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-
Copyright 2018 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6215F-00 September 2018
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
