SimCom SIM900D EVB Supplement

SIM900D_Hardware Design_V2.02

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SIM900D_Hardware Design_V2.02 2 2012-05-07
Document Title SIM900D Hardware Design
Version 2.02
Date 2012-05-07
Status Release
Document Control ID SIM900D_Hardware Design_V2.02
General Notes
SIMCom offers this information as a service to its customers, to support application and engineering efforts that
use the products designed by SIMCom. The information provided is based upon requirements specifically
provided to SIMCom by the customers. SIMCom has not undertaken any independent search for additional
relevant information, including any information that may be in the customer’s possession. Furthermore, system
validation of this product designed by SIMCom within a larger electronic system remains the responsibility of the
customer or the customer’s system integrator. All specifications supplied herein are subject to change.
Copyright
This document contains proprietary technical information which is the property of SIMCom Limited, copying of
this document and giving it to others and the using or communication of the contents thereof, are forbidden
without express authority. Offenders are liable to the payment of damages. All rights reserved in the event of grant
of a patent or the registration of a utility model or design. All specification supplied herein are subject to change
without notice at any time.
Copyright © Shanghai SIMCom Wireless Solutions Ltd. 2012

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SIM900D_Hardware Design_V2.02 3 2012-05-07
Contents
Contents.................................................................................................................................................................... 3
Version History........................................................................................................................................................ 7
1Introduction....................................................................................................................................................... 8
2SIM900D Overview........................................................................................................................................... 8
2.1 SIM900D Key Features............................................................................................................................ 8
2.2 Operating Modes .................................................................................................................................... 10
2.3 SIM900D Functional Diagram ................................................................................................................11
3Package Information ...................................................................................................................................... 13
3.1 Pin out Diagram...................................................................................................................................... 13
3.2 Pin Description ....................................................................................................................................... 14
3.3 Package Dimensions............................................................................................................................... 16
4Application Interface...................................................................................................................................... 18
4.1 Power Supply.......................................................................................................................................... 18
4.1.1 Minimizing Voltage Drop of VBAT................................................................................................... 19
4.1.2 Monitoring Power Supply ................................................................................................................... 19
4.2 Power on/down Scenarios ...................................................................................................................... 19
4.2.1 Power on SIM900D............................................................................................................................. 19
4.2.1.1 Turn on SIM900D Using the PWRKEY Pin (Power on) ..................................................................... 19
4.2.1.2 Turn on the SIM900D using the VCHG signal .................................................................................... 20
4.2.2 Power down SIM900D........................................................................................................................ 21
4.2.2.1 Power down SIM900D by the PWRKEY Pin...................................................................................... 21
4.2.2.2 Power down SIM900D by AT Command............................................................................................ 21
4.2.2.3 Over-voltage or Under-voltage Power down ....................................................................................... 22
4.2.2.4 Over-temperature or Under-temperature Power down ......................................................................... 22
4.2.3 Restart SIM900D by PWRKEY Pin.................................................................................................... 22
4.3 Power Saving Mode................................................................................................................................ 23
4.3.1 Minimum Functionality Mode ............................................................................................................ 23
4.3.2 Sleep Mode 1 (AT+CSCLK=1) .......................................................................................................... 23
4.3.3 Wake Up SIM900D from Sleep Mode 1 (AT+CSCLK=1) ................................................................ 24
4.3.4 Sleep Mode 2 (AT+CSCLK=2) .......................................................................................................... 24
4.3.5 Wake Up SIM900D from Sleep Mode 2 (AT+CSCLK=2) ................................................................ 24
4.4 Charging interface .................................................................................................................................. 24
4.4.1 Battery pack characteristics................................................................................................................. 25
4.4.2 Recommended battery pack ................................................................................................................ 25
4.4.3 Implemented charging technique ........................................................................................................ 26
4.4.4 Operating modes during charging ....................................................................................................... 27
4.4.5 Charger requirements .......................................................................................................................... 28
4.5 RTC Backup ........................................................................................................................................... 28
4.6 Serial Interfaces ...................................................................................................................................... 29
4.6.1 Function of Serial Port and Debug Port .............................................................................................. 30
4.6.2 Software Upgrade and Debug ............................................................................................................. 31
4.7 Audio Interfaces ..................................................................................................................................... 31

