AAT1218 Datasheet, PDF (8/15 Pages) Advanced Analogic Technologies – 1A, 1.2MHz Synchronous Boost Converter

SwitchReg^TM
PRODUCT DATASHEET
AAT1218
1A, 1.2MHz Synchronous Boost Converter
Functional Block Diagram
VIN 1.4V–5.5V
VIN
L1 _LX
CIN
FB
Enable Logic
EN
Soft Start
Slope
Vss
Compensation
–
Start-Up
Oscillator
Start-Up
Current Limit
Current
Sense
Bandgap
1.2V
To VIN
+
EA
–
Antiringing
Control
+
Comp
–
Shutdown
Control
SHUTDOWN
MUX
+
VOUT
GOOD
– ^2.3V
PWM
Logic
Oscillator
1.2MHz
OUT
COUT
PGND
GND
VOUT
R1
R2
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.
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
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.
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