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ltc 3107 1 3107f for more information www.linear.com/ltc3107 typical application features description ultra-low voltage energy harvester and primary battery life extender the lt c ? 3107 is a highly integrated dc / dc converter de - signed to extend the life of a primary battery in low power wireless systems by harvesting and managing surplus en - ergy f rom extremely lo w input voltage sources such as tegs ( thermoelectric generators) and thermopiles. the step - up topology operates from input voltages as low as 20 mv . using a small step - up transformer, the ltc3107 provides a complete power management solution for typical wireless sensor applications that operate from a primary battery. the 2.2 v ldo can be used to power an external microprocessor, while the main output voltage automatically adapts to match the voltage of the primary battery. the ltc3107 seamlessly transitions from battery power to harvested power whenever harvested energy is available, extending the life of the battery. the bat_off indicator can be used to track battery usage. an optional storage capacitor accumulates excess harvested energy, further extending battery life. the ltc3107 is available in a small, thermally enhanced 10-lead (3mm 3mm) dfn package. teg powered thermal harvester with primary cell life extender percentage of added battery life vs teg surface temperature applications n thermal energy harvesting assisted power management system n v out tracks the primary battery voltage n 2.2v ldo output n reserve energy output, clamped to 4.3v n operates from inputs as low as 20mv n battery in-use indicator (bat_off) n i q from battery: n 80na when energy harvesting n 6a no energy harvesting n standard, compact step-up transformer n small, thermally enhanced 10-lead (3mm 3mm) dfn package n industrial wireless sensing n remote sensor and radio power n hvac n automatic metering n building automation, security n predictive maintenance, condition monitoring l , lt , lt c , lt m , linear technology and the linear logo are registered trademarks and vldo is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. 3107 ta01a c1 thermoelectric generator c2sw gnd 10f 10f v bat v in bat_off cstore (optional) ltc3107 vaux vstore 3.6v t1 1nf 1:100 330pf + 2.2f vldo vldo v out v out c out 3.6v + surface temperature (c) t a = 23c 25 battery life extension (%) 100000 35 30 50 45 40 3107 ta01 100 1000 10000 10 1 0.5hz x mt rate (227w avg) 1hz x mt rate (437w avg) 2hz x mt rate (679w avg) cui cp20151 teg 24 24 22mm heatsink natural convection downloaded from: http:///
ltc 3107 2 3107f for more information www.linear.com/ltc3107 pin configuration absolute maximum ratings sw voltage ................................................. C0.3 v to 2v c1 voltage ( note 5) ...................... C0.3 v to ( vaux +0.6 v) c2 voltage ( note 5) ......................................... C8 v to 8v vaux ..................................................... 15 ma into vaux v bat , vstore ........................................... C0.3 v to 4.5 v v out , bat _off .......................................... C0.3 v to 4.5 v vldo ........................................................ C0.3 v to 4.5 v operating junction temperature range ( note 2) ............................................. C40 c to 125 c storage temperature range .................. C65 c to 150 c (note 1) top view dd package 10-lead (3mm 3mm) plastic dfn 10 96 7 8 45 3 2 1 swc2 c1 bat_off gnd vaux vstore v out v bat vldo 11 gnd t jmax = 125c, ja = 43c/w, jc = 5.5c/w exposed pad (pin 11) is gnd, must be soldered to pcb (note 4) order information lead free finish tape and reel part marking* package description temperature range ltc3107edd#pbf ltc3107edd#trpbf lgmd 10-lead (3mm 3mm) plastic dfn C40c to 125c ltc3107idd#pbf ltc3107idd#trpbf lgmd 10-lead (3mm 3mm) plastic dfn C40c to 125c consult lt c marketing for parts specified with wider operating temperature ranges . * the temperature grade is identified by a label on the shipping container . for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ downloaded from: http:///
ltc 3107 3 3107f for more information www.linear.com/ltc3107 electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the ltc3107 is tested under pulsed load conditions such that t j t a . the ltc3107e is guaranteed to meet specifications from 0c to 85c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the ltc3107i is guaranteed over the full C40c to 125c operating junction temperature range. note that the maximum ambient temperature consistent with these specifications, is determined by specific operating conditions in conjunction with board layout, the rated thermal package thermal resistance and other environmental factors. the junction temperature (t j ) parameter conditions min typ max units minimum harvester start-up voltage using 1:100 transformer turns ratio 20 30 mv harvester no-load input current using 1:100 transformer turns ratio, v in = 20mv, all outputs charged and in regulation 3 5 ma harvester input voltage range using 1:100 transformer turns ratio l v startup 500 mv v bat voltage range l 2.0 4.0 v v bat current limit v out = 0v, vaux = 0v (battery insertion) l 2 30 60 ma v out = (v bat C 0.4v) l 30 70 100 ma v bat quiescent current vaux > v bat (harvesting) vaux < v bat (not harvesting) 80 6 110 7.5 na a v bat reverse current vaux = 4v, v bat = 2.0v 0 na v out voltage (average) vaux > v bat (harvesting), relative to v bat c out 47f vaux < v bat (not harvesting), relative to v bat c out 47f l l C70 C270 C30 C220 C15 C140 mv mv ldo output voltage 0.5ma load l 2.134 2.2 2.266 v ldo load regulation i vldo = 0ma to 2ma 0.8 1.5 % ldo line regulation for v out from 2.5v