SIM Tech SIMCom SIM900-DS Hardware Design page 6

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Figure Index
Figure 1: SIM900-DS functional diagram ........................................................................................................ 11
Figure 2: SIM900-DS pin out diagram (Top view) .......................................................................................... 12
Figure 3: Dimensions of SIM900-DS（Unit: mm）........................................................................................ 15
Figure 4: Recommended PCB footprint outline（Unit: mm） ........................................................................ 16
Figure 5: Reference circuit of the LDO power supply...................................................................................... 17
Figure 6: Reference circuit of the DC-DC power supply ................................................................................. 17
Figure 7: VBAT voltage drop during transmit burst......................................................................................... 18
Figure 8: The minimal VBAT voltage requirement at VBAT drop.................................................................. 18
Figure 9: Powered on/down module using transistor........................................................................................ 18
Figure 10: Powered on/down module using button .......................................................................................... 19
Figure 11: Timing of power on module............................................................................................................ 19
Figure 12: Timing of power down SIM900-DS by PWRKEY......................................................................... 20
Figure 13: Timing of restart SIM900-DS ......................................................................................................... 21
Figure 14: RTC supply from capacitor ............................................................................................................. 23
Figure 15: RTC supply from non-chargeable battery ....................................................................................... 23
Figure 16: RTC supply from rechargeable battery ........................................................................................... 23
Figure 17: Seiko XH414H-IV01E Charge-Discharge Characteristic ............................................................... 24
Figure 18: Connection of the serial interfaces .................................................................................................. 24
Figure 19: Connection of RXD and TXD only................................................................................................. 25
Figure 20: Connection for software upgrading and debugging ........................................................................ 26
Figure 21: Speaker reference circuit ................................................................................................................. 26
Figure 22: Speaker with amplifier reference circuit ......................................................................................... 27
Figure 23 : Microphone reference circuit ......................................................................................................... 27
Figure 24: Earphone reference circuit............................................................................................................... 28
Figure 25: Reference circuit of the 8-pin SIM card holder............................................................................... 29
Figure 26: Reference circuit of the 6-pin SIM card holder............................................................................... 29
Figure 27: Amphenol C707 10M006 5122 SIM card holder............................................................................ 30
Figure 28: Molex 91228 SIM card holder ........................................................................................................ 31
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SIM900-DS_Hardware Design_V1.00 2013-01-20