Datasheet LTC3108 (Analog Devices) - 14
| Manufacturer | Analog Devices |
| Description | Ultralow Voltage Step-Up Converter and Power Manager |
| Pages / Page | 22 / 14 — APPLICATIONS INFORMATION. Thermopile Generator. COMPONENT SELECTION. … |
| File Format / Size | PDF / 643 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Thermopile Generator. COMPONENT SELECTION. Step-Up Transformer. Photovoltaic Cell
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link to page 14 LTC3108
APPLICATIONS INFORMATION Thermopile Generator
these applications the C2 and SW pins are not used and Thermopile generators (also called powerpile generators) can be grounded or left open. are made up of a number of series-connected thermo- Examples of such input sources would be piezoelectric couples enclosed in a metal tube. They are commonly transducers, vibration energy harvesters, low current used in gas burner applications to generate a DC output generators, a stack of low current solar cells or a 60Hz of hundreds of millivolts when exposed to the high tem- AC input. perature of a flame. Typical examples are the Honeywell A series resistance of at least 100Ω/V should be used CQ200 and Q313. These devices have an internal series to limit the maximum current into the VAUX shunt resistance of less than 3Ω, and can generate as much regulator. as 750mV open-circuit at their highest rated tempera- ture. For applications in which the temperature rise is too high for a solid-state thermoelectric device, a thermopile
COMPONENT SELECTION
can be used as an energy source to power the LTC3108. Because of the higher output voltages possible with a
Step-Up Transformer
thermopile generator, a lower transformer turns ratio can The step-up transformer turns ratio will determine how be used (typically 1:20, depending on the application). low the input voltage can be for the converter to start. Using a 1:100 ratio can yield start-up voltages as low as
Photovoltaic Cell
20mV. Other factors that affect performance are the DC The LTC3108 converter can also operate from a single resistance of the transformer windings and the inductance photovoltaic cell (also known as a PV or solar cell) at of the windings. Higher DC resistance will result in lower light levels too low for other low input voltage boost con- efficiency. The secondary winding inductance will deter- verters to operate. However, many variables will affect mine the resonant frequency of the oscillator, according the performance in these applications. Light levels can to the following formula. vary over several orders of magnitude and depend on lighting conditions (the type of lighting and indoor versus Frequency 1 = Hz 2 • π • L(sec)• C outdoor). Different types of light (sunlight, incandescent, fluorescent) also have different color spectra, and will Where L is the inductance of the transformer secondary produce different output power levels depending on which winding and C is the load capacitance on the secondary type of photovoltaic cell is being used (monocrystalline, winding. This is comprised of the input capacitance at pin polycrystalline or thin-film). Therefore, the photovoltaic C2, typically 30pF, in parallel with the transformer sec- cell must be chosen for the type and amount of light avail- ondary winding’s shunt capacitance. The recommended able. Note that the short-circuit output current from the resonant frequency is in the range of 10kHz to 100kHz. cell must be at least a few milliamps in order to power See Table 5 for some recommended transformers. the LTC3108 converter
Table 5. Recommended Transformers Non-Boost Applications VENDOR PART NUMBER
The LTC3108 can also be used as an energy harvester Coilcraft LPR6235-752SML (1:100 Ratio) www.coilcraft.com LPR6235-253PML (1:20 Ratio) and power manager for input sources that do not require LPR6235-123QML (1:50 Ratio) boosting. In these applications the step-up transformer Würth 74488540070 (1:100 Ratio) can be eliminated. www.we-online 74488540120 (1:50 Ratio) 74488540250 (1:20 Ratio) 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 Rev. D 14 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
APPLICATIONS INFORMATION Thermopile Generator
these applications the C2 and SW pins are not used and Thermopile generators (also called powerpile generators) can be grounded or left open. are made up of a number of series-connected thermo- Examples of such input sources would be piezoelectric couples enclosed in a metal tube. They are commonly transducers, vibration energy harvesters, low current used in gas burner applications to generate a DC output generators, a stack of low current solar cells or a 60Hz of hundreds of millivolts when exposed to the high tem- AC input. perature of a flame. Typical examples are the Honeywell A series resistance of at least 100Ω/V should be used CQ200 and Q313. These devices have an internal series to limit the maximum current into the VAUX shunt resistance of less than 3Ω, and can generate as much regulator. as 750mV open-circuit at their highest rated tempera- ture. For applications in which the temperature rise is too high for a solid-state thermoelectric device, a thermopile
COMPONENT SELECTION
can be used as an energy source to power the LTC3108. Because of the higher output voltages possible with a
Step-Up Transformer
thermopile generator, a lower transformer turns ratio can The step-up transformer turns ratio will determine how be used (typically 1:20, depending on the application). low the input voltage can be for the converter to start. Using a 1:100 ratio can yield start-up voltages as low as
Photovoltaic Cell
20mV. Other factors that affect performance are the DC The LTC3108 converter can also operate from a single resistance of the transformer windings and the inductance photovoltaic cell (also known as a PV or solar cell) at of the windings. Higher DC resistance will result in lower light levels too low for other low input voltage boost con- efficiency. The secondary winding inductance will deter- verters to operate. However, many variables will affect mine the resonant frequency of the oscillator, according the performance in these applications. Light levels can to the following formula. vary over several orders of magnitude and depend on lighting conditions (the type of lighting and indoor versus Frequency 1 = Hz 2 • π • L(sec)• C outdoor). Different types of light (sunlight, incandescent, fluorescent) also have different color spectra, and will Where L is the inductance of the transformer secondary produce different output power levels depending on which winding and C is the load capacitance on the secondary type of photovoltaic cell is being used (monocrystalline, winding. This is comprised of the input capacitance at pin polycrystalline or thin-film). Therefore, the photovoltaic C2, typically 30pF, in parallel with the transformer sec- cell must be chosen for the type and amount of light avail- ondary winding’s shunt capacitance. The recommended able. Note that the short-circuit output current from the resonant frequency is in the range of 10kHz to 100kHz. cell must be at least a few milliamps in order to power See Table 5 for some recommended transformers. the LTC3108 converter
Table 5. Recommended Transformers Non-Boost Applications VENDOR PART NUMBER
The LTC3108 can also be used as an energy harvester Coilcraft LPR6235-752SML (1:100 Ratio) www.coilcraft.com LPR6235-253PML (1:20 Ratio) and power manager for input sources that do not require LPR6235-123QML (1:50 Ratio) boosting. In these applications the step-up transformer Würth 74488540070 (1:100 Ratio) can be eliminated. www.we-online 74488540120 (1:50 Ratio) 74488540250 (1:20 Ratio) 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 Rev. D 14 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
