SIM8905-EVB Kit_User Guide_V1.02 switched to VBAT to ensure the conduction of the path. The function of S101 here is to avoid the inconvenience of frequently plugging and unplugging the adapter when the adapter is powered, and only need to toggle the switch and short connect J102 to realize the charging function when charging with the adapter.
Method 2:
The module is powered by the battery 3.5V-4.4V: In order to prevent the adapter and the battery from being connected at the same time, the MOS control (Q102) is added to the battery power supply path. When the adapter is inserted, the MOS (Q102) disconnects the battery powered by.
In order to facilitate the user to test the current consumption of the module, the VBAT and GND test points are added to the TE Board. The customer can test the power consumption of the module by powering the
VBAT test point and disconnecting the jumper J104.
When the module is powered by an adapter, it is necessary to pull down BATT_THERM (Pin 134) of
SIM8905 module to GND with a 47K resistor, otherwise charging and power supply will be abnormal.
The priority selection of EVB adapter or battery power supply is as follows:
MIRCO
USB
J604
Adapter
J101
Battery
J103
S101
Q102
J102
LDO
U101
J104
VBUS
VBAT
SIM8905
Module
Figure 13: Power Supply Diagram
Customer can choose to use S101 to select charge function or not.
If the customers do not want to use charge function, they may disconnect jumper J102, then S101 will be the switch for the power control.
4.1.1 Adapter Interface
The following figure shows the DC power jack of the SIM8905 EVB. www.simcom.com 26 / 56
SIM8905-EVB Kit_User Guide_V1.02
Figure 14: Placement of EVB power supply
Before connecting the power supply, customers have to select a proper +5V DC power adapter to supply power for the SIM8905 EVB, and the power plug design of the adapter is shown as below.
Figure 15: Power Plug Design www.simcom.com 27 / 56
