SIM900D Hardware Design
3 Application Interface
SIM900D is equipped with a 48-pin SMT pad that connects to the cellular application platform. Sub-interfaces
included in these SMT pads are described in detail in following chapters:
z
Power supply and charging control
(please refer to Chapter 3.3 and 3.5)
z
Serial interface and Debug interface
(please refer to chapter3.9)
z
Two analog audio interfaces
(please refer to Chapter 3.10)
z
SIM interface
(please refer to Chapter 3.11)
Electrical and mechanical characteristics of the SMT pad are specified in
Chapter 5.
3.1 SIM900D Pin Description
Table5: Pin description
Power Supply
PIN NAME
I/O DESCRIPTION
DC CHARACTERISTICS
COMMENT
VBAT
I
2 VBAT pins are dedicated to
connect the supply voltage.
The power supply of
SIM900D has to be a single
voltage source of VBAT=
3.4V...4.5V. It must be able
to provide sufficient current
in a transmit burst which
typically rises to 2A
Vmax= 4.5V
Vmin=3.4V
Vnorm=4.0V
VRTC
I/O Current input for RTC when
the battery is not supplied for
the system.
Current output for backup
battery when the main
battery is present and the
backup battery is in low
voltage state.
Vmax=3.15V
Vmin=2.0V
Vnorm=3.0V
Iout(max)= 200uA
Iin= 3uA
If the RTC
function is
enabled, a
battery or
capacitor
should be
connected to
the VRTC pin.
Otherwise the
VRTC pin
should be keep
open.
VCHG
I
Voltage input for the charge
circuit, as the signal for
Vmax=7.5V
Vmin=4.5V
If unused keep
open.
SIM900D_HD_V1.02
09.04.2010
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