RT9206 Ver la hoja de datos (PDF) - Richtek Technology

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Fabricante

RT9206

High Efficiency, Synchronous Buck with Dual Linear Controllers

Richtek Technology 

RT9206

Operation

Introduction

The RT9206 is a combo controller, which integrates an

adjustable frequency, voltage mode synchronous step

down controller and two HV linear controllers. The

synchronous step down controller consists of an internal

precision reference, an internal oscillator, an error amplifier,

a PWM comparator, control logic and floating gate driver,

a programmable soft-start, a power good indicator, an over

voltage protection, an over temperature protection and short

circuit protection.

The output voltage of the synchronous converter is set

and controlled by the output of the error amplifier, which is

the amplified error signal from the sensed output voltage

and the voltage on non-inverting input, which is connected

with internal 0.8V reference voltage. The amplified error

signal is compared to a fixed frequency linear sawtooth

ramp and generates fixed frequency pulse of variable duty-

cycle, which drivers the two N-Channel external MOSFETs.

The timing of the synchronous converter is provide through

an internal oscillator circuit and can be programmed

between 200kHz to 600kHz via an external resistor

connected between RT pin and ground.

Soft-Start

RT9206 has a programmable soft-start to control the output

voltage rise time and limit the current surge at the start-

up. The soft-start will begin while VDD rises above POR

threshold for correct start-up. Soft-start function operates

by an internal sourcing current to charge an external

capacitor to around the voltage of VINT. The soft-start signal,

SS pin, is the third input non-inverting input of the PWM

comparator. Before soft-start signal reach the bottom of

the sawtooth ramp, inverting input of the PWM comparator,

the soft-start current is twice of the normal soft-start current.

Once the soft-start signal reach the bottom of the ramp,

the soft-start current became normal, and start to increase

duty cycle from zero to the point the feedback loop takes

control.

Power On Reset (POR)

The power on reset circuit assures that the MOSFET driver

outputs remain in the off state whenever the VDD supply

voltages lower than the POR threshold.

Over-Current Protection

Whenever the over-current is occurred in soft-start or in

normal operation period, It will shut down PWM signal,

the MOSFET driver outputs remain in the off state, and

latch soft-start signal low until restart VDDsupply voltage.

Over-Voltage Protection

Once over-voltage protection occurred, it will turn on low

side MOSFET and latch soft-start signal low to prevent

end device form abnormal voltage stress. Restart VDD

supply voltage will release the protection.

Power Good Indicator

The power good indicator is an open drain output to show

whether the synchronous converter output ready or not.

The power good indicator is available after soft-start end.

Short-Circuit Protection

The short-circuit phenomenon is sensed by the drop of

output voltage, synchronous converter and two linear

controller. Once the short-circuit occurred, the drop of output

voltage lower than the under voltage threshold, 0.6V on

feedback, the PWM signal will shut down and both of the

external MOSFET will turn off and soft-start signal latch

low. Soft-start signal, SS, is also connected to two linear

controller error amplifier non-inverting input. Therefore,

whenever the drop of output of the synchronous converter

or two linear controllers lower than under voltage threshold,

all MOSFET drivers will turn off.

www.richtek.com

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DS9206-11 March 2007

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