to 4v 0.1 0.2 % ldo dropout voltage i vldo = 2ma l 100 200 mv ldo current limit vldo = 0v l 10 20 40 ma vaux/vstore clamp voltage current into vaux = 1ma l 4.13 4.3 4.48 v v out quiescent current vaux > v out > v bat 10 100 na vstore leakage current vstore = 4v, vaux > vstore 10 100 na vstore to v out discharge path resistance vstore = 4v v out < v bat C60mv 120 200 bat_off threshold (falling) measured on v out relative to v bat C280 C230 C180 mv bat_off threshold (rising) measured on v out relative to v bat C60 C30 C15 mv bat_off v ol sink current = 100a 0.15 0.2 v bat_off v oh source current = 0 v out v bat_off pull-up resistance 0.6 1 1.4 m n-channel mosfet on-resistance c2 = 5v (note 3) 0.5 the l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at t a = 25c (note 2). vaux = 4v, v b at = 3.6v unless otherwise noted. is calculated from the ambient temperature (t a ) and power dissipation (p d ) according to the formula: t j = t a + (p d ? ja c/w), where ja is the package thermal impedance.note 3: specification is guaranteed by design and not 100% tested in production.note 4: failure to solder the exposed backside of the package to the pc board ground plane will result in a thermal resistance much higher than 43c/w. note 5: the absolute maximum rating is a dc rating. under certain conditions in the applications shown, the peak ac voltage on the c1 and c2 pins may exceed their absolute maximum rating. this behavior is normal and acceptable because the current into the pin is limited by the impedance of the coupling capacitor. downloaded from: http:///
ltc 3107 4 3107f for more information www.linear.com/ltc3107 typical performance characteristics t a = 25c, unless otherwise noted. i vout and efficiency vs v in , 1:20 ratio transformer i in vs v in , (v out = 0v) i vout and efficiency vs v in , 1:50 ratio transformer i vout and efficiency vs v in , 1:100 ratio transformer input resistance vs v in i vout vs v in and source resistance, 1:100 ratio resonant switching waveforms ldo dropout voltage v in (mv) i in (ma) 3107 g01 1000 100 10 1 10 100 1000 1:50 ratio, c1 = 4.7n 1:100 ratio, c1 = 1n 1:20 ratio , c1 = 10n v in (mv) 0 input resist ance () 5 6 74 3 100 200 400 300 500 10 2 8 9 10 3107 g05 1:20 ratio 1:50 ratio 1:100 ratio v in open-circuit (mv) i vout (a) 100 1000 10 3107 g06 0 100 200 300 400 500 12 5 10 c1 = 1nf 10s/div c1 pin 2v/div c2 pin 2v/div sw pin 50mv/ div 3107 g07 v in = 20mv 1:100 ratio transformer ldo load (ma) 0 0.00 dropout voltage (v) 0.04 0.08 0.12 0.5 1 1.5 2 3 2.5 3.5 0.16 0.20 0.02 0.06 0.10 0.14 0.18 4 3107 g08 load (ma) change in vldo (%) 3107 g10 0.00 C0.50C1.00 C1.50 C2.00 C2.50 C3.00 C3.50 C4.00 0.01 0.10 1.00 10.00 ldo load regulation v in (mv) 0 i vout (a) efficiency (%) 2500 3000 3500 20001500 100 200 400 300 500 500 0 1000 4000 50 60 7040 30 10 0 20 80 3107 g02 i vout (v out = 3.6v) efficiency(v out = 3.6v) c1 = 10nf v in (mv) 0 i vout (a) efficiency (%) 2000 2400 2800 16001200 100 200 400 300 500 400 0 800 3200 50 60 7040 30 10 0 20 80 3107 g03 c1 = 4.7nf i vout (v out = 3.6v) efficiency(v out = 3.6v) v in (mv) 0 i vout (a) efficiency (%) 1000 1200 800600 100 200 400 300 500 200 0 400 1400 50 60 7040 30 10 0 20 3107 g04 c1 = 1nf i vout (v out = 3.6v) efficiency(v out = 3.6v) downloaded from: http:///
ltc 3107 5 3107f for more information www.linear.com/ltc3107 typical performance characteristics t a = 25c, unless otherwise noted. i clamp (ma) change in vaux (%) 3107 g11 1.801.50 1.20 0.90 0.60 0.30 0.00 0.01 0.1 1 10 5ms/div 100mv/div 20ma/div 3107 g13 i ldo c ldo = 2.2f v bat = 3.6v vldo 200ms/div 200mv/div 2v/div 3107 g14 bat_off 20a load with a20ma, 10ms long pulse every second v bat v out v bat = 3.6v 200ms/div 200mv/div 2v/div 3107 g15 bat_off 20a load with a20ma, 10ms long pulse every second v bat v out v bat = 3.6v 200ms/div 200mv/div 2v/div 3107 g16 bat_off 20a load with a20ma, 50ms long pulse every second v bat v out v bat = 3.6v 5ms/div 2v/div 3107 g19 v bat v out vaux vldo ldo step load response (10a to 10ma) vaux voltage vs clamp current i vout current limit vs v out pulsed v out load, no harvesting pulsed v out load, harvesting (not using battery) pulsed v out load, harvesting insufficient c out or insufficient harvested energy voltage sequencing when battery is connected v bat (v) current limit (ma) 3107 g12 8070 50 6040 30 20 10 0 2.0 3.0 2.5 3.5 4.0 v out = v bat C0.4v v out = 0v, harvesting v out = 0v, v aux = 0v, not harvesting downloaded from: http:///
ltc 3107 6 3107f for more information www.linear.com/ltc3107 10s/div 2v/div 3107 g20 v bat on off v out vstore batt_off 500ms/div 2v/div 100mv/div 3107 g21 v bat harvester off harvester on v out batt_off v bat = 3.6v 5s/div 2v/div 3107 g22 v bat v out batt_off vstore 10ms/div 20mv/div (ac-coupled) 3107 g23 v bat = 3.6v 10ms/div 20mv/div (ac-coupled) 3107 g24 v bat = 3.6v voltage sequencing while harvester is turned on and off v out transitioning between harvester and battery power v out ripple while harvesting v out ripple, not harvesting v store holding-up v out (v b at = 3v, c store = 1300f, i out = 50a, holdup = 37 sec) typical performance characteristics t a = 25c, unless otherwise noted. downloaded from: http:///
