LTC3108IGN#PBF Linear Technology, LTC3108IGN#PBF Datasheet - Page 14

• Manufacturer Part Number: LTC3108IGN#PBF
• Description: IC CONV BOOST PROG 4.5MA 16SSOP
• Manufacturer: Linear Technology

Specifications of LTC3108IGN#PBF

• Applications: Energy Harvesting
• Current - Supply: 3mA
• Voltage - Supply: 20mV ~ 500mV
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Primary Input Voltage: 500mV
• No. Of Outputs: 3
• Output Voltage: 5V
• Output Current: 300mA
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +85°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Min: 20mV
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

applicaTions inForMaTion
LTC3108
Thermopile Generator
Thermopile generators (also called powerpile generators)
are made up of a number of series-connected thermo-
couples enclosed in a metal tube. They are commonly
used in gas burner applications to generate a DC output
of hundreds of millivolts when exposed to the high tem-
perature of a flame. Typical examples are the Honeywell
CQ200 and Q313. These devices have an internal series
resistance of less than 3Ω, and can generate as much as
750mV open-circuit at their highest rated temperature. For
applications in which the temperature rise is too high for
a solid-state thermoelectric device, a thermopile can be
used as an energy source to power the LTC3108. Because
of the higher output voltages possible with a thermopile
generator, a lower transformer turns ratio can be used
(typically 1:20, depending on the application).
Photovoltaic Cell
The LTC3108 converter can also operate from a single
photovoltaic cell (also known as a PV or solar cell) at light
levels too low for other low input voltage boost convert-
ers to operate. However, many variables will affect the
performance in these applications. Light levels can vary
over several orders of magnitude and depend on light-
ing conditions (the type of lighting and indoor versus
outdoor). Different types of light (sunlight, incandescent,
fluorescent) also have different color spectra, and will
produce different output power levels depending on which
type of photovoltaic cell is being used (monocrystalline,
polycrystalline or thin-film). Therefore, the photovoltaic
cell must be chosen for the type and amount of light avail-
able. Note that the short-circuit output current from the
cell must be at least a few milliamps in order to power
the LTC3108 converter
Non-Boost Applications
The LTC3108 can also be used as an energy harvester
and power manager for input sources that do not require
boosting. In these applications the step-up transformer
can be eliminated.
Any source whose peak voltage exceeds 2.5V AC or 5V
DC can be connected to the C1 input through a current-
limiting resistor where it will be rectified/peak detected. In

these applications the C2 and SW pins are not used and
can be grounded or left open.
Examples of such input sources would be piezoelectric
transducers, vibration energy harvesters, low current
generators, a stack of low current solar cells or a 60Hz
AC input.
A series resistance of at least 100Ω/V should be used
to limit the maximum current into the VAUX shunt
regulator.
COMPONENT SELECTION
Step-Up Transformer
The step-up transformer turns ratio will determine how
low the input voltage can be for the converter to start.
Using a 1:100 ratio can yield start-up voltages as low as
20mV. Other factors that affect performance are the DC
resistance of the transformer windings and the inductance
of the windings. Higher DC resistance will result in lower
efficiency. The secondary winding inductance will deter-
mine the resonant frequency of the oscillator, according
to the following formula.
Where L is the inductance of the transformer secondary
winding and C is the load capacitance on the secondary
winding. This is comprised of the input capacitance at pin
C2, typically 30pF , in parallel with the transformer secondary
winding’s shunt capacitance. The recommended resonant
frequency is in the range of 10kHz to 100kHz. See Table 5
for some recommended transformers.
Table 5. Recommended Transformers
VENDOR
Coilcraft
www.coilcraft.com
Frequency
=
2 • •
π
1
L
PART NUMBER
LPR6235-752SML (1:100 Ratio)
LPR6235-253PML (1:20 Ratio)
LPR6235-123QML (1:50 Ratio)
(sec)•
C
Hz
3108fa