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max17710 energy-harvesting charger and protector ????????????????????????????????????????????????????????????????? maxim integrated products 1 simplified operating circuit 19-5872; rev 1; 7/11 ordering information appears at end of data sheet. for related parts and recommended products to use with this part, refer to: www.maxim-ic.com/max17710.related general description the max17710 is a complete system for charging and protecting micropower-storage cells such as infinite power solutions thinergy ? microenergy cells (mecs). the ic can manage poorly regulated sources such as energy- harvesting devices with output levels ranging from 1 f w to 100mw. the device also includes a boost regulator circuit for charging the cell from a source as low as 0.75v (typ). an internal regulator protects the cell from overcharging. output voltages supplied to the target applications are regulated using a low-dropout (ldo) linear regulator with selectable voltages of 3.3v, 2.3v, or 1.8v. the output regu - lator operates in a selectable low-power or ultra-low-power mode to minimize drain of the cell. internal voltage protec - tion prevents the cell from overdischarging. the device is available in an ultra-thin, 3mm x 3mm x 0.5mm 12-pin utdfn package. applications features s integrated power-management ic for energy storage and load management s lithium charger 1na standby i qbatt 625na linear charging 1w boost charging s lithium cell undervoltage protection s charger overvoltage shunt protection s 1.8v, 2.3v, or 3.3v ldo (150na i qbatt ) s lithium cell output buffering s ultra-thin, 3mm x 3mm x 0.5mm utdfn package powered/smart cards remote wireless sensors memory and real-time clock backup semiactive rfid tags medical devices high-temperature applications military/dod and aerospace toys thinergy is a registered trademark of infinite power solutions, inc. e v a l u a t i o n k i t a v a i l a b l e lx fb gnd ep pgnd sel1 chg sel2 batt teg, solar, or other low-voltage source rf or other high-voltage source thinergy mec101 pckp reg ae lce ldo control signals unregulated output regulated output max17710 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxims website at www.maxim-ic.com.
????????????????????????????????????????????????????????????????? maxim integrated products 2 max17710 energy-harvesting charger and protector batt to gnd ........................................................... -0.3v to +6v chg to gnd ........................................................... -0.3v to +6v lx to pgnd ............................................................. -0.3v to +6v gnd to pgnd ...................................................... -0.3v to +0.3v fb, ae, lce, sel1, sel2, reg, pckp to gnd ....................................... -0.3v to v batt + 0.3v chg continuous current (limited by power dissipation of package) ................... 100ma continuous power dissipation (t a = +70 n c) 12-pin utdfn (derate 15mw/ n c above +70 n c) ....... 1200mw operating temperature range .......................... -40 n c to +85 n c junction temperature ..................................................... +150 n c storage temperature range ............................ -65 n c to +150 n c lead temperature (soldering, 10s) ................................ +300 n c lead temperature (reflow) .............................................. +260 n c absolute maximum ratings stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional opera - tion of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. electrical characteristics (v chg = +4.3v, figure 1 , t a = -40 n c to +85 n c, unless otherwise noted. typical values are at t a = +25 n c.) (note 1) parameter symbol conditions min typ max units chg input maximum voltage limited by shunt regulator (note 2) 4.875 5.3 5.7 v chg enable threshold v ce 4.07 4.15 4.21 v chg quiescent current i qchg v chg = 4.0v rising, v batt = 4.0v 625 1300 na chg shunt delay 25 f s chg input shunt limit (note 2) 50 ma chg maximum input current v chg input current limited by absolute maximum ratings 50 100 ma chg-to-batt dropout voltage v chg = 4.0v, i chg = 1 f a 45 mv v chg = 4.0v, i batt = -6ma 55 v chg = 4.0v, i batt = -20ma 65 v chg = 4.0v, i batt = -40ma 100 batt reg batt regulator voltage 4.065 4.125 4.160 v batt regulation delay v chg = 4.2v, starting at 4v 30 f s batt quiescent current i qbatt regulator in dropout; v chg = 4.15v, v batt = 4.12v 450 1030 na harvest standby (ae pulse low) v chg = 0v, v batt = 2.1v to 4.0v 1 165 ae regulator on, boost off; v chg = 0v, v batt = 4.0v, ae high 725 1650 lce regulator on, boost off; v batt = 4.0v, lce mode (note 3) 150 550