ltc 3107 7 3107f for more information www.linear.com/ltc3107 pin functions vaux ( pin 1): output of the internal rectifier circuit and v cc for the ic. bypass vaux with 10 f of capacitance. an active shunt regulator clamps vaux to 4.3 v ( typical). vstore ( pin 2): output for the optional energy storage capacitor. a large capacitor may be connected from this pin to gnd to store excess harvested energy, further ex - tending batter y life in the event of an increase in load. it will be charged up to the maximum vaux clamp voltage. if not used, this pin should be left open or tied to vaux. v out ( pin 3): main output of the converter. when harvested energy is available, the voltage at this pin is regulated to 30 mv below the voltage on the v bat pin. if no ( or insufficient) harvested energy is available to power the load, v out will be regulated to a voltage about 230 mv below the voltage at v bat . a large decoupling capacitor is usually required from v out to gnd, to allow the output to ride-through short duration load transients without drawing current from the battery. a minimum capacitance value of 47 f is recommended for all applications. see the applications information section for details on sizing the capacitor. v b at ( pin 4): primary battery input. this pin must be connected to a primary battery. this input will be used during start-up to bring v out into regulation ( as well as vaux and vldo). after start-up, this input is used only as a reference voltage for v out , unless there is insufficient harvested power available, in which case it will power the ic and the loads on v out and vldo. a ceramic decoupling capacitor with a minimum value of 10 f is recommended from v bat to gnd. vldo ( pin 5): output of the 2.2 v ldo, which is powered from the higher of v out or vaux. connect a 2.2 f or larger ceramic capacitor from vldo to gnd. if not used, this pin should be tied to vaux. gnd ( pin 6 and exposed pad pin 11): ground pin for the ic. the exposed pad must be soldered to the pcb ground plane. it serves as a ground connection, and as a means of conducting heat away from the die.bat _ off ( pin 7): battery off output. this pin is an indicator of when the battery is in use. a logic low indicates that the battery is being used to assist in regulating v out . the pin will go high when v out is in regulation and the battery is not being used. it is not designed to source any current. it has an internal 1m pull-up resistor to v out . c 1 ( pin 8): input to the charge pump and rectifier circuit. connect a capacitor from this pin to the secondary winding of the step-up transformer.c 2 ( pin 9): input to the n-channel gate drive circuit. con - nect a capacitor from this pin to the secondary winding of the step-up transformer.sw ( pin 10): drain of the internal n-channel switch. con - nect this pin to the primary winding of the transformer. downloaded from: http:///
ltc 3107 8 3107f for more information www.linear.com/ltc3107 block diagram 3107 bd c1c2 sw 4.3v 1.2vv ref sw primary battery 3.6v typ v bat v out c out bat_off pbad 200mv 30mv v out c1 c in v in vldo v store c store (optional) 10f 1:100 c2 sync rectify reference v out v out 2.2v charge control vaux + ? + ? ilim s r q ltc3107 pon 25mv hyst 25mv hyst 1.3 60 70ma 0.5 60 1m gnd 2.2f 10f pad v ref ldo v best + C C + downloaded from: http:///
ltc 3107 9 3107f for more information www.linear.com/ltc3107 operation the ltc3107 is an ultra-low input voltage step-up dc/dc converter and power manager for extending the battery life of low power wireless sensors and other low power applications that utilize a primary battery. the ltc3107 intelligently manages harvested energy from sources such as tegs ( thermo-electric generators) to service the output while minimizing battery drain, thereby maximizing battery life. to simplify the adoption of energy harvesting by applica - tions presently powered by a primary battery, the ltc3107 is designed to use the voltage on the v bat pin not only as an energy source to power the outputs in the absence of harvested input energy, but also as a voltage reference to regulate v out . in this way, the ltc3107 automatically adapts v out to track whatever battery voltage the applica- tion is already designed for, in the range of 2v to 4.0v. the ltc3107 is suitable for extending the battery life in applications where the average power draw is very low, but where periodic pulses of higher load current may be required. this is typical of wireless sensor applications, where the quiescent power draw is extremely low a high percentage of the time, except during transmit bursts when circuitry is powered up to make measurements and transmit data. the ltc3107 can also be used to trickle charge a standard capacitor or supercapacitor to store excess harvested energy when it is available. this further extends the life of the primary battery, by allowing the converter to ride- through periods of heavier load, or times when no harvested energy is coming in by drawing from this reservoir before switching over to the battery. v b at input the v bat input should be connected to a primary battery with a voltage between 2 v and 4.0 v. typical examples are 2 alkaline cells, a single 3 v lithium coin cell, or a 3.6 v li-socl 2 battery. these are representative batteries that would normally power the application without the benefit of energy harvesting. the ltc3107 is designed to use the battery to start-up the ic and power v out and vldo with or without any harvested energy available. if there is no harvester input, or insufficient harvester input to power the load, then v out will be provided by the battery through a current-limited switch internal to the ltc3107, and will be hysteretically regulated to a voltage 230 mv below the battery voltage. the vldo output will be fixed at 2.2 v unless v bat is below 2.2v, in which case it will track v bat . when no harvested energy is available, the ltc3107 average quiescent current draw from the battery is typically 6a. if there is sufficient harvested energy available, then v out will be regulated to a voltage approximately 30 mv below the v bat voltage, and the battery will not be used to power v out . in this case, the battery current draw will drop to just 80na typical.oscillator the ltc3107 utilizes