Telit GM862-QUAD/-QUAD-PY
Hardware User Guide
1vv0300692, Rev. ISSUE#0, - 04/10/2005
Reproduction forbidden without DAI Telecom written authorization – All Right reserved – Right of modification reserved
page 13 of 69
Once the battery voltage reaches its maximum voltage then the process goes into its third state:
Final charging. The voltage measure to change the process status into final charge is very
important. It must be ensured that the maximum battery voltage is never exceeded, otherwise the
battery may be damaged and even explode. Moreover for the constant voltage final chargers, the
constant voltage phase (final charge) must not start before the battery voltage has reached its
maximum value, otherwise the battery capacity will be highly reduced.
The final charge can be of two different types: constant voltage or pulsed.
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 pulsed charge process has no voltage regulation, instead the charge continues with pulses.
Usually the pulse charge works in the following manner: the charge is stopped for some time, let's
say few hundreds of ms, then the battery voltage will be measured and when it drops below its
maximum value a fixed time length charging pulse is issued. As the battery approaches its full
charge the off time will become longer, hence the duty-cycle of the pulses will decrease. The
battery is considered fully charged when the pulse duty-cycle is less than a threshold value,
typically 10%, the pulse charge stops and eventually the maintenance starts.
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 charge leak typical of a Li-Ion battery. 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 GM862-QUAD 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 deteriorate 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, GM862-QUAD 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.
The GM862-QUAD measures the temperature of its internal component, in order to satisfy this last
requirement, it's not exactly the same as the battery temperature but in common application the two
temperature should not differ too much and the charging temperature range should be guaranteed.
