AAT1151 Datasheet, PDF (8/16 Pages) Advanced Analogic Technologies – 850kHz 700mA Synchronous Buck DC/DC Converter

Functional Block Diagram
DATA SHEET
AAT1151
850kHz 700mA Synchronous Buck DC/DC Converter
VCC
VP = 2.7V to 5.5V
1.0V REF
FB
OP. AMP
CMP
DH
LOGIC
LX
1MΩ
DL
Temp.
Sensing
OSC
SGND
EN
PGND
Operation
Control Loop
The AAT1151 is a peak current mode buck converter. The
inner wide bandwidth loop controls the peak current of
the output inductor. The output inductor current is
sensed through the P-channel MOSFET (high side) and is
also used for short-circuit and overload protection. A
fixed slope compensation signal is added to the sensed
current to maintain stability. The loop appears as a volt-
age programmed current source in parallel with the out-
put capacitor.
The voltage error amplifier output programs the current
loop for the necessary inductor current to force a con-
stant output voltage for all load and line conditions. The
voltage feedback resistive divider is internal, dividing the
output voltage to the error amplifier reference voltage of
1.0V. The voltage error amplifier does not have the large
DC gain typical of most error amplifiers. This eliminates
the need for external compensation components, while
still providing sufficient DC loop gain for load regulation.
The voltage loop crossover frequency and phase margin
are set by the output capacitor value only.
PFM/PWM Operation
Light load efficiency is maintained by way of PFM control.
The AAT1151 PFM control forces the peak inductor cur-
rent to a minimum level regardless of load demand. At
medium to high load demand, this has no effect on cir-
cuit operation and normal PWM controls take over. PFM
reduces the switching frequency at light loads, thus
reducing the associated switching losses.
Soft Start/Enable
Soft start increases the inductor current limit point in
discrete steps when the input voltage or enable input is
applied. It limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT1151 into a low-power,
non-switching state. The total input current during shut-
down is less than 1μA.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201991B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013