LTC3588-2_10 Datasheet, PDF (10/18 Pages) Linear Technology – Piezoelectric Energy Harvesting Power Supply with 14V Minimum VIN

LTC3588-2
Operation
transition low until the new regulation point is reached.
When V_OUT is programmed to a lower voltage, PGOOD
will remain high through the transition.
Energy Storage
Harvested energy can be stored on the input capacitor
or the output capacitor. The high UVLO threshold takes
advantage of the fact that energy storage on a capacitor is
proportional to the square of the capacitor voltage. After
the output voltage is brought into regulation any excess
energy is stored on the input capacitor and its voltage
increases. When a load exists at the output the buck can
efficiently transfer energy stored at a high voltage to the
regulated output. While energy storage at the input utilizes
the high voltage at the input, the load current is limited
to what the buck converter can supply. If larger loads
need to be serviced the output capacitor can be sized to
support a larger current for some duration. For example,
a current burst could begin when PGOOD goes high and
would continuously deplete the output capacitor until
PGOOD went low.
The output voltages available on the LTC3588-2 are par-
ticularly suited to Li-Ion and LiFePO₄ batteries as well as
supercapacitors for applications where energy storage at
the output is desired.
Applications Information
Introduction
The LTC3588-2 harvests ambient vibrational energy
through a piezoelectric element in its primary application.
Common piezoelectric elements are PZT (lead zirconate
titanate) ceramics, PVDF (polyvinylidene fluoride) poly-
mers, or other composites. Ceramic piezoelectric elements
exhibit a piezoelectric effect when the crystal structure
of the ceramic is compressed and internal dipole move-
ment produces a voltage. Polymer elements comprised
of long-chain molecules produce a voltage when flexed
as molecules repel each other. Ceramics are often used
under direct pressure while a polymer can be flexed more
INCREASING
VIBRATION ENERGY
0
0
PIEZO CURRENT
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Figure 4. Typical Piezoelectric Load Lines
10
readily. A wide range of piezoelectric elements are avail-
able and produce a variety of open-circuit voltages and
short-circuit currents. Typically the open-circuit voltage
and short-circuit currents increase with available vibra-
tional energy as shown in Figure 4. Piezoelectric elements
can be placed in series or in parallel to achieve desired
open-circuit voltages.
The LTC3588-2 is well-suited to a piezoelectric energy
harvesting application. The 20V input protective shunt
can accommodate a variety of piezoelectric elements. The
low quiescent current of the LTC3588-2 enables efficient
energy accumulation from piezoelectric elements which
can have short-circuit currents on the order of tens of
microamps. Piezoelectric elements can be obtained from
manufacturers listed in Table 2.
Table 2. 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
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