Operating Modes During Charging - SimCom SIM900D Hardware Design

4.2V is reached. Charging is stopped when the charging current at constant voltage has decreased down to the
pre-set current.
4.4.4

Operating modes during charging

The battery can be charged during various operating mode. That means that charging can be in progress while
SIM900D is in Normal mode (SLEEP, IDLE, TALK, GPRS IDLE or GPRS DATA mode). In this case the
voltage supply should be sufficient. Here Charging in Normal mode is named as Charge mode.
If the charger is connects to the module's VCHG Pin and the battery is connected to the VBAT Pin while
SIM900D is in POWER DOWN mode, SIM900D will go into the Charge-only Mode .
The following table gives the difference between Charge mode and Charge-only mode：
Table 7: Charge operating modes
How to activate mode
Connect charger to module's VCHG Pin
and connect battery to VBAT Pin of
module while SIM900D is in Normal
operating mode, including:
IDLE, TALK mode; SLEEP mode etc;
Connect charger to module's VCHG Pin
while SIM900D is in POWER DOWN
mode.
IMPORTANT: Here Charge-only mode is
charging when power down, it means that
not all software tasks are running.
Note: VBAT can not provide more than 5mA current while SIM900D module is during the DDLO charge state. In other words it
is strongly recommended that VBAT should not be the main power supply in the application subsystem if SIM900D DDLO
charging state occurs.
Table 8: AT Command usually used in Charge-only mode
AT command
AT+CCLK
AT+CPOWD
AT+CBC
AT+CFUN
SIM900D_Hardware Design_V2.02
Features
GSM remains operational and registers
GSM network while charging is in
progress;
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.
SIM900D will exit the SLEEP mode.
Battery can be charged when GSM
engine is not registered to GSM
network;
Only a few AT commands is available,
as listed below.
Function
Set data and time of RTC
Power down
Indicated charge state and voltage
Start or close the protocol
Set AT command "AT+CFUN =1", module
27
Smart Machine Smart Decision
2012-05-07