AN4050 Application note STEVAL-ISV012V1: lithium-ion solar battery charger By Domenico Ragonese, Alessandro Nicosia and Giovanni Conti Introduction The STEVAL-ISV012V1 is a demonstration board that mounts the SPV1040 (solar energy harvester) as the input stage and the L6924D (Li-Ion battery charger) as the output stage. It targets any portable application powered by lithium-ion batteries and merges the capability of the SPV1040 to maximize the power extraction from the solar module with the linear regulation of the L6924D, to optimize the battery charge and to protect the load while reducing the power dissipation at the bottom. It is shown in Figure 1. Figure 1. STEVAL-ISV012V1 demonstration board The board has been designed to charge lithium-ion and lithium-polymer batteries with VBATT_max = 4.1 or 4.2 V and it includes a 400 mWpk polycrystalline PV panel (SZGD6060-4P from NBSZGD) with Voc = 2.2 V and Isc = 220 mA. According to specific application requirements, some components may be replaced as per the following guidelines: • • • • The PV panel can be replaced by a different one as long as Voc < VBATT_max and Isc < 1.65 A. The inductor L1 can be replaced by considering that it affects the maximum peak current and that an input overcurrent limit must not be triggered. The maximum output current can be limited by replacing the current sensing resistor Rs (0 Ω by default). The resistor R14, which limits the charge current threshold, by default is set to 500 mA. For further details on component selection, please refer to the section “external component selection” of the AN3319 application note. For details about SPV1040 and L6924D features please refer to the related datasheets. March 2013 DocID022816 Rev 2 1/19 www.st.com Contents AN4050 Contents 1 SPV1040 operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 L6924D operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 L6924D operation in solar powered applications . . . . . . . . . . . . . . . . . . 7 4 Reference design description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Schematic and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6 Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2/19 DocID022816 Rev 2 AN4050 List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. STEVAL-ISV012V1 demonstration board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Typical application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 SPV1040 equivalent circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 MPPT working principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 SPV1040 internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Basic application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Typical charge curve in Quasi-pulse mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Battery charging at low irradiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Battery charging at low irradiation, zoomed in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Maximum available current vs. Pin, 200 mW peak PV panel . . . . . . . . . . . . . . . . . . . . . . . . 9 Maximum available current vs. Pin, 2 W peak PV panel . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Application set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 V-I and P-V plot diagrams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Partial charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Full charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 STEVAL-ISV012V1 schematic, battery charge section . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 STEVAL-ISV012V1 schematic, solar power optimizer section . . . . . . . . . . . . . . . . . . . . . . 