Datasheet LTC3588-2 (Analog Devices) - 10

LTC3588-2
OPERATION
transition low until the new regulation point is reached. regulated output. While energy storage at the input utilizes When VOUT is programmed to a lower voltage, PGOOD the high voltage at the input, the load current is limited will remain high through the transition. to what the buck converter can supply. If larger loads need to be serviced the output capacitor can be sized to
Energy Storage
support a larger current for some duration. For example, Harvested energy can be stored on the input capacitor a current burst could begin when PGOOD goes high and or the output capacitor. The high UVLO threshold takes would continuously deplete the output capacitor until advantage of the fact that energy storage on a capacitor is PGOOD went low. proportional to the square of the capacitor voltage. After The output voltages available on the LTC3588-2 are par- the output voltage is brought into regulation any excess ticularly suited to Li-Ion and LiFePO4 batteries as well as energy is stored on the input capacitor and its voltage supercapacitors for applications where energy storage at increases. When a load exists at the output the buck can the output is desired. efficiently transfer energy stored at a high voltage to the
APPLICATIONS INFORMATION Introduction
The LTC3588-2 harvests ambient vibrational energy readily. A wide range of piezoelectric elements are avail- through a piezoelectric element in its primary application. able and produce a variety of open-circuit voltages and Common piezoelectric elements are PZT (lead zirconate short-circuit currents. Typically the open-circuit voltage titanate) ceramics, PVDF (polyvinylidene fluoride) poly- and short-circuit currents increase with available vibra- mers, or other composites. Ceramic piezoelectric elements tional energy as shown in Figure 4. Piezoelectric elements exhibit a piezoelectric effect when the crystal structure can be placed in series or in parallel to achieve desired of the ceramic is compressed and internal dipole move- open-circuit voltages. ment produces a voltage. Polymer elements comprised The LTC3588-2 is well-suited to a piezoelectric energy of long-chain molecules produce a voltage when flexed harvesting application. The 20V input protective shunt as molecules repel each other. Ceramics are often used can accommodate a variety of piezoelectric elements. The under direct pressure while a polymer can be flexed more low quiescent current of the LTC3588-2 enables efficient energy accumulation from piezoelectric elements which can have short-circuit currents on the order of tens of microamps. Piezoelectric elements can be obtained from manufacturers listed in Table 2. INCREASING VIBRATION ENERGY TAGE
Table 2. Piezoelectric Element Manufacturers
Advanced Cerametrics www.advancedcerametrics.com PIEZO VOL Piezo Systems www.piezo.com Measurement Specialties www.meas-spec.com PI (Physik Instrumente) www.pi-usa.us MIDE Technology Corporation www.mide.com 0 0 Morgan Technical Ceramics www.morganelectroceramics.com PIEZO CURRENT 35882 F04
Figure 4. Typical Piezoelectric Load Lines
35882fc 10 For more information www.linear.com/LTC3588-2 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Revision History Typical Application Related Parts