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ltc3109 1 3109fa typical application features description auto-polarity, ultralow voltage step-up converter and power manager the ltc ? 3109 is a highly integrated dc/dc converter ideal for harvesting surplus energy from extremely low input voltage sources such as tegs (thermoelectric genera- tors) and thermopiles. its unique, proprietary autopolarity topology* allows it to operate from input voltages as low as 30mv, regardless of polarity. using two compact step-up transformers and external energy storage elements, the ltc3109 provides a com- plete power management solution for wireless sensing and data acquisition. the 2.2v ldo can power an external microprocessor, while the main output can be programmed to one of four ? xed voltages. the power good indicator signals that the main output is within regulation. a second output can be enabled by the host. a storage capacitor (or battery) can also be charged to provide power when the input voltage source is unavailable. extremely low quies- cent current and high ef? ciency maximizes the harvested energy available for the application. the ltc3109 is available in a small, thermally enhanced 20-lead (4mm 4mm) qfn package and a 20-lead ssop package. v out current vs teg voltage applications n operates from inputs as low as 30mv n less than 1c needed across teg to harvest energy n proprietary auto-polarity architecture n complete energy harvesting power management system C selectable v out of 2.35v, 3.3v, 4.1v or 5v C 2.2v, 5ma ldo C logic-controlled output C energy storage capability for operation during power interruption n power good indicator n uses compact step-up transformers n small, 20-lead (4mm 4mm) qfn package or 20-lead ssop n remote sensor and radio power n hvac systems n automatic metering n building automation n predictive maintenance n industrial wireless sensing l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. *patent pending. gnd 1f 5.25v 2.2v ltc3109 3.3v c store 3109 ta01a c1a 1nf 2.2f 470pf 47f 1nf 470pf 1:100 teg (thermoelectric generator) 30mv to 500mv ?? 1:100 ?? v out2 c2a c1b c2b swb v inb vs1 vs2 swa v ina v out vldo pg00d v out2_en vstore vaux vaux + 470f optional switched output for sensors + p low power radio sensor(s) v teg (mv) C300 0 i vout (a) 100 300 400 500 100 900 3109 ta01b 200 C100 C200 200 0300 600 700 800 1:100 transformers c1a = c1b = 1nf v out = 3.3v
ltc3109 2 3109fa absolute maximum ratings swa, swb, v ina , v inb voltage .................... C0.3v to 2v c1a, c1b voltage ......................................... C0.3v to 6v c2a, c2b voltage (note 6) .............................. C8v to 8v v out2 , v out2_en .......................................... C0.3v to 6v vs1, vs2, v out , pgood .............................. C0.3v to 6v (note 1) order information lead free finish tape and reel part marking* package description temperature range ltc3109euf#pbf ltc3109euf#trpbf 3109 20-lead (4mm 4mm) plastic qfn C40c to 125c ltc3109iuf#pbf ltc3109iuf#trpbf 3109 20-lead (4mm 4mm) plastic qfn C40c to 125c ltc3109egn#pbf ltc3109egn#trpbf ltc3109gn 20-lead plastic ssop C40c to 125c ltc3109ign#pbf ltc3109ign#trpbf ltc3109gn 20-lead plastic ssop C40c to 125c consult ltc marketing for parts speci? ed with wider operating temperature ranges. *the temperature grade is identi? ed by a label on the shipping container. consult ltc marketing for information on non-standard lead based ? nish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/ 20 19 18 17 16 6 7 8 top view 21 gnd uf package 20-lead (4mm s 4mm) plastic qfn 9 10 5 4 3 2 1 11 12 13 14 15 vstore vaux v out v out2 v out2_en swa v ina v inb swb gnd vs2 vs1 c1a c2a gnd pgood vldo gnd c1b c2b t jmax = 125c, ja = 37c/w exposed pad (pin 21) is gnd (note 5) gn package 20-lead plastic ssop 1 2 3 4 5 6 7 8 9 10 top view 20 19 18 17 16 15 14 13 12 11 vs1 vs2 vstore vaux v out v out2 v out2_en pgood vldo gnd c1a c2a gnd swa v ina v inb swb gnd c2b c1b t jmax = 125c, ja = 90c/w pin configuration vldo, vstore ............................................ C0.3v to 6v vaux ...................................................... 15ma into v aux operating junction temperature range (note 2) .................................................. C40c to 125c storage temperature range .................. C65c to 125c
ltc3109 3 3109fa 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 ltc3109 is tested under pulsed load conditions such that t j t a . the ltc3109e is guaranteed to meet speci? cations from the l denotes the speci? cations which apply over the full operating junction temperature range, otherwise speci? cations are for t a = 25c (note 2). vaux = 5v unless otherwise noted. parameter conditions min typ max units minimum start-up voltage using 1:100 transformer turns ratio, vaux = 0v 30 50 mv no-load input current using 1:100 transformer turns ratios, v in = 30mv, v out2_en = 0v, all outputs charged and in regulation 6ma input voltage range using 1:100 transformer turns ratios l v startup 500 mv output voltage vs1 = vs2 = gnd vs1 = vaux, vs2 = gnd vs1 = gnd, vs2 = vaux vs1 = vs2 = vaux l l l l 2.30 3.234 4.018 4.875 2.350 3.300 4.100 5.000 2.40 3.366 4.182 5.10 v v v v vaux quiescent current no load, all outputs charged 7 10 a vaux clamp voltage current into vaux = 5ma l 5.0 5.25 5.55 v v out quiescent current v out = 3.3v, v out2_en = 0v 0.2 a v out current limit v out = 0v l 61526 ma n-channel mosfet on-resistance c2b = c2a = 5v (note 3) measured from v ina or swa, v inb or swb to gnd 0.35 ldo output voltage 0.5ma load on v ldo l 2.134 2.2 2.30 v ldo load regulation for 0ma to 2ma load 0.5 1 % ldo line regulation for v aux from 2.5v to 5v 0.05 0.2 % ldo dropout voltage i ldo = 2ma l 100 200 mv ldo current limit v ldo = 0v l 512 ma vstore leakage current vstore = 5v 0.1 0.3 a vstore current limit vstore = 0v l 61526 ma v out2 leakage current v out2 = 0v, v out2_en = 0v 50 na vs1, vs2 threshold voltage l 0.4 0.85 1.2 v vs1, vs2 input current v s1 = v s2 = 5v 1 50 na pgood threshold (rising) measured relative to the v out voltage C7.5 % pgood threshold (falling) measured relative to the v out voltage C9 % pgood v ol sink current = 100a 0.12 0.3 v pgood v oh source current = 0 2.1 2.2 2.3 v pgood pull-up resistance 1m v out2_en threshold voltage v out2_en rising l 0.4 1.0 1.3 v v out2_en threshold hysteresis 100 mv v out2_en pull-down resistance 5m v out2 turn-on time 0.5 s v out2 turn-off time (note 3) 0.15 s v out2 current limit v out = 3.3v l 0.2 0.3 0.5 a v out2 current limit response time (note 3) 350 ns v out2 p-channel mosfet on-resistance v out = 5v (note 3) 1.0 0c to 85c junction temperature. speci? cations over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the ltc3109i is guaranteed over the full C40c to 125c operating junction temperature range. note that the maximum ambient temperature is determined by speci? c operating conditions in conjunction with