a mosfet switch to form a resonant step-up oscillator using an external step-up transformer and a small coupling capacitor. this allows it to boost input voltages as low as 20 mv up to values high enough to provide multiple regulated output voltages for powering other circuits. the frequency of oscillation is determined by the inductance of the transformer secondary winding, and is typically in the range of 10 khz-100khz. for input voltages as low as 20 mv, a primary-secondary turns ratio of about 1:100 is recommended. for higher input voltages, this ratio can be lower. see the applications section for more information on selecting the transformer.charge pump and rectifier the ac voltage produced on the secondary winding of the transformer is boosted and rectified using an external charge pump capacitor ( from the secondary winding to pin c1) and the rectifiers internal to the ltc3107. the rectifier circuit feeds current into the vaux pin, providing charge to the external vaux capacitor. once vaux exceeds 2 v, synchronous rectifiers in parallel with each of the diodes take over the job of rectifying the input voltage, improv - ing efficiency. downloaded from: http:///
ltc 3107 10 3107f for more information www.linear.com/ltc3107 vaux the active circuits within the ltc3107 are powered from vaux, which should be bypassed with a capacitor of 10 f minimum. the quiescent current draw on vaux is typically just 6 a. if harvested energy is available, this current will come from the harvesting source. if there is no harvesting energy available, the vaux supply current will come from v bat . a shunt regulator limits the maximum voltage on vaux to 4.3 v typical. it shunts to ground any excess harvested current into vaux when there is no load on the converter or the input source is generating more power than is required by the load. if the optional storage capacitor is connected to vstore, then the excess current will be used to charge the storage capacitor, and current will not be shunted to ground until the storage capacitor is charged up to the 4.3v clamp level. voltage reference the ltc3107 includes a precision, micropower reference, for accurate regulated output voltages. this reference becomes active as soon as vaux exceeds 1.9v. low dropout linear regulator (ldo) the ltc3107 includes a low current ldo to provide a regulated 2.2 v output for powering low power processors . the ldo is powered by the higher of vaux or v out , and requires a minimum of 2.2 f ceramic decoupling capacitor . larger capacitor values can be used without limitation. if the ldo is not being used, the vldo pin should be tied to vaux. v out the ltc3107 is designed to fit seamlessly into existing applications that run from a primary battery, while adding the benefit of energy harvesting to increase the life of the battery. the main output voltage on v out is designed to track the battery voltage on v bat . if no harvested energy is available, or the energy is insufficient to maintain v out , then v out will be hysteretically regulated 230 mv below v bat by periodically connecting it to v bat . when enough harvested energy is available to power the load, v out will be hysteretically regulated to a voltage typically 30 mv below v bat , and the battery will not be used. in this condition, the current drain on the battery is only 80na typical.in a typical application, a bulk decoupling capacitor ( usually a few hundred microfarads) is connected to v out to allow it to ride-through small, periodic load transients typical of a wireless sensor application. if the v out capacitor is sized appropriately ( see the applications information section for more detail), and the average harvested input power exceeds the average load power, then battery energy will never be used.bat_off the bat_off output is a digital output with an internal pull-up to v out . bat_off is an indicator of when the battery is being used to help maintain v out . if bat_off is high, it indicates that v out ( and vldo) are being powered entirely by the harvested input power ( including the vstore capacitor), and the battery is not being used. in this case, the battery current draw is only 80 na typical. when bat_off goes low, it indicates that the battery is being used to help maintain v out and vldo in regulation. this indicates that either there is no harvested energy available, or it is insufficient to power the load entirely. if the c out capacitor is not sized properly, the bat_off indicator may go low during a pulsed load event, to in- dicate that current is being drawn from the battery. see the applications information section of this data sheet for guidance on sizing the c out capacitor. vstore the vstore output can be used to charge an optional storage capacitor, after v out has reached regulation. the vstore capacitor value can range from hundreds of micro-farads up to farads. once v out has reached regula- tion, the vstore output will be allowed to charge up to the maximum v aux voltage if excess harvested energy is available. the storage capacitor on vstore can be used to power the system in the event that the input source is lost, or is unable to provide the current demanded by the loads on v out and vldo, or simply to supplement the operation downloaded from: http:///
