Smart Machine Smart Decision
SIM808_Hardware Design_V1.00 2014.03.27
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Max Charge Current
1.0C
Charge Method
CC / CV (Constant Current / Constant Voltage)
Max Discharge Current
1.0C (for continuous discharging mode)
Discharge Cut-off Voltage
3.0V/ cell
Internal resistance
Initial
≤
150m
Ω
4.4.3
Implemented Charging Technique
SIM808 has battery charging function, but default function is not support for charging, the customer should input
AT command to enable charging function. There are two pins related to the battery charging function: there are
VBUS, VBAT and pins. The VBUS Pin is driven by an external voltage (AC adapter or USB host), system can
use this Pin to detect a charger supply and provide most charging current through SIM808 module to battery when
charging is in fast charge state. VBAT pin gives charging current to external battery from SIM808 module.
It is very simple to implement charging function, user just needs to connect the charger to the VBUS Pin and
connect the battery to the VBAT Pin.
SIM808 battery charging happens after detecting charger supply and the presence of battery. If there is no charger
supply or no battery present, charging function will not be enabled.
Normally, there are three states in the whole charging procedure.
z
DDLO charge (Pull-up mode) and UVLO charge (Pre-charge mode);
z
Constant current mode (CC);
z
Constant voltage mode and over-voltage protection(OV)
DDLO charge and UVLO charge:
DDLO is the state of battery when its voltage is under 2.2V. And UVLO means the battery voltage is less than
3.3V and more than 2.2V. The battery is not suitable for fast charging when its condition is DDLO or UVLO. The
SIM808 provides a small constant current to the battery when the battery is between DDLO and UVLO. In DDLO
charging state, SIM808 gives out pu1se 70mA current to the battery. And in UVLO charging state, SIM808
provides about 200mA (AC<7V) or 70mA (USB mode) current to the battery.
DDLO charging terminates when the battery voltage reaches 2.2V. UVLO charging terminates when the battery
voltage is up to 3.4V. Both DDLO and UVLO charge are controlled by the SIM808 hardware only.
Constant current mode (CC):
As the battery voltage is charged up and over3.4V, the SIM808 will enter CC mode. The CC mode charging
current can be set from 70 to 800mA by the software.
Constant voltage mode (CV) and over-voltage protection (OV):
As the battery is charged up and over 4.05V, the SIM808 will enter CV mode. While the batter voltage actually
reaches 4.2V, the charging current is gradually decreased step by step until stop charging.
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
SIM808 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 connected to the module’s VBUS Pin and the valid battery is connected to the VBAT Pin while
SIM808 is in POWER DOWN mode, SIM808 will auto power up.
Содержание SIM808
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