ltc3109 4 3109fa typical performance characteristics electrical characteristics board layout, the rated thermal package thermal resistance and other environmental factors. the junction temperature (t j ) 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: speci? cation is guaranteed by design and not 100% tested in production. note 4: current measurements are made when the output is not switching. note 5: failure to solder the exposed backside of the qfn package to the pc board ground plane will result in a thermal resistance much higher than 37c/w. note 6: the absolute maximum rating is a dc rating. under certain conditions in the applications shown, the peak ac voltage on the c2a and c2b pins may exceed 8v. this behavior is normal and acceptable because the current into the pin is limited by the impedance of the coupling capacitor. input resistance vs v in ef? ciency vs v in open-circuit start-up voltage vs source resistance i in vs v in i vout vs v in v in (mv) 10 1 i in (ma) 10 100 1000 100 1000 3109 g01 1:100 ratio, c1 = 1nf 1:50 ratio, c1 = 4.7nf 1:20 ratio, c1 = 10nf v out = 0v v in (mv) 10 10 i vout (a) 100 1000 10000 100 1000 3109 g02 1:100 ratio, c1 = 1nf 1:50 ratio, c1 = 4.7nf 1:20 ratio, c1 = 10nf v out = 3.3v no load on vldo v in (mv) 10 2.0 r in () 3.0 4.0 5.0 6.0 100 1000 3109 g03 7.0 2.5 3.5 4.5 5.5 6.5 1:100 ratio, c1 = 1nf 1:50 ratio, c1 = 4.7nf 1:20 ratio, c1 = 10nf v out = 0v source resistance () 0 0 v startup (open circuit) (mv) 10 30 40 50 6789 90 3109 g05 20 12345 10 60 70 80 v in (mv) 10 0 efficiency (%) 10 20 30 40 100 1000 3109 g04 50 5 15 25 35 45 1:100 ratio, c1 = 1nf 1:50 ratio, c1 = 4.7nf 1:20 ratio, c1 = 10nf v out = 0v t a = 25c, unless otherwise noted. v in (mv) 10 0.1 p vout (mw) 1 10 100 100 1000 3109 g18 1:50 ratio c1 = 4.7nf v out = 5v v out = 3.3v p vout vs v in
ltc3109 5 3109fa typical performance characteristics resonant switching waveforms ldo load regulation ldo dropout voltage start-up voltage sequencing v out and pgood response during a step load v out ripple v out and vldo vs temperature vaux clamp voltage vs shunt current p vout vs dt and teg size, 1:100 ratio, v out = 5v t a = 25c, unless otherwise noted. temperature (c) C50 change (%) (relative to 25c) 0.75 25 3109 g06 0 C0.50 C25 0 50 C0.75 C1.00 1.00 0.50 0.25 C0.25 75 100 125 vldo v out vaux shunt current (ma) 0 vaux (v) 5.3 5.4 5.5 12 3109 g07 5.2 5.1 5.0 3 6 9 15 dt (k) 0 p vout (mw) 1.0 2.0 3.0 0.5 1.5 2.5 2468 3109 g08 10 1 03579 ferrotec 9500/127/100b 40mm ferrotec 9501/071/040b 22mm 20s/div c1 a or b 2v/div c2 a or b 2v/div 3109 g9 ldo load (ma) 0 C1.00 drop in vldo (%) C0.75 C0.50 0.5 1 1.5 2 3 2.5 3.5 C0.25 0.00 4 3109 g10 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 3109 g11 10sec/div 3109 g12 ch1 vstore 1v/div ch2, v out 1v/div ch3, v ldo 1v/div v in = 50mv 1:100 ratio transformer c out = 220f c store = 470f c ldo = 2.2f 5ms/div 3109 g13 ch2 v out 1v/div ch1 pgd 1v/div 50ma load step c out = 220f 100ms/div 3109 g14 20mv/ div 30a load c out = 220f
ltc3109 6 3109fa ldo step load response enable input and v out2 running on storage capacitor pin functions (qfn/ssop) vstore (pin 1/pin 3): output for the storage capacitor or battery. a large storage capacitor may be connected from this pin to gnd for powering the system in the event the input voltage is lost. it will be charged up to the maximum vaux clamp voltage. if not used, this pin should be left open or tied to vaux. vaux (pin 2/pin 4): output of the internal recti? er cir- cuit and v cc for the ic. bypass vaux with at least 1f of capacitance to ground. an active shunt regulator clamps vaux to 5.25v (typical). v out (pin 3/pin 5): main output of the converter. the voltage at this pin is regulated to the voltage selected by vs1 and vs2 (see table 1). connect this pin to a reservoir capacitor or to a rechargeable battery. any high current pulse loads must be fed by the reservoir capacitor on this pin. v out2 (pin 4/ pin 6): switched output of the converter. connect this pin to a switched load. this output is open until v out_en is driven high, then it is connected to v out through a 1 pmos switch. if not used, this pin should be left open or tied to v out . v out2_en (pin 5/pin 7): enable input for v out2 . v out2 will be enabled when this pin is driven high. there is an internal 5m pull-down resistor on this pin. if not used, this pin can be left open or grounded. pgood (pin 6/pin 8): power good output. when v out is within 7.5% of its programmed value, this pin will be pulled up to the ldo voltage through a 1m resistor. if v out drops 9% below its programmed value pgood will go low. this pin can sink up to 100a. vldo (pin 7/pin 9): output of the 2.2v ldo. connect a 2.2f or larger ceramic capacitor from this pin to gnd. if not used, this pin should be tied to vaux. gnd (pins 8, 11, 16, exposed pad pin 21/pins 10, 13, 18): ground pins. connect these pins directly to the ground plane. the exposed pad serves as a ground connection and as a means of conducting heat away from the die. vs2 (pin 20/pin 2): v out select pin 2. connect this pin to ground or vaux to program the output voltage (see table 1). vs1 (pin 19/pin 1): v out select pin 1. connect this pin to ground or vaux to program the output voltage (see table 1). table 1. regulated output voltage using pins vs1 and vs2 vs2 vs1 v out gnd gnd 2.35v gnd vaux 3.3v vaux gnd 4.1v vaux vaux 5.0v typical performance characteristics t a = 25c, unless otherwise noted. v ldo 20mv/div i ldo 5ma/div 200s/div 3109 g15 0ma to 3ma load step c ldo = 2.2f 1ms/div 3109 g16 ch2 v out2 1v/div ch1 v out2_en 1v/div 10ma load on v out2 c out = 220f 5sec/div 3109 g17 ch2, v out 1v/div ch1, v in 50mv/div ch3 vstore 1v/div ch4, v ldo 1v/div c store = 470f v out load = 100a