ltc 3107 11 3107f for more information www.linear.com/ltc3107 v out capacitor to reduce v out ripple during load steps. the ltc3107 will automatically use energy from the vstore capacitor to maintain v out in regulation before drawing any current from the battery. note that it may take a long time to charge a large vstore capacitor, depending on the harvested energy available and the loading on v out and vldo. if a storage capacitor is not being used, the vstore pin can be left open or tied to vaux. short circuit protection all outputs of the ltc3107 are current limited to protect against short circuits. output voltage sequencing a diagram showing the typical output voltage profiles dur - ing start-up with an energy harvesting source is shown in figure 1. operation operation with battery removedalthough the ltc3107 is designed to have a primary battery connected to v bat , there may be times when the battery is removed for a short duration ( such as for maintenance). if there is sufficient harvested energy ( or stored energy) available to maintain v out and vldo, then the current draw on v bat will be only 80 na, plus any leakage from the v bat decoupling capacitor, which should be very small ( typically less than 1 a). in this case, if the battery is removed, the capacitor on v bat will hold-up the v bat voltage, allowing v out to maintain regulation. as the v bat voltage slowly decays due to leakage, v out will follow it. for example, if the v bat decoupling capacitor is 20 f nominal, and the total leakage on v bat is 0.1 a, then v bat and v out will decay at a rate of 5mv per second. if there is no harvested or stored energy available to power v out and vldo, then these voltages will drop when the battery is removed. in this case, their rate of decay will be determined solely by the amount of capacitance on v out (since it is generally much larger than the vldo capaci- tor) and the combined load current on v out and vldo. downloaded from: http:///
ltc 3107 12 3107f for more information www.linear.com/ltc3107 operation i out 2ma/div v out 1v/div v bat 1v/div bat_off 1v/div i harvest 50a/div vstore 1v/div vldo 1v/div 100 200 300 400 500 600 700 800 900 1000 battery connected time (not to scale) 3107 f01 figure 1. typical start-up voltage waveforms downloaded from: http:///
ltc 3107 13 3107f for more information www.linear.com/ltc3107 volts i out bat_off stays high pulsed load battery switchover threshold 230mv230mv v out v out v bat v bat 20ma 20a volts battery switchover threshold bat_off pulses time (not to scale) time (not to scale) i out pulsed load 20ma 20a time (not to scale) 3107 f02c 3107 f02b time (not to scale) figure 2a. v out waveform during a pulsed load, with correctly sized c out and i harvest > i load (average) figure 2b. v out waveform during a pulsed load, with insufficient c out value, i harvest > i load (average) operation downloaded from: http:///
ltc 3107 14 3107f for more information www.linear.com/ltc3107 operation volts i out bat_off stays low pulsed load 230mv v out v bat 20ma 20a time (not to scale) time (not to scale) i out pulsed load 20ma 20a time (not to scale) 3107 f02d 3107 f02c volts bat_off stays low 230mv v out v bat time (not to scale) figure 2c. v out waveform during a pulsed load when i harvest < i load (average) figure 2d. v out waveform during a pulsed load when not harvesting downloaded from: http:///
ltc 3107 15 3107f for more information www.linear.com/ltc3107 introduction the ltc3107 is designed to gather energy from very low input voltage sources and use it to extend the life of a primary battery in applications such as wireless sensors. the ltc3107 is designed to accumulate and manage energy over long periods of time to enable short power bursts for acquiring and transmitting data. these bursts must occur at a low enough duty cycle such that the total output energy during the burst does not exceed the aver - age source power integrated over the accumulation time between bursts. in these instances, the battery will not be used at all, so the battery life may be extended up to the shelf life of the battery. harvesting input voltage sources the ltc3107 can operate from a number of low input voltage sources, such as thermoelectric generators, ther - mopiles and coil and magnet transducers. the minimum input voltage required for a given application will depend on the transformer turns ratio, the load power required, and the internal dc resistance ( esr) of the voltage source. lower esr sources ( typically less than 10) will allow the use of lower input voltages, and higher output power capability. for a given transformer turns ratio, there is a maximum recommended input voltage to avoid excessively high secondary voltages and power dissipation in the shunt regulator. it is recommended that the maximum input voltage times the turns ratio be less than 50. note that a low esr bulk decoupling capacitor may be required across the input source to prevent large voltage droop and ripple caused by the sources esr and the peak primary switching current ( which can reach hundreds of milliamps). the time constant of the filter capacitor and the esr of the voltage source should be much longer than the period of the resonant switching frequency. applications information peltier module (thermoelectric generator) a peltier module ( also known as a thermoelectric cooler) is made up of a number of series-connected p-n junctions, sandwiched between two parallel ceramic plates. although peltier modules are often used as coolers by applying a dc voltage to their inputs, they will also generate a dc output voltage, using the seebeck effect, when the two plates are held at different temperatures. the polarity of the output voltage will depend on the polarity of the tem - perature differential between the plates. the magnitude of the output voltage is proportional to the magnitude of the temperature differential between the plates. when used in this manner, a peltier module is referred to as a thermoelectric generator (teg). the low voltage capability of the ltc3107 design allows it to operate from a teg with temperature differentials as low as 1 c to 2 c, making it ideal for harvesting energy in