????????????????????????????????????????????????????????????????? maxim integrated products 3 max17710 energy-harvesting charger and protector electrical characteristics (continued) (v chg = +4.3v, figure 1 , t a = -40 n c to +85 n c, unless otherwise noted. typical values are at t a = +25 n c.) (note 1) parameter symbol conditions min typ max units linear ldo regulator reg voltage v pckp = 4.0v, i reg = 50 f a, sel1 = open 3.22 3.3 3.37 v v pckp = 4.0v, i reg = 50 f a, sel1 = gnd 2.25 2.3 2.375 v pckp = 4.0v, i reg = 50 f a, sel1 = batt 1.75 1.8 1.9 reg voltage, lce mode (note 3) v pckp = 4.0v, i reg = 50 f a, sel1 = open 2.9 3.3 3.7 v v pckp = 4.0v, i reg = 50 f a, sel1 = gnd 2.1 2.3 2.5 v pckp = 4.0v, i reg = 50 f a, sel1 = batt 1.6 1.8 2.05 reg current limit v reg = 2.15v, v pckp = 3.8v, ae high 75 ma v reg = 2.15v, v pckp = 3.8v, lce mode (note 3) 50 f a reg startup time v pckp = 4.0v, ae rising, c reg = 1 f f 5.3 ms lce threshold high (note 4) v ih-lce sel1 = open 2.175 v sel1 = gnd 1.575 sel1 = batt 1.30 lce threshold low (note 5) v il-lce sel1 = open 0.9 v sel1 = gnd 0.6 sel1 = batt 0.5 pckp regulator ae threshold high v ih-ae 1.13 v ae threshold low v il-ae 0.15 v ae low input current v ae = 0v, persists < 1 f s -4 -2 f a v ae = 0v, persists > 1 f s 1 na ae high input current v ae = 3.6v 1 na pckp enable threshold reg enabled 3.62 3.7 3.78 v pckp charge current v pckp = 0v, v batt = 2.2v 100 ma pckp impedance ramp rate v batt = 4.0v, resistance between batt and pckp from high impedance to 5 i 5 ms batt undervoltage lockout (uvlo) delay t uvlo1 v batt = 2.15v, ae high, first ramp of pckp 5 s batt uvlo delay t uvlo2 v batt = 2.15v, ae high, not first pckp ramp 0.5 ms batt uvlo threshold ae regulator active, lce regulator inactive 1.990 2.15 2.30 v lce regulator active, ae regulator inactive 3
????????????????????????????????????????????????????????????????? maxim integrated products 4 max17710 energy-harvesting charger and protector electrical characteristics (continued) (v chg = +4.3v, figure 1 , t a = -40 n c to +85 n c, unless otherwise noted. typical values are at t a = +25 n c.) (note 1) note 1: specifications are 100% production tested at t a = +25 n c. limits over the operating temperature range are guaranteed by design and characterization. note 2: since the chg shunt regulator has a 25 f s delay, the user must limit the voltage to the absolute maximum rating until the internal chg shunt provides the voltage limit at the pin in response to 50ma input. larger currents must be shunted with an external clamp to protect the chg pin from damage. note 3: lce mode is entered by pulsing ae high, then pulsing ae low. note 4: for logic-high, connect lce to the reg output. do not connect to the batt or pckp pins. note 5: since lce is compared to the reg pin voltage for operation, the low-power regulator cannot be switched off under condi - tions where the reg output is shorted to gnd. parameter symbol conditions min typ max units boost regulator chg regulation voltage v batt = 4.125v 4.3 4.5 4.7 v frequency v batt = 3.9v, v chg = 3.95v 0.73 1 1.27 mhz boost turn-on time t boost-on design guidance, typical only 850 ns fb threshold fb on rising (enable) 0.485 0.75 1.0 v fb off falling (disable), v chg = 3.8v 0.22 0.25 0.27 fb input current low v fb = gnd, momentary 600 na lx nmos on-resistan c e r ds-on i lx = 20ma, v batt = 3.8v, sel2 = gnd 0.275 0.5 0.7 i i lx = 10ma, v batt = 3.8v, sel2 = open 4 8 12
????????????????????????????????????????????????????????????????? maxim integrated products 5 max17710 energy-harvesting charger and protector table 1. summary of typical quiescent current vs. operating conditions name mode conditions i qbatt (na) i qchg (na) total quiescent current (na) standby cell connection: regulator outputs off, no charger present cell connected to circuit during assembly 1 1 (from cell) shutdown uvlo or shutdown: regulator outputs off, no charger present v batt falls below 2.15v or ae and lce pulsed low 1 1 (from cell) full charge charger present: regulator outputs off, cell charging v chg = 4v, v chg > v batt, ae pulsed low 1 625 626 (from energy-harvesting cell); can harvest down to 1w dropout charge charger in dropout: regulator outputs off, charger present, but below regulation voltage v chg = 4.15v, v batt = 4.12v, ae pulsed low 450 450 (from cell) ae active ae regulator on: boost off, no charge source present ae pulsed high 725 725 (from cell) ae and lce active ae and lce regulators on: boost off, no charge source present lce pulsed high after ae pulsed high 875 875 (from cell) lce active lce regulator on: boost off, no charge source present ae pulsed high, then lce pulsed high, then ae pulsed low 150 150 (from cell)