ltc3109 7 3109fa pin functions (dfn/ssop) c1b (pin 9/pin 11): input to the charge pump and recti? er circuit for channel b. connect a capacitor from this pin to the secondary winding of the b step-up transformer. see the applications information section for recommended capacitor values. c1a (pin 18/pin 20): input to the charge pump and recti- ? er circuit for channel a. connect a capacitor from this pin to the secondary winding of the a step-up transformer. see the applications information section for recommended capacitor values. c2b (pin 10/pin 12): input to the gate drive circuit for swb. connect a capacitor from this pin to the secondary winding of the b step-up transformer. see the applications information section for recommended capacitor values. c2a (pin 17/pin 19): input to the gate drive circuit for swa. connect a capacitor from this pin to the secondary winding of the a step-up transformer. see the applications information section for recommended capacitor values. swa (pin 15/pin 17): connection to the internal n-chan- nel switch for channel a. connect this pin to the primary winding of the a transformer. swb (pin 12/pin 14): connection to the internal n-chan- nel switch for channel b. connect this pin to the primary winding of the b transformer. v ina (pin 14/pin 16): connection to the internal n-channel switch for channel a. connect this pin to one side of the input voltage source (see typical applications). v inb (pin 13/pin 15): connection to the internal n-channel switch for channel b. connect this pin to the other side of the input voltage source (see typical applications).
ltc3109 8 3109fa block diagram vs1 v out v out2_en v out2 1 v out c out v out2 v out program vs2 vstore v ldo pg00d pg00d 1m v ref 1.2v C + C + v ref v store v out v ref vaux c aux 1f c ldo 2.2f vldo 2.2v v out 5.25v c1a charge control power switches ldo sync rectify sync rectify reference c2a c1b c2b swa v ina v inb swb ? ? ? ? v in gnd + c store 3109 bd +
ltc3109 9 3109fa operation (refer to the block diagram) the ltc3109 is designed to use two small external step-up transformers to create an ultralow input voltage step-up dc/dc converter and power manager that can operate from input voltages of either polarity. this unique capability enables energy harvesting from thermoelectric generators (tegs) in applications where the temperature differential across the teg may be of either (or unknown) polarity. it can also operate from low level ac sources. it is ideally suited for low power wireless sensors and other applications in which surplus energy harvesting is used to generate system power because traditional battery power is inconvenient or impractical. the ltc3109 is designed to manage the charging and regulation of multiple outputs in a system in which 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 most of the time, except for transmit pulses when circuitry is powered up to make measure- ments and transmit data. the ltc3109 can also be used to trickle charge a standard capacitor, super capacitor or rechargeable battery, using energy harvested from a teg or low level ac source. resonant oscillator the ltc3109 utilizes mosfet switches to form a reso- nant step-up oscillator that can operate from an input of either polarity using external step-up transformers and small coupling capacitors. this allows it to boost input voltages as low as 30mv 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 10khz to 100khz. for input voltages as low as 30mv, transformers with a turns ratio of about 1:100 is recommended. for operation from higher input voltages, this ratio can be lower. see the applications information section for more information on selecting the transformers. charge pump and recti? er the ac voltage produced on the secondary winding of the transformer is boosted and recti? ed using an external charge pump capacitor (from the secondary winding to pin c1a or c1b) and the recti? ers internal to the ltc3109. the recti? er circuit feeds current into the v aux pin, provid- ing charge to the external vaux capacitor and the other outputs. vaux the active circuits within the ltc3109 are powered from vaux, which should be bypassed with a 1f minimum capacitor. once vaux exceeds 2.5v, the main v out is al- lowed to start charging. an internal shunt regulator limits the maximum voltage on vaux to 5.25v typical. it shunts to ground any excess 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. this current should be limited to 15ma max. voltage reference the ltc3109 includes a precision, micropower reference, for accurate regulated output voltages. this reference becomes active as soon as vaux exceeds 2v. synchronous recti? ers once vaux exceeds 2v, synchronous recti? ers in paral- lel with each of the internal recti? er diodes take over the job of rectifying the input voltage at pins c1a and c1b, improving ef? ciency. low dropout linear regulator (ldo) the ltc3109 includes a low current ldo to provide a regulated 2.2v output for powering low power proces- sors or other low power ics. the ldo is powered by the higher of vaux or v out . this enables it to become active as soon as vaux has charged to 2.3v, while the