14 STEVAL-ISV012V1 PCB top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 STEVAL-ISV012V1 PCB bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 DocID022816 Rev 2 3/19 SPV1040 operation description 1 AN4050 SPV1040 operation description The SPV1040 is a high efficiency, low power and low voltage DC-DC converter that provides a single output voltage up to 5.2 V. If combined with the L6924D, it provides the ideal solution for charging lithium battery packs by harvesting energy from a very small solar panel. The SPV1040 is a 100 kHz fixed frequency PWM step-up converter able to maximize the energy harvested by few solar cells. thanks to the embedded MPPT algorithm which maximizes the power generated from the panel by continuously tracking its output voltage and current. The converter guarantees the safety of the overall application and its own by stopping the PWM switching in case of an overvoltage, overcurrent or overtemperature condition. The IC integrates a 120 mΩ N-channel MOSFET power switch and a 140 mΩ Pchannel MOSFET synchronous rectifier. Figure 2. Typical application circuit L VPV XSHUT I CTRL_PLUS GND I CTRL_MINUS R3 RF1 CF RF2 R1 COUT VCTRL SET MPP- SET MPP CIN VBATT RS VOUT Lx CINsns D OUT R2 COUTsns AM11733v1 The SPV1040 acts as an impedance adapter between the PV module and the output load. In fact, the equivalent circuit can be seen below: Figure 3. SPV1040 equivalent circuit 639 , ,1 9 39 3DQHO JPĆ9 ,1 & ,1 , 287 & 287 ,1 5 287 9287 = '& $0Y The MPPT algorithm properly sets up the DC working point by guaranteeing Zin = Zm (assuming Zm is the impedance of the supply source). In this way, the power extracted from the supply source (Pin = Vin * Iin) is maximum (Pm = Vm * Im). The voltage-current curve shows all the available working points of the PV panel at a given solar irradiation. The voltage-power curve is derived from the voltage-current curve by 4/19 DocID022816 Rev 2 AN4050 SPV1040 operation description plotting the product V*I for each voltage generated. For further details of the MPPT algorithm, please refer to the SPV1040 datasheet. Figure 4. MPPT working principle PMAX I MP Power [W] Current [A] 0 Voltage [V] VMP VOC AM11735v1 Figure 5. SPV1040 internal block diagram V OUT Lx START SIGNAL ANALOG BLOCK ZERO CROSSING DETECTOR VREF + I CTRL_PLUS VMPP-REF OVER TEMPERATURE REVERSE POLARITY MPP BLOCK I CTRL_MINUS PWM CLOCK MPP-SET + DRIVERS CONTROL OVER CURRENT CLOCK Burst Ref XSHUT BURST MODE + DIGITAL CORE - DAC CODE Iout Reg Vin Reg Vout Reg GND V MPP-REF MPP-SET V CTRL + - VREF AM11736v1 The duty cycle set by the MPPT algorithm can be overwritten if one of the following conditions is triggered: • Input overcurrent protection (OVC): inductor peak current ≤ 1.65 A • Overtemperature protection (OVT): internal temperature ≤ 155 °C • Output voltage regulation: VCTRL pin triggers the 1.25 V internal reference • Output current limitation: Rs * (ICTRL_PLUS - ICTRL_MINUS) ≤ 50 mV • MPP-SET voltage VMPP-SET ≤ 300 mV at the startup and VMPP-SET ≤ 450 mV in running mode. Application components must be carefully selected to avoid any undesired trigger of the above thresholds. DocID022816 Rev 2 5/19 L6924D operation description 2 AN4050 L6924D operation description The L6924D is a fully monolithic battery charger dedicated to single-cell Li-Ion/polymer battery packs. It is designed with BCD6 technology and integrates all of the power elements (the Power MOSFET, reverse blocking diode and the sense resistor) in a small VFQFPN16 3 mm x 3 mm package. It normally works as a linear charger when powered from an external voltage regulated adapter. However, thanks to its very low minimum input voltage (down to 2.5 V) the L6924D can also work as a quasi-pulse charger when powered from a current limited adapter, dramatically reducing the power dissipation. The L6924D charges the battery in three phases: • • • Pre-charge constant current: a deeply discharged battery is charged with a low current. Fast-charge constant current: the device charges the battery with the maximum current. Constant voltage: when the battery voltage is close to the selected output voltage, the device starts to reduce the current, until the charge termination is completed. Regardless of the charging approach, a closed loop thermal control avoids device overheating. The L6924D allows the user to program many parameters, such as pre-charge current, fast-charge current, pre-charge voltage threshold, end-of-charge current threshold, and charge timer. The L6924D offers two open collector outputs for diagnostic purposes, which can be used to either drive two external LEDs or communicate with a host microcontroller. Finally, the L6924D also provides other battery related functions, such as checking for battery presence, monitoring, and protection from unsafe thermal conditions. Figure 6. Basic application schematic 5 9 5() 9 ,1 &+$5*(5 5 7+ 9 287 %$77(5< 9 2616 & 9 ,1616 5 5 7 35* & /' & , (1' /' , 35* /' /' 5 67 67 9 35( 6+'1 9 235* , 35( *1' 5 - 5 5 21 2)) 9UHI 5 5 $0Y 6/19 DocID022816 Rev 2 AN4050 3 L6924D operation in solar powered applications L6924D operation in solar powered applications Thanks to its very low minimum input voltage (down to 2.5 V), the L6924D can also work as a quasi-pulse charger when powered from a current limited adapter such as a PV panel or a current limit device such as the SPV1040 step-up. To work in this condition, it is enough to set the device's charging current (by R14) higher than the maximum peak current of the PV panel. During the fast-charge phase, the output voltage of the SPV1040 that supplies the L6924D goes down to the battery voltage plus the voltage drop across the power MOSFET of the charger. In this mode, the L6924D charges the battery with the same three phases as in linear mode, but the power dissipation is greatly reduced, as shown in Figure 7. Figure 7. Typical charge curve in Quasi-pulse mode DocID022816 Rev 2 7/19 L6924D operation in solar powered applications AN4050 During the fast-charge phase, the output voltage of the SPV1040 (VIN of L6924D) goes down to the battery voltage (VBAT) plus the voltage drop across the Power MOSFET (ΔVMOS) of the charger. Consequently, the internal MOSFET works in saturation mode with a voltage drop given by the following formula: Equation 1 V IN = V ADP = V BAT + ΔV MOS where Equation 2 ΔV MOS = R DS ( on ) × I LIM ILIM is the current limit of the SPV1040, which depends on solar irradiation. Neglecting the voltage drop across the charger (ΔVMOS) when the device operates in this condition, its input voltage is equal to the battery one, and so a very low operating input voltage (down to 2.5 V) is required. The power dissipated by the device during this phase is: Equation 3 P CH = R DS ( on ) × ILIM 2 The advantage of the quasi-pulse charging method allows the energy harvested by few solar cells to be maximized. Note that the STEVAL-ISV0012V1 mounts two LEDs, D1 and D2, which indicate (when ON) whether the charge is in progress or is completed, respectively. R14, and consequently ILIM, must be set up according to the power provided by the PV panel at the maximum irradiation, but it is possible that at lower irradiations D1 starts flickering (or appearing ON), while D2 is ON as well. This is due to the battery charger which tries to charge the battery at 4.2 V (or 4.1 V, depending on the VOPRG setting) and ILIM, but the required power can be sustained only if enough irradiation is available at the PV panel side. If the irradiation is not sufficient, the input voltage of the L6924D drops down to the battery voltage, causing the battery charging to stop and D1 turns ON. Shortly after, the voltage rises back to 4.2 V (or 4.1 V) and the battery charge starts again (D1 turns OFF). In these low irradiation conditions the battery is charged by current packets anyway. The plots below show behavior in the case of low irradiation: 8/19 DocID022816 Rev 2 AN4050 L6924D operation in solar powered applications Figure 8. Battery charging at low irradiation Figure 9. Battery charging at low irradiation, zoomed in The plots below show the maximum available current that can be provided to the battery charger according to the input power. Figure 10. Maximum available current vs. Pin, 200 mW peak PV panel 80 70 Iout max [mA] 60 50 40 Vout = 4.5V 30 20 10 0 0 50 100 150 200 250 300 350 400 Pin [mW] AM12667V1 DocID022816 Rev 2 9/19 L6924D operation in solar powered applications AN4050 Figure 11. Maximum available current vs. Pin, 2 W peak PV panel 350 Iout max [mA] 300 250 200 150 Vout = 4.5V 100 50 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Pin [mW] AM12668V1 10/19 DocID022816 Rev 2 AN4050 4 Reference design description Reference design description The set-up environment used for the measurement campaign is shown below. Figure 12. Application set-up A solar array simulator (SAS, SAS-FL05/01 from CBL Electronics) to simulate the PV module with Voc = 2.5 V, Isc = 210 mA, Vmp = 2.0 V, Imp = 200 mA (@ 1000 W/m2 irradiance) and a Li-Ion battery 3.7 V-700 mAh, are used. Figure 13 shows the I-V and P-V curves generated by the SAS, obtained using a PV module analyzer (ISM490 from ISOTECH): Figure 13. V-I and