????????????????????????????????????????????????????????????????? maxim integrated products 6 max17710 energy-harvesting charger and protector typical operating characteristics (t a = +25c, unless otherwise noted.) regulator startup max17710 toc01 time (ms) ae reg volts (v) 5 1 2 3 4 5 6 0 0 10 pckp max17710 toc04 v batt (v) i dd (na) 4.0 3.5 110 130 150 170 190 90 3.0 i dd vs. v batt overtemperature lce = vreg, ae, and sel1 = gnd t a = +25c t a = -40c t a = +85c boost startup max17710 toc02 time (s) chg solar volts (v) 8 6 4 2 1 2 3 4 5 6 0 0 lx max17710 toc05 v batt (v) i dd (na) 4.0 3.5 3.0 i dd vs. v batt overtemperature ae = batt, lce, and sel1 = gnd t a = +85c 575 625 675 725 775 825 525 t a = +25c t a = -40c i dd vs. v batt overtemperature lce and ae and sel1 = gnd max17710 toc03 v batt (v) t a = +25c t a = -40c t a = +85c i dd (na) 4.0 3.5 1 2 3 4 5 6 7 8 9 10 0 3.0 mec101 cell charge profile 2.5mw charge source max17710 toc06 time (minutes) cell voltage (v) charge current (ma) 3.80 3.85 3.90 3.95 4.00 4.05 4.10 4.15 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 3.75 0 5 0 100 150 200 250 v batt i batt boost circuit break-even threshold vs. cell voltage (standard application circuit) max17710 toc07 v batt (v) harvest source power (w) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 3.5 3.7 4.1 4.0 3.6 3.9 3.8 ae load regulation max17710 toc08 load (ma) regulator voltage (v) 150 100 50 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5 1.5 0 200 lce load regulation max17710 toc09 load (a) regulator voltage (v) 100 50 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5 1.5 0
????????????????????????????????????????????????????????????????? maxim integrated products 7 max17710 energy-harvesting charger and protector pin description pin configuration pin name function 1 batt cell input. connect to the positive terminal of the cell without a bypass capacitor. 2 chg charge input. the ic charges the cell from the power source applied to this pin. connect to the output of the boost circuit or directly to a 4.21v or higher charge source. 3 fb boost enable. the boost circuit is enabled by driving this pin above the fb on threshold. afterwards, the boost circuit is disabled by driving this pin below fb off . 4 gnd device ground. connect to system ground. 5 lx boost input. controls current drive through inductor of external boost circuit. 6 pgnd power ground. connect to system ground. 7 ae active enable. pulse high to enable high-power regulator output. pulse low to disable regulator output. 8 sel2 boost r ds-on select. connect to system ground to select a boost r ds-on of 0.5 i for typical applications. 9 sel1 regulator voltage select. ground this pin to select a regulator output voltage of 2.3v, leave disconnected for a regulator output voltage of 3.3v, or connect to the batt pin for a regulator output voltage 1.8v. 10 reg regulator output. connect to load circuit. bypass to system ground with a 1 f f (typ) capacitor. 11 lce low-current enable. pulse high to enable the low-current regulator output after the high-current regulator output is already active. pulse low to disable. 12 pckp protected output of pack. connect an external capacitor to pckp to support energy buffering to the load, especially in low-temperature applications (see table 4). pckp is used for pulsed current storage. ep exposed pad. connect to gnd. pckp 12 lce 11 re g 10 sel1 9 sel2 8 ae 7 1 + batt 2 chg 3 fb 4 ep gnd 5 lx 6 pgnd utdfn max17710 top view
????????????????????????????????????????????????????????????????? maxim integrated products 8 max17710 energy-harvesting charger and protector block diagram overdischarge and undervoltage protection linear charge and idea l diode contro l ref lx chg zlls410ta batt 1.5h 0.1f pgnd sel2 47f state machine disable 5.3v shunt protection to reject overcharge batt boost reg fb fb on threshold output linear reg 3.3v/2.3v/1.8v select mechanical, rf, piezo, or other event detector sel 1 ae reg 300ki teg, solar, or othe r low-voltage source rf, solar, or othe r high-voltage source thinergy mec101 1.0f 10f lce gnd microcontroller load v dd pckp unregulated output max17710 load v dd
