PRODUCT DATASHEET
AAT2713
SystemPowerTM
Low Noise Dual 600mA Step-Down Converter with Synchronization
Functional Block Diagram
FB1
VIN1
VCC
DH
DL
Comp
Err.
Amp.
LX1
Logic
Voltage
Reference
Control
Logic
EN1
PGND1
VIN2
AGND
Oscillator
MODE/SYNC
PS
DH
DL
Comp.
FB
Err.
Amp.
LX2
Logic
Voltage
Reference
Control
Logic
EN2
PGND2
Soft-Start / Enable
Functional Description
The AAT2713 soft-start control prevents output voltage
overshoot and limits inrush current when either the input
power or the enable input is applied. When pulled low,
the enable input forces the converter into a low power
non-switching state (shutdown) with a bias current of
less than 1μA.
The AAT2713 is a peak current mode pulse width modu-
lated (PWM) converter with internal compensation. Each
channel has independent input, enable, feedback, and
ground pins with a 1.7MHz clock. Both converters operate
in either a fixed-frequency (PWM) mode under all load
conditions or a light load (LL) mode operation for light
loads combined with PWM mode operation for heavy
loads. The AAT2713 also produces reduced ripple and
spectral noise due to a low noise architecture. A phase
shift pin programs the converters to operate in phase or
180° out of phase. The converter can also be synchro-
nized to an external clock during PWM operation.
Low Dropout Operation
For conditions where the input voltage drops to the out-
put voltage level, the converter duty cycle increases to
100%. As the converter approaches the 100% duty
cycle, the minimum off time initially forces the high side
on time to exceed the 1.7MHz clock cycle and reduce the
effective switching frequency. Once the input drops
below the level where the converter can regulate the
output, the high side P-channel MOSFET is enabled con-
tinuously for 100% duty cycle. At 100% duty cycle the
output voltage tracks the input voltage minus the I*R
drop of the high side P-channel MOSFET.
The input voltage range is 2.7V to 5.5V. An external
resistive divider as shown in Figure 1 programs the out-
put voltage up to the input voltage. The converter
MOSFET power stage is sized for 600mA load capability
with up to 96% efficiency. Light load efficiency is up to
90% for a 1mA load.
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2713.2008.01.1.0
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