Lithium-Ion%20Battery/Charger%20pair%20for%20imbedded%20MP3%20player%20and%20FM%20transmitter

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

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System Overview

• Complete System

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Design requirements

• Battery Requirements
• Capacity 2200 mAh
• Voltage 3.6 - 3.7V
• Cylindrical shape
• Life-cycle of 2 years
• Chemistry Li-Ion

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Selected Batteries

• Li-Ion 18650 Cell LG CR18650 3.6V 2400mAh Cell
• Li-Ion 18650 3.7V 2200 mAh rechargeable battery

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Design requirements

• Battery Charger Circuit Requirements
• Charging Current ? 1.0 A
• Charging Voltage 4.2V
• Current Control
• Voltage Control
• Temperature Control

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Battery Charging Module

• Texas Instruments BQ24008 IC

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Our Circuit
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Current Regulation Circuit

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

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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.

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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

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Charge Profile
22 min
22 min
Charging time, 4 hours, 5 min

• Note charge time4hours, 5 minutes, at room
  temperature

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Temperature sensing circuit
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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)

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Simulation

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

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Resultssimulated vs. measured
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Implementation

• Our solution was implemented and tested.

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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

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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

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References

• A.G. Ritchie. (2001). Recent developments and
  future prospects for lithium rechargeable
  batteries. Journal of Power Sources 96.  1-4
• 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
• Single-Cell Li-Ion Charge Management IC with
  Timer-Enable for PDAs and Internet Appliances.
  Texas Instruments. January 2001, Revised November
  2004.

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Special thanks to

• Mohamad for his continued support throughout the
  term.
• Martin for his help with the surface mounting of
  the IC.