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4.7.1 Speaker Interface Configuration ......................................................................................................... 32
4.7.2 Microphone Interfaces Configuration ................................................................................................. 32
4.7.3 Earphone Interface Configuration....................................................................................................... 33
4.7.4 Audio Electronic Characteristics......................................................................................................... 33
4.8 SIM Card Interface ................................................................................................................................. 34
4.8.1 SIM Card Application......................................................................................................................... 34
4.8.2 Design Considerations for SIM Card Holder...................................................................................... 35
4.9 LCD Display/SPI Interface..................................................................................................................... 37
4.10 ADC........................................................................................................................................................ 37
4.11 RI Behaviors........................................................................................................................................... 37
4.12 Network Status Indication ...................................................................................................................... 38
4.13 General Purpose Input/Output (GPIO) ................................................................................................... 39
4.14 PWM ...................................................................................................................................................... 39
4.15 Antenna Interface ................................................................................................................................... 40
5Electrical, Reliability and Radio Characteristics......................................................................................... 41
5.1 Absolute Maximum Ratings................................................................................................................... 41
5.2 Recommended Operating Conditions..................................................................................................... 41
5.3 Digital Interface Characteristics ............................................................................................................. 41
5.4 SIM Card Interface Characteristics ........................................................................................................ 41
5.5 SIM_VDD Characteristics...................................................................................................................... 42
5.6 VRTC Characteristics ............................................................................................................................. 42
5.7 Current Consumption (VBAT = 3.8V) ................................................................................................... 42
5.8 Electro-Static Discharge ......................................................................................................................... 43
5.9 Radio Characteristics.............................................................................................................................. 44
5.9.1 Module RF Output Power ................................................................................................................... 44
5.9.2 Module RF Receive Sensitivity........................................................................................................... 45
5.9.3 Module Operating Frequencies ........................................................................................................... 46
6Manufacturing ................................................................................................................................................ 47
6.1 Top and Bottom View of SIM900D ....................................................................................................... 47
6.2 Typical Solder Reflow Profile................................................................................................................ 47
Appendix ................................................................................................................................................................ 48
A. Related Documents.......................................................................................................................................... 48
B. Terms and Abbreviations ................................................................................................................................. 49
C. Safety Caution ................................................................................................................................................. 50

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Table Index
TABLE 1: SIM900D KEY FEATURES ............................................................................................................................. 8
TABLE 2: CODING SCHEMES AND MAXIMUM NET DATA RATES OVER AIR INTERFACE ............................ 10
TABLE 3: OVERVIEW OF OPERATING MODES........................................................................................................ 10
TABLE 4: PIN DESCRIPTION ....................................................................................................................................... 14
TABLE 5:THE CURRENT CONSUMPTION OF MINIMUM FUNCTIONALITY MODE ......................................... 23
TABLE 6: SPECIFICATION OF RECOMMENDED BATTERY PACK........................................................................ 26
TABLE 7: CHARGE OPERATING MODES .................................................................................................................. 27
TABLE 8: AT COMMAND USUALLY USED IN CHARGE-ONLY MODE ................................................................ 27
TABLE 9: MICROPHONE INPUT CHARACTERISTICS ............................................................................................ 33
TABLE 10: AUDIO OUTPUT CHARACTERISTICS .................................................................................................... 34
TABLE 11: PIN DESCRIPTION (AMPHENOL SIM CARD HOLDER)....................................................................... 36
TABLE 12: PIN DESCRIPTION (MOLEX SIM CARD HOLDER) .............................................................................. 36
TABLE 13: ADC SPECIFICATION ................................................................................................................................37
TABLE 14: RI BEHAVIORS ........................................................................................................................................... 37
TABLE 15: STATUS OF THE NETLIGHT PIN.............................................................................................................. 39
TABLE 16: PIN DEFINITION OF THE GPIO INTERFACE ......................................................................................... 39
TABLE 17: ABSOLUTE MAXIMUM RATINGS........................................................................................................... 41
TABLE 18: RECOMMENDED OPERATING CONDITIONS ....................................................................................... 41
TABLE 19: DIGITAL INTERFACE CHARACTERISTICS ........................................................................................... 41
TABLE 20: SIM CARD INTERFACE CHARACTERISTICS........................................................................................ 42
TABLE 21: SIM_VDD CHARACTERISTICS................................................................................................................ 42
TABLE 22: VRTC CHARACTERISTICS ....................................................................................................................... 42
TABLE 23: CURRENT CONSUMPTION ...................................................................................................................... 42
TABLE 24: THE ESD CHARACTERISTICS (TEMPERATURE: 25℃, HUMIDITY: 45 %) ....................................... 43
TABLE 25: SIM900D GSM 900 AND GSM 850 CONDUCTED RF OUTPUT POWER ............................................. 44
TABLE 26: SIM900D DCS 1800 AND PCS 1900 CONDUCTED RF OUTPUT POWER............................................ 45
TABLE 27: SIM900D CONDUCTED RF RECEIVE SENSITIVITY ............................................................................ 46
TABLE 28: SIM900D OPERATING FREQUENCIES.................................................................................................... 46
TABLE 29: RELATED DOCUMENTS ........................................................................................................................... 48
TABLE 30: TERMS AND ABBREVIATIONS................................................................................................................ 49
TABLE 31: SAFETY CAUTION..................................................................................................................................... 50

