Advanced Analog Technology, Inc.
October 2007
AAT7301
DETAILED DESCRIPTION
The AAT7301 is a current-mode buck switch-mode
regulator with a fixed switching frequency of 380kHz. It
uses an internal P-channel MOSFET switch to step
down the input voltage to the regulated output voltage.
The converter regulates input voltages from 4V to 15V
down to an output voltage as low as 0.9V, and is able to
supply up to 2A of load current.
DESIGN PROCEDURE
Programming the Output Voltage
The output voltage for the AAT7301 is programmed
using a resistor divider from the output connected to the
feedback pins (Figure 1). When setting the output
voltage, connect a resistive voltage divider from the
output to IN pin and then to GND. Choose the
lower-side (IN-to-GND) resistor, then calculate the
upper-side (output-to-IN) resistor as follows:
ENC Control Input
The AAT7301 contains built-in pull high logic. The IC is
1.6V). When the voltage is lower than 0.4V, the IC is
disabled.
Soft-Start
The AAT7301 has built-in 700µs soft-start time. Upon
power turn-on, if ENC pin is not pulled low; and V
DD
is
above V
UVLO
(typ. 3.48V), IN pin will climb from 0V to
0.9V during 700µs soft-start time to reduce inrush
current.
Short Circuit Protection
When short circuit happens, and the feedback voltage
(IN) is less than 0.7V, the switching frequency will
change to 47kHz to reduce the power supply from input
to output to protect the system. The frequency will
switch back to 380kHz after the short circuit is released.
Figure 1. Feedback Network
Thermal Shutdown
The AAT7301 includes a thermal-limit circuit that shuts
down the IC at approximately +160
C
. The part turns
on after the IC cools by approximately 20
C
.
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Advanced Analog Technology, Inc. –
Version 1.00
Page 8 of 11
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enabled even ENC left floating (ENC pin voltage
V
R
UPPER
=
R
LOWER
OUT
−
1
V
IN
Where V
IN
is the feedback regulation voltage, 0.9V (typ).
Typical values for R
LOWER
are in the range of 10k
100k .
to
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
