V20W Datasheet, PDF (23/24 Pages) List of Unclassifed Manufacturers – PIEZOELECTRIC ENERGY HARVESTERS

APPLICATIONS INFORMATION - POWER MANAGEMENT IC INTEGRATION
Integration with LTC3588 Charge
Management IC
The LTC3588-1 is an ultra low quiescent current power
supply designed specifically for energy harvesting
applications. The part is designed to interface directly to
a piezoelectric or alternative A/C power source such as
the Volture™. The part rectifies a voltage waveform and
stores harvested energy on an external capacitor,
bleeds off any excess power via an internal shunt
regulator, and maintains a regulated output voltage by
means of a nanopower high efficiency synchronous
buck regulator. When combined with a Volture™ energy
harvester the LTC3588-1 forms the base of a full energy
harvesting solution.
advantage of the high voltage input since the buck
converter on the chip can deliver 100mA average
current efficiently to the load. The input capacitor
should then be sized to store enough energy to provide
output power for the length of time required, while also
not dropping to the undervoltage lockout falling
threshold (UVLO falling). This threshold is
approximately 300mV above the selected regulated
output. The following simple equation shows energy
out on the left-hand side, and effective energy in on the
right-hand side.
P_LOAD t _LOAD
1
2
C _IN V_IN2
V
2
UVLOFALLING
The LTC3588-1 will gather energy and convert it to a
useable output voltage to power any type of electronic
system. Some applications may require much more
peak power than a typical piezo can produce. The
LTC3588-1 accumulates energy over a long period of
time to enable efficient use for short power bursts. The
frequency of bursts allowed is directly proportional to
the power coming in from the piezo, and the total energy
per burst. The LTC3588-1 allows for four different pin
selectable output voltages (1.8, 2.5, 3.3 and 3.6).
PGOOD Signal
The PGOOD Signal is a logical high when V_OUT reaches
92% of the target value. This behavior is ideal for an
enable or interrupt pin on a microprocessor. That way,
the microprocessor can be idle until there is enough
energy to supply the burst.
Capacitor Selection
The input and output capacitors should be selected
based on the energy needs and load requirements of
the application. The V_IN capacitor is placed between
V_IN and GND. It should be rated to withstand the
highest voltage that the piezo can put out. For 100mA
or smaller loads, storing energy at the input takes
and
V_UVLOFALLING V_IN V_SHUNT
Where η is the efficiency of the buck converter, and
V_SHUNT is the voltage at which the input shunt
regulator bleeds power from the input (typically 20V).
See LTC3588 datasheet for more detail on η, as it
depends on the selected regulated output, the value of
the inductor, the load current, and temperature.
Keeping C_IN at this value or greater ensures that there
is enough power stored at the input to perform each
burst.
To size the output capacitor, the following equation is
used:
24mV
t _SLEEP C _{OUT I LOAD}
For capacitor values on the order of 10uF, some non-
ideal delays are introduced, resulting in V_OUT ripple.
For smoother operation, it is recommended that C_OUT
be kept higher than 10uF.
REVISION N0. 002 REVISION DATE: 01-23-2013
23