AAT1230/1230-1
18V 100mA Step-Up Converter
Functional Block Diagram
VIN
LIN
VP
Soft-Start
Timer
EN/SET
FB1
SW
Control
VREF1
Output
Select
VREF2
FB2
SEL
PGND
GND
The switching cycle initiates when the N-channel
MOSFET is turned ON and current ramps up in the
inductor. The ON interval is terminated when the
inductor current reaches the programmed peak
current level. During the OFF interval, the input
current decays until the lower threshold, or zero
inductor current, is reached. The lower current is
equal to the peak current minus a preset hystere-
sis threshold - which determines the inductor ripple
current. The peak current is adjusted by the con-
troller until the output current requirement is met.
Functional Description
The AAT1230/1230-1 consists of a DC/DC boost
controller, an integrated slew rate controlled input
disconnect MOSFET switch, and a MOSFET power
switch. A high voltage rectifier, power inductor, out-
put capacitor, and resistor divider network are
required to implement a DC/DC boost converter.
Control Loop
The AAT1230/1230-1 provides the benefits of cur-
rent mode control with a simple hysteretic feedback
loop. The device maintains exceptional DC regula-
tion, transient response, and cycle-by-cycle current
limit without additional compensation components.
The magnitude of the feedback error signal deter-
mines the average input current. Therefore, the
AAT1230/1230-1 controller implements a pro-
grammed current source connected to the output
capacitor and load resistor. There is no right-half
plane zero, and loop stability is achieved with no
additional compensation components.
The AAT1230/1230-1 modulates the power MOS-
FET switching current in response to changes in
output voltage. This allows the voltage loop to
directly program the required inductor current in
response to changes in the output load.
Increased load current results in a drop in the out-
put feedback voltage (FB1 or FB2) sensed through
the feedback resistors (R1, R2, R3). The controller
8
1230.2007.06.1.6
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
