PRODUCT DATASHEET
AAT1218
SwitchReg
TM
Functional Block Diagram
Soft Start
1A, 1.2MHz Synchronous Boost Converter
V
IN
1.4V–5.5V
VIN
Slope
Compensation
LX
Vss
Start-Up
Oscillator
–
Start-Up
Current Limit
MUX
V
OUT
GOOD
– 2.3V
OUT
V
OUT
+
L1
C
IN
Current
Sense
To V
IN
Antiringing
Control
C
OUT
R1
Bandgap
1.2V
+
+
FB
Enable Logic
EN
EA
–
Shutdown
Control
–
Comp
PWM
Logic
R2
PGND
SHUTDOWN
Oscillator
1.2MHz
GND
Functional Description
The AAT1218 is a synchronous step-up DC-DC converter.
It utilizes internal MOSFETs to achieve high efficiency
over the full load current range. It operates at a fixed
switching frequency of 1.2MHz, and uses the slope com-
pensated current mode architecture. The device can
operate at 0.5V input after start up. The typical start-up
voltage is 0.85V.
diode. It is implemented by a PMOS driven by a gate
driver with break-before-make timing. When the output
voltage is greater than 4.5V, an external rectifier diode
is necessary for proper operation.
Low Voltage Start-Up
The AAT1218 can start up at supply voltages as low as
1V. During the start-up phase, the internal low voltage
start-up circuitry controls the NMOS switch to soft-start
the device. A comparator (V
OUT
GOOD Comp) monitors
the output voltage. If V
OUT
exceeds 2.3V, the device exits
start-up phase and enters normal operation mode. The
internal circuitry power supply of the device is connected
to V
IN
during start-up phase and automatically switches
to V
OUT
during normal operation.
Synchronous Rectification
The AAT1218 integrates a synchronous rectifier to
improve efficiency and eliminate the external rectifier
diode if output voltage is lower than 4.5V. The synchro-
nous rectifier is used to reduce conduction loss contrib-
uted by the forward voltage of the external rectifier
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