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Figure Index
FIGURE 1: SIM900D FUNCTIONAL DIAGRAM......................................................................................................... 12
FIGURE 2: SIM900D PIN OUT DIAGRAM (TOP VIEW) ............................................................................................ 13
FIGURE 3: SIM900D TOP MECHANICAL DIMENSIONS (UNIT: MM).................................................................... 16
FIGURE 4: SIM900D BOTTOM MECHANICAL DIMENSIONS (UNIT: MM) .......................................................... 16
FIGURE 5: SIM900D SIDE MECHANICAL DIMENSIONS (UNIT: MM) .................................................................. 17
FIGURE 6: RECOMMENDED PCB DECAL (UNIT: MM)........................................................................................... 17
FIGURE 7: REFERENCE CIRCUIT OF THE LDO POWER SUPPLY ......................................................................... 18
FIGURE 8: REFERENCE CIRCUIT OF THE DC-DC POWER SUPPLY..................................................................... 18
FIGURE 9: VBAT VOLTAGE DROP DURING TRANSMIT BURST........................................................................... 19
FIGURE 10: THE MINIMAL VBAT VOLTAGE REQUIREMENT AT VBAT DROP .................................................. 19
FIGURE 11: POWERED ON/DOWN MODULE USING TRANSISTOR ..................................................................... 20
FIGURE 12: POWERED ON/DOWN MODULE USING BUTTON ............................................................................. 20
FIGURE 13: TIMING OF POWER ON MODULE......................................................................................................... 20
FIGURE 14: TIMING OF POWER DOWN SIM900D BY PWRKEY ........................................................................... 21
FIGURE 15: TIMING OF RESTART SIM900D ............................................................................................................. 23
FIGURE 16: SIM900D WITH BATTERY CHARGER AND PACK CONNECTION.................................................... 25
FIGURE 17: RTC SUPPLY FROM CAPACITOR........................................................................................................... 28
FIGURE 18: RTC SUPPLY FROM NON-CHARGEABLE BATTERY ......................................................................... 28
FIGURE 19: RTC SUPPLY FROM RECHARGEABLE BATTERY .............................................................................. 29
FIGURE 20: SEIKO XH414H-IV01E CHARGE-DISCHARGE CHARACTERISTIC ................................................. 29
FIGURE 21: CONNECTION OF THE SERIAL INTERFACES..................................................................................... 29
FIGURE 22: CONNECTION OF RXD AND TXD ONLY ............................................................................................. 30
FIGURE 23: CONNECTION FOR SOFTWARE UPGRADING AND DEBUGGING.................................................. 31
FIGURE 24: SPEAKER REFERENCE CIRCUIT .......................................................................................................... 32
FIGURE 25: SPEAKER WITH AMPLIFIER REFERENCE CIRCUIT ......................................................................... 32
FIGURE 26 : MICROPHONE REFERENCE CIRCUIT................................................................................................. 32
FIGURE 27: EARPHONE REFERENCE CIRCUIT....................................................................................................... 33
FIGURE 28: REFERENCE CIRCUIT OF THE 8-PIN SIM CARD HOLDER............................................................... 34
FIGURE 29: REFERENCE CIRCUIT OF THE 6-PIN SIM CARD HOLDER............................................................... 35
FIGURE 30: AMPHENOL C707 10M006 5122 SIM CARD HOLDER......................................................................... 35
FIGURE 31: MOLEX 91228 SIM CARD HOLDER ...................................................................................................... 36
FIGURE 32: RI BEHAVIOUR OF VOICE CALLING AS A RECEIVER...................................................................... 38
FIGURE 33: RI BEHAVIOUR OF DATA CALLING AS A RECEIVER........................................................................ 38
FIGURE 34: RI BEHAVIOUR OF URC OR RECEIVE SMS ........................................................................................ 38
FIGURE 35: RI BEHAVIOUR AS A CALLER ............................................................................................................... 38
FIGURE 36: REFERENCE CIRCUIT OF NETLIGHT .................................................................................................. 39
FIGURE 37: ANTENNA MATCHING CIRCUIT ........................................................................................................... 40
FIGURE 38: TOP AND BOTTOM VIEW OF SIM900D ................................................................................................ 47
FIGURE 39: TYPICAL SOLDER REFLOW PROFILE ................................................................................................. 47

