RT6318B datasheet(16/25 Pages) RICHTEK

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RT6318B/C

DS6318B/C-01 December 2021

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Part.

VCC

VOUT

3.3V

(LDO)

RT6318B

RT6318C

Table 1. RT6318B/C Power Logic

Internal Output Voltage Discharge

An internal open-drain logic output is implemented on LX

pin. As operating in OVP, UVP, OTP, enable low and VIN

low status, the internal discharge path is activated and

the residual energy from output terminal can be released

from an internal resistor(50

Ω) to ground.

Soft-Start

The RT6318B/C provides an internal soft-start function to

prevent large inrush current and output voltage overshoot

when the converter starts up. The soft-start (SS)

automatically begins once the chip is enabled. During soft-

start, it clamps the ramping of internal reference voltage

which is compared with FB signal. The typical soft-start

duration is 0.6ms.

Power Good Output (PGOOD)

The power good output is an open drain output that requires

a pull-up resistor. When the output voltage is 15% (typical)

below its set voltage, PGOOD will be pulled low. It is held

low until the output voltage returns to 90% of its set voltage

once more. During soft-start, PGOOD is actively held low

and only allowed to be pulled high after soft-start is over

and the output reaches 90% of its set voltage. There is a

μs delay built into PGOOD circuitry to prevent false

transition.

External Bootstrap Capacitor and Resistor (CBOOT

and RBOOT)

Connect a 0.1

μF low ESR ceramic capacitor and at least

Ω resistor between BOOT pin and LX pin. This bootstrap

capacitor provides the gate driver supply voltage for the

high-side N-channel MOSFET switch.

The internal power MOSFET switch gate driver is

optimized to turn the switch on fast enough for low power

loss and good efficiency, but also slow enough to reduce

EMI. Switch turn-on is when most EMI occurs since VLX

rises rapidly. In some cases, it is desirable to reduce EMI

further, by the expense of some additional power

dissipation.

Inductor Selection

Selecting an inductor involves specifying its inductance

and also its required peak current. The exact inductor value

Input Under-Voltage Lock-Out

In addition to the enable function, the RT6318B/C provides

an Under-Voltage Lock-Out (UVLO) function that monitors

the input voltage. To prevent operation without fully-

enhanced internal MOSFET switches, this function inhibits

switching when input voltage drops below the UVLO-falling

threshold. The IC resumes switching when input voltage

exceeds the UVLO-rising threshold.

Over-Temperature Protection

The RT6318B/C includes an Over-Temperature Protection

(OTP) circuitry to prevent overheating due to excessive

power dissipation. The OTP will shut down switching

operation when the junction temperature exceeds 150

°C.

The RT6318B/C uses latch-off mode in OTP. When the

protection function is triggered, the IC will shut down. The

IC stops switching and is latched off. To restart operation,

toggle EN or power the IC off and then on again. For

continuous operation, provide adequate cooling so that

the junction temperature does not exceed 150

°C.

Enable and Disable

The RT6318B/C's EN is used to control converter, the

enable voltage (EN) has a logic-low level of 0.4V. When

VEN is below this level the IC enters shutdown mode When

VEN exceeds its logic-high level of 0.8V the converter is

fully operational. The 3.3V/5V linear regulators (LDO) is

always on when VIN exceeds the UVLO threshold. See

Table 1 for the RT6318B/C power logic.

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