AAT1150 Advanced Analogic Technologies, AAT1150 Datasheet - Page 9

• Manufacturer Part Number: AAT1150
• Description: 1MHz 1A Step-Down DC/DC Converter
• Manufacturer: Advanced Analogic Technologies

Functional Block Diagram
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-
1150.2005.03.1.2
FB
1.0V REF
SGND
1MΩ
OSC
OP. AMP
Sensing
Temp.
V
CC
1MHz 1A Step-Down DC/DC Converter
CMP
EN
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.
LOGIC
DH
DL
V
P
= 2.7V- 5.5V
PGND
LX
AAT1150
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