????????????????????????????????????????????????????????????????? maxim integrated products 9 max17710 energy-harvesting charger and protector detailed description operation the max177710 controls two main functions related to management of an energy-harvesting application: charging a low-capacity cell with overcharge protection and an ldo regulator output with overdischarge protection. with the exception of protection features, charging and regulation functions operate completely independently of one another. initial power-up of the device occurs when a cell is con - nected to the batt pin. in this state, the device pulls only 1na (typ) from the cell and ldo functions are disabled. only after a charger has been applied and v chg rises above 4.15v (v ce ) does the device initialize to full operation and allow discharging. charge-regulator operation the device charges the cell from an external energy source connected to the chg pin. whenever the volt - age on chg is greater than the voltage on batt, the energy-harvesting circuit directly passes current to the cell without any interaction from the device. when chg rises above v ce , the input linear regulator turns on to limit the charging voltage to 4.125v and protects the cell from overcharge. also at this time, any uvlo is reset, allow - ing the ldo to power the application load. this release of the lockout is latched by chg exceeding v ce and remains active after the removal of the charge voltage. the state of this latch is off when initial power is applied to the batt pin. while charging, the device consumes approximately 625na from the chg source until the voltage on chg exceeds 4.15v. above 4.15v, the ic enters dropout and batt quiescent current increases from 1na to 450na. chg shunt whenever a harvest source pulls the chg pin above 5.3v, an internal shunt regulator enables a path to gnd to limit the voltage at the chg pin. the internal shunt path can sustain currents up to 50ma. if it is possible for the harvest source to exceed this power limit, an external protection circuit is required to prevent damage to the device. figure 1 shows the typical application charge cir - cuit harvesting from high-voltage charge sources. note that a 0.22 f f on chg is recommended for shunt stability when charging from high-voltage sources. in the application circuit example, the cell is charged by several high-voltage harvest sources. whenever either har - vest source voltage is higher than the cell voltage, charge is transferred directly. if either charge source exceeds 4.15v, the device begins to limit current flow to regulate the cells voltage to 4.125v. if either charge source exceeds 5.3v, the internal chg shunt discharges up to 50ma through the device to gnd to protect the chg pin. figure 1. typical application charge circuit harvesting from high-voltage charge sources lx fb gnd pgnd pckp chg sel2 batt ep high-voltage dc charging source (solar, piezo) thinergy mec101 reg load v dd ae mechanical, rf, piezo, or other event detector lce max17710 microcontroller load v dd sel1 0.22f 1 f 10f high-voltage ac charging source (solar, piezo)
???????????????????????????????????????????????????????????????? maxim integrated products 10 max17710 energy-harvesting charger and protector boost regulator operation the device includes a simple boost regulator controller to support energy harvesting from low-voltage solar or ther - moelectric generator (teg) devices. the boost converter can harvest energy down to approximately 1 f w when operated in pulsed harvest mode and as high as 100mw in continuous conversion. for a 0.8v harvest source and a 4.1v cell, the device can deliver over 20ma (80mw), as long as the harvest source can support it. figure 2 shows the typical application boost circuit boost harvesting from a low-voltage solar-cell array. in the application circuit example, the solar cell array charges the 47 f f harvest-source capacitor until the volt - age on fb exceeds the fb on threshold. at this time, the lx pin is pulled low to force current through the external inductor. lx begins to oscillate at a fixed 1.0mhz with 90% duty cycle. each time lx is released by the device, the external inductor forces the voltage of lx above chg and charges the 0.1 f f chg pin capacitor. when chg rises above the voltage of v batt , charge is delivered to the cell. if the chg pin exceeds 4.5v during this time, the boost converter enters a skip-mode operation to limit voltage on chg to 4.5v. operation continues until the voltage of the harvest-source capacitor collapses, driving fb below the fb off threshold, which disables the boost circuit. the process repeats after the harvest source capacitor is recharged. because the boost converter draws its quiescent current directly from the cell (for startup reasons), it is important to only enable the boost converter when it can provide more power than the boost converter consumes from the cell. this can be guaranteed as long as the capacitor across the teg is large enough to boost chg above the batt pin. note that it is important to use a high-speed schottky diode between lx and chg to guarantee lx does not exceed its absolute maximum voltage rating during boost operation. charge regulator component selection external