AAT1230/1230-1
18V 100mA Step-Up Converter
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.
S2Cwire functionality is enabled by pulling the SEL
pin low and providing S2Cwire digital clock input to
the EN/SET pin. Table 2 details the FB2 reference
voltage versus S2Cwire rising clock edges.
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
responds by increasing the peak inductor current,
resulting in higher average current in the inductor.
Alternatively, decreased output load results in an
increase in the output feedback voltage (FB1 or
FB2 pin). The controller responds by decreasing
the peak inductor current, resulting in lower aver-
age current in the inductor.
Soft Start / Enable
The input disconnect switch is activated when a
valid input voltage is present and the EN/SET pin
is pulled high. The slew rate control on the P-chan-
nel MOSFET ensures minimal inrush current as
the output voltage is charged to the input voltage,
prior to switching of the N-channel power MOS-
FET. Monotonic turn-on is guaranteed by the built-
in soft-start circuitry. Soft-start eliminates output
voltage overshoot across the full input voltage
range and all loading conditions.
At light load, the inductor OFF interval current goes
below zero and the boost converter enters discon-
tinuous mode operation. Further reduction in the
load results in a corresponding reduction in the
switching frequency. The AAT1230/1230-1 provide
pulsed frequency operation which reduces switching
losses and maintains high efficiency at light loads.
Fast and slow start-up time options are available.
The AAT1230 provides start-up to regulated output
voltage within 0.35ms of a low-to-high transition on
the EN/SET pin. Alternatively, the AAT1230-1 pro-
vides start-up to regulated output voltage within
3.5ms of a low-to-high transition on the EN/SET
pin, which dramatically reduces inrush current. A
longer soft-start, or turn-on, time is a preferred fea-
ture in battery-powered systems that exhibit higher
source impedances.
Operating frequency varies with changes in the
input voltage, output voltage, and inductor size.
Once the boost converter has reached continuous
mode, further increases in the output load will not
significantly change the operating frequency.
A
small 2.2µH (±20%) inductor is selected to maintain
high frequency switching (up to 2MHz) and high
efficiency operation for outputs from 10V to 18V.
Current Limit and Over-Temperature
Protection
The switching of the N-channel MOSFET termi-
nates when current limit of 3.0A (typical) is exceed-
ed. This minimizes power dissipation and compo-
nent stresses under overload and short-circuit con-
ditions. Switching resumes when the current
decays below the current limit.
Output Voltage Programming
The output voltage may be programmed through a
resistor divider network located from output capaci-
tor to FB1/FB2 pins to ground. Pulling the SEL pin
high activates the FB1 pin which maintains a 1.2V
reference voltage, while the FB2 reference is dis-
abled. Pulling the SEL pin low activates the FB2 pin
which maintains a 0.6V reference, while the FB1
reference is disabled. This function allows dynam-
ic selection between two distinct output voltages
across a 2X range (maximum). An additional resis-
tor between FB1 and FB2 allows the designer to
program the outputs across a reduced <2X range.
Thermal protection disables the AAT1230/1230-1
when internal dissipation becomes excessive.
Thermal protection disables both MOSFETs. The
junction over-temperature threshold is 140°C with
-15°C of temperature hysteresis. The output voltage
automatically recovers when the over-temperature
or over-current fault condition is removed.
Under-Voltage Lockout
Alternatively, the output voltage may be dynamical-
ly programmed to any of 16 voltage levels using the
S2Cwire serial digital input. The single wire S2Cwire
interface provides high-speed output voltage pro-
grammability across a 2X output voltage range.
Internal bias of all circuits is controlled via the VIN
input. Under-voltage lockout (UVLO) guarantees
sufficient VIN bias and proper operation of all inter-
nal circuitry prior to soft start.
1230.2006.10.1.4
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