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SIM900_Hardware Design_V2.02 7 2012-05-07
Version History
Date Version Description of change Author
2010-03-31 1.01 Origin Jing.zhou
Changed GHOST mode to Charge-only mode
§3.4.1.1Update the Figure8: Timing of turn on system
using PWRKEY
§3.4.2.1Update the Figure9: Timing of turn off system
using PWRKEY
2010-04-09 1.02
§4.2Update the Table25: SIM900D conducted RF
receive sensitivity
Jing.zhou
§3.8, Modify the VRTC pin connection when backup is
not needed.
§2.1, §3.3. §3.4 Modify the power supply range from
3.4V~4.5V to 3.1V~4.8V.
2010-06-24 1.03
§3.4.1.1Update the Figure8: Timing of turn on system
using PWRKEY
Jing.zhou
2010-10-09 1.04 Modify the power supply range to 3.2V~4.8V.
§3.3.2 Add Figure6: The minimal VBAT voltage at
VBAT drop
§3.4 Modified figure7，figure8，figure11.
§3.6 Add 3.6.4 and 3.6.5 description.
§3.11.1 Update the Figure25
§3.7 Update the Figure13
Jing.zhou
2011-04-01 2.00 Arrange the structure of document. Jing.zhou
2012-02-23 2.01 Modify chapter6 Manufacturing Juntao.zhao
2012-05-07 2.02 Add illustration of SIM900 module information and
some notes in chapter 5.
Modify §6
Add some notes in chapter 5.
Juntao.zhao

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SIM900D_Hardware Design_V2.02 8 2012-05-07
1Introduction
This document describes SIM900D hardware interface in great detail.
This document can help user to quickly understand SIM900D interface specifications, electrical and mechanical
details. With the help of this document and other SIM900D application notes, user guide, users can use SIM900D
to design various applications quickly.
2SIM900D Overview
Designed for global market, SIM900D is a quad-band GSM/GPRS module that works on frequencies GSM
850MHz, EGSM 900MHz, DCS 1800MHz and PCS 1900MHz. SIM900D features GPRS multi-slot class 10/
class 8 (optional) and supports the GPRS coding schemes CS-1, CS-2, CS-3 and CS-4.
With a tiny configuration of 33*33*3mm, SIM900D can meet almost all the space requirements in user
applications, such as M2M, smart phone, PDA, FWP, and other mobile devices.
SIM900D has 48 SMT pads, and provides all hardware interfaces between the module and customers’ boards.
zSerial port and debug port can help user easily develop user’s applications.
zAudio channel which includes two microphone inputs and two receiver outputs.
zProgrammable general purpose input and output.
zThe SPI display interface will give users the flexibility to develop customized applications.
SIM900D is designed with power saving technique so that the current consumption is as low as 1.0mA in sleep
mode.
SIM900D integrates TCP/IP protocol and extended TCP/IP AT commands which are very useful for data transfer
applications. For details about TCP/IP applications, please refer to document [2].
2.1 SIM900D Key Features
Table 1: SIM900D key features
Feature Implementation
Power supply 3.2V ~ 4.8V
Power saving Typical power consumption in sleep mode is 1.0mA ( BS-PA-MFRMS=9 )
Frequency bands zSIM900D Quad-band: GSM 850, EGSM 900, DCS 1800, PCS 1900.

