Gnd - SimCom SIM8905A User Manual

Linear Battery Charger
SIM8905A module integrates a 1.44A linear battery charger for single-cell lithium-ion batteries.
Charging Control
Battery charging is controlled by a PMIC state-machine. The first step in the automated charging process
determines if trickle charging is needed. Charging of a severely depleted battery must begin with trickle charging
to limit the current, avoid pulling VDD down, and protect the battery from more charging current than it can
handle. Once a minimum battery voltage is established using trickle charging, constant-current charging is enabled
to charge the battery quickly – this mode is sometimes called fast charging. Once the battery approaches its target
voltage, the charge is completed using constant-voltage charging.
V
BAT
4.2V
V
BAT-MAX
3.2V
V
WEAK
2.8V
V
TRKL
TRKL-A
Table 3: Linear battery charger performance specifications
Parameter
External 5V
USB_VBUS
USB_DP
USB_DM
USB_ID

GND

Module
Figure14: USB_OTG reference circuit
I 450
TRKL-B
I
90mA
TRKL-A
TRKL-B CC
Figure15: Charging control diagram
Comments
Smart Machine Smart Decision
VBUS
USB_DP
USB_DM
USB_ID
<1pF
GND
Connector
450mA/1440mA
mA
CV
Min
13
I
BAT
I
BAT-MAX
Time
Typ
Max Units