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OVERCHARGE/OVERDISCHARGE/OVERCURRENT SAFETY CIRCUITS · The…
Tags: 3v, battery pack, charge batteries, charge voltage, model number, output terminals, ov, reference example, safety circuits, safety function, typical functions, typical values,Pages: 4
Language: english
Created: Wed Oct 22 11:36:48 2003
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OVERCHARGE/OVERDISCHARGE/OVERCURRENT SAFETY CIRCUITS
· The Functions of the Safety Circuits (Typical Functions)
The voltages listed below are typical values and are not guaranteed. The charge voltage varies according to
model number.
1. The Overcharge Safety Function
The charge stops when the voltage per cell rises above 4.30 ± 0.05 V.
The charge restarts when the voltage per cell falls below 4.00 ± 0.15 V.
2. The Overdischarge Safety Function
The discharge stops when the voltage per cell falls below 2.3 ± 0.1 V.
The discharge restarts when the voltage per cell rises above 3.0 ± 0.15 V.
3. The Overcurrent Safety Function
The discharge is stopped when the output terminals are shorted.
The discharge restarts when the short is removed.
· Reference Example of the Safety Circuits
Battery Pack
Unusable Region
4.3V
4.2V
Charge
Batteries Safety Circuits Region Used by the Set Charger
Discharge
3.0V
2.3V
Overdischarge Region
Unusable Region
· The safety circuits in the diagram above are for overcharging, overdischarging, and overcurrent for a single
cell battery pack. Please contact Panasonic when two or more cells are connected or when actually using
this or other circuits.
LITHIUM ION AUGUST 2003
This information is generally descriptive only and is not intended to make or imply any representation, guarantee or warranty with respect to any cells and batteries. Cell and battery designs/specifications are subject to
modification without notice. Contact Panasonic for the latest information.
OVERCHARGE/OVERDISCHARGE/OVERCURRENT SAFETY CIRCUITS - CONTINUED
· Battery Pack Block Diagram (Reference Example)
The diagram below shows a diagram of a lithium ion battery pack. The battery pack includes the batteries, the
safety circuits, and thermistors.
1. The Safety Circuits
1.1 The Controller IC
The controller IC measures the voltage for each cell (or for each parallel battery block) and shuts off a
control switch to either prevent overcharging (if the voltage exceeds the specified voltage range) or to
prevent overdischarging (if the voltage falls below the specified voltage range). Moreover, the voltage of
the control switch is measured on both ends and in order to prevent overcurrent, both control switches
are shut off if the voltage exceeds specifications.
1.2 The Control Switches
The control switches usually comprise FET structures, and they turn off the charge or discharge
depending on the output of the controller IC.
1.3 The Temperature Fuse (Reference Materials)
If the control switches experience abnormal heating, this fuse cuts off the current (non-restoring).
2. The Thermistors
The thermistors are included in order to accurately measure the battery temperature within the lithium ion
battery packs. The battery or charger measures the resistance value of the thermistor between the T-
terminal and the negative terminal and during the charging process, controls the charge current along with
controlling until the charge is terminated.
+
Battery Pack Safety Circuits
Controller IC
T Thermistor
- Temperature Fuse Control SW Control SW
· The battery pack must be equipped with a noise filter at the voltage detectors in the block diagram above to
insure that outside noise does not cause the battery to malfunction. Please check against the final product.
· Please include a total charge timer and a charge completion timer on the charging circuit in order to provide
redundant safety control.
LITHIUM ION AUGUST 2003
This information is generally descriptive only and is not intended to make or imply any representation, guarantee or warranty with respect to any cells and batteries. Cell and battery designs/specifications are subject to
modification without notice. Contact Panasonic for the latest information.
HOW TO CHARGE THE BATTERIES
We recommend the following charging process to insure the optimal performance of the lithium ion battery.
· Applicable Battery Packs
The discussion below assumes that the battery packs are equipped with internal safety circuits to prevent
overcharging and overdischarging, and assumes that the battery is a single cell battery.
· Charging Method
The lithium ion battery can be charged by the constant voltage/constant current charging method found in the
"Notes and Precautions" at the beginning of this document. (See page 2, "Notes and Precautions")
· Functions and Performance Required in the Charger (Recommendations)
(1) Charge Voltage
The voltage between the charging terminals should be no more than 4.20 V (Set this at 4.20 V (max) after
taking into account fluctuations in power supply voltages, temperature deviations, etc.).
(2) Charge Current
The reference charge current should be 0.7 CmA.
(3) Ambient Temperature of the Battery Pack During Charge
0°C to 45°C (Consult Panasonic if the battery pack is to be used outside of this temperature range).
(4) Low-Voltage Battery Pack Charge
When the voltage per cell is 2.9 V or less, charge using a charge current of 0.1 CmA or less.
(5) Termination of Charging
The system will determine that the battery is full by detecting the charge current.
Stop charging once the current has reached 0.1 CmA to 0.07 CmA. Note that there will be some degree of
variation for each individual battery.
(6) Charge Timer
A total charge timer and a charge completion timer should be included.
(7) Countermeasures for Battery Problems
Select an overvoltage guard in the power supply so that there will be no excessive voltage applied to the
battery even if there is a problem with the power supply.
· The discussion above assumes a single cell battery. If two or more cells will be used or if there are other
situations, please consult with Panasonic.
LITHIUM ION AUGUST 2003
This information is generally descriptive only and is not intended to make or imply any representation, guarantee or warranty with respect to any cells and batteries. Cell and battery designs/specifications are subject to
modification without notice. Contact Panasonic for the latest information.
FLOWCHART FOR CHARGING LITHIUM ION BATTERY PACKS
Lithium Ion Battery Pack Charge Flowchart (Example)
Reference example of charging a single-cell lithium ion battery pack
OCV: Battery pack load open voltage
START
T1 : Charge total timer count
tmin : Low temperature threshold setting value
Battery pack insertion check tbat : Battery temperature
NO
Is the battery pack tmax : High temperature threshold setting value
inserted? CV : Constant voltage
YES ichg : Charge current
A iset1 : Electrical current set value
iset2 : Electrical current set value
Charge total timer count T1 T2 : Charge complete timer count
T3 : Recharge timer count
Total timer end decision
YES
T1 > 720 minutes
Battery temperature check
tmin