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LTC3331

3331fc

For more information www.linear.com/LTC3331

AsecondpiezomaybeconnectedfromAC2toground.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. 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 LTC3331. 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 LTC3331 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

amountoflightfallingonit.Figure5showstherelationship

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

GND

LTC3331

PIEZO MODEL

VIN

CIN

AC1

3331 F04

IP sin(ωt)

Figure 4. LTC3331 Voltage Doubler Configuration

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.

Two solar panels can be connected to the LTC3331, one

fromAC1togroundandanotherfromAC2toground.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 so that

the selected UVLO window is optimal for both panels.

BB_IN/BAT_OUT, BAT_IN, VIN, and VOUT Capacitors

The input to the buck-boost, BB_IN, must be connected to

BAT_OUTforproperoperation.BAT_OUTistheoutputside

of the low battery disconnect switch. The series resistance

of this switch must be considered when selecting a bypass

capacitorforthecommonBAT_OUT=BB_INnode.Atleast

4.7μF to GND or greater should be used. For the higher

IPEAK_BB settings the capacitor may need to be larger to

smooth the voltage at the common BAT_OUT = BB_IN

node. The goal is to average the input current to the buck

boost so that the voltage droop at the common BAT_OUT

= BB_IN node is minimized.

A bypass capacitor of 1µF or greater can also be placed

at the BAT_IN pin. In cases where the series resistance of

the battery is high, a larger capacitor may be desired to

handle transients.

Figure 5. Typical Solar Panel Characteristics

VPANEL (V)

500

400

300

200

100

1500

1200

900

600

300

3331 F05

SANYO 1815 SOLAR PANEL

1800 LUX

500 LUX

200 LUX

1000 LUX

PANEL CURRENT

PANEL POWER

APPLICATIONS INFORMATION

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