Hardware Design V1.01(091226)
Table Of Contents
- Contents
- Version history
- 1 Introduction
- 2 SIM900 Overview
- 3 Application Interface
- 3.1 SIM900 Pin Description
- 3.2 Operating Modes
- 3.3 Power Supply
- 3.4 Power Up and Power Down Scenarios
- 3.5 Power Saving
- 3.6 Summary of State Transitions (except SLEEP mode)
- 3.7 RTC Backup
- 3.8 Serial Interfaces
- 3.9 Audio Interfaces
- 3.10 SIM Card Interface
- 3.11 LCD Display Interface
- 3.12 Keypad Interface
- 3.13 ADC
- 3.14 Behaviors of the RI
- 3.15 Network Status Indication
- 3.16 General Purpose Input Output (GPIO)
- 3.17 External Reset
- 3.18 PWM
- 3.19 I2C Bus
- 4 Antenna Interface
- 5 Electrical, Reliability and Radio Characteristics
- 6 Mechanics
SIM900 Hardware Design
module is ready to send and receive.
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.
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 shutdown by sending the “AT+CPOWD=1” command or using the PWRKEY. The
power management ASIC disconnects the power supply from 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. Operating voltage (connected to VBAT) remains applied.
Minimum
functionality
mode (without
remove power
supply)
Use the “AT+CFUN” command can set the module to a minimum functionality mode
without remove the power supply. In this case, 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 case is very low.
3.3 Power Supply
The power supply of SIM900 is from a single voltage source of VBAT= 3.4V...4.5V. In some case, the ripple in a
transmitting burst may cause voltage drops when current consumption rises 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. A capacitor (about 100 µF, low ESR) is
recommended. Multi-layer ceramic chip (MLCC) capacitors can provide the best combination of low ESR and
small size but may not be cost effective. A lower cost choice may be a 100 µF tantalum capacitor (low ESR) with
a small (0.1µF to 1µF) ceramic in parallel, which is illustrated as following figure. The capacitors should be
placed as close as possible to the SIM900 VBAT pins. The following figure is the recommended circuit.
SIM900_HD_V1.01 26.12.2009
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