LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3
Preliminary
System description
Page 28 of 125
charger parts and to gently charge the deeply discharged batteries: the average pre-charge current is ~1/8 (i.e.
12.5%) of the current provided by the external charger, so it is ~1/8 of the external charger current limit.
Pre-charging phase is hardware controlled and continues as long as the
VCC
voltage reaches the 3.1 V typical
limit, so the module is able to start the following fast charging phase.
During fast charging phase (following the pre-charging phase) the charge transistor switch mounted inside the
module is pulsed with a 100 Hz and an on-time of 99% of a period: the average charge current is almost equal
(i.e. 99%) to the current provided by the external charger, so it is almost equal to the external charger current
limit. The remaining off time (i.e. 1% of a period) is used to check if the external charger is still connected since
detection is critical when charging switch is closed.
The integrated charging circuit doesn’t have any voltage or current limitation, therefore the charger must be
chosen very carefully: during the fast charging phase, the battery is charged with the maximum DC current
provided by the external DC supply used as charger, which must be current limited as described in the charger
specification section.
When the battery voltage reaches the nominal maximum voltage (4.2 V typical with 2% tolerance due to change
in temperature and life time), charging enters the constant voltage phase (top charge algorithm): in this phase
the average charging current decreases until the battery is completely charged.
After the constant voltage phase, the battery is maintained at a higher level of charge with the trickle charge
algorithm until an external charger is connected to the module.
The charging process is enabled only within the temperature range from 0°C to 40°C, with a 5°C hysteresis to
prevent rapid switching on and off as the temperature drifts around the set point: charging is disabled when the
temperature falls below 0°C and then enabled when it rises above 5°C; charging is disabled when the measured
temperature rises above 40°C and then enabled when falls below 35°C.
Battery over-voltage detection is implemented to switch-off charging if the battery is removed during charging.
The
VCC
over-voltage threshold level is set to the nominal value of 4.47 V (evaluated with 2% of tolerance due
to change in temperature and life time).
The charging process is disabled when an external charger is removed from
V_CHARGE
and
CHARGE_SENSE
pins.
1.5.4.2
External charger specification
It is suggested to use a charger with the following electrical characteristics:
6 V DC voltage
500 mA current limit (if it is less than the maximum DC charging current specified by the used battery)
To avoid damage to the module, the external supply used as charging source must be voltage
and current limited, with a voltage limit
≤
15 V and a current limit
≤
1.0 A.
DC supplies with fold-back current protection cannot be used as charger for the module.
The V-I output characteristics of the external supply used as charger must be within the valid area delineated by:
the maximum acceptable charging voltage (equal to 15 V in any case)
the minimum open circuit voltage valid for charger detection (equal to 5.6 V in any case)
the maximum acceptable charging current (equal to 1.0 A or to the maximum DC charging current specified
by the used battery if it is less than 1.0 A)
the minimum charging current (specified by the application, e.g. 400 mA)