ltc3109 10 3109fa v out storage capacitor is still charging. in the event of a step load on the ldo output, current can come from the main v out reservoir capacitor. the ldo requires a 2.2f ceramic capacitor for stability. larger capacitor values can be used without limitation, but will increase the time it takes for all the outputs to charge up. the ldo output is current limited to 5ma minimum. v out the main output voltage on v out is charged from the vaux supply, and is user-programmed to one of four regulated voltages using the voltage select pins vs1 and vs2, ac- cording to table 2. although the logic-threshold voltage for vs1 and vs2 is 0.85v typical, it is recommended that they be tied to ground or vaux. table 2 vs2 vs1 v out gnd gnd 2.35v gnd vaux 3.3v vaux gnd 4.1v vaux vaux 5v when the output voltage drops slightly below the regulated value, the charging current will be enabled as long as vaux is greater than 2.5v. once v out has reached the proper value, the charging current is turned off. the resulting ripple on v out is typically less than 20mv peak to peak . the internal programmable resistor divider, controlled by vs1 and vs2, sets v out , eliminating the need for very high value external resistors that are susceptible to noise pickup and board leakages. in a typical application, a reservoir capacitor (typically a few hundred microfarads) is connected to v out . as soon as vaux exceeds 2.5v, the v out capacitor will begin to charge up to its regulated voltage. the current available to charge the capacitor will depend on the input voltage and transformer turns ratio, but is limited to about 15ma typical. note that for very low input voltages, this current may be in the range of 1a to 1000a. pgood a power good comparator monitors the v out voltage. the pgood pin is an open-drain output with a weak pull- up (1m) to the ldo voltage. once v out has charged to within 7.5% of its programmed voltage, the pgood output will go high. if v out drops more than 9% from its programmed voltage, pgood will go low. the pgood output is designed to drive a microprocessor or other chip i/o and is not intended to drive a higher current load such as an led. the pgood pin can also be pulled low in a wire-or con? guration with other circuitry. v out2 v out2 is an output that can be turned on and off by the host using the v out2_en pin. when enabled, v out2 is con- nected to v out through a 1 p-channel mosfet switch. this output, controlled by a host processor, can be used to power external circuits such as sensors and ampli? ers, that dont have a low power sleep or shutdown capabil- ity. v out2 can be used to power these circuits only when they are needed. minimizing the amount of decoupling capacitance on v out2 enables it to be switched on and off faster, allow- ing shorter pulse times and therefore smaller duty cycles in applications such as a wireless sensor/transmitter. a small v out2 capacitor will also minimize the energy that will be wasted in charging the capacitor every time v out2 is enabled. v out2 has a current limiting circuit that limits the peak current to 0.3a typical. the v out2 enable input has a typical threshold of 1v with 100mv of hysteresis, making it logic compatible. if v out2_en (which has an internal 5m pull-down resistor) is low, v out2 will be off. driving v out2_en high will turn on the v out2 output. note that while v out2_en is high, the current limiting cir- cuitry for v out2 draws an extra 8a of quiescent current from v out . this added current draw has a negligible effect operation (refer to the block diagram)
ltc3109 11 3109fa on the application and capacitor sizing, since the load on the v out2 output, when enabled, is likely to be orders of magnitude higher than 8a. vstore the vstore output can be used to charge a large storage capacitor or rechargeable battery. once v out has reached regulation, the vstore output will be allowed to charge up to the clamped vaux voltage (5.25v typical). the storage element on vstore can then 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 v out , v out2 and ldo outputs. if vaux drops below vstore, the ltc3109 will automati- cally draw current from the storage element. note that it may take a long time to charge a large storage capacitor, depending on the input energy available and the loading on v out and vldo. since the maximum charging current available at the vstore output is limited to about 15ma, it can safely be used to trickle charge nicd or nimh batteries for energy storage when the input voltage is lost. note that vstore is not intended to supply high pulse load currents to v out . any pulse load on v out must be handled by the v out reservoir capacitor. short-circuit protection all outputs of the ltc3109 are current limited to protect against short circuits to ground. output voltage sequencing a timing diagram showing the typical charging and voltage sequencing of the outputs is shown in figure 1. note that the horizontal (time) axis is not to scale, and is used for illustration purposes to show the relative order in which the output voltages come up. operation (refer to the block diagram) 5.0 vstore pgood v out vldo 3.0 2.0 1.0 0 3.0 2.0 1.0 0 2.5 0 5.0 2.5 0 010203040 time (ms) 3109 f01 50 60 70 80 5.0 2.5 voltage (v) 0 vaux figure 1. output voltage sequencing (with v out programmed for 3.3v). time not to scale
ltc3109 12 3109fa applications information introduction the ltc3109 is designed to gather energy from very low input voltage sources and convert it to usable output voltages to power microprocessors, wireless transmit- ters and analog sensors. its architecture is speci? cally tailored to applications where the input voltage polarity is unknown, or can change. this auto-polarity capability makes it ideally suited to energy harvesting applications using a teg whose temperature differential may be of either polarity. applications such as wireless sensors typically require much more peak power, and at higher voltages, than the input voltage source can produce. the ltc3109 is designed to accumulate and manage energy over a long period of time to enable short power pulses for acquiring and transmitting data. the pulses must occur at a low enough duty cycle that the total output energy during the pulse does not exceed the average source power integrated over the accumulation time between pulses. for many applications, this time between pulses could be seconds, minutes or hours. the pgood signal can be used to enable