EVALUATION KIT AVAILABLE MAX17710 Energy-Harvesting Charger and Protector General Description Features 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 energyharvesting devices with output levels ranging from 1FW 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. S Integrated Power-Management IC for Energy Storage and Load Management S Lithium Charger S 1.8V, 2.3V, or 3.3V LDO (150nA IQBATT) S Lithium Cell Output Buffering S Ultra-Thin, 3mm x 3mm x 0.5mm UTDFN Package Ordering Information appears at end of data sheet. Applications Remote Wireless Sensors High-Temperature Applications Memory and Real-Time Clock Backup Military/DoD and Aerospace Semiactive RFID Tags Toys 1µW Boost Charging S Charger Overvoltage Shunt Protection The device is available in an ultra-thin, 3mm x 3mm x 0.5mm 12-pin UTDFN package. Medical Devices S Lithium Cell Undervoltage Protection 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 regulator operates in a selectable low-power or ultra-low-power mode to minimize drain of the cell. Internal voltage protection prevents the cell from overdischarging. Powered/Smart Cards 1nA Standby IQBATT 625nA Linear Charging For related parts and recommended products to use with this part, refer to: www.maximintegrated.com/MAX17710.related. Simplified Operating Circuit THINERGY MEC101 BATT RF OR OTHER HIGH-VOLTAGE SOURCE CHG PCKP UNREGULATED OUTPUT SEL2 REG REGULATED OUTPUT MAX17710 TEG, SOLAR, OR OTHER LOW-VOLTAGE SOURCE LX AE FB EP GND PGND LCE LDO CONTROL SIGNALS SEL1 THINERGY is a registered trademark of Infinite Power Solutions, Inc. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. 19-5872; Rev 2; 12/12 MAX17710 Energy-Harvesting Charger and Protector ABSOLUTE MAXIMUM RATINGS 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 VBATT + 0.3V CHG Continuous Current (limited by power dissipation of package)....................100mA Continuous Power Dissipation (TA = +70NC) UTDFN (derate 15mW/NC above +70NC)....................1200mW Operating Temperature Range........................... -40NC to +85NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation 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 (VCHG = +4.3V, Figure 1, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1) PARAMETER SYMBOL CHG Input Maximum Voltage CONDITIONS Limited by shunt regulator (Note 2) CHG Enable Threshold VCE CHG Quiescent Current IQCHG MIN TYP MAX UNITS 4.875 5.3 5.7 V 4.07 4.15 4.21 V 625 1300 nA VCHG = 4.0V rising, VBATT = 4.0V CHG Shunt Delay 25 CHG Input Shunt Limit (Note 2) CHG Maximum Input Current VCHG input current limited by Absolute Maximum Ratings CHG-to-BATT Dropout Voltage Fs 50 50 100 VCHG = 4.0V, ICHG = 1FA 45 VCHG = 4.0V, IBATT = -6mA 55 VCHG = 4.0V, IBATT = -20mA 65 VCHG = 4.0V, IBATT = -40mA 100 mA mA mV BATT REG BATT Regulator Voltage 4.065 BATT Regulation Delay BATT Quiescent Current Maxim Integrated IQBATT 4.125 4.160 VCHG = 4.2V, starting at 4V 30 Regulator in dropout; VCHG = 4.15V, VBATT = 4.12V 450 1030 1 165 AE regulator on, boost off; VCHG = 0V, VBATT = 4.0V, AE high 725 1650 LCE regulator on, boost off; VBATT = 4.0V, LCE mode (Note 3) 150 550 Harvest standby (AE pulse low) VCHG = 0V, VBATT = 2.1V to 4.0V V Fs nA 2 MAX17710 Energy-Harvesting Charger and Protector ELECTRICAL CHARACTERISTICS (continued) (VCHG = +4.3V, Figure 1, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX