LTC3588EDD-2#TRPBF Linear Technology, LTC3588EDD-2#TRPBF Datasheet - Page 11

• Manufacturer Part Number: LTC3588EDD-2#TRPBF
• Description: IC ENERGY HARVESTING PSU 10DFN
• Manufacturer: Linear Technology

Specifications of LTC3588EDD-2#TRPBF

• Applications: Energy Harvesting
• Current - Supply: 950nA
• Voltage - Supply: 2.7 V ~ 20 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
The LTC3588-2 will gather energy and convert it to a use-
able output voltage to power microprocessors, wireless
sensors, and wireless transmission components. Such a
wireless sensor application may require much more peak
power than a piezoelectric element can produce. However,
the LTC3588-2 accumulates energy over a long period of
time to enable effi cient use for short power bursts. For
continuous operation, these bursts must occur with a low
duty cycle such that the total output energy during the burst
does not exceed the average source power integrated over
an energy accumulation cycle. For piezoelectric inputs the
time between cycles could be minutes, hours, or longer
depending on the selected capacitor values and the nature
of the vibration source.
PGOOD Signal
The PGOOD signal can be used to enable a sleeping
microprocessor or other circuitry when V
regulation, as shown in Figure 5. Typically V
somewhere between the UVLO thresholds at this time
and a load could only be supported by the output capaci-
tor. Alternatively, waiting a period of time after PGOOD
goes high would let the input capacitor accumulate more
energy allowing load current to be maintained longer as
the buck effi ciently transfers that energy to the output.
While active, a microprocessor may draw a small load
when operating sensors, and then draw a large load to
transmit data. Figure 5 shows the LTC3588-2 responding
smoothly to such a load step.
10μF
25V
1μF
6V
4.7μF
6V
PZ1
V
CAP
V
D1
D0
IN
IN2
LTC3588-2
GND
Figure 5. 5V Piezoelectric Energy Harvester Powering a Microprocessor
with a Wireless Transmitter and 50mA Load Step Response
PGOOD
V
PZ2
OUT
SW
22μH
OUT
5V
IN
47μF
6V
reaches
will be
EN
CORE
MICROPROCESSOR
35882 F05a
GND
Input and Output Capacitor Selection
The input and output capacitors should be selected based
on the energy needs and load requirements of the ap-
plication. In every case the V
to withstand the highest voltage ever present at V
For 100mA or smaller loads, storing energy at the input
takes advantage of the high voltage input since the buck
can deliver 100mA average load current effi ciently to the
output. The input capacitor should then be sized to store
enough energy to provide output power for the length of
time required. This may involve using a large capacitor,
letting V
should be stored on the input so that the buck does not
reach the UVLO falling threshold which would halt energy
transfer to the output. In general:
The above equation can be used to size the input capaci-
tor to meet the power requirements of the output for an
application with continuous input energy. Here η is the
average effi ciency of the buck converter over the input
range and V
switch. This equation may overestimate the input capaci-
tor necessary since load current can deplete the output
capacitor all the way to the lower PGOOD threshold. It also
assumes that the input source charging has a negligible
T
X
P
V
LOAD
UVLO(FALLING)
IN
t
LOAD
AC-COUPLED
charge to a high voltage, or both. Enough energy
IN
25mA/DIV
50mV/DIV
CURRENT
VOLTAGE
OUTPUT
is the input voltage when the buck begins to
LOAD
=
5mA
2
1
≤ V
V
L = 22μH, C
LOAD STEP BETWEEN 5mA and 55mA
ηC
IN
= 18V
IN
IN
(
≤ V
V
OUT
IN
SHUNT
IN
2
= 47μF
− V
capacitor should be rated
250μs/DIV
UVLO(FALLING)
LTC3588-2
35882 F05b
2
)
11
35882f
IN
.