a sleeping microprocessor or other circuitry when v out reaches regulation, indicating that enough energy is available for a transmit pulse. input voltage sources the ltc3109 can operate from a number of low input voltage sources, such as peltier cells (thermoelectric generators), or low level ac sources. the minimum input voltage required for a given application will depend on the transformer turns ratios, the load power required, and the internal dc resistance (esr) of the voltage source. lower esr sources will allow operation from lower input voltages, and provide 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 decoupling capacitor may be required across a dc 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). since the input voltage may be of either polarity, a ceramic capacitor is recommended. peltier cell (thermoelectric generator) a peltier cell is made up of a large number of series-con- nected p-n junctions, sandwiched between two parallel ceramic plates. although peltier cells 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 at different temperatures. when used in this manner, they are referred to as thermo- electric generators (tegs). the polarity of the output voltage will depend on the polarity of the temperature differential between the teg plates. the magnitude of the output volt- age is proportional to the magnitude of the temperature differential between the plates. the low voltage capability of the ltc3109 design allows it to operate from a typical teg with temperature differentials as low as 1c of either polarity, making it ideal for harvest- ing energy in applications where a temperature difference exists between two surfaces or between a surface and the ambient temperature. the internal resistance (esr) of most tegs is in the range of 1 to 5, allowing for reasonable power transfer. the curves in figure 2 show the open-circuit output voltage and maximum power transfer for a typical teg with an esr of 2, over a 20c range of temperature differential (of either polarity). dt (c) 1 1 teg v open-circuit (mv) teg maximum p out C ideal (mw) 10 100 1000 0.1 1 10 100 10 100 3109 f02 teg: 30mm square 127 couples r = 2 v oc max p out (ideal) figure 2. typical performance of a peltier cell acting as a power generator (teg)
ltc3109 13 3109fa applications information teg load matching the ltc3109 was designed to present an input resistance (load) in the range of 2 to 10, depending on input volt- age, transformer turns ratio and the c1a and c2a capacitor values (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 ltc3109 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 capability by providing a higher input voltage under load. unipolar applications the ltc3109 can also be con? gured to operate from two independent unipolar voltage sources, such as two tegs in different locations. in this con? guration, energy can be harvested from either or both sources simultaneously. see the typical applications for an example. the ltc3109 can also be con? gured to operate from a single unipolar source, using a single step-up transformer, by ganging its v in and sw pins together. in this manner, it can extract the most energy from very low resistance sources. see figure 3 for an example of this con? guration, along with the performance curves. peltier cell (teg) suppliers peltier cells are available in a wide range of sizes and power capabilities, from less than 10mm square to over 50mm square. they are typically 2mm to 5mm in height. a list of some peltier cell manufacturers is given in table 3 and some recommended part numbers in table 4. component selection step-up transformer the turns ratio of the step-up transformers will determine how low the input voltage can be for the converter to start. due to the auto-polarity architecture, two identical step-up transformers should be used, unless the temperature drop across the teg is signi? cantly different in one polarity, in which case the ratios may be different. table 3. peltier cell manufacturers cui inc www.cui.com ferrotec www.ferrotec.com/products/thermal/modules/ fujitaka www.fujitaka.com/pub/peltier/english/thermoelectric_power.html hi-z technology www.hi-z.com kryotherm www.kryotherm laird technologies www.lairdtech.com micropelt www.micropelt.com nextreme www.nextreme.com te technology www.tetech.com/peltier-thermoelectric-cooler-modules.html tellurex www.tellurex.com/ table 4. recommended teg part numbers by size manufacturer 15mm 20mm 30mm 40mm cui inc. (distributor) cp60133 cp60233 cp60333 cp85438 ferrotec 9501/031/030 b 9501/071/040 b 9500/097/090 b 9500/127/100 b fujitaka fph13106nc fph17106nc fph17108ac fph112708ac kryotherm tgm-127-1.0-0.8 lcb-127-1.4-1.15 laird technology pt6.7.f2.3030.w6 pt8.12.f2.4040.ta.w6 marlow industries rc3-8-01 rc6-6-01 rc12-8-01ls tellurex c2-15-0405 c2-20-0409 c2-30-1505 c2-40-1509 te technology te-31-1.0-1.3 te-31-1.4-1.15 te-71-1.4-1.15 te-127-1.4-1.05
ltc3109 14 3109fa applications information gnd 10f ltc3109 3109 f03a c1a c1 1nf 330k t1 ?? v out2 v out2 c2a c1b c2b swb v inb vs1 v out set vs2 swa v ina v out vldo vldo v out 2.2f c in v in pg00d v out2_en pg00d v out2_enable note: values for c in , t1, c1 and c out are determined by the application vstore vaux + c out + figure 3. unipolar application typical i vout vs v in for unipolar con? guration typical ef? ciency vs v in for unipolar con? guration v in (mv) 10 10 i vout (a) 100 1000 10000 100 1000 3109 f03b 1:100, c1 = 6.8nf 1:50, c1 = 33nf 1:20, c1 = 68nf v out = 3.3v v in (mv) 10 20 efficiency (%) 30 40 100 1000 3109 f03c 10 0 60 50 15 25 35 5 55 45 1:100, c1 = 6.8nf 1:50, c1 = 33nf 1:20, c1 = 68nf typical input current vs v in for unipolar con? guration typical r in vs v in for unipolar con? guration v in (mv) 10 200 input current (ma) 300 400 100 1000 3109 f03d 100 0 600 500 150 250 350 50 550 450 1:100, c1 = 6.8nf 1:50, c1 = 33nf 1:20, c1 = 68nf v in (mv) 10 input resistance () 1.0 2.0 100 1000 3109 f03e 0 4.0 3.0 1.5 0.5 3.5 2.5 1:100, c1 = 6.8nf 1:50, c1 = 33nf 1:20, c1 = 68nf dt (k) 100 0.1 p out (mw) 1 10 10 3109 f03f v out = 5v v out = 3.3v ferrotec 9500/127/100b, 40mm teg c1 = 33nf, t1 = coilcraft lpr6235-123qml 1:50 ratio typical p vout vs dt for unipolar con? guration
