LTC3330_15 Datasheet, PDF (20/32 Pages) Linear Technology – Nanopower Buck-Boost DC/DC with Energy Harvesting Battery Life Extender

LTC3330
APPLICATIONS
PIEZO MODEL
LTC3330
AC1
V_IN
I_P sin(wt)
C_P
C_IN
GND
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Figure 4. LTC3330 Voltage Doubler Configuration
A second piezo may be connected from AC2 to ground. This
may be of use if the second piezo is mechanically tuned to
a different resonant frequency present in the system than
the first piezo. Of the two piezos the one operating at the
higher open circuit voltage will win over the other piezo
and its doubled voltage will appear on the V_IN capacitor.
To achieve maximum power transfer from the piezo with
the doubler the UVLO window should be set to the open
circuit voltage of the piezo.
Piezoelectric elements are available from the manufactur-
ers listed in Table 5.
Table 5. Piezoelectric Element Manufacturers
Advanced Cerametrics
www.advancedcerametrics.com
Piezo Systems
www.piezo.com
Measurement Specialties
www.meas-spec.com
PI (Physik Instrumente)
www.pi-usa.us
MIDE Technology Corporation www.mide.com
Morgan Technical Ceramics www.morganelectroceramics.com
Electromagnetic Energy Harvesting
Another alternative AC source is an electromagnetic vibra-
tion harvester in which a magnet vibrating inside a coil
induces an AC voltage and current in the coil that can then
be rectified and harvested by the LTC3330. The vibration
could be ambient to the system or it could be caused by
an impulse as in a spring loaded switch.
Solar Energy Harvesting
The LTC3330 can harvest solar energy as the bridge recti-
fier can be used to provide reverse protection for a solar
panel. A solar cell produces current in proportion to the
amount of light falling on it. Figure 5 shows the relationship
between current and voltage for a solar panel illuminated
with several levels of light. The maximum power output
occurs near the knee of each curve where the cell transi-
tions from a constant current device to a constant voltage
device. Fortunately, the peak power point doesn’t change
much with illumination and an appropriate UVLO window
can be selected so that the panel operates near the peak
power point for a majority of light conditions.
500
PANEL VOLTAGE
PANEL POWER
400 ^{1800 LUX}
1500
SANYO 1815 SOLAR PANEL
1200
300
900
1000 LUX
200
600
500 LUX
100
300
200 LUX
0
0
0
1
2
3
4
5
6
V_PANEL (V)
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Figure 5. Typical Solar Panel Characteristics
Two solar panels can be connected to the LTC3330, one
from AC1 to ground and another from AC2 to ground. Each
panel could be aimed in a different direction to capture light
from different angles or at different times of the day as the
sun moves. The panels should be similar or the same so
that the selected UVLO window is optimal for both panels.
BAT, V_IN, and V_OUT Capacitors
The input capacitor for the buck-boost on the BAT pin should
be bypassed with at least 4.7µF to GND. In cases where the
series resistance of the battery is high, a larger capacitor
may be desired to handle transients. A larger capacitor may
also be necessary when operating close to 1.8V with the
higher I_{PEAK_BB} selections to prevent the battery voltage
from falling below 1.8V when the buck-boost is switching.
The input capacitor to the buck on V_IN and the V_OUT capaci-
tor can vary widely and should be selected to optimize the
use of an energy harvesting source depending on whether
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For more information www.linear.com/LTC3330
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