Transcript Lithium-Ion Battery/Chargers

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
MP3
player
External
Charger
Tempera
ture
control
FM
Transmi
tter
FM
Receiver
Battery
Block diagram
for the
entireComplete
system
Block Diagram
for
System
Design requirements
Battery Requirements:
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Capacity: 2200 mAh
Voltage: 3.6 - 3.7V
Cylindrical shape
Life-cycle of 2 years
Chemistry: Li-Ion
Selected Batteries
Li-Ion 18650 Cell LG
CR18650 3.6V
2400mAh Cell
Li-Ion 18650 3.7V
2200 mAh
rechargeable battery
Design requirements
Battery Charger Circuit Requirements:
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Charging Current  1.0 A
Charging Voltage: 4.2V
Current Control
Voltage Control
Temperature Control
Battery Charging Module
Texas Instruments BQ24008 IC
Our Circuit
Vcc
R1 = 1Ω
Vcc
C1 10µF
1
N/C
N/C
2
3
IN
OUT
IN
Vcc
OUT
4
5
6
7
8
C2 = 0.1µF
9
10
VSENSE
ISNS
AGND
N/C
N/C
APG/THM
STAT1
TMR EN
TMR SEL
20
19
18
PACK+
17
C4 = 1µF
16
15
PACK14
13
VSEL
CR
12
GND
N/C
11
bq24008PWP
RT1
18.7KΩ
RT2
95.3KΩ
+
Vcc
C3
0.22µF
R5=500Ω
TEMP
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
22 min
22 min
Charging time, 4 hours, 5 min
Note: charge time=4hours, 5 minutes, at room
temperature
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
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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) FuzzyControlled Li-Ion Battery Charge System with Active State-ofCharge Controller, IEEE Transactions on industrial electronics,
48, 3.
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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 2004.
Special thanks to:
Mohamad: for his continued support
throughout the term.
Martin: for his help with the surface
mounting of the IC.