10
dc2042af
DEMO MANUAL DC2042A
LTC3588-1: PIEZOELECTRIC ENERGY HARVESTING
POWER SUPPLY (VIBRATION OR HIGH IMPEDANCE
AC SOURCE)
The LTC3588-1 piezoelectric energy harvesting power
supply is selected by installing the power selection jumper,
JP1. The PGOOD signal can be routed to the Dust Header
by installing jumper JP5. The Dust Eterna board will switch
from battery power to energy harvester power whenever
the PGOOD signal is high,
provided that resistor R3 on
the Dust Mote board (DC9003A-B) is changed to 750kΩ
and R4 is changed to 5.1MΩ.
If the application requires a wide hyteresis window for
the PGOOD signal, the board has the provision to use the
independent PGOOD signal, shown in Figure 12, generated
by the LTC2935-2 and available on JP8. This signal is
labeled as the PGOOD signal for the LTC3459 circuit
(PGOOD_LTC3459), because the LTC3459 does not have
its own PGOOD output. The PGOOD_LTC3459 signal can
be used in place of any of the PGOOD signals generated
by the harvester circuits.
The board is configured from
the factory to use the PGOOD_LTC3459 signal as the
PGOOD signal to switch from battery power to energy
harvesting power.
The PGOOD_LTC3459 signal is always used to switch
the output voltage on the header.
Some loads do not like
to see a slowly rising input voltage. Switch Q3 ensures
that VSUPPLY and VMCU on the headers are off until the
energy harvested output voltage is high enough to power
the load. The LTC2935-2 is configured to turn on Q3 at
3.15V and turn off Q3 at 2.25V. With this circuit, the load
will see a fast voltage rise at start-up and be able to utilize
all the energy stored in the output capacitors between the
3.15V and 2.25V levels.
The optional components R1, R4, Q1 and C5 shown on
the schematic are not populated for a standard assembly.
The function of R1, R4, Q1 and C5 is to generate a short
PGOOD pulse that will indicate when the output capacitor
is charged to its maximum value. The short pulse occurs
every time the output capacitor charges up to the “output
sleep threshold,” which for a 3.3V output is 3.312V. By
populating these components the application can use
this short pulse as a sequence timer to step through the
program sequence or as an indication of when it can
perform energy-intensive functions, such as a sensor
read or a wireless transmission and/or receive, knowing
precisely how much charge is available in the output
capacitors. When this optional circuit is not used, the
amount of charge in the output capacitors is anywhere
between the maximum (C
OUT
• V
OUT_SLEEP
) to eight per-
cent low. In the case where the energy harvesting source
can support the average load continuously, this optional
circuit is not needed.
Diode D2 is an optional component used to “Diode-OR”
multiple energy harvesting sources together. This diode
would be used in conjunction with one or more of the
other Oring diodes, D3, D4 or D5. When the Oring diodes
are installed the parallel jumper would not be populated.
The diode drop will be subtracted from the output volt-
age regulation point, so it is recommended to change
the feedback resistors or select a higher output voltage
setpoint to compensate for the diode drop. When more
than one of these diodes is installed and the associated
energy harvester inputs are powered, the board will switch
between energy harvester power circuits as needed to
maintain the output voltage.
APPLICATION INFORMATION
Figure 8. Detailed Schematic of LTC3588-1 Piezoelectric Energy Harvesting Power Supply
