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Power Management - Low-Cost, Two-Cell
Li-Ion/Li-Pol Battery Charger with
Cell-Balancing Support
AN2309
Author: Oleksandr Karpin
Associated Project: Yes
Associated Part Family: CY8C24x23A, CY8C24794, CY8C27x43, CY8C29x66
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Software Version: PSoC Designer™ 5.0 SP1
Associated Application Notes: AN2107, AN2258, AN2267, AN2294
PSoC Application Notes Index
Application Note Abstract
This application note describes a low cost, two-cell Li-Ion/Li-Pol battery
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AN2309 Table 1. Specifications for Two-Cell Li-Ion/Li-Pol Battery Charger with Cell-Balancing Support Item Item Value Battery Charger Parameters Built-In Battery Charger Type Two-cell Li-Ion/Li-Pol battery charger Power Supply Voltage 10…14V Power Consumption 35 mA Battery Current Measurement Error (Not Calibrated) 5 percent Battery Voltage Measurement Error (After Calibration) 0.5 percent Battery Thermistor Resistance Measurement Error 5 percent User Interface 2 LEDs PC Communi
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AN2309 The balancing circuit is represented by (R1, Q1) and (R2, Temperature gradient across the battery pack. Q2). These transistors and resistors dissipate energy and Temperature mismatches of 15 degrees Celsius can control the amount of balancing current. cause up to 5- percent capacity differential among cells. Such a temperature gradient is relatively common in If cell balancing is performed during the charge phase, the densely packed products, where multiple heat sources c
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AN2309 for most applications it is not necessary to use this Cell Balancing Time: If C is the cell capacity and V is b algorithm. the battery voltage, and the requirement is to eliminate The cell-balancing technique is explained in detail in the amount of imbalance (in percent) in one hour of AN2258, “Cell Balancing in a Multi-Cell Li-Ion/Li-Pol Battery balancing time, then the power dissipation on balancing Charger.” circuit P is: bal Two-Cell Battery Charger Hardware CV b
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AN2309 A two-cell battery charger structure with cell-balancing support is shown in Figure 3. Similar battery charger structures are explained in detail in AN2258, AN2294, and AN2267. Note that the fuel gauge function can easily be added to this project without changing any hardware: It is only necessary to switch from the CY8C24423A to a PSoC device with more program memory. The main fuel gauge calculation parameters are described in AN2294, “The Li-Ion/Li-Pol Battery Charger with Fuel
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AN2309 The resistive network (R6, R7, R12, R13, R15, R16, and Device Schematic R18-R22) and the reference voltage V from the divider on bias The schematics shown in Figure 4 on page 7 and Figure 5 R29 and D8, allow transformation of the battery current, on page 8 constitute a complete two-cell battery charger. voltage, and temperature into signals suitable for the PSoC device. The 100 mΩ resistor R23 is a current-sense resistor A signal from the PWM goes to the RC-filter, which con
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AN2309 Figure 4. Two-Cell Battery Charger Schematic – CPU, Cell Balancing, and Measuring Equipment Q1 IRLML6402 D1 POWER+ BAT+ C1 R1 C2 C3 MBR360 + 47uF 0.01uF 10K 1uF CER R4 1K Q2 DRIVE BC817 C4 R5 0.1uF 15K R7 150K 0.1% V2 C5 R6 0.01u VCC U1 50K 0.1% R8 28 1M Vcc 1 27 Vbias Vi2 Vi1 P0[7] P0[6] TP1 2 26 Q4 Tbat P0[5] P0[4] 3 25 V2 IRLML6402 Vref P0[3] P0[2] V1 4 24 BAT_GND P0[1] P0[0] R9 5 23 Q3 BAL2 P2[7] P2[6] 6 22 BC817 P2[5] P2[4] 7 21 330R R10 R11 LED_YELLOW P2[3] P2[2] 8 20 LED_GR
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AN2309 Figure 5. Two-Cell Battery Charger Schematic – Power Supply and User Interface VCC Close to PSoC SW1 J4 + R29 VCC POWER+ 1 2 C9 C10 1K + C15 Vbias POWER 12V DC 100u 16V 0.1u 16V D8 0.1u POWER- BAS16 D6 VCC BAT+ U2 L78L05/TO 1 3 R30 IN OUT R28 POWER+ 33 BAT54C C12 470 C11 C13 C14 + + 0.33u 16V D7 100u 16V 22u 0.1u POWER PSoC J3 D4 Q6 1 POWER+ 2 MBR360 R25 IRLML6402 LOAD D5 1M BAT+ MBR360 R26 R2 D2 Q7 LOAD_EN LED_YELLOW BC817 470 330R R27 LED 10K R3 D3 LED_GREEN 470 LED The ADC
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AN2309 Figure 6. PSoC Internal User Module Configuration The following equation represents the current measurement Battery Measurement scheme: To provide a correct implementation of the charge and cell- balancing algorithms, the charge current, battery voltage V G I R ADC ina I bat sense and temperature must be measured accurately. n n n Equation 16 max max VV ref ref These three parameters are measured as the voltage drops on corresponding resistors by using the instrumental
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AN2309 The voltage measurement also is performed by the INA on For temperature measurement, a reference voltage resistive the corresponding resistor. The resistive dividers (R7, R6), divider is employed based on a thermistor and a precision (R13, R12), and (R18, R19) transform cell voltage into resistor (R6). Thermistor resistance is calculated according signals suitable for the PSoC device. It is very important to to the voltage drop on the precision resistor and the value of use the h