VPCKP = 4.0V, IREG = 50FA, SEL1 = open 3.22 3.3 3.37 VPCKP = 4.0V, IREG = 50FA, SEL1 = GND 2.25 2.3 2.375 VPCKP = 4.0V, IREG = 50FA, SEL1 = BATT 1.75 1.8 1.9 VPCKP = 4.0V, IREG = 50FA, SEL1 = open 2.9 3.3 3.7 VPCKP = 4.0V, IREG = 50FA, SEL1 = GND 2.1 2.3 2.5 VPCKP = 4.0V, IREG = 50FA, SEL1 = BATT 1.6 1.8 2.05 UNITS LINEAR LDO REGULATOR REG Voltage REG Voltage, LCE Mode (Note 3) V V VREG = 2.15V, VPCKP = 3.8V, AE high 75 mA REG Current Limit VREG = 2.15V, VPCKP = 3.8V, LCE mode (Note 3) 50 FA REG Startup Time VPCKP = 4.0V, AE rising, CREG = 1FF LCE Threshold High (Note 4) LCE Threshold Low (Note 5) VIH-LCE VIL-LCE 5.3 SEL1 = open 2.175 SEL1 = GND 1.575 SEL1 = BATT 1.30 ms V SEL1 = open 0.9 SEL1 = GND 0.6 SEL1 = BATT 0.5 V PCKP REGULATOR AE Threshold High VIH-AE AE Threshold Low VIL-AE 1.13 V 0.15 VAE = 0V, persists < 1Fs -2 FA VAE = 0V, persists > 1Fs 1 nA AE High Input Current VAE = 3.6V 1 nA PCKP Enable Threshold REG enabled PCKP Charge Current VPCKP = 0V, VBATT = 2.2V PCKP Impedance Ramp Rate AE Low Input Current 3.7 3.78 V mA VBATT = 4.0V, resistance between BATT and PCKP from high impedance to 5I 5 ms 5 s 0.5 ms tUVLO1 VBATT = 2.15V, AE high, first ramp of PCKP BATT UVLO Delay tUVLO2 VBATT = 2.15V, AE high, not first PCKP ramp Maxim Integrated 3.62 100 BATT Undervoltage Lockout (UVLO) Delay BATT UVLO Threshold -4 V AE regulator active, LCE regulator inactive LCE regulator active, AE regulator inactive 1.990 2.15 3 2.30 V 3 MAX17710 Energy-Harvesting Charger and Protector ELECTRICAL CHARACTERISTICS (continued) (VCHG = +4.3V, Figure 1, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS BOOST REGULATOR CHG Regulation Voltage VBATT = 4.125V 4.3 4.5 4.7 V Frequency VBATT = 3.9V, VCHG = 3.95V 0.73 1 1.27 MHz Boost Turn-On Time FB Threshold tBOOST-ON Design guidance, typical only ns Rising (enable) 0.485 0.75 1.0 FBOFF Falling (disable), VCHG = 3.8V 0.22 0.25 0.27 FB Input Current Low LX nMOS On-Resistance 850 FBON VFB = GND, momentary RDS-ON 600 V nA ILX = 20mA, VBATT = 3.8V, SEL2 = GND 0.275 0.5 0.7 ILX = 10mA, VBATT = 3.8V, SEL2 = open 4 8 12 I Note 1: Specifications are 100% production tested at TA = +25NC. Limits over the operating temperature range are guaranteed by design and characterization. Note 2: Since the CHG shunt regulator has a 25Fs 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 conditions where the REG output is shorted to GND. Maxim Integrated 4 MAX17710 Energy-Harvesting Charger and Protector Table 1. Summary of Typical Quiescent Current vs. Operating Conditions NAME MODE CONDITIONS IQBATT (nA) IQCHG (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 VBATT falls below 2.15V or AE and LCE pulsed low 1 — 1 (from cell) Full Charge Charger Present: Regulator outputs off, cell charging VCHG = 4V, VCHG > VBATT, AE pulsed low 1 625 Dropout Charge Charger in Dropout: Regulator outputs off, charger present, but below regulation voltage VCHG = 4.15V, VBATT = 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 626 (from energy-harvesting cell); can harvest down to 1μW 5 MAX17710 Energy-Harvesting Charger and Protector Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) 5 VOLTS (V) AE 3 REG 9 8 7 4 4 CHG SOLAR 3 PCKP 1 TA = +85°C 6 5 TA = +25°C 4 2 2 MAX17710 toc03 LX IDD (nA) 5 10 MAX17710 toc02 6 MAX17710 toc01 6 VOLTS (V) IDD vs. VBATT OVERTEMPERATURE LCE AND AE AND SEL1 = GND BOOST STARTUP