RT6203ENGSP datasheet(4/21 Pages) RICHTEK

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RT6203E

DS6203E-00 January 2019

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

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 ACOTTM 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.

Enable Control

The RT6203E 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 (VIL) 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 (VUVLO). During shutdown mode, the supply

current can be reduced to ISHDN (10

μA or below). If the EN

voltage rises above the logic-high threshold voltage (VIH)

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 (VOUT from 0V to 1.1V) is 1.1ms.

VOUT

VIN

VCC

VIN = 12V

VCC = 5V

1.1ms

0.6ms

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