Rainbow Electronics GM862-QUAD-PY - Manual (Page 27)

GM862-QUAD / PY Hardware User Guide
1vv0300748 Rev. 5 - 20/09/07
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 27 of 68
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 / PY 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, GM862-QUAD / PY 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 / PY 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.
NOTE: In this particular application the battery charger input current must be limited to less than 1A. Using a
current limited wall adapter as the power source can do this.
For your convenience in the EVK there's also a current unlimited input, where the input source is not limited in
current and the drawn current is limited to about 0,5A by a MOSFET in the EVK.
The external battery charger is suggested in applications where the total consumption is higher than the current
provided by the GM862-QUAD / PY module.
NOTE: For all the threshold voltages, inside the GM862-QUAD / PY all threshold are fixed 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.
NOTE: When starting the charger from Module powered off the startup will be in CFUN4; to activate the
normal mode a command AT+CFUN=1 has to be provided. This is also possible using the POWER ON.
There is also the possibility to activate the normal mode using the ON_OFF* signal.
In this case, when HW powering off the module with the same line (ON_OFF*) and having the charger still
connected, the module will go back to CFUN4.