REGULATOR STARTUP 3 2 1 TA = -40°C 1 0 0 TIME (ms) 4 TIME (µs) IDD vs. VBATT OVERTEMPERATURE LCE = VREG, AE, AND SEL1 = GND IDD vs. VBATT OVERTEMPERATURE AE = BATT, LCE, AND SEL1 = GND 190 2 0 8 775 MEC101 CELL CHARGE PROFILE 2.5mW CHARGE SOURCE 575 90 525 3.5 4.0 0.30 3.95 0.25 3.90 3.0 3.5 0.4 0.3 MAX17710 toc08 3.1 2.9 2.7 2.5 2.3 2.1 3.1 2.5 2.3 2.1 1.7 0 1.5 Maxim Integrated 50 100 LOAD (mA) 250 2.7 1.9 0 200 2.9 1.7 4.1 150 3.3 0.1 4.0 100 LCE LOAD REGULATION 1.9 3.9 50 3.5 0.2 VBATT (V) 0 0 REGULATOR VOLTAGE (V) 0.5 3.8 0.05 TIME (Minutes) 3.3 REGULATOR VOLTAGE (V) 0.6 3.7 0.10 AE LOAD REGULATION 0.7 0.15 3.85 4.0 3.5 MAX17710 toc07 0.8 0.20 VBATT VBATT (V) 0.9 3.6 0.35 4.00 3.75 BOOST CIRCUIT BREAK-EVEN THRESHOLD vs. CELL VOLTAGE (STANDARD APPLICATION CIRCUIT) 3.5 0.40 3.80 VBATT (V) 1.0 0.45 150 200 MAX17710 toc09 3.0 TA = +25°C TA = -40°C 110 0.50 IBATT 4.10 CELL VOLTAGE (V) IDD (nA) TA = +25°C TA = -40°C 675 625 MAX17710 toc06 4.15 4.05 725 150 4.0 1.5 0 50 100 LOAD (µA) 6 CHARGE CURRENT (mA) TA = +85°C 3.5 3.0 VBATT (V) 825 130 HARVEST SOURCE POWER (µW) 6 TA = +85°C 170 IDD (nA) 0 10 MAX17710 toc05 5 MAX17710 toc04 0 MAX17710 Energy-Harvesting Charger and Protector Pin Configuration TOP VIEW BATT 1 CHG 2 FB 3 GND + 12 PCKP 11 LCE 10 REG 4 9 SEL1 LX 5 8 SEL2 PGND 6 7 AE MAX17710 EP UTDFN Pin Description PIN NAME 1 BATT Cell Input. Connect to the positive terminal of the cell without a bypass capacitor. FUNCTION 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 4 GND Boost Enable. The boost circuit is enabled by driving this pin above the FBON threshold. Afterwards, the boost circuit is disabled by driving this pin below FBOFF. Device Ground. Connect to system ground. 5 LX 6 PGND 7 AE 8 SEL2 Boost RDS-ON Select. Connect to system ground to select a boost RDS-ON of 0.5I 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 1FF (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 — EP Maxim Integrated Boost Input. Controls current drive through inductor of external boost circuit. Power Ground. Connect to system ground. Active Enable. Pulse high to enable high-power regulator output. Pulse low to disable regulator output. 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. Exposed Pad. Connect to GND. 7 MAX17710 Energy-Harvesting Charger and Protector Block Diagram BATT PCKP 10µF LINEAR CHARGE AND IDEAL DIODE CONTROL THINERGY MEC101 OVERDISCHARGE AND UNDERVOLTAGE PROTECTION UNREGULATED OUTPUT MAX17710 REF CHG 0.1µF RF, SOLAR, OR OTHER HIGH-VOLTAGE SOURCE LOAD VDD OUTPUT LINEAR REG 1.0µF 5.3V SHUNT PROTECTION TO REJECT OVERCHARGE ZLLS410TA REG 3.3V/2.3V/1.8V SELECT SEL 1 BATT 1.5µH LX DISABLE 47µF AE PGND 300kI TEG, SOLAR, OR OTHER LOW-VOLTAGE SOURCE FBON THRESHOLD BOOST REG MECHANICAL, RF, PIEZO, OR OTHER STATE MACHINE SEL2 FB EVENT DETECTOR LOAD VDD LCE MICROCONTROLLER GND Maxim Integrated 8 MAX17710 Energy-Harvesting Charger and Protector Detailed Description 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. Operation 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. The MAX17710 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. 