applications where a temperature difference exists between two surfaces or between a surface and the ambient temperature. the internal resistance ( acr) of most tegs is in the range of 1 to 10, allowing for reasonable power transfer. the curves in figure 3 show the open-circuit output voltage and maximum power transfer for a typical teg with an acr of 2 over a 20 c range of temperature differential. it can be seen that an output power of a few hundred microwatts is easily achievable with a small temperature differential. this is often more than enough to satisfy the average power demand of a low power wireless sensor. note that the thermal resistance of most tegs is typically quite low (2 k/w to 20 k/w). therefore, it may be difficult to sustain a large temperature differential across the teg. the temperature differential will depend on the amount of heat transfer available. in most applications, this will be determined by the size of the heat sink used on the teg, and the amount of air flow. for optimal performance, the thermal resistance of the heat sink should be at least as low as the thermal resistance of the teg being used. downloaded from: http:///
ltc 3107 16 3107f for more information www.linear.com/ltc3107 applications information also note that most peltier cells are limited to a maximum absolute temperature of around 125 c. for applications with a heat source above this temperature, a thermopile generator should be considered, as they are designed for much higher operating temperatures.teg load matching the ltc3107 was designed to present a minimum input resistance ( load) in the range of 2 to 10, depending primarily on input voltage and transformer turns ratio ( as shown in the typical performance curves). for a given turns ratio, as the input voltage drops, the input resistance increases. this feature allows the ltc3107 to optimize power transfer from sources with a few ohms of source resistance, such as a typical teg. note that a lower source resistance will always provide more output current capa - bility ( all other things being equal) by providing a higher input voltage under load to the converter. delta t (c) across teg 0 teg open ckt voltage (v) max p out (mw) 0.30.1 0.2 0 100.1 10.01 20 10 15 5 3107 f03 25 max p out voc teg acr = 2 figure 3. typical performance of a peltier module acting as a power generator table 1. peltier module manufacturers manufacturer web address marlow industries www.marlow.com nextreme www.nextreme.com tellurex www.tellurex.com ferro tec www.ferrotec.com z-max www.z-max.jp/peltier_en/peltier cui www.cui.com laird technologies www.lairdtech.com table 2. peltier module distributors manufacturer web address digi-key www.digikey.com newark www.newark.com farnell www.farnell.com uk.farnell.comde.farnell.com peltier module suppliers peltier modules are available in a wide range of sizes and power capabilities, from less than 10 mm square to over 50mm square. they are typically 2 mm to 5 mm thick. a list of manufacturers that make peltier modules appropriate for use with the ltc3107 is given in table 1. distributors that sell peltier modules are shown in table 2. thermopile generatorthermopile generators ( also called powerpile generators) are made up of a number of series connected thermocouples , 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 temperature of a flame. typical examples are the honeywell cq200 and q 313. these devices have an internal series resistance of less than 3, and can generate as much as 750 mv open circuit at their highest rated temperature. for applications where the temperature rise is too high for a traditional peltier thermoelectric device, a thermopile can be used as an energy source to power the ltc3107. because of the higher output voltages possible with a thermopile generator, a much lower transformer turns ratio is recommended ( typically 1:10 or 1:20, depending on the application). 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 downloaded from: http:///
ltc 3107 17 3107f for more information www.linear.com/ltc3107 applications information 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 formula: freq = 1 2 ? ? l ? c hz 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 30 pf, in parallel with the transformer sec - ondary windings shunt capacitance. the recommended resonant frequency is in the range of 10 khz to 100 khz. note that the loading also plays a role in the effective load capacitance, and will therefore have an effect on the fre - quency. see tab le 3 for some recommended transformers . squeggingcertain types of oscillators, including transformer coupled oscillators such as the resonant oscillator of the ltc3107 , can exhibit a phenomenon called squegging. this term refers to a condition that can occur which blocks or stops the oscillation for a period of time much longer than the period of oscillation, resulting in bursts of oscillation. an example of this is the blocking oscillator, which is designed to squegg to produce bursts of oscillation. squegging is also encountered in rf oscillators and regenerative receivers . in the case of the ltc3107, squegging can occur when a charge builds up on the c2 gate coupling capacitor, such that the dc bias point shifts and oscillation is extinguished for a certain period of time, until the charge on the capacitor bleeds off, allowing oscillation to resume. it is difficult to predict when and if squegging will occur in a given ap - plication. while squegging is not harmful, it reduces the average output current capability of the ltc3107. squegging can easily be avoided by the addition of a bleeder resistor in parallel with the coupling capacitor on the c2 pin. resistor values in the range of 100 k to 1 m are sufficient