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SIM900D can search the 4 frequency bands automatically. The frequency
bands also can be set by AT command “AT+CBAND”. For details, please
refer to document [1].
zCompliant to GSM Phase 2/2+
Transmitting power
zClass 4 (2W) at GSM 850 and EGSM 900
zClass 1 (1W) at DCS 1800 and PCS 1900
GPRS connectivity
zGPRS multi-slot class 10（default）
zGPRS multi-slot class 8 (option)
Temperature range
zNormal operation: -30°C ~ +80°C
zRestricted operation: -40°C ~ -30°C and +80 °C ~ +85°C*
zStorage temperature -45°C ~ +90°C
Data GPRS
zGPRS data downlink transfer: max. 85.6 kbps
zGPRS data uplink transfer: max. 42.8 kbps
zCoding scheme: CS-1, CS-2, CS-3 and CS-4
zIntegrate the TCP/IP protocol.
zSupport Packet Broadcast Control Channel (PBCCH)
CSD zSupport CSD transmission
USSD zUnstructured Supplementary Services Data (USSD) support
SMS
zMT, MO, CB, Text and PDU mode
zSMS storage: SIM card
FAX Group 3 Class 1
SIM interface Support SIM card: 1.8V, 3V
External antenna Antenna pad
Audio features
Speech codec modes:
zHalf Rate (ETS 06.20)
zFull Rate (ETS 06.10)
zEnhanced Full Rate (ETS 06.50 / 06.60 / 06.80)
zAdaptive multi rate (AMR)
zEcho Cancellation
zNoise Suppression
Serial port and
debug port
Serial port:
zFull modem interface with status and control lines, unbalanced,
asynchronous.
z1200bps to 115200bps.
zCan be used for AT commands or data stream.
zSupport RTS/CTS hardware handshake and software ON/OFF flow control.
zMultiplex ability according to GSM 07.10 Multiplexer Protocol.
zAutobauding supports baud rate from 1200 bps to 57600bps.
Debug port:
zNull modem interface DBG_TXD and DBG_RXD.
zCan be used for debugging and upgrading firmware.
Phonebook management Support phonebook types: SM, FD, LD, RC, ON, MC.
SIM application toolkit GSM 11.14 Release 99
Real time clock Support RTC
Physical characteristics Size: 33*33*3mm
Weight: 6.2g

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Firmware upgrade Firmware upgradeable by debug port.
*SIM900D does work at this temperature, but some radio frequency characteristics may deviate from the GSM specification.
Table 2: Coding schemes and maximum net data rates over air interface
Coding scheme 1 timeslot 2 timeslot 4 timeslot
CS-1 9.05kbps 18.1kbps 36.2kbps
CS-2 13.4kbps 26.8kbps 53.6kbps
CS-3 15.6kbps 31.2kbps 62.4kbps
CS-4 21.4kbps 42.8kbps 85.6kbps
2.2 Operating Modes
The table below summarizes the various operating modes of SIM900D.
Table 3: Overview of operating modes
Mode Function
GSM/GPRS
SLEEP
Module will automatically go into sleep mode if the conditions of sleep
mode are enabling and there is no on air and no hardware interrupt (such as
GPIO interrupt or data on serial port).
In this case, the current consumption of module will reduce to the minimal
level.
In sleep mode, the module can still receive paging message and SMS.
GSM
IDLE
Software is active. Module registered to the GSM network, and the module
is ready to communicate.
GSM
TALK
Connection between two subscribers is in progress. In this case, the power
consumption depends on network settings such as DTX off/on,
FR/EFR/HR, hopping sequences, antenna.
GPRS
STANDBY
Module is ready for GPRS data transfer, but no data is currently sent or
received. In this case, power consumption depends on network settings and
GPRS configuration.
Normal
operation
GPRS
DATA
There is GPRS data transfer (PPP or TCP or UDP) in progress. In this case,
power consumption is related with network settings (e.g. power control
level); uplink/downlink data rates and GPRS configuration (e.g. used
multi-slot settings).
Power down
Normal power down by sending the AT command “AT+CPOWD=1” or using the PWRKEY.
The power management unit shuts down the power supply for the baseband part of the
module, and only the power supply for the RTC is remained. Software is not active. The
serial port is not accessible. Power supply (connected to VBAT) remains applied.
Minimum AT command “AT+CFUN” can be used to set the module to a minimum functionality mode

