Minimizing Voltage Drop Of Vbat; Monitoring Power Supply; Power On/Down Scenarios; Power On Sim900D - SimCom SIM900D Hardware Design

4.1.1

Minimizing Voltage Drop of VBAT

When designing the power supply in user's application, pay special attention to power losses. Ensure that the
input voltage never drops below 3.1V even when current consumption rises to 2A in the transmit burst. If the
power voltage drops below 3.1V, the module may be shut down automatically. The PCB traces from the VBAT
pins to the power supply must be wide enough (at least 60mil) to decrease voltage drops in the transmit burst. The
power IC and the bypass capacitor should be placed to the module as close as possible.
Figure 10: The minimal VBAT voltage requirement at VBAT drop
4.1.2

Monitoring Power Supply

The AT command "AT+CBC" can be used to monitor the VBAT voltage. For detail, please refer to
4.2

Power on/down Scenarios

4.2.1

Power on SIM900D

4.2.1.1

Turn on SIM900D Using the PWRKEY Pin (Power on)

User can power on SIM900D by pulling down the PWRKEY pin for at least 1 second and release. This pin is
already pulled up to 3V in the module internal, so external pull up is not necessary. Reference circuit is shown as
below.
SIM900D_Hardware Design_V2.02
Figure 9: VBAT voltage drop during transmit burst
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Smart Machine Smart Decision
document [1].
2012-05-07