ACT81460
Rev 1.0, 18-Dec-2018
synchronous boost converter, this limits the maximum
allowable output current in normal operation, but does
not limit short circuit current. Short circuit current is not
limited because the synchronous FET does not block
current flow from the SWBST pin to the output. The
VSYS voltage is always connected to VBST.
capacitance includes both the capacitance at the
boost’s output and at the load’s input.
Be sure to consider the capacitor’s DC bias effects and
maximum ripple current rating when using capacitors
smaller than 0805.
The user must take care to not load or leave a load con-
nected to the boost regulator output when it is disabled.
The output of the boost regulator cannot be discharged
to 0V due to these constraints and any load left con-
nected to the boost regulator can continue to draw
power because the boost regulator output voltage al-
ways trails the input voltage by one diode voltage.
A capacitor’s actual capacitance is strongly affected by
its DC bias characteristics. The output capacitor is typi-
cally an X5R, X7R, or similar dielectric. Use of Y5U, Z5U,
or similar dielectrics are not recommended due to their
wide variation in capacitance over temperature and volt-
age ranges.
Maximum Output Current
The maximum allowable output current is a function of
the peak switch current, the input voltage, and the out-
put voltage. The peak switch current limit can be set to
1.0A or 1.35A. This setting is not user adjustable. See
the CMI Options section of the datasheet for each CMI’s
setting. The following equation approximates the maxi-
mum available output current. Note that this is the boost
output current. The constant current into the ISNS pin is
still limited to 39.375mA.
ꢁꢕꢖ_ꢟꢠꢝꢡ
ꢅ
ꢓꢔ
ꢁꢘꢙꢙꢚꢛ_ꢜꢝꢞ
Compensation
ꢀ
∗
2
ꢅꢐꢑꢒ
The boost converter utilizes a proprietary internal com-
pensation scheme. No compensation design is required;
simply follow a few simple guide lines described below
when choosing external components.
Input Capacitor Selection
The boost converter requires dedicated input capacitor.
It should be a high quality, low-ESR, ceramic input ca-
pacitor. 1uF capacitors are typically suitable, but this
value can be increased without limit.
Inductor Selection
The boost converter requires a 2.2µH inductor. Ensure
that the inductor is rated for at least 1A peak current.
The inductor’s peak current is much higher than the
average output current.
Output Capacitor Selection
The boost converter is designed to take advantage of
the benefits of ceramic capacitors, namely small size
and very-low ESR capacitors. It is designed to operate
with a 10µF output capacitor. In order to ensure stability,
the Boost effective capacitance must be greater than
4µF and less than 22µF. The maximum allowable
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