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 circuit harvesting from high-voltage charge sources. Note that a 0.22FF on CHG is recommended for shunt stability when charging from high-voltage sources. Initial power-up of the device occurs when a cell is connected 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 VCHG rises above 4.15V (VCE) 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 voltage 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 VCE, 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, allowing the LDO to power the application load. This release of the lockout is latched by CHG exceeding VCE and In the application circuit example, the cell is charged by several high-voltage harvest sources. Whenever either harvest 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 cell’s 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. LOAD VDD THINERGY MEC101 REG BATT 1µF SEL2 EVENT DETECTOR SEL1 AE CHG 0.22µF MECHANICAL, RF, PIEZO, OR OTHER MAX17710 LOAD VDD HIGH-VOLTAGE AC CHARGING SOURCE (SOLAR, PIEZO) HIGH-VOLTAGE DC CHARGING SOURCE (SOLAR, PIEZO) LX LCE MICROCONTROLLER FB GND EP PGND PCKP 10µF Figure 1. Typical Application Charge Circuit Harvesting from High-Voltage Charge Sources Maxim Integrated 9 MAX17710 Energy-Harvesting Charger and Protector Boost Regulator Operation driving FB below the FBOFF threshold, which disables the boost circuit. The process repeats after the harvest source capacitor is recharged. The device includes a simple boost regulator controller to support energy harvesting from low-voltage solar or thermoelectric generator (TEG) devices. The boost converter can harvest energy down to approximately 1FW 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. 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. In the application circuit example, the solar cell array charges the 47FF harvest-source capacitor until the voltage on FB exceeds the FBON 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 0.1FF CHG pin capacitor. When CHG rises above the voltage of VBATT, 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, 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 voltages between 1.0V and 2.0V, additional components are required. See the FB Divider section for a detailed description. LOAD VDD THINERGY MEC101 REG BATT 1µF SEL2 SEL1 EVENT DETECTOR CHG 0.1µF AE ZLLS410TA HIGH-SPEED SCHOTTKY MAX17710 MECHANICAL, RF, PIEZO, OR OTHER LOAD VDD 1.5µH LX SOLAR CELL 2 SOLAR CELL 1 47µF 300kI LCE FB GND EP PGND MICROCONTROLLER PCKP 10µF Figure 2. Typical Application Boost Circuit Boost Harvesting from a Low-Voltage Solar-Cell Array Maxim Integrated 10 MAX17710 Energy-Harvesting Charger and Protector CHG Capacitor The CHG pin capacitor should be minimized to 0.1FF for highest charge efficiency. However, when charging from a high-voltage source, at least 0.22FF 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 0.68FH is required to prevent the maximum current rating of the LX pin from being exceeded. Minimum inductor value is calculated as follows: LX inductor = VFB-ON x tBOOST-ON/LXIMAX = 1.0V x 850ns/1A = 0.85FH 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 voltage 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 worstcase 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 (< 10FW), but care should be taken not to increase the capacitor so large that the harvest source cannot overcome the capacitor’s leakage. A maximum value of 47FF 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 conditions, 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 FBON and FBOFF thresholds during boosting. The value for R2 