SIM900 Reference Design Guide SIM900_AN_ Reference Design Guide_V1.
SIM900 Reference Design Guide Notes Document Title: SIM900 Reference Design Guide Version: 1.01 Date: 2010-01-27 10Status: Released Document Control ID: SIM900_AN_ Reference Design Guide_V1.01 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.
SIM900 Reference Design Guide Notes Contents Version history..................................................................................................................................4 1. Introduction...................................................................................................................................5 1.1 References Document ..........................................................................................................5 2 Application Interface................
SIM900 Reference Design Guide Notes Version history Date Version Description of change Author 2010-01-01 1.01 First Release Zhou Qiang SIM900_AN_Reference Design Guide_V1.01 4 01.27.
SIM900 Reference Design Guide Notes 1 Introduction This document describes how to design peripheral interface of SIMCOM module providing in your application. 1.1 References Document SN Document name Remark [1] SIM900_ATC SIM900 AT command Set [2] SIM900_HD SIM900 Hardware Specification [3] SIM900_EVB_UGD SIM900 EVB User Guide [4] SMT MODULE Design Guide RF SMT MODULE RF Design Guide SIM900_AN_Reference Design Guide_V1.01 5 01.27.
SIM900 Reference Design Guide Notes 2 Application Interface 2.1 Power Supply Design 2.1.1 VBAT design The power supply of SIM900 is from a single voltage source of VBAT which normal operating range is form 3.4V to 4.5V. The peak working current can rise up to 2A in maximum power transmiting period, which will cause a voltage drop. So the power supply must be able to provide sufficient peak current, if not, the voltage may drop lower than 3.4V, and the module will auto power down.
SIM900 Reference Design Guide Notes efficiency. When the module is powered by a DC-DC converter, then should pay more attention to the switching noise suppression design, otherwise the RF performance of SIM900 will be interfered by the switching noise of DC-DC, and cause some RF performance degraded, for example, modulation spectrum, switching spectrum will exceed the limit.
SIM900 Reference Design Guide Notes Figure 3: Battery Charge Supply 2.1.3 PWRKEY ON/OFF design The simplest way to turn on/off SIM900 is driving the PWRKEY to a low level for 1S then release. PWRKEY pin has been pulled up to 3V inside the module. Following figure is the recommended connection with a NPN transistor. You can choose a GPIO of your MCU to control the POWER ON/OFF. Please note that don’t add a capacitor on PWRKEY pin, or it may cause some unexpected problems when power on/off process.
SIM900 Reference Design Guide Notes 2.1.4 Reset design SIM900 support the reset function, when the MCU find the module is in an abnormal state, SIM900 can be restarted by pulling the RESET pin to ground for a typical 50uS. Reset is a noise sensitivity pin, it should be kept away from the high speed signal line (eg. clock) when layout. This pin is internal pull up to 2.8V through a 100k resistor. So it’s not necessary to add an external pull up resistor for stable consideration if it is not used.
SIM900 Reference Design Guide Notes Serial Port Connection DBG_TXD DBG_TXD TXD DBG_RXD DBG_RXD RXD GND GND GND Figure 7: UART Figure 6: Debug Port Connection 2.3 GPIO selection 2.3.1 STATUS and NETLIGHT STATUS pin can be used to monitor the module state during the power on/off process. After power up, AT command will response till the STATUS change high, and it will change low after the module log off from the base station in a power down procedure. It can be connected to a GPIO of the MCU.
SIM900 Reference Design Guide Notes VBAT 510R NETLIGH T 4.7K BC847 47K Figure 8: NETLIGHT indicator 2.3.2 GPIO SIM900 serves 12 GPIO which can be controlled by the customer. As a GPI, the status can be read by the AT command and as a GPO, it also can be controlled by the AT command. The customer can use this GPIO to achieve some simple control. For more detail, please refer to Document[1]. 2.
SIM900 Reference Design Guide Notes 2.4.1 Referenced circuit of headset design Figure 9: Referenced circuit of headset 2.4.2 Referenced circuit of hand free design Figure 10: Referenced circuit of audio PA 2.5 Antenna matching circuit design Because the module is working under 50ohm system in RF part, so, to get the best RF performance, the SMT module’s load impedance should be tuned to 50ohm.
SIM900 Reference Design Guide Notes antenna matching circuit should be needed. Furthermore, to facilitate the antenna debugging and certification testing of RF performance, we suggested the customer add a RF test connector in series between the module’s RF port and the antenna matching circuit.
SIM900 Reference Design Guide Notes Figure 12: Reference circuit with 8-pin SIM card holder 2.7 ESD protection It is suggested that it’s better to do some ESD protection in your application to improve the ESD character of the module, especially for the signal connecting to external interface, for example, MIC, SPK,PWRKEY,VBAT,DBG,SIMCARD. 2.
SIM900 Reference Design Guide Notes 9) RF trace between SMT module RF pad with the RF test connector, RF trace between RF test connector with the antenna matching circuit, RF trace between the antenna matching circuit with the antenna feed PAD all should be controlled to 50 Ohm 10) All layers under the antenna feed pad should be copper keep out.
SIM900 Reference Design Guide Notes Contact us: Shanghai SIMCom Wireless Solutions Ltd. Add: Building A，SIM Technology Building，No.633，Jinzhong Road，Changning District, Shanghai,P. R. China 200335 Tel: +86 21 3235 3300 Fax: +86 21 3235 3301 URL: www.sim.com/wm SIM900_AN_Reference Design Guide_V1.01 12 01.27.
