SIM802 Hardware Design
serial interfaces is still accessible. The power consumption in this case
is very low.
Alarm mode
RTC alert function launches this restricted operation while the module
is in POWER DOWN mode. SIM802 will not be registered to GSM
network and only parts of AT commands can be available.
GHOST Mode
(Charge-only mode)
GHOST mode means off and charging mode. In this mode, the
module can not be registered to GSM network and only limited AT
commands can be accessible, the following way will launch GHOST
mode:
z
From POWER DOWN mode: Connect charger to the module’s
VCHG Pin and VBAT Pin while SIM802 is power down.
z
From Normal mode: Connect charger to the module’s VCHG Pin
and VBAT Pin, then power down the module by “AT+CPOWD”
z
From Normal mode: Connect charger to the module’s VCHG Pin
and VBAT Pin, then press the PWRKEY get a low level voltage
for about 2s.
Charge mode during
normal operation
Start charging while the module is in normal mode including: SLEEP,
IDLE, TALK, GPRS
STANDBY and GPRS DATA
3.3 Power supply
The power supply of VBAT voltage range is from 3.4 to 4.5V .The ripple in a transmitting burst
may cause voltage drops when current consumption rise to typical peaks of 2A, So the power
supply must be able to provide sufficient current up to 2A.
For the VBAT input, a local bypass capacitor is recommended. For example, a lower cost choice
may be a 100 µF tantalum capacitor (low ESR) with a small (0.1 µF to 1 µF) ceramic in parallel,
which is illustrated as figure 3. The capacitors should be put as closer as possible to the SIM802
VBAT pins.
Figure
3: VBAT input
The circuit design of the power supply depends strongly from the power source where this power
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