User's Manual

GE864- QUAD Har dwar e User Guide
1vv0300872 Rev.1 2010-04-02
- All Rights Reserved. Page 30 of 77
6.2.1.3. Batter y Sour ce Power Supply Design Guidel ines
The desired nominal output for the power supply is 3.8V and the maximum voltage
allowed is 4.5 V , hence a single 3.7V Li-Ion cell battery type is suited for supplying
the power to the Telit GE864-QUAD module.
CAUTION:
The three cells Ni/Cd or Ni/MH 3,6 V Nom. battery types or 4V PB types MUST NOT
BE USED DIRECTLY since their maximum voltage can rise over the absolute
maximum voltage for the GE864-QUAD and damage it.
CAUTION:
DO NOT USE any Ni-Cd, Ni- MH, and Pb battery types directly connected with GE864-
QUAD. Their use can lead to overvoltage on the GE864-QUAD and damage it. USE
ONLY Li- Ion battery types.
A Bypass low ESR capacitor of adequate capacity must be provided in order to cut the
curr ent absorption peaks, a 100μF tantalum capacitor is usually suited.
Make sur e the low ESR capacitor (usually a tantalum one) is rated at least 10V.
A protection diode must be inserted close to the power input, in order to save the
GE864-QUAD fr om power polarity inversion. Otherwise the battery connector must be
done in a way to avoid polarity inversions when connecting the battery.
The battery capacity must be at least 500mAh in order to withstand the current peaks
of 2A; the suggested capacity is fr om 500mAh to 1000mAh.
6.2.1.4. Batter y Char ge Contr ol Cir cuitr y Design Guidel ines
The charging process for Li-Ion Batter ies can be divided into 4 phases:
Qualification and trickle charging
Fast charge 1 – constant cur rent
Final charge – constant voltage or pulsed charging
Maintenance charge
The qualification process consists in a battery voltage measure, indicating roughly its
charge status. If the battery is deeply discharged, that means its voltage is lower
than the trickle charging thr eshold, then the charge must start slowly possibly with a
curr ent limited pre-charging process where the cur r ent is kept very low with respect
to the fast charge value: the tr ickle charging.
Dur ing the tr ickle charging the voltage across the battery terminals rises; when it
reaches the fast charge threshold level the charging process goes into fast charge
phase.