AAT1150_06 Datasheet, PDF (9/17 Pages) Advanced Analogic Technologies – 1MHz 1A Step-Down DC/DC Converter

Functional Block Diagram
AAT1150
1MHz 1A Step-Down DC/DC Converter
VCC
VP = 2.7V- 5.5V
1.0V REF
FB
OP. AMP
CMP
DH
LOGIC
LX
1MΩ
DL
Temp.
Sensing
OSC
SGND
EN
PGND
Applications Information
Control Loop
The AAT1150 is a peak current mode buck con-
verter. 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-cir-
cuit and overload protection. A fixed slope com-
pensation signal is added to the sensed current to
maintain stability. The loop appears as a voltage-
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 constant output voltage for all load and line
conditions. The feedback resistive divider is inter-
nal, dividing the output voltage to the error amplifi-
er reference voltage of 1.0V. The error amplifier
does not have a large DC gain typical of most error
amplifiers. This eliminates the need for external
compensation components while still providing suf-
ficient DC loop gain for load regulation. The
crossover frequency and phase margin are set by
the output capacitor value only.
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. The
enable input, when pulled low, forces the AAT1150
into a low power, non-switching state. The total input
current during shutdown is less than 1μA.
1150.2006.09.1.5
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