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AN2309 Figure 7. Temperature Profile No Discharge TDISCH_HOT_STOP THOT_STOP THOT_RESTART No Charge TBATT Charge in Charge in process Process TCOLD_RESTART TCOLD_STOP TDISCH_COLD_STOP No Discharge Two-Cell Battery Charger Algorithm Two-Cell Battery Charger Firmware The two-cell battery charge algorithm is implemented in the The two-cell battery charger firmware is separated into charger firmware as a state machine. The following states several modules that serve distinct functions
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AN2309 Figure 8. Two-Cell Battery Charger State Diagram 10 Initialization 7 6 9 1 13 Wait For Activation Discharge Temperature 4 2 11 12 8 5 Rapid Error Full Discharge 3 Charge Complete Initially the charger is in the Initialization state. After some Regardless of the state of the charger, it jumps to the device preparation, the charger goes to the Activation Discharge state when the external power supply is switched state (1). When the battery voltage reaches the rapid start off
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AN2309 Figure 9. Two-Cell Battery Charger Firmware Flowchart Part 1 Start Init Device Set Initialization State Send Debug Data Measure V , V , b1 b2 I , T ch b Calc Vbmin, Vbmax State is not Yes Check For Yes Yes Error or Check For Set Wait For Discharge Stop Wait For Negative Ich Temperature State Temperature Temperature No No No Check Full Yes Set Full Discharge Discharge State Condition No Set Full Discharge State Check for Yes Set Wait For charge stop Temperature stat
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AN2309 Figure 10. Two-Cell Battery Charger Firmware Flowchart Part 2 1 2 State Check Charge Yes Yes Charge Off Set Initialization Charge Restart Timers Off State Complete Condition No No State Yes Check For Charge Off Cell Balancing Yes Set Wait For Wait For Discharge Stop Timers Off Reset Temperature State Temperature Temperature No No Yes Check For Set Initialization Negative Ich State No Check For Yes Set Initialization Charge Restart State Temperature No Set Wait For Temper
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AN2309 The minimum cell-balance parameter consists of the voltage measure error value plus the internal impedance error value. The cell-balancing algorithm that is implemented here does not significantly lengthen the charge time. The charger monitors all of the cell voltages. Cell balancing is performed during both phases and it is realized in one common module. The cell- balancing algorithm is represented in Figure 11. The cell-balancing profile examples are shown in the Appendix, Figure
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AN2309 Two-Cell Battery Charger Parameters All two-cell battery charger parameters are located in the header file globdefs.h in the project folder. The header file globdefs.h contains the following parameters: Table 2. Two-Cell Battery Charger Parameters Parameter Unit Description Charging Parameters V Rapid-Charge Stage Start Condition V rs V Full Charge Voltage (Constant Charge Voltage) V rap V Recharge Voltage V crst V Emergency Shutdown Voltage V bmax V Full Discharge
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AN2309 Cell-Balancing Parameters All cell-balancing parameters are located in the header file globdefs.h in the project folder. The header file globdefs.h contains the following parameters: Table 3. Cell-Balancing Parameters Parameter Unit Description Vmeas_err V Resistor Matrix Error for Measuring Cell Voltage Vin_err V Internal Cell Impedance Error V Minimum Cell Balance for Charge Phase Vch_bal_min Vdisch_bal_min V Minimum Cell Balance for Discharge Phase Vdisch_mid V Voltage
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AN2309 Appendix Charge/Discharge and Cell-Balancing Profile Examples Figure 13. Charge/Discharge Manager Profile COM # Start Button Cell-Balancing Drop-Down Cell Voltages Without Charger State State Field Charge Interrupt Charge /Discharge Thermistor Current Resistance Constant Voltage Charge Constant Current Charge Battery Discharge November 25, 2007 Document No. 001-17394 Rev. *B - 18 - [+] Feedback
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AN2309 Figure 14. Cell-Balancing Activity Profile Cell Voltages With Charge Interrupt Voltage Imbalance Value November 25, 2007 Document No. 001-17394 Rev. *B - 19 - [+] Feedback
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AN2309 Figure 15. Cell-Balancing Parameter Profile Screen About the Author Name: Oleksandr Karpin Title: Application Engineer Background: Oleksandr received a PhD’s degree in computer science in 2008 from Lviv Polytechnic National University (Ukraine). His interests include embedded systems design and new technologies. Contact: oleksandr.karpin@cypressua.com November 25, 2007 Document No. 001-17394 Rev. *B - 20 - [+] Feedback