component selection depends on the charge sources available to the device. proper component selection provides the highest efficiency operation of the ic during energy harvesting. see figure 2 as a reference. this section describes component selection for boost sources with operational voltages of 1.0v or high-voltage sources. for boost charge sources with operational volt - ages between 1.0v and 2.0v, additional components are required. see the fb divider section for a detailed description. figure 2. typical application boost circuit boost harvesting from a low-voltage solar-cell array pckp sel1 0.1f 1 f 47 f 300ki 1.5h 10f lx fb chg sel2 batt solar cell 2 solar cell 1 thinergy mec101 reg load v dd ae mechanical, rf, piezo, or other event detector lce max17710 microcontroller load v dd zlls410ta high-speed schottky gnd pgnd ep
???????????????????????????????????????????????????????????????? maxim integrated products 11 max17710 energy-harvesting charger and protector chg capacitor the chg pin capacitor should be minimized to 0.1 f f for highest charge efficiency. however, when charging from a high-voltage source, at least 0.22 f f is required for shunt stability. lx inductor the lx pin inductor is not required for high-voltage charge sources. for low-voltage sources, a minimum inductor value of 0.68 f h is required to prevent the maxi - mum current rating of the lx pin from being exceeded. minimum inductor value is calculated as follows: lx inductor = v fb-on x t boost-o n /lx im a x = 1.0v x 850ns/1a = 0.85 f h boost diode the boost circuit diode must be a high-speed schottky, such as the zlls410ta from diodes incorporated. the diode must turn on quickly to clamp the lx pin volt - age rise at 6.0v or lower when the lx driver turns off. the lx pin can be damaged if the maximum voltage is exceeded. harvest source capacitor the harvest source capacitor must be a minimum of 70 times larger than the chg pin capacitor to boost the charge pin to the maximum charge voltage under worst- case conditions: source capacitor = (4.125v) 2 /(0.485v) 2 x chg capacitor this is the minimum size required for operation. increasing the size of the harvest source capacitor beyond this level improves charge circuit efficiency at extremely low input power (< 10 f w), but care should be taken not to increase the capacitor so large that the harvest source cannot overcome the capacitors leakage. a maximum value of 47 f f is recommended. table 2 lists boost converter external component values. minimum capacitor and inductor values are required for proper operation of the charge circuit. recommended capacitor and inductor values provide optimum charge efficiency. components should be sized as close to the recommended values that the application allows. component values below the minimum values, or above the optimum values, are not recommended. fb divider charge sources with operational voltages between 1.0v and 2.0v require boosting, but are too high a voltage to control the boost circuit efficiently. under these condi - tions, a voltage-divider is required to lower the voltage seen by the fb pin (see figure 3 ). the divider formed by r1 and r2 allows the voltage on the fb pin to transition properly between the fb on and fb off thresholds during boosting. the value for r2 is calculated as follows: v harvest-on = f bon x (r1 + r2)/r1 r2 = (v harvest-on - 1.0v) x 500k i where v harvest-on is the operational voltage of the harvest source. table 2. boost converter external component values application charge source chg capacitor (f) minimum lx inductor (h) recommended lx inductor (h) minimum harvest source capacitor (f) recommended harvest source capacitor (f) high voltage 0.22 n/a n/a n/a n/a low voltage < 10 f w 0.1 0.85 1.5 7.0 47 low voltage > 10 f w 0.1 0.85 1.5 7.0 7.0 high voltage and low voltage < 10 f w 0.22 0.85 1.5 15.4 47 high voltage and low voltage > 10 f w 0.22 0.85 1.5 15.4 15.4
???????????????????????????????????????????????????????????????? maxim integrated products 12 max17710 energy-harvesting charger and protector the c1 1nf capacitor acts as a voltage-level feed for - ward to increase the responsiveness of the divider circuit as the harvest source capacitor is discharged. the mini - mum voltage is defined as: v harvest-off ~= v harvest-on - (fb on - fb off ) v harvest-off ~= v harvest-on - 0.5v (typ) where v harvest-off is the lowest voltage of the harvest source capacitor during boost. because of the divider on the fb pin, the voltage seen by the lx pin inductor is higher than the typical circuit. the inductor must be resized so that the lx pin current limits are not exceeded: lx inductor = v harvest-on x t boost-on /lx imax = v harvest-on x (8.5 x 