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functionality
mode
without removing the power supply. In this mode, the RF part of the module will not work or
the SIM card will not be accessible, or both RF part and SIM card will be closed, and the
serial port is still accessible. The power consumption in this mode is lower than normal
mode.
Charge-only
mode
The module will systematically enter Charge-only mode when a charger and battery are
connected to a switched-off SIM900D. In the mode, the module does not search for network
and has limited AT commands available. The module also can enter Charge-only mode from
Charge mode during normal operation by normally shutdown the module.
Charge mode
during normal
operation
The module will automatically go to this mode when a charger is connected to a Normal
operation mode module of which battery voltage is not lower than 3.2V. Normal operation
mode includes: SLEEP, IDLE, TALK, GPRS IDLE and GPRS DATA.
2.3 SIM900D Functional Diagram
The following figure shows a functional diagram of SIM900D:
zThe GSM baseband engine
zFlash
zThe GSM radio frequency part
zThe antenna interface
zThe other interfaces

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Flash+SRAM
RF
Power Amplifier
26MHz
Transceiver
Analog
Controller
With PMU
Digital Baseband
RTC
Reset
I/Q
COL
POWER
32.768KHz
RF
interface
Battery
interface
ANTBattery
GPIO
Serial
Interface
GPIO
Digital interface
Serial Port
Debug/upgrading
program
SIM interface
LCD interface
PWRKEY
RTC Analog interface
Audio interface ADC Charger
Figure 1: SIM900D functional diagram
SIM900D_Hardware Design_V2.02 12 2012-05-07

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3Package Information
3.1 Pin out Diagram
SIM900D_Hardware Design_V2.02 13 2012-05-07
SIM900D
TOP VIEW
1
2
17
3
4
10
5
11
6
12
13
7
14
8
15
16
9
34
35
33
36
37 42
38 43 39 44 45 46 40 47 48 41
31 30
18 29 25 28 24 27 23 22 21 20 19 26
DBG_TXD
DBG_RXD
RXD
TXD
STATUS
SIM_DATA
SIM_CLK
SIM_RST
SIM_VDD
KBR0
RI
PWRKEY
DISP_CLK
DISP_DATA
VRTC
DISP_D/C
GND
MIC2P
MIC2N MIC1N
MIC1P
AGND
SPK1P
SPK1N
SPK2N
SPK2P
VCHG
ADC0
GND GND
GND GND
GND
RTS
DTR
DCD
GND
GND
GND
GPO1
32
CTS
TEMP_BAT
ANT
VBAT VBAT
NETLIGHT
DISP_CS
PWM
Figure 2: SIM900D pin out diagram (Top view)

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3.2 Pin Description
Table 4: Pin description
Pin name Pin number I/O Description Comment
Power supply
VBAT 38,39 I Power supply
VRTC 15 I/O Power supply for RTC
It is recommended to
connect with a battery or
a capacitor (e.g. 4.7uF).
AGND 22 Analog GND
GND
17,30,31,32,
34,35,36,37,
48
Ground
Power on/down
PWRKEY 12 I
PWRKEY should be pulled low at least
1 second and then released to power
on/down the module.
Pulled up internally.
Audio interfaces
MIC1P 21
MIC1N 20
I Differential audio input
SPK1P 23
SPK1N 24
O Differential audio output
MIC2P 18
MIC2N 19
I Differential audio input
SPK2P 26
SPK2N 25
O Differential audio output
If these pins are unused,
keep open.
Status
STATUS 5 O Power on status
NETLIGHT 41 O Network status
If these pins are unused,
keep open.
LCD interface
DISP _CLK 13 O
DISP_DATA 14 I/O
DISP _D/C 16 O
DISP _CS 46 O
Display interface If these pins are unused,
keep open.
GPIOs
GPO1 40 GPIO
KBR0 10
I/O
GPIO
If these pins are unused,
keep open.
Serial port
RXD 3 I Receive data
This pin should be
pulled up to 3V
externally.
TXD 4 O Transmit data If these pins are unused,

