RT8079 查看數據表（PDF） - Richtek Technology
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RT8079 Datasheet PDF : 13 Pages
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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.
RT8079
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 (2.2μA) 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 :
CSS
(nF) =
TSS
(ms)× 2.2 (μA)
0.827 (V)
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.
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8079-01 February 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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