10 -7 ) all other components are selected as normal. energy-harvesting design approaches when designing an optimal energy harvest system, there are three types of design approaches: linear har - vest, boost harvest, and maximum-power-point tracking (mppt). in harvesting applications, it is very critical to not discharge the cell when charging is failing. when the harvesting power is low enough, eventually the sys - tem discharges the cell rather than charges. this is the break-even point of the harvester. for linear harvesting, this break-even point is lower because the required quiescent current is less. however, for boost harvesting, the breakeven threshold is 1 f a. while an mppt system can utilize the harvesting source more intelligently in high-power situations, it inevitably results in higher qui - escent current and a poorer break-even threshold. mppt systems must measure the current and voltage, multiply to determine power, and make decisions to improve the power. these required measurements automatically significantly increase the quiescent current budget by tens of a . figure 4 shows energy-harvesting modes of operation vs. charge efficiency. ldo output operation the device regulates voltage from the cell to a load circuit on the reg pin through an ldo regulator. the regulator can be configured for 3.3v, 2.3v, or 1.8v opera - tion. the ldo supports loads up to 75ma (high-current mode). for lighter load applications, a low-power mode of operation reduces the quiescent current drain on the cell. a uvlo circuit prevents the regulator from start - ing up or disabling the regulator when active if the cell becomes overdischarged. figure 3. fb divider circuit to improve boost efficiency for charge sources between 1.0v and 2.0v figure 4. energy-harvesting modes of operation vs. charge efficiency chg 0.1f r2 c1 1nf r1 500ki lx l1 fb max17710 47f zlls410ta 1.0v to 2.0v charge source charge efficiency power from harvest source break-even thresholds linear harvest boost harvest mppt (max power tracking)
???????????????????????????????????????????????????????????????? maxim integrated products 13 max17710 energy-harvesting charger and protector figure 5. regulator output state diagram the ldo becomes active when the ae pin is pulsed above or held above its logic-high threshold, but the regulator output is not immediately enabled. the device first charges the external capacitor on pckp. when the voltage level on pckp reaches 3.7v, the regulator output is enabled in high-current mode. powering the ldo from pckp instead of directly from the cell allows the device to support large surge or startup inrush currents from the load that the cell would be unable to handle directly. once in high-current mode, the ae pin can remain logic- high or transition to an open state, and the ouput remains active. the ldo returns to shutdown only when the ae pin is driven below its logic-low threshold. alternatively, the ldo is transitioned to low-current mode by pulsing or holding the lce to the reg pin voltage, followed by pulsing or holding the ae pin logic-low. note that the reg - ulator transitions through a state where both high-current and low-current modes are active at the same time. while in low-current mode, the quiescent current drain of the cell is reduced to 150na, while the maximum load current able to be supplied becomes 50 f a. similar to the ae pin operation, the regulator remains active if the lce pin is open or pulled to reg, and returns to shutdown mode when lce is driven below its logic-low threshold. figure 5 is the regulator output state diagram. cell undervoltage lockout (uvlo) if the cell and pckp capacitance cannot provide sus - tained support for the load, then the voltage at pckp col - lapses. when pckp collapses, the system load typically stops and allows the pckp voltage to recover, resulting in a perpetual retry in a futile attempt to support a load that cannot be supported. when pckp fails in this way, the device shuts off the reg output to prevent futile load retries and protect the cell from overdischarge. when the reg output is latched off, the batt quiescent current reduces to 1na (typ). once uvlo occurs, the regulator output remains disabled until the device detects that a charge source has been connected to the system (v chg > 4.15v). figure 6 shows the uvlo protection modes. connecting any load to reg or pckp instead of connect - ing directly to the cell is highly recommended. this con - trols the quiescent current during shutdown, enables the device to support startup during cold, and also protects the cell from overdischarge. startu p pckp on reg of f i qbatt = pckp capacitor charge current + 725na (typ) shutdown pckp of f reg of f i qbatt = 1na (typ) ae regulator active pckp on reg on i qbatt = 725na (typ) startu p success v pckp > 3.7v ae pulsed hig h undervoltage lockout pckp of f reg of f i qbat t = 1na (typ) startup fail v pckp < 2.15v after 5s charge detected vchg > vce power-on reset (por) ae and lc e regulators active pckp on reg on i qbatt = 875na (typ) lce pulsed high lce pulsed low lce regulator active pckp on reg on i qbatt = 150na (typ) ae pulsed low ae pulsed low lce pulsed low ae pulsed high cell undervoltag e v pckp < 2.15v (high-current mode) v pckp < 3.0v (low-current mode) after 500 s
