Lithium-Ion Battery/Charger pair for imbedded MP3 player and FM transmitter Federico Carvajal Misun Heo

Objectives To review existing technologies Perform a comparative study among leading solutions Address shortcomings of existing technologies Recommend a battery/charger pair, either from commercial available solutions or from modified technologies

System Overview Complete System Block Diagram for the Complete System

Design requirements Battery Requirements: Capacity: 2200 mAh Capacity: 2200 mAh Voltage: V Voltage: V Cylindrical shape Cylindrical shape Life-cycle of 2 years Life-cycle of 2 years Chemistry: Li-Ion Chemistry: Li-Ion

Selected Batteries Li-Ion Cell LG CR V 2400mAh Cell Li-Ion V 2200 mAh rechargeable battery

Design requirements Battery Charger Circuit Requirements: Charging Current  1.0 A Charging Current  1.0 A Charging Voltage: 4.2V Charging Voltage: 4.2V Current Control Current Control Voltage Control Voltage Control Temperature Control Temperature Control

Battery Charging Module Texas Instruments BQ24008 IC

Our Circuit

Current Regulation Circuit Current Regulation starts when the battery-pack voltage is less than the regulation voltage

Voltage Regulation Voltage regulation feedback is through pin VSENSE. This input is tied directly to the positive side of the battery pack. Pin VSEL selects the charge regulation voltage. The bq2400x supports cells with either coke (4.1 V) or graphite (4.2 V) anode.

Battery Charging Performance Three distinct phases of battery charging -Preconditioning Phase -Current Regulation Phase -Voltage Regulation Phase -Charge Termination: maximum charge time, minimum current, temperature protection

Charge Profile Note: charge time=4hours, 5 minutes, at room temperature 22 min Charging time, 4 hours, 5 min 22 min

Temperature sensing circuit

Temperature Sensing Voltage divider translates resistance changes at the Thermistor into voltage levels IC compares voltage at APG/THERM input to internal threshold levels If the temperature is above or below the maximum and minimum thresholds, charge is suspended. (-20ºC to 65ºC)

Simulation The temperature sensing portion of the circuit was simulated to obtain threshold values for the thermistor

Results: simulated vs. measured

Implementation Our solution was implemented and tested.

Future considerations The design will continue with further testing Thermistor to be included in the next iteration Circuit to be migrated to a printed PCB Further consideration needs to be given to EMI

Conclusions A battery meeting the design requirements was chosen and tested A battery charging circuit was designed, implemented and tested The complete system meets the design criteria. Measured values matched simulated values The design will move to the next phase of integration with the larger system EMI needs to be address in the next stage

References A.G. Ritchie. (2001). Recent developments and future prospects for lithium rechargeable batteries. Journal of Power Sources A.G. Ritchie. (2001). Recent developments and future prospects for lithium rechargeable batteries. Journal of Power Sources Liang-Rui Chen and Kuo-Shun Huang. (2001, June) Fuzzy- Controlled Li-Ion Battery Charge System with Active State-of- Charge Controller, IEEE Transactions on industrial electronics, 48, 3. Liang-Rui Chen and Kuo-Shun Huang. (2001, June) Fuzzy- Controlled Li-Ion Battery Charge System with Active State-of- Charge Controller, IEEE Transactions on industrial electronics, 48, 3. Teofilo, L.V. Merritt and R.p. Hollandsworth (1997, November). Advanced Lithium Ion Battery Charger, IEEE AES Systems Magazine Teofilo, L.V. Merritt and R.p. Hollandsworth (1997, November). Advanced Lithium Ion Battery Charger, IEEE AES Systems Magazine Single-Cell Li-Ion Charge Management IC with Timer-Enable for PDA ’ s and Internet Appliances. Texas Instruments. January 2001, Revised November Single-Cell Li-Ion Charge Management IC with Timer-Enable for PDA ’ s and Internet Appliances. Texas Instruments. January 2001, Revised November 2004.

Special thanks to: Mohamad: for his continued support throughout the term. Martin: for his help with the surface mounting of the IC.