to eliminate squegging without having any negative impact on performance. for the 330 pf capacitor used for c2 in most applications, a 499 k bleeder resistor is recommended. see the typical applications schematics for an example.using external charge pump rectifiers the synchronous charge pump rectifiers in the ltc3107 (connected to the c1 pin) are low current and optimized for operation from very low input voltage sources, using typical transformer step-up ratios between 1:100 and 1:50, and typical c1 charge pump capacitor values less than 10nf. operation from higher input voltage sources ( typically 250mv or greater, under load), allows the use of lower transformer step-up ratios ( such as 1:20 and 1:10) and larger c1 capacitor values to provide higher output current capability from the ltc3107. however, due to the result- ing increase in rectifier currents and resonant oscillator frequency in these applications, the use of external charge pump rectifiers is recommended for optimal performance in these applications. table 3. recommended transformers vendor part number coilcraft www.coilcraft.com lpr6235-752sml (1:100 ratio) lpr6235-123qml (1:50 ratio) lpr6235-253pml (1:20 ratio) wrth www.we-online 74488540070 (1:100 ratio) 74488540120 (1:50 ratio) 74488540250 (1:20 ratio) c1 capacitor the charge pump capacitor that is connected from the transformers secondary winding to the c1 pin has an effect on converter input resistance and maximum output current capability. generally a minimum value of 1 nf is recommended when operating from very low input volt - ages using a transformer with a ratio of 1:100. too large a capacitor value can compromise performance when operating at low input voltage or with high resistance sources. for higher input voltages and lower turns ratios, the value of the c1 capacitor can be increased for higher output current capability. refer to the typical application schematic examples for the recommended value for a given turns ratio. downloaded from: http:///
ltc 3107 18 3107f for more information www.linear.com/ltc3107 in applications where the step-up ratio is 1:20 or less, and the c1 capacitor is 10 nf or greater, the c1 pin should be grounded and two external rectifiers ( such as 1 n4148 or 1n914 diodes) should be used. these are available as dual diodes in a single package, such as the bas 31. ( avoid the use of schottky rectifiers, as their lower forward voltage drop increases the minimum start-up voltage.) see the typical applications schematics for an example. v out capacitor for pulsed load applications where there is no energy available from the vstore capacitor, the v out capacitor should be sized to provide the necessary current when the load is pulsed on. the capacitor value required will be dictated by the combined load current on v out and vldo ( i load ), the duration of the load pulse ( t), and the amount of voltage droop on the capacitor ( v vout ). with the goal being to extend battery life as much as possible, the maximum capacitor droop should be less than the amount required to trip the bat_off comparator ( which will connect the battery to maintain v out ). therefore, the minimum recommended v out capacitor value in pulsed load applications is: c out (f) = i load (ma) ? t(ms) v vout (v) where v vout is typically 200 mv. note that even with a properly sized output capacitor, there must be more average harvested power available than the average load power requirement on v out to prevent using the battery. a minimum c out capacitor value of 47 f is recommended for all applications, even if there is no pulsed load.vstore capacitor the v store capacitor, c store , may be of very large value (thousands of microfarads or even farads), to provide energy storage for times when the harvested input power may be lost or the load requirement is higher. note that this capacitor can charge up to 4.48 v max, so be sure that the holdup capacitor has a working voltage rating of at least 4.5v at the temperature that it will be used. the ltc3107 is designed to use energy from the v store capacitor to maintain v out before using the battery. applications information table 4. recommended storage capacitors manufacturer series avx bestcap series taj , tps series tantalum cap-xx g series (dual cell) h series (dual cell) cooper bussmann kr series kw series pa , pb, pm, ph series illinois capacitor dcn series vishay 293d series (tantalum) 595d series (tantalum) 153 crv (aluminum, low leakage) 150 crz (aluminum, low leakage) 196 dlc (double layer aluminum) c store can be sized using the following equation ( assum- ing no harvested energy or battery usage): c store (mf) = i load (ma) ? t(s) (4.3 ? v bat ? 0.2)(v) where i load is the average load on v out and vldo combined. this assumes that the storage cap has had a chance to charge up to its typical clamp voltage of 4.3v. to minimize losses and capacitor charge time , all capacitors used for v out and v store should be chosen for low leakage , relative to the average load current in the application. see table 4 for recommended storage capacitors. note that leakage is generally worse at higher temperatures, so be sure to take into account the actual operating temperature the capacitor will see in the application.pcb layout guidelines due to the rather low switching frequency of the resonant converter and the low power levels involved, pcb layout is not as critical as with many other dc/dc converters. there are however, a number of things to consider. downloaded from: http:///
