RT6203E
Operation
The RT6203E is a high-efficiency, synchronous step-down
DC-DC converter that can deliver up to 6A output current
from a 4.5V to 18V input supply.
Advanced Constant On-Time Control and PWM
Operation
The RT6203E adopts ACOT
TM
Enable Control
The RT6203E 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
IL
) of the enable
input (EN), the converter will disable output voltage, 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
IH
)
while the VIN voltage is higher than UVLO threshold, the
device will be turned on, that is, switching being enabled
and soft-start sequence being initiated. This EN pin is a
high voltage pin and has an internal pull-high current to
implement automatic start-up.
Soft-Start (SS)
The RT6203E provides an internal soft-start feature for
inrush control. At power up, the internal capacitor is
charged by an internal current source to generate a soft-
start ramp voltage as a reference voltage to the PWM
comparator. The device will initiate switching and the
output voltage will smoothly ramp up to its targeted
regulation voltage only after this ramp voltage is greater
than the target voltage to ensure the converters have a
smooth start-up from pre-biased output. The output voltage
starts to rise in 0.6ms from EN rising, and the soft-start
ramp-up time (V
OUT
from 0V to 1.1V) is 1.1ms.
VIN = 12V
VIN
VCC = 5V
VCC
EN
VOUT
0.6ms
1.1ms
control for its ultrafast
transient response, low external component counts and
stable with low ESR MLCC output capacitors. When the
feedback voltage falls below the feedback reference
voltage, the minimum off-time one-shot (230ns, typ.) has
timed out and the inductor current is below the current
limit threshold, then the internal on-time one-shot circuitry
is triggered and the high-side switch is turn-on. Since the
minimum off-time is short, the device exhibits ultrafast
transient response and enables the use of smaller output
capacitance.
The on-time is inversely proportional to input voltage and
directly proportional to output voltage to achieve pseudo-
fixed frequency over the input voltage range. After the on-
time one-shot timer expired, the high-side switch is turn-
off and the low-side switch is turn-on until the on-time
one-shot is triggered again. To achieve stable operation
with low-ESR ceramic output capacitors, an internal ramp
signal is added to the feedback reference voltage to
simulate the output voltage ripple.
Power Saving Mode
The RT6203E automatically enters power saving mode
(PSM) at light load to maintain high efficiency. As the
load current decreases and eventually the inductor current
ripple valley touches the zero current, which is the
boundary between continuous conduction and
discontinuous conduction modes. The low-side switch is
turned off when the zero inductor current is detected. As
the load current is further decreased, it takes longer time
to discharge the output capacitor to the level that requires
the next on-time. The switching frequency decreases and
is proportional to the load current to maintain high
efficiency at light load.
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6203E-00 January 2019
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
