SIM900A 데이터 시트보기 (PDF) - Unspecified

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SIM900A

SIM900 Quad-band/SIM900A Dual-band GSM/GPRS module

Unspecified 

SIM900 Hardware