ltc3109 15 3109fa applications information using a 1:100 primary-secondary ratio yields start-up voltages as low as 30mv. other factors that affect per- formance are the resistance of the transformer windings and the inductance of the windings. higher dc resistance will result in lower ef? ciency and higher start-up volt- ages. the secondary winding inductance will determine the resonant frequency of the oscillator, according to the formula below. freq = 1 2? ?l sec ?c hz where l sec is the inductance of one of the secondary windings and c is the load capacitance on the second- ary winding. this is comprised of the input capacitance at pin c2a or c2b, typically 70pf each, in parallel with the transformer secondary windings shunt capacitance. the recommended resonant frequency is in the range of 10khz to 100khz. note that loading will also affect the resonant frequency. see table 5 for some recommended transformers. table 5. recommended transformers vendor typical start- up voltage part number coilcraft www.coilcraft.com 25mv 35mv 85mv lpr6235-752sml (1:100 ratio) lpr6235-123qml (1:50 ratio) lpr6235-253pml (1:20 ratio) wrth www.we-online 25mv 35mv 85mv s11100034 (1:100 ratio) s11100033 (1:50 ratio) s11100032 (1:20 ratio) using external charge pump rectifiers the synchronous recti? ers in the ltc3109 have been optimized for low frequency, low current operation, typical of low input voltage applications. for applications where the resonant oscillator frequency exceeds 100khz, or a transformer turns ratio of less than 1:20 is used, or the c1a and c1b capacitor values are greater than 68nf, the use of external charge pump recti? ers (1n4148 or 1n914 or equivalent) is recommended. see the typical application circuits for an example. avoid the use of schottky recti- ? ers, as their low forward voltage increases the minimum start-up voltage. c1 capacitor the charge pump capacitor that is connected from each transformers secondary winding to the corresponding c1a and c1b pins has an effect on converter input resis- tance and maximum output current capability. generally a minimum value of 1nf is recommended when operating from very low input voltages using a transformer with a ratio of 1:100. capacitor values of 2.2nf to 10nf will provide higher output current at higher input voltages, however larger capacitor values can compromise perfor- mance 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 applications examples for the recommended value for a given turns ratio. c2 capacitor the c2 capacitors connect pins c2a and c2b to their respective transformer secondary windings. for most applications a capacitor value of 470pf is recommended. smaller capacitor values tend to raise the minimum start-up voltage, and larger capacitor values can lower ef? ciency. note that the c1 and c2 capacitors must have a voltage rating greater than the maximum input voltage times the transformer turns ratio. v out and vstore capacitor for pulsed load applications, 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 load current (i load ), the duration of the load pulse (t pulse ), and the amount of v out voltage droop the ap- plication can tolerate ( v out ). the capacitor must be rated for whatever voltage has been selected for v out by vs1 and vs2: c out (f) i load(ma) ?t pulse(ms) v out (v)
ltc3109 16 3109fa applications information note that there must be enough energy available from the input voltage source for v out to recharge the capacitor during the interval between load pulses (as discussed in design example 1). reducing the duty cycle of the load pulse will allow operation with less input energy. the vstore capacitor may be of very large value (thou- sands of microfarads or even farads), to provide energy storage at times when the input voltage is lost. note that this capacitor can charge all the way to the vaux clamp voltage of 5.25v typical (regardless of the settings for v out ), so be sure that the holdup capacitor has a work- ing voltage rating of at least 5.5v at the temperature that it will be used. the vstore input is not designed to provide high pulse load currents to v out . the current path from vstore to v out is limited to about 26ma max. the vstore capacitor can be sized using the following formula: c store 7a + i q + i ldo + i pulse ?t pulse ?f () () ?t store 5.25 C v out where 7a is the quiescent current of the ltc3109, i q is the load on v out in between pulses, i ldo is the load on the ldo between pulses, i pulse is the total load during the pulse, t pulse is the duration of the pulse, f is the frequency of the pulses, t store is the total storage time required and v out is the output voltage required. note that for a programmed output voltage of 5v, the vstore capacitor cannot provide any bene? cial storage time to v out . to minimize losses and capacitor charge time, all capaci- tors used for v out and vstore should be low leakage. see table 6 for recommended storage capacitors. table 6. recommended storage capacitors vendor part number/series avx www.avx.com bestcap series taj and tps series tantalum cap-xx www.cap-xx.com gz series cooper/bussman www.bussmann.com/3/powerstor.html kr series p series vishay/sprague www.vishay.com/capacitors tantamount 592d 595d tantalum note that storage capacitors requiring voltage balancing resistors are not recommended due to the steady-state current draw of the resistors. 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. due to the very low input voltages the circuit operates from, the connections to v in , the primary of the transformers and the sw, v in and gnd pins of the ltc3109 should be designed to minimize voltage drop from stray resistance, and able to carry currents as high as 500ma. any small voltage drop in the primary winding conduction path will lower ef? ciency and increase start-up voltage and capaci- tor charge time. also, due to the low charge currents available at the out- puts of the ltc3109, any sources of leakage current on the output voltage pins must be minimized. an example board layout is shown in figure 4. figure 4. example component placement for 2-layer pc board (qfn package). note that vstore and vout capacitor sizes are application dependent