???????????????????????????????????????????????????????????????? maxim integrated products 14 max17710 energy-harvesting charger and protector figure 6. ulvo protection modes bat t 4.1v 2.15v 0v 4.1v 3.7v 0v v oh-ae v oh-ae v ol-ae 3.3v v ol-ae pckp ae re g a. normal regulator output enable sequence 0v b. regulator output enable fail due to uvlo timeout bat t 4.1v 2.15v 0v 4.1v 0v pckp ae uvlo 0v > t uvlo1 (5s typ) c. high-current mode regulator output disabled due to uvlo timeout bat t 4.1v 2.15v 0v 4.1v 2.15v 0v 3.3v 4.1v 0v pckp reg uvlo > t uvlo2 (500s typ) 0v d. low-current mode regulator output disabled due to uvlo detectio n bat t pckp 4.1v 3.0v 0v 3.3v 0v 0v reg uvlo
???????????????????????????????????????????????????????????????? maxim integrated products 15 max17710 energy-harvesting charger and protector table 3. regulator output voltage selection *capacitance value tolerances need to be considered. table 4. pckp pin capacitor values by application regulator voltage selection the sel1 pin selects at which voltage reg operates. connect sel1 to batt for 1.8v operation, three-state for 3.3v operation, or connect to gnd for 2.3v operation. note that the voltage regulation value is latched when enabled. to change the regulation voltage point, the reg - ulator must be disabled and then reenabled. see table 3 . pckp pin capacitor selection there are several cases when the system might overload the cell, potentially causing damage. they are prevented with the pckp load switch block and external capacitor: u during startup, when there is an inrush current due to the applications load and capacitance. u when the cell is cold (such as -40 n c), and due to increased cell resistance, it is unable to support high- load currents. u if the system requires a load current higher than can be supported by the cell alone. the device provides cell undervoltage protection by limiting the current from batt to pckp and guarantee - ing that the cell voltage does not fall below 2.15v. in addition to voltage protection, the ramp of the pckp switch impedance is changed slowly (5ms to full on) to gradually load the cell and not collapse the voltage on a room-temperature cell. because of these protection fea - tures, an application can now support brief high-current pulses by including a large capacitance at pckp. this allows support for pulse loads many times higher than that naturally supported by the cell alone. a large pckp capacitance can be selected to support a pulse load even while the cell is very cold, and would normally be incapable of supporting a significant load. choose this capacitor according to table 4 or the follow - ing equation: c pckp = i task x t task /(3.7 - v min ) where: i task is the current required to sustain a required task, t task is the time duration of the task, and v min is the minimum voltage of the load doing the task. this equation assumes that the batt impedance is high and cannot support the load. sel1 pin connection reg pin output voltage (v) connect to batt 1.8 open circuit 3.3 connect to gnd 2.3 v min t task (ms) i task (ma) c pckp (f)* 3.0 5 8 100 3.0 5 4 50 2.8 5 5 28 2.8 5 2.5 14 2.3 5 5 18 2.3 5 10 36
???????????????????????????????????????????????????????????????? maxim integrated products 16 max17710 energy-harvesting charger and protector ordering information package information for the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. + denotes a lead (pb)-free/rohs-compliant package. u = signifies tape cut. t = tape and reel. * ep = exposed pad. package type package code outline no. land pattern no. 12 utdfn-ep v1233n+1 21-0451 90-0339 part temp range pin-package max17710g+u -40 n c to +85 n c 12 utdfn-ep* max17710g+t -40 n c to +85 n c 12 utdfn-ep*
max17710 energy-harvesting charger and protector maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 17 ? 2011 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 6/11 initial release 1 7/11 corrections and clarifications made based on customer feedback; added new toc #9 and updated two ec table limits 3C7, 9, 10, 12C15

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