is calculated as follows: VHARVEST-ON = FBON x (R1 + R2)/R1 R2 = (VHARVEST-ON - 1.0V) x 500kI where VHARVEST-ON is the operational voltage of the harvest source. Table 2. Boost Converter External Component Values APPLICATION CHARGE SOURCE CHG CAPACITOR (µF) MINIMUM LX INDUCTOR (µH) RECOMMENDED LX INDUCTOR (µH) MINIMUM HARVEST SOURCE CAPACITOR (µF) RECOMMENDED HARVEST SOURCE CAPACITOR (µF) N/A High voltage 0.22 N/A N/A N/A Low voltage < 10FW 0.1 0.85 1.5 7.0 47 Low voltage > 10FW 0.1 0.85 1.5 7.0 7.0 High voltage and low voltage < 10FW 0.22 0.85 1.5 15.4 47 High voltage and low voltage > 10FW 0.22 0.85 1.5 15.4 15.4 Maxim Integrated 11 MAX17710 Energy-Harvesting Charger and Protector The C1 1nF capacitor acts as a voltage-level feed forward to increase the responsiveness of the divider circuit as the harvest source capacitor is discharged. The minimum voltage is defined as: CHG 0.1µF VHARVEST-OFF ~= VHARVEST-ON - (FBON - FBOFF) ZLLS410TA VHARVEST-OFF ~= VHARVEST-ON - 0.5V (typ) where VHARVEST-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: MAX17710 L1 1.0V TO 2.0V CHARGE SOURCE LX 47µF C1 1nF R2 FB LX Inductor = VHARVEST-ON x tBOOST-ON/LXIMAX = VHARVEST-ON x (8.5 x 10-7) R1 500kI All other components are selected as normal. Energy-Harvesting Design Approaches Figure 3. FB Divider Circuit to Improve Boost Efficiency for Charge Sources Between 1.0V and 2.0V MPPT (MAX POWER TRACKING) BOOST HARVEST CHARGE EFFICIENCY When designing an optimal energy harvest system, there are three types of design approaches: linear harvest, 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 system 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 1FA. While an MPPT system can utilize the harvesting source more intelligently in high-power situations, it inevitably results in higher quiescent 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 µA. Figure 4 shows energy-harvesting modes of operation vs. charge efficiency. LINEAR HARVEST BREAK-EVEN THRESHOLDS 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 operation. 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 starting up or disabling the regulator when active if the cell becomes overdischarged. Maxim Integrated POWER FROM HARVEST SOURCE Figure 4. Energy-Harvesting Modes of Operation vs. Charge Efficiency 12 MAX17710 Energy-Harvesting Charger and Protector 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 logichigh 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 regulator transitions through a state where both highcurrent 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 50FA. 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 sustained support for the load, then the voltage at PCKP collapses. 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 (VCHG > 4.15V). Figure 6 shows the UVLO protection modes. Connecting any load to REG or PCKP instead of connecting directly to the cell is highly recommended. This controls the quiescent current during shutdown, enables the device to support startup during cold, and also protects the cell from overdischarge. LCE PULSED LOW SHUTDOWN PCKP OFF REG OFF IQBATT = 1nA (typ) AE PULSED LOW AE PULSED HIGH STARTUP CHARGE DETECTED VCHG > VCE PCKP ON REG OFF IQBATT = PCKP CAPACITOR CHARGE CURRENT + 725nA (typ) STARTUP SUCCESS VPCKP > 3.7V STARTUP FAIL VPCKP < 2.15V AFTER 5s AE REGULATOR ACTIVE PCKP ON REG ON IQBATT = 