SIM802 Hardware Design
UVLO (under voltage lock out) means the battery voltage less than 3.2V and more than 2.4V. The
battery is not suitable for fast charge when its condition is DDLO or UVLO. The SIM802
provides a small constant current to the battery when the battery is between DDLO and UVLO. In
DDLO charge, SIM802 gives out 5mA current to the battery. And in UVLO charge, SIM802
provides about 25mA current to the battery.
DDLO charge terminated when the battery voltage reaches 2.4V. UVLO charge terminated when
the battery voltage is up to 3.2V. Both DDLO and UVLO charge are controlled by the SIM802
hardware only.
Fast charge:
If there is a charger supply and battery present and the battery is not in DDLO and UVLO,
SIM802 will enter fast charge state. Fast charge is controlled by the software. Fast charge delivers
a strong and constant current (about 550mA) through VBAT Pin to the battery until battery
voltage reach 4.2V.
Trickle charge:
After fast charging, the battery voltage is close to the whole battery capacity, trickle charge begins.
In this state, the SIM802 charges the battery under constant voltage.
3.5.4 Operating modes during charging
The battery can be charged during various operating mode. That means that when the GSM
engine is in Normal mode (SLEEP, IDLE, TALK, GPRS IDLE or GPRS DATA mode), charging
can be in progress while SIM802 remains operational (In this case the voltage supply should be
sufficient). Here we name Charging in Normal mode as Charge mode.
If the charger is connected to the module’s VCHG Pin and the battery is connected to the VBAT
Pin while SIM802 is in POWER DOWN mode, SIM802 will go into the GHOST mode (Off and
charging). The following table gives the difference between Charge mode and GHOST mode
：
Table 9: operating modes
How to activate mode
Features
C
h
arge M
o
de
Connect charger to module’s VCHG Pin
and connect battery to VBAT Pin of
module while SIM802 is in Normal
operating mode, including:
IDLE, TALK mode; SLEEP mode etc;
z
GSM remains operational and
registered GSM network while
charging is in progress;
z
The serial interfaces are available in
IDLE, TALK mode, the AT command
set can be used fully in this case;
In SLEEP mode, the serial interfaces are
not available, once the serial port is
connected and there is data in transfer.
Then SIM802 will exit the SLEEP mode.
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