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RTS 44 I Request to send
CTS 45 O Clear to send
DCD 42 O Data carrier detect
RI 11 O Ring indicator
DTR 43 I Data terminal ready
keep open.
Debug interface
DBG_TXD 2 O
DBG_RXD 1 I
For debugging and upgrading firmware If these pins are unused,
keep open.
SIM interface
SIM_VDD 9 O Voltage supply for SIM card. Support
1.8V or 3V SIM card
SIM_DATA 6 I/O SIM data input/output
SIM_CLK 7 O SIM clock
SIM_RST 8 O SIM reset
All signals of SIM
interface should be
protected against ESD
with a TVS diode array.
ADC
ADC0 29 I Input voltage range: 0V ~ 2.8V If it is unused, keep open.
Pulse width modulation( PWM )
PWM 47 O PWM If these pins are unused,
keep open.
RF interface
ANT 33 I/O Radio antenna connection Impendence must be
controlled to 50Ω.
Charging
VCHG 28 I Charger input These pins should be
kept open.
TEMP_BAT 27 I Battery temperature sensor If it is unused, keep open.

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3.3 Package Dimensions
Following shows the Mechanical dimensions of SIM900D (top view, side view and bottom view).
Figure 3: SIM900D top mechanical dimensions (Unit: mm)
Figure 4: SIM900D bottom mechanical dimensions (Unit: mm)
SIM900_Hardware Design_V2.02 7 2012-05-07

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Figure 5: SIM900D side mechanical dimensions (Unit: mm)
FOOT PRINT RECOMMENDATION:
Figure 6: Recommended PCB decal (Unit: mm)
Note: Keep copper out of area A,B,C. Do not place via in area A, B and C to avoid short circuit between via on customer board
and the test points on the bottom side of the module.
SIM900D_Hardware Design_V2.02 17 2012-05-07

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4Application Interface
4.1 Power Supply
The power supply range of SIM900D is from 3.2V to 4.8V. The transmitting burst will cause voltage drop and the
power supply must be able to provide sufficient current up to 2A. For the VBAT input, a bypass capacitor (low
ESR) such as a 100 µF is strongly recommended; this capacitor should be placed as close as possible to SIM900D
VBAT pins. The following figure is the reference design of +5V input power supply. The designed output for the
power supply is 4.1V, thus a linear regulator can be used.
GND
Figure 7: Reference circuit of the LDO power supply
If there is a high drop-out between the input and the desired output (VBAT), a DC-DC power supply will be
preferable because of its better efficiency especially with the 2A peak current in burst mode of the module. The
following figure is the reference circuit.
Figure 8: Reference circuit of the DC-DC power supply
The single 3.6V Li-ion cell battery can be connected to SIM900D VBAT pins directly. But the Ni-Cd or Ni-MH
battery must be used carefully, since their maximum voltage can rise over the absolute maximum voltage of the
module and damage it.
When battery is used, the total impedance between battery and VBAT pins should be less than 150mΩ.
The following figure shows the VBAT voltage drop at the maximum power transmit phase, and the test condition
is as following:
VBAT=4.0V,
A VBAT bypass capacitor CA=100µF tantalum capacitor (ESR=0.7Ω),
Another VBAT bypass capacitor CB=1µF.
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Figure 9: VBAT voltage drop during transmit burst
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 document [1].
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.
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Figure 11: Powered on/down module using transistor
Figure 12: Powered on/down module using button
The power on scenarios is illustrated as following figure.
Figure 13: Timing of power on module
When power on procedure is completed, SIM900D will send following URC to indicate that the module is ready
to operate at fixed baud rate.
RDY
This URC does not appear when autobauding function is active.
Note: User can use AT command “AT+IPR=x” to set a fixed baud rate and save the configuration to non-volatile flash memory.
After the configuration is saved as fixed baud rate, the Code “RDY” should be received from the serial port every time when
SIM900D is powered on. For details, please refer to the chapter “AT+IPR” in document [1].
4.2.1.2 Turn on the SIM900D using the VCHGsignal
The SIM900D will be automatically turned on when a charger is connected to the switched-off SIM900D of
which VBAT pin voltage is greater than 3.2V. SIM900D will go into the Charge-only Mode. In this mode, the
module does not register to the network, and has only a few AT commands available. For detailed information
please refer to chapter 3.5.
When module is powered on using the VCHG signal, SIM900D sends out result code as following when fixed
baud rate set:
RDY
CHARGE-ONLY MODE
When user drives the PWRKEY of Charge-only mode SIM900D to a low level voltage for a period of time
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