AAT1232 Datasheet, PDF (12/17 Pages) Advanced Analogic Technologies – 24V 100mA Step-Up Converter

RMS calculation yields worst-case inductor loss.
The RMS value should be compared against the
manufacturer's temperature rise, or thermal derat-
ing, guidelines.
I_RMS =
I_PEAK
3
For a given inductor type, smaller inductor size leads
to an increase in DCR winding resistance and, in
most cases, increased thermal impedance. Winding
resistance degrades boost converter efficiency and
increases the inductor operating temperature.
P_{LOSS_INDUCTOR} = I_RMS2 · DCR
To ensure high reliability, the inductor temperature
should not exceed 100ºC. Manufacturer's recom-
mendations should be consulted. In some cases,
PCB heatsinking applied to the AAT1232 L_IN node
(non-switching) can improve the inductor's thermal
capability. PCB heatsinking may degrade EMI per-
formance when applied to the SW node (switching)
of the AAT1232.
Shielded inductors provide decreased EMI and
may be required in noise sensitive applications.
Unshielded chip inductors provide significant space
savings at a reduced cost compared to shielded
(wound and gapped) inductors. Chip-type induc-
tors have increased winding resistance when com-
pared to shielded, wound varieties.
Setting the Output Voltage
The output voltage may be programmed through a
resistor divider network located from the output to
FB1 and 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.
The AAT1232 output voltage can be programmed
by one of three methods. First, the output voltage
can be static by pulling the SEL logic pin either high
AAT1232
24V 100mA Step-Up Converter
or low. Second, the output voltage can be dynam-
ically adjusted between two pre-set levels within a
2X operating range by toggling the SEL logic pin.
Third, the output can be dynamically adjusted to
any of 16 preset levels within a 2X operating range
using the integrated S²Cwire single wire interface
via the EN/SET pin.
Option 1: Static Output Voltage
A static output voltage can be configured by pulling
the SEL either high or low. SEL pin high activates the
FB1 reference pin to 1.2V (nominal). Alternatively,
the SEL pin is pulled low to activate the FB2 refer-
ence at 0.6V (nominal). Table 1 provides details of
resistor values for common output voltages from 10V
to 24V for SEL = High and SEL = Low options.
In the static configuration, the FB1 pin should be
directly connected to FB2. The resistor between
FB1 and FB2 pins is not required.
Option 2: Dynamic Voltage Control Using SEL Pin
The output may be dynamically adjusted between
two output voltages by toggling the SEL logic pin.
Output voltages V_OUT(1) and V_OUT(2) correspond to
the two output references, FB1 and FB2. Pulling
the SEL logic pin high activates V_OUT(1), while
pulling the SEL logic pin low activates V_OUT(2).
The minimum output voltage must be greater than
the specified maximum input voltage plus margin to
maintain proper operation of the AAT1232 boost
converter. In addition, the ratio of output voltages
V_OUT(2)/V_OUT(1) is always less than 2.0, correspon-
ding to a 2X (maximum) programmable range.
Table 1 is provided to allow programming of com-
mon output voltages using Option 1 or 2. The feed-
back references FB1 and FB2 are enabled or dis-
abled using the SEL logic pin, corresponding to
V_OUT(1) and V_OUT(2).
Option 3: Dynamic Voltage Control Using
S²Cwire Interface
The output can be dynamically adjusted by the host
controller to any of 16 pre-set output voltage levels
using the integrated S²Cwire interface. The
EN/SET pin serves as the S²Cwire interface input.
The SEL pin must be pulled low when using the
S²Cwire interface.
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