725nA (typ) LCE PULSED HIGH LCE PULSED LOW AE AND LCE REGULATORS ACTIVE PCKP ON REG ON IQBATT = 875nA (typ) AE PULSED LOW AE PULSED HIGH LCE REGULATOR ACTIVE PCKP ON REG ON IQBATT = 150nA (typ) CELL UNDERVOLTAGE VPCKP < 2.15V (HIGH-CURRENT MODE) VPCKP < 3.0V (LOW-CURRENT MODE) AFTER 500µs UNDERVOLTAGE LOCKOUT PCKP OFF REG OFF IQBATT = 1nA (typ) POWER-ON RESET (POR) Figure 5. Regulator Output State Diagram Maxim Integrated 13 MAX17710 Energy-Harvesting Charger and Protector 4.1V BATT 4.1V BATT 2.15V 0V 2.15V 0V 4.1V PCKP 4.1V 3.7V PCKP 0V 0V AE VOH-AE VOH-AE AE VOL-AE VOL-AE 3.3V REG UVLO 0V 0V a. NORMAL REGULATOR OUTPUT ENABLE SEQUENCE > tUVLO1 (5s typ) b. REGULATOR OUTPUT ENABLE FAIL DUE TO UVLO TIMEOUT 4.1V BATT 2.15V 0V 4.1V PCKP 2.15V BATT 4.1V 3.0V PCKP 0V 0V 3.3V REG 3.3V 0V 4.1V REG 0V > tUVLO2 (500µs typ) UVLO UVLO 0V 0V c. HIGH-CURRENT MODE REGULATOR OUTPUT DISABLED DUE TO UVLO TIMEOUT d. LOW-CURRENT MODE REGULATOR OUTPUT DISABLED DUE TO UVLO DETECTION Figure 6. ULVO Protection Modes Maxim Integrated 14 MAX17710 Energy-Harvesting Charger and Protector 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 regulator 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: UDuring startup, when there is an inrush current due to the application’s load and capacitance. UWhen the cell is cold (such as -40NC), and due to increased cell resistance, it is unable to support highload currents. UIf 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 guaranteeing 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 features, 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 following equation: CPCKP = ITASK x tTASK/(3.7 - VMIN) where: ITASK is the current required to sustain a required task, tTASK is the time duration of the task, and VMIN is the minimum voltage of the load doing the task. This equation assumes that the BATT impedance is high and cannot support the load. Table 3. Regulator Output Voltage Selection SEL1 PIN CONNECTION REG PIN OUTPUT VOLTAGE (V) Connect to BATT 1.8 Open circuit 3.3 Connect to GND 2.3 Table 4. PCKP Pin Capacitor Values by Application VMIN tTASK (ms) ITASK (mA) CPCKP (µF)* 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 10 36 2.3 5 *Capacitance value tolerances need to be considered. Maxim Integrated 15 MAX17710 Energy-Harvesting Charger and Protector Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.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. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 12 UTDFN-EP V1233N+1 21-0451 90-0339 Maxim Integrated Ordering Information TEMP RANGE PIN-PACKAGE MAX17710G+T* PART -40NC to +85NC 12 UTDFN-EP** MAX17710G+U* -40NC to +85NC 12 UTDFN-EP** MAX17710GB+ -40NC to +85NC 12 UTDFN-EP** MAX17710GB+T -40NC to +85NC 12 UTDFN-EP** +Denotes a lead(Pb)-free/RoHS-compliant package. U = Signifies tape cut. T = Tape and reel. *Not recommended for new designs. **EP = Exposed pad. 16 MAX17710 Energy-Harvesting Charger and Protector Revision History REVISION NUMBER REVISION DATE 0 12/12 DESCRIPTION Initial release PAGES CHANGED — Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated 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 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 © 2012 Maxim Integrated Products, Inc. 17 Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. MAX17710 Energy-Harvesting Charger and Protector Maxim Integrated 18