ltc3109 17 3109fa applications information design example 1 this design example will explain how to calculate the necessary reservoir capacitor value for v out in pulsed- load applications, such as a wireless sensor/transmitter. in these types of applications, the load is very small for a majority of the time (while the circuitry is in a low power sleep state), with pulses of load current occurring periodi- cally during a transmit burst. the reservoir capacitor on v out supports the load during the transmit pulse; the long sleep time between pulses allows the ltc3109 to accumulate energy and recharge the capacitor (either from the input voltage source or the storage capacitor). a method for calculating the maximum rate at which the load pulses can occur for a given output current from the ltc3109 will also be shown. in this example, v out is set to 3.3v, and the maximum allowed voltage droop during a transmit pulse is 10%, or 0.33v. the duration of a transmit pulse is 5ms, with a total average current requirement of 20ma during the pulse. given these factors, the minimum required capacitance on v out is: c out f () 20ma ? 5ms 0.33v = 303f note that this equation neglects the effect of capacitor esr on output voltage droop. for ceramic capacitors and low esr tantalum capacitors, the esr will have a negligible effect at these load currents. however, beware of the voltage coef? cient of ceramic capacitors, especially those in small case sizes. this greatly reduces the effective capacitance when a dc bias is applied. a standard value of 330f could be used for c out in this case. note that the load current is the total current draw on v out , v out2 and vldo, since the current for all of these outputs must come from v out during a pulse. current contribution from the capacitor on vstore is not considered, since it may not be able to recharge between pulses. also, it is assumed that the harvested charge current from the ltc3109 is negligible compared to the magnitude of the load current during the pulse. to calculate the maximum rate at which load pulses can occur, you must know how much charge current is avail- able from the ltc3109 v out pin given the input voltage source being used. this number is best found empirically, since there are many factors affecting the ef? ciency of the converter. you must also know what the total load cur- rent is on v out during the sleep state (between pulses). note that this must include any losses, such as storage capacitor leakage. lets assume that the charge current available from the ltc3109 is 150a and the total current draw on v out and vldo in the sleep state is 17a, including capacitor leakage. well also use the value of 330f for the v out capacitor. the maximum transmit rate (neglecting the duration of the transmit pulse, which is very short compared to the period) is then given by: t = 330f ? 0.33v 150a C 17a = 0.82sec or f max = 1.2hz therefore, in this application example, the circuit can sup- port a 5ms transmit pulse of 20ma every 0.82 seconds. it can be seen that for systems that only need to transmit every few seconds (or minutes or hours), the average charge current required is extremely small, as long as the sleep or standby current is low. even if the available charge current in the example above was only 21a, if the sleep current was only 5a, it could still transmit a pulse every seven seconds. the following formula will allow you to calculate the time it will take to charge the ldo output capacitor and the v out capacitor the ? rst time, from zero volts. here again, the charge current available from the ltc3109 must be known. for this calculation, it is assumed that the ldo output capacitor is 2.2f: t ldo = 2.2v ? 2.2f i chg Ci ldo if there was 150a of charge current available and a 5a load on the ldo (when the processor is sleeping), the time for the ldo to reach regulation would be only 33ms.
ltc3109 18 3109fa applications information the time for v out to charge and reach regulation can be calculated by the formula below, which assumes v out is programmed to 3.3v and c out is 330f: t vout = 3.3v ? 330f i chg Ci vout Ci ldo + t ldo with 150a of charge current available and 5a of load on both v out and vldo, the time for v out to reach regula- tion after the initial application of power would be 7.81 seconds. design example 2 in most pulsed-load applications, the duration, magnitude and frequency of the load current pulses are known and ? xed. in these cases, the average charge current required from the ltc3109 to support the average load must be calculated, which can be easily done by the following: i chg i q + i pulse ?t pulse t where i q is the sleep current supplied by v out and v ldo to the external circuitry in-between load pulses, including output capacitor leakage, i pulse is the total load current during the pulse, t pulse is the duration of the load pulse and t is the pulse period (essentially the time between load pulses). in this example, i q is 5a, i pulse is 100ma, t pulse is 5ms and t is one hour. the average charge current required from the ltc3109 would be: i chg 5a + 100ma ? 0.005sec 3600sec = 5.14a therefore, if the ltc3109 has an input voltage that allows it to supply a charge current greater than just 5.14a, the application can support 100ma pulses lasting 5ms every hour. it can be seen that the sleep current of 5a is the dominant factor in this example, because the transmit duty cycle is so small (0.00014%). note that for a v out of 3.3v, the average power required by this application is only 17w (not including converter losses). keep in mind that the charge current available from the ltc3109 has no effect on the sizing of the v out capacitor, and the v out capacitor has no effect on the maximum allowed pulse rate.
