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PRODUCT DATASHEET
AAT2158
SwitchReg
TM
Functional Block Diagram
VCC
1.5A Low Noise Step-Down Converter
VP
0.6V REF
FB
OP. AMP
CMP
DH
LOGIC
LX
1MΩ
DL
Temp.
Sensing
OSC
SGND
EN
PGND
Functional Description
The AAT2158 is a high performance 1.5A monolithic
step-down converter operating at a 1.4MHz switching
frequency. It minimizes external component size, opti-
mizes efficiency over the complete load range, and pro-
duces reduced ripple and spectral noise. Apart from the
small bypass input capacitor, only a small L-C filter is
required at the output. Typically, a 3.3µH inductor and a
22µF ceramic capacitor are recommended for a 3.3V
output (see table of recommended values).
At dropout, the converter duty cycle increases to 100%
and the output voltage tracks the input voltage minus
the R
DS(ON)
drop of the P-channel high-side MOSFET (plus
the DC drop of the external inductor). The device inte-
grates extremely low R
DS(ON)
MOSFETs to achieve low
dropout voltage during 100% duty cycle operation. This
is advantageous in applications requiring high output
voltages (typically > 2.5V) at low input voltages.
The integrated low-loss MOSFET switches can provide
greater than 95% efficiency at full load. Light load oper-
ation maintains high efficiency, low ripple and low spec-
tral noise even at lower currents (typically <150mA).
In battery-powered applications, as V
IN
decreases, the
converter dynamically adjusts the operating frequency
prior to dropout to maintain the required duty cycle and
provide accurate output regulation. Output regulation is
maintained until the dropout voltage, or minimum input
voltage, is reached. At 1.5A output load, dropout voltage
headroom is approximately 200mV.
The AAT2158 typically achieves better than ±0.5% out-
put regulation across the input voltage and output load
range. A current limit of 2.0A (typical) protects the IC
and system components from short-circuit damage.
Typical no load quiescent current is 42µA.
Thermal protection completely disables switching when
the maximum junction temperature is detected. The
2158.2008.10.1.5
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