Power Down Sim900B By The Pwrkey Pin; Power Down Of Sim900B By At Command; Over-Voltage Or Under-Voltage Power Down - SimCom SIM900B Hardware Design

3.3.2.1

Power down SIM900B by the PWRKEY Pin

User can power down SIM900B by pulling down the PWRKEY pin for at least 1 second and release. Please refer
to the power on circuit. The power down scenario is illustrated in the following figure.
PWRKEY
(INPUT)
VDD_EXT
（OUTPUT）
This procedure makes the module log off from the network and allows the software to enter into a secure state to
save data before completely shut down.
Before the completion of the power down procedure, the module will send URC:
NORMAL POWER DOWN
At this moment, AT commands can not be executed any more, and only the RTC is still active. Power down mode
can also be indicated by STATUS pin, which is at low level at this time.
3.3.2.2

Power down of SIM900B by AT Command

SIM900B can be powered down by AT command "AT+CPOWD=1". This procedure makes the module log off
from the network and allows the software to enter into a secure state to save data before completely shut down.
Before the completion of the power down procedure, the module will send URC:
NORMAL POWER DOWN
At this moment, AT commands can not be executed any more, and only the RTC is still active. Power down mode
can also be indicated by STATUS pin, which is at low level at this time.
For detail about the AT command "AT+CPOWD", please refer to document [1]
3.3.2.3

Over-voltage or Under-voltage Power down

The module software monitors the VBAT voltage constantly.
If the voltage ≤ 3.3V, the following URC will be reported:
UNDER-VOLTAGE WARNNING
If the voltage ≥ 4.7V, the following URC will be reported:
OVER-VOLTAGE WARNNING
If the voltage < 3.2V, the following URC will be reported, and the module will be automatically powered down.
SIM900B_Hardware Design_V2.01
5s >Pulldown >1s
V <0.9V
IL
Figure 9: Timing of power down SIM900B by PWRKEY
Delay > 1.7s
Logout net
V > 2.55V
IH
V
OL
17
Smart Machine Smart Decision
< 0.1V
2012-05-07