P-V plot diagrams Figure 14 and 15 show the partial and full charge curves respectively. The “partial charge” curve shows charge current and voltage within a one hour time frame at full irradiation starting from 3.4 V condition. The “full charge” curve shows charge current and voltage until the fully charged status is triggered, starting from a 3.4 V condition. After the one hour charge period time, the battery voltage reaches 3.8 V. Different results can be obtained if a different PV panel and/or battery are used. If any help is required regarding the use of different PV panels and/or batteries, please go to the support area at www.st.com. The average overall power efficiency is ~85% (94% for SPV1040 and 90% for L6924D). DocID022816 Rev 2 11/19 Reference design description AN4050 Figure 14. Partial charge 2XWSXWĆ&XUUHQWĆ>P$@ 2XWSXWĆ9ROWDJHĆ>9@ 7LPHĆ>P@ $0Y Figure 15. Full charge 2XWSXWĆ&XUUHQWĆ>P$@ 2XWSXWĆ9ROWDJHĆ>9@ 7LPHĆ>P@ $0Y 12/19 DocID022816 Rev 2 AN4050 5 Schematic and bill of material Schematic and bill of material The schematic, bill of material and Gerber files can be downloaded from www.st.com. Figure 16. STEVAL-ISV012V1 schematic, battery charge section 95() 5 NĆ2KP -- GHIDXOWĆRSHQ 5 '10 5 '10 39 5 NĆ2KP 5 NĆ2KP ' PF 9LQ 9LQBVQV 67 ' PF 6: / ' 9)4)31 & Q) 5 & X) - - GHIDXOWĆFORVHG -- GHIDXOWĆFORVHG & Q) 39 17& 5 Ć2KP 6:Ć6: GHIDOXWĆLVĆĆ2KPĆRQĆOHGĆĆFORVHG - 9%$7 P N 2KP 5 NĆ2KP & X) 67 7+ 6+':1 39 7SUJ 9%$7 9R 9RVQV 9RSUJ 6: 73 95() 9287B639 39 5 '10 ,HQG 9SUH ,SUJ ,SUH 73 5 '10 39 73 - - 17& 9%$7 P F 39 P F & 2 1 & 2 1 $0Y DocID022816 Rev 2 13/19 Schematic and bill of material AN4050 Figure 17. STEVAL-ISV012V1 schematic, solar power optimizer section 73 9,1BVQV ;B6+87 ,FWUO ,FWUO 9FWUO 5) ,FWUO 9UV &) X) ,FWUO 5) 639 N - &21% 9,1BVQV 39 /;B 9RXW 9UV 76623 39 9UV 5V Ć2KP 9UV 5 Ć2KP N 73 9287B639 95V P9Ć#Ć,PD[ 5 N 5 0 9FWUO 9FWUOĆ 9Ć #9RXWĆ Ć9 'RXW 5 '10 & Q) &RXW X) 75,6,/ 600)$ & Q) 5 N 73 73 39Ć 39 ! /;B 39 X+Ć0+] %7ĆX+ 9Ć$ 6=*'3 / &LQ X) 39 39Ć ! 73 $0Y 14/19 DocID022816 Rev 2 AN4050 Schematic and bill of material Table 1 shows the STEVAL-ISV012V1 list of components. Table 1. BOM Item Quantity Reference Value Voltage current 400 mW Vmp:1.92 V; Imp:200 mA; Voc:2.2 V; Isc:220 mA Package Manufacturer Manufacturer code NBSZGD SZGD6060-4P 1 1 PV1(1) 2 1 Cin1 47 μF 6.3 V 0805 KEMET C0805C476M9PAC7800 3 1 C2 1 nF 50 V 0805 KEMET C0805C102K5RAC 4 1 C4 1 nF 50 V 0805 KEMET C0805C102K5RAC 5 1 Cout1 10 μF 16 V 0805 KEMET C0805C106K4PAC7800 6 1 R3 1 kΩ 0805 VISHAY CRCW08051K00FKEA 7 1 R4 DNM (3.3 MΩ) 63M 8 1 L1 10 μH Isat > 1.5 A @vmp =2 V 2220(EIA) Coilcraft EPCOS MSS7341-103ML_ B82442T1103K050 9 1 VRS 0 50 mV @Iout_max 0805 VISHAY CRCW08050000Z0EA 10 1 R1 2.2 MΩ 0805 MULTICOMP MCHV05WAJ0225T5E 11 1 R2 820 kΩ 0805 VISHAY CRCW0805820KFKEA 12 1 R5 0 0805 VISHAY CRCW08050000Z0EA 13 1 J26 SPV1040 TSSOP8 STM SPV1040T 14 1 Dout1 SMM4F5.0 STmite flat STM SMM4F5.0 15 1 J28 L6924D MLPD 4x4 STM L6934D 15 2 RF1, RF2 1 kΩ 0805 VISHAY CRCW08051K00FKEA 17 1 CF1 1 μF 10 V 0805 Murata GRM21BR71C105KA01L 18 2 D1, D2 SMD LED 2.5 V, 25 mA 0805 Kingbright KP-2012SGC 20 3 R6, R7, R8 1 kΩ 0805 VISHAY CRCW08051K00FKEA 23 1 C6 47 μF 6.3 V 0805 KEMET C0805C476M9PAC7800 24 1 C7 10 nF 50 V 0805 KEMET C0805C103K5RAC 25 1 C8 1 nF 50 V 0805 KEMET C0805C102K5RAC 26 1 C9 4.7 μF 0805 Murata GRM21BF51A475ZA01L 27 1 R10 3.3 kΩ 0805 BOURNS CR0805-FX-3301GLF 28 1 R9 470 Ω 0805 BOURNS CR0805-FX-4700GLF 29 1 R14 24 kΩ 0805 MULTICOMP MC 0.1W 0805 1% 24K Vbr = 5 V, Vcl =9V DocID022816 Rev 2 15/19 Schematic and bill of material AN4050 Table 1. BOM (continued) Item Quantity Reference Value Voltage current Package Manufacturer Manufacturer code CRCW08050000Z0EA 30 3 J1, J2, J3 Jumper100 33 2 SW3; SW4 0 Ohm 0805 VISHAY 34 1 J29 3-pole connectors Phoenix Contact 1935174 1. Polycrystalline. 16/19 DocID022816 Rev 2 AN4050 6 Layout Layout Figure 18. STEVAL-ISV012V1 PCB top view Figure 19. STEVAL-ISV012V1 PCB bottom view DocID022816 Rev 2 17/19 Revision history 7 AN4050 Revision history Table 2. Document revision history 18/19 Date Revision Changes 11-Jun-2012 1 Initial release. 21-Mar-2013 2 Updated Figure 5: SPV1040 internal block diagram. DocID022816 Rev 2 AN4050 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. 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