UC864-E Hardware User Guide
1vv0300766a Rev.1 - 31/01/08
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The constant voltage charge proceeds with a fixed voltage regulator (very accurately set to the
maximum battery voltage) and hence the current will decrease while the battery is becoming charged.
When the charging current falls below a certain fraction of the fast charge current value, then the
battery is considered fully charged, the final charge stops and eventually starts the maintenance.
The last phase is not properly a charging phase, since the battery at this point is fully charged and the
process may stop after the final charge. The maintenance charge provides an additional charging
process to compensate for the typical Li-Ion battery charge leak. It is done by issuing pulses with a
fixed time length, again few hundreds of ms, and a duty-cycle around 5% or less.
This last phase is not implemented in the UC864-E internal charging algorithm, so that the battery
once charged is left discharging down to a certain threshold so that it is cycled from full charge to
slight discharge even if the battery charger is always inserted. This guarantees that anyway the
remaining charge in the battery is a good percentage and that the battery is not damaged by keeping it
always fully charged (Li-Ion rechargeable battery usually deteriorates when kept fully charged).
Last but not least, in some applications it is highly desired that the charging process restarts when the
battery is discharged and its voltage drops below a certain threshold, UC864-E internal charger does
it.
As you can see, the charging process is not a trivial task to be done; moreover all these operations
should start only if battery temperature is inside a charging range, usually +5°C ÷ +45°C.
In order to satisfy this last requirement, the UC864-E measures the temperature of its internal
components even if it is not exactly the same as the battery temperature; but in common application
the two temperatures should not differ too much and the charging temperature range should be
guaranteed.
NOTE: All voltage thresholds are provided, inside UC864-E, in order to maximize Li-Ion battery
performances and do not need to be changed.
NOTE: In this application the battery charger input current must be limited to less than 400mA. This can be done by using a current limited wall adapter as the power source.