ltc 3107 19 3107f for more information www.linear.com/ltc3107 figure 4. example component placement for two layer pc board due to the very low input voltage the circuit may operate from, the connections to v in , the primary of the transformer and the sw and gnd pins of the ltc3107 should be designed to minimize voltage drop from stray resistance, and able to carry currents as high as 500 ma. any small voltage drop in the primary winding conduction path will lower efficiency, as well as the minimum start-up voltage. applications information also, due to the low charge currents available at the out- puts of the ltc3107, any sources of leakage current on the output voltage pins must be minimized. an example board layout is shown in figure 4. v out v in v bat gnd gnd vldo vstore vaux bat_off 3107 f04 downloaded from: http:///
ltc 3107 20 3107f for more information www.linear.com/ltc3107 thermopile-powered battery life extender typical applications remote sensor application using thermal energy harvesting to extend primary battery life 0.55f vstore capacitor provides 6 hours of holdup at an average load of 200w before using the battery 3107 ta03 c1 honeywell cq200 thermopile c2sw gnd 10f 22f 220f4v v bat vldo bat_off vaux v out v out 100f4v ltc3107 vaux vstore 3vcr2032 coin cell 3v t1 t1: coilcraft lpr6235-123 4.7nf 1:50 330pf 499k + + 3107 ta02 c1 thermoelectric generator c2sw gnd 2.2f 10f 10f 0.55fcap-xx hw203f v bat c in vldo bat_off v out 680f6.3v ltc3107 vaux vstore 3.6v saft ls14250 li-soci 2 3.6v 2.2v t1 marlow rc3-2.5 16mm 20mm with heatsink thermal resistance <15c/w t1: wrth 74488540250 1nf 1:100 330pf 499k + + + + p sensors xmtr downloaded from: http:///
ltc 3107 21 3107f for more information www.linear.com/ltc3107 typical applications 3.6v solar powered battery life extender works from indoor lighting dual input harvester utilizes thermal and solar energy 3107 ta04 c1 powerfilm sp3-37 3.7cm 6.4cm c2sw gnd 10f 22f 22f v bat vldo bat_off vldo v out v out 220f6.3v cstore (optional) ltc3107 vaux vstore 3.6v saft ls14250 li-soci 2 3.6v 2.2v + + 2.2f +C 3107 ta04a c1 thermoelectric generator c2sw gnd 2.2f 22f6.3v 22f6.3v cstore (optional) v bat v in 100f vldo batsave v out v out c out ltc3107 vaux vstore 3.0v vldo t1 t1: wrth 74488540070 mbr0520lt 1nf 1:100 330pf 499k + + sanyoam-1815 4.8cm 5.8cm downloaded from: http:///
ltc 3107 22 3107f for more information www.linear.com/ltc3107 battery life extender utilizing scavenged 60hz ac typical applications 3107 ta05 c1c2 sw gnd 10f 22f 10f ac 60hz >2v rms v bat vldo bat_off vldo v out v out r in >100/v c out 4v cstore (optional) ltc3107 vaux vstore 2 alkaline 3v 3v 2.2v + + 2.2f downloaded from: http:///
ltc 3107 23 3107f for more information www.linear.com/ltc3107 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description please refer to http:// www .linear.com/designtools/packaging/ for the most recent package drawings. dd package 10-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1699 rev c) 3.00 0.10 (4 sides) note:1. drawing to be made a jedec package outline m0-229 variation of (weed-2). check the ltc website data sheet for current status of variation assignment 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom viewexposed pad 1.65 0.10 (2 sides) 0.75 0.05 r = 0.125 typ 2.38 0.10 (2 sides) 1 5 10 6 pin 1 top mark (see note 6) 0.200 ref 0.00 C 0.05 (dd) dfn rev c 0310 0.25 0.05 2.38 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 0.05 (2 sides) 2.15 0.05 0.50bsc 0.70 0.05 3.55 0.05 packageoutline 0.25 0.05 0.50 bsc pin 1 notchr = 0.20 or 0.35 45 chamfer downloaded from: http:///
ltc 3107 24 3107f for more information www.linear.com/ltc3107 ? linear technology corporation 2013 lt 1213 ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/ltc3107 related parts typical application thermal harvester for higher v in applications, using external rectifiers part number description comments lt3009 3a i q , 20ma linear regulator v in : 1.6v to 20v; v out(min) : 0.6v to 19.5v, 1.2v, 1.5v, 1.8v, 2.5v, 3.3v, 5v fixed; i q = 3a; i sd < 1a; 2mm 2mm dfn-8 and sc70 packages ltc3103 ltc3104 15v, 300ma synchronous step-down dc/dc converter with ultralow quiescent current v in = 2.2v to 15v, v out = 0.8v to 13.8v, i q = 1.8a, i sd < 1a, 10ma ldo (ltc3104), dfn and msop packages ltc3105 400ma step - up converter with mppc and 250 mv start - up v in : 0.2v to 5v; v out = 1.5v to 5.25v, i q = 24a, i sd < 1a 3 3 dfn-10/msop-12 ltc3108, ltc3108-1 ultralow voltage step - up converter and power manager v in : 0.02v to 1v; v out = 2.5v, 3v, 3.7v, 4.5v fixed; i q = 6a; 3mm 4mm dfn-12 and ssop-16 packages ltc3109 auto - polarity, ultralow voltage step - up converter and power manager v in : .03v to 1v; v out = fixed 2.35v to 5v, i q = 7a 4mm 4mm qfn-20 and ssop-20 packages ltc3129/ ltc3129-1 micropower 200ma synchronous buck-boost dc/dc converter v in : 2.42v to 15v; v out = 1.4v to 15.75v, i q = 1.3a, i sd < 100na 3mm 3mm qfn-16 and msop-16e packages ltc3330 nano power buck-boost dc/dc with energy harvester battery life extender v bat : 1.8v to 5.5v, v in 3v to 19v, v out = fixed 1.8v to 5v, i q = 750na; 5mm 5mm qfn packages ltc3388-1/ltc3388-3 20v, 50ma high efficiency nano power step-down regulator v in : 2.7v to 20v; v out = fixed 1.1v to 5.5v, i q = 720na, i sd = 400na 3mm 3mm dfn-10 and msop-10 packages ltc3588-1 ltc3588-2 piezoelectric energy generator with integrated high efficiency buck converter v in : 2.7v to 20v; v out : fixed to 1.8v, 2.5v, 3.3v, 3.6v; i q = 950na; 3mm 3mm dfn-10 and msop-10e packages ltc4070, ltc4071 micropower shunt li-ion chargers controls charging with a source 3107 ta06 c1 thermoelectric generator c2sw gnd 2.2f 22f 10f bas31 47nf v bat v in v in = 100mv to 750mv vldo bat_off vldo v out v out 220f6.3v c store (optional) ltc3107 vaux vstore 3.6v t1 1:20 330pf 499k + + ti: coilcraft lpr6235-253pml tadiran tl-4903 li-soci 2 downloaded from: http:///

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