RT8409GS datasheet(3/11 Pages) RICHTEK

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RT8409

DS8409-00

September 2016

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Functional Block Diagram

Operation

The RT8409 senses the output voltage via the bootstrap

loop. The output voltage feedback signal is compared to

an internal reference voltage for the output voltage

regulation. The COMP pin, which is the operational

amplifier output node, is used for the control loop

compensation to obtain stable response. To stabilize the

system properly select the compensation network is

required.

The FB pin is the voltage loop input for the system

regulation. The above COMP pin related compensation

will be determined by specified system demand and be

adapted to various applications.

Burst Mode

For the no load power saving demand, burst mode is a

way to save power and maintain output regulation. High

efficiency is achieved at light loads when Burst Mode

operation is entered. The typical burst mode trigger levels

are defined as follows. The MOSFET will stop switching

when VC voltage goes lower than 200mV (typ.). The

MOSFET will resume switching again once the VC voltage

goes higher than 300mV (typ.).

In this mode the output ripple has a variable frequency

component that depends upon load current. Burst Mode

operation ripple can be reduced slightly by using more

output capacitance.

VDS

IOUT

VC.high

VC.low

State Machine

Regulator

VCC

DRAIN

SGND

SENSE

COMP

1.75V

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