LTC3330_15 Datasheet, PDF (27/32 Pages) Linear Technology – Nanopower Buck-Boost DC/DC with Energy Harvesting Battery Life Extender

LTC3330
APPLICATIONS
Alternative Power Sources
The LTC3330 can accommodate a wide variety of input
sources. Figure 10 shows the LTC3330 internal bridge
rectifier connected to a 120V RMS AC line in series with
four 150k current limiting resistors. This produces a
peak current of 250µA with the LTC3330 shunt holding
V_IN at 20V. This current may be increased by reducing
the resistor values since the shunt can sink 25mA and
the bridge is rated for 50mA. An optional external Zener
diode (shown) may be required if the current exceeds
25mA. A transformer may also be used to step down the
voltage and reduce the power loss in the current limiting
resistors. This is a high voltage application and minimum
spacing between the line, neutral, and any high voltage
components should be maintained per the applicable UL
specification. For general off-line applications refer to UL
Regulation 1012.
Figure 11 shows an application where copper panels are
placed near a standard fluorescent room light to capaci-
tively harvest energy from the electric field around the
light. The frequency of the emission will be double the
line frequency for magnetic ballasts but could be higher
if the light uses electronic ballast. The peak AC voltage
and the total available energy will scale with the size of
the panels used and with the proximity of the panels to
the electric field of the light.
Using EH_ON to Program V_OUT
The EH_ON output indicates whether the energy harvesting
input or the battery is powering the output. The application
on the last page of this data sheet shows the EH_ON output
tied to the OUT2 input. When EH_ON is low the output is
programmed to 2.5V and the battery powers the output.
When energy harvesting is available EH_ON is high and
the output is programmed to 3.6V allowing for increased
storage of harvested energy. If energy harvesting goes
away, the output is again programmed to 2.5V and the
buck-boost converter will be in sleep until the output is
discharged to the wake-up threshold. If the energy stored
at 3.6V is enough to ride through a temporary loss of
energy harvesting then the only drain on the battery will
be the quiescent current in sleep.
For more information www.linear.com/LTC3330
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