RT8079 datasheet(3/13 Pages) RICHTEK

3 / 13 page

DS8079-01

February 2013

www.richtek.com

RT8079

is a registered trademark of Richtek Technology Corporation.

Operation

The RT8079 is a synchronous step-down DC/DC converter

with two integrated power MOSFETs. It can deliver up to

3A output current from a 2.95V to 6V input supply. The

RT8079's current mode architecture allows the transient

response to be optimized over a wider input voltage and

load range. Cycle-by-cycle current limit provides protection

against shorted outputs and soft-start eliminates input

current surge during start-up. The RT8079 is

synchronizable to an external clock with frequency ranging

from 300kHz to 2MHz. The RT8079 is available in

WQFN-16L 3x3 package.

High side MOSFET peak current is measured by internal

sensing resistor. The Current Signal is where Slope

Compensator works together with sensing voltage sensing

resistor. The error amplifier adjusts COMP voltage by

comparing the feedback signal (VFB) from the output

voltage with the internal 0.827V reference. When the load

current increases, it causes a drop in the feedback voltage

relative to the reference, the COMP voltage then rises to

allow higher inductor current to match the load current.

EN Comparator

The RT8079 is enable when EN pin is higher than 1.25V.

It is disable when EN pin lower than 1.18V. There is an

internal pull-high current source to charge the EN pin to

high when the EN pin is floating.

Oscillator (OSC)

The internal oscillator that provides switching frequency

from 300kHz to 2MHz. It is adjusted using an external

timing resistor. It also can be synchronized by an external

clock in the range between 300kHz and 2MHz from RT/

SYNC pin.

PGOOD Comparator

When the feedback voltage (VFB) rises above 93% or falls

below 107% of reference voltage the PGOOD open drain

output will be high impedance. The PGOOD open drain

output will be internally pulled low when the feedback

voltage (VFB) falls below 88% or rises above 113% of

reference voltage.

Soft-Start (SS)

An internal current source (2.2

μA) charges an external

capacitor to build the soft-start ramp voltage (VSS). The

VFB voltage will track the VSS during soft-start interval.

The Soft-Start setting capacitor (CSS) for the Soft-Start

time (TSS) can be easily calculated by the following

equation :

Over Temperature Protection (OTP)

The RT8079 implement an internal over temperature

protection. When junction temperature is higher than

145

°C, it will stop switching. Until the junction temperature

decreases below 125

°C, the RT8079 will re-soft-start from

initial condition.

×μ

(ms) 2.2 ( A)

(nF) =

0.827 (V)

RT8079 Datasheet(PDF) 3 Page - Richtek Technology Corporation

RT8079 Datasheet(HTML) 3 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13

Datasheet Descarga

Enlace URL