PRODUCT DATASHEET
AAT1218
TM
SwitchReg
1A, 1.2MHz Synchronous Boost Converter
Functional Block Diagram
Soft Start
Vss
+
VIN 1.4V–5.5V
VIN
Start-Up
V
OUT
Oscillator
GOOD
2.3V
Slope
–
MUX
Compensation
Start-Up
Current Limit
–
L1
LX
VOUT
OUT
Current
Sense
CIN
COUT
R1
Antiringing
Control
To VIN
Bandgap
1.2V
R2
PWM
Logic
+
–
Comp
+
–
EA
FB
EN
PGND
GND
Enable Logic
Shutdown
Control
Oscillator
1.2MHz
SHUTDOWN
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.
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.
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 (VOUT GOOD Comp) monitors
the output voltage. If VOUT 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 VIN during start-up phase and automatically switches
to VOUT 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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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
