Safety Considerations 193
Passive Protection
Reverse Charging: A reverse protection diode prevents against damage or lost
data due to a reverse charge polarity applied to the battery terminals.
Primary Overtemperature: A PTC(positive temperature coefficient) polyfuse in
series between the Li-ion cells and the charging and discharging transistors will
open up and limit current flow to the battery terminals as a function of very high
temperatures. This protection is resettable once the overstress condition is
removed.
The maximum operating temperature of this fuse is 85C.
Secondary Overtemperature: A second PTC polyfuse built into each Li-ion cell
will open up and limit current flow as a function of very high temperatures.
Tertiary Overtemperature: A current interrupt device (CID) within each Li-ion
cell will permanently open up when the temperature reaches 95C. As each cell
fuse is permanently interrupted, overall battery performance will become
severely degraded, up to and including disabling the battery.
Overcurrent Fuse: This is a one-time blow fuse with a rated current of 12A.
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