ltc3109 19 3109fa typical applications energy harvester operates from small temperature differentials of either polarity gnd 1f 5.25v 2.2v ltc3109 3.3v c store 3109 ta02 c1a 1nf 2.2f 470pf 1nf 470pf t1 1:100 teg (thermoelectric generator) 30mv to 500mv ?? t2 1:100 ?? v out2 c2a c1b c2b swb v inb vs1 vs2 t1, t2: coilcraft lpr6235-752sml swa v ina v out vldo pg00d v out2_en vstore vaux + 470f optional switched output for sensors + p low power radio sensor(s) li-ion battery charger and ldo operates from a low level ac input gnd 1f 2.2v ltc3109 3109 ta03 c1a 1nf li-ion battery *the ltc4070 is a precision battery charger offering undervoltage protection, with a typical supply current of only 0.45a fairchild fdg328p 470pf 60hz 1nf 470pf t1 1:100 50mv to 300mv rms t2 1:100 ?? ?? v out2 c2a c1b c2b swb v inb t1, t2: coilcraft lpr6235-752sml vs1 vs2 swa v ina v out vldo vldo to load 4.1v nc 2.2f pg00d v out2_en vstore vaux + ac lbo ntc v cc adj nc nc nc hbo drv ntcbias ltc4070* gnd
ltc3109 20 3109fa typical applications dual-input energy harvester generates 5v and 2.2v from either or both tegs, operating at different temperatures of fixed polarity gnd 1f 2.2v ltc3109 5v v out vldo 3109 ta04 c1a 1nf + C + C 2.2f 470pf thermoelectric generator 25mv to 500mv thermoelectric generator or thermopile 35mv to 1000mv 4.7nf 470pf coilcraft lpr6235-752sml 1:100 ?? coilcraft lpr6235-123qml 1:50 ?? v out2 c2a c1b c2b swb v inb vs1 vs2 swa v ina v out vldo pg00d pg00d *the value of the c out capacitor is detemined by the load characteristics v out2_en vstore vaux c out * + unipolar energy harvester charges battery backup gnd 1f ltc3109 3109 ta06a c1a 33nf li-ion battery fairchild fdg328p 1nf 330k t1 1:50 + C ?? v out2 c2a c1b c2b swb v inb t1: coilcraft lpr6235-123qml vs1 vs2 swa v ina v out vldo vldo pgood v out 3.3v 4.1v nc 2.2f 47f thermoelectic generator ferrotec 9500/127/100b 330f 4v 2.2v pg00d v out2_en vstore vaux + lbo ntc v cc adj nc nc nc hbo drv ntcbias ltc4070 gnd + dt (k) 0 p out (mw) 3.0 4.0 5.0 8 3109 ta06b 2.0 1.0 2.5 3.5 4.5 1.5 0.5 0 2 1 4 3 67 9 5 10 ferrotec 9500/127/100b c1 = 33nf t1 = coilcraft lpr6235-123qml 1:50 ratio v out = 3.3v typical p vout vs dt for unipolar con? guration
ltc3109 21 3109fa package description 4.00 0.10 4.00 0.10 note: 1. drawing is proposed to be made a jedec package outline mo-220 variation (wggd-1)to be approved 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 pin 1 top mark (note 6) 0.40 0.10 20 19 1 2 bottom viewexposed pad 2.00 ref 2.45 0.10 0.75 0.05 r = 0.115 typ r = 0.05 typ 0.25 0.05 0.50 bsc 0.200 ref 0.00 C 0.05 (uf20) qfn 01-07 rev a recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 0.05 0.25 0.05 0.50 bsc 2.00 ref 2.45 0.05 3.10 0.05 4.50 0.05 package outline pin 1 notch r = 0.20 typ or 0.35 w 45 chamfer 2.45 0.10 2.45 0.05 uf package 20-lead plastic qfn (4mm w 4mm) (reference ltc dwg # 05-08-1710 rev a) please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
ltc3109 22 3109fa package description .337 C .344* (8.560 C 8.738) gn20 rev b 0212 12 3 4 5 6 7 8910 .229 C .244 (5.817 C 6.198) .150 C .157** (3.810 C 3.988) 16 17 18 19 20 15 14 13 12 11 .016 C .050 (0.406 C 1.270) .015 .004 (0.38 0.10) w 45 s 0 C 8 typ .0075 C .0098 (0.19 C 0.25) .0532 C .0688 (1.35 C 1.75) .008 C .012 (0.203 C 0.305) typ .004 C .0098 (0.102 C 0.249) .0250 (0.635) bsc .058 (1.473) ref .254 min recommended solder pad layout .150 C .165 .0250 bsc .0165 .0015 .045 .005 * dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side ** dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side inches (millimeters) note: 1. controlling dimension: inches 2. dimensions are in 3. drawing not to scale 4. pin 1 can be bevel edge or a dimple gn package 20-lead plastic ssop (narrow .150 inch) (reference ltc dwg # 05-08-1641 rev b) please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
ltc3109 23 3109fa 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. revision history rev date description page number a 06/12 added vendor information to table 5 15
ltc3109 24 3109fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2010 lt 0612 rev a ? printed in usa related parts typical application unipolar teg energy harvester for low resistance/high current inputs, using external charge pump recti? ers gnd 10f 2.2v ltc3109 3.3v v out v out2 switched v out goes high when pgood is high vldo 3109 ta05 c1a vaux bas31 1.0f 1nf 2.2f 0.1f + 70mv to 1v coilcraft lpr6235-253pml 1:20 ?? v out2 c2a c1b c2b swb v inb vs1 vs2 swa v ina v out vldo pg00d pg00d v out2_en vstore vaux vaux c out + c store + part number description comments ltc3108/ ltc3108-1 ultralow voltage step-up converter and power manager v in : 0.02v to 1v, v out = 2.2v, 2.35v, 3.3v, 4.1v, 5v, i q = 6a, 4mm 3mm dfn-12, ssop-16; ltc3108-1 v out = 2.2v, 2.5v, 3v, 3.7v, 4.5v ltc4070 micropower shunt battery charger 1% float voltage accuracy, 50ma max shunt current, v out = 4.0v, 4.1v, 4.2v, i q = 450na, 2mm 3mm dfn-8, msop-8 ltc1041 bang-bang controller v in : 2.8v to 16v; v out(min) = adj; i q = 1.2ma; i sd < 1a; so-8 package ltc1389 nanopower precision shunt voltage reference v out(min) = 1.25v; i q = 0.8a; so-8 package lt1672/lt1673/ lt1674 single-/dual-/quad-precision 2a rail-to-rail op amps so-8, so-14 and msop-8 packages lt3009 3a i q , 20ma linear regulator v in : 1.6v to 20v; v out(min) : 0.6v to adj, 1.2v, 1.5v, 1.8v, 2.5v, 3.3v, 5v to fixed; i q = 3a; i sd < 1a; 2mm 2mm dfn-8 and sc70 packages ltc3588-1 piezoelectric energy generator with integrated high ef? ciency buck converter v in : 2.7v to 20v; v out(min) : fixed to 1.8v, 2.5v, 3.3v, 3.6v; i q = 0.95a; 3mm 3mm dfn-10 and msop-10e packages LT8410/LT8410-1 micropower 25ma/8ma low noise boost converter with integrated schottky diode and output disconnect v in : 2.6v to 16v; v out(min) = 40v max ; i q = 8.5a; i sd < 1a; 2mm 2mm dfn-8 package i vout vs v in v in (mv) 0 i vout (ma) 8 12 800 3109 ta05b 4 0 200 400 600 100 300 500 700 16 6 10 2 14 1:20 ratio c1 = 1f external diodes typical v in (mv) 10 0 efficiency (%) 10 20 30 40 100 1000 3109 ta05c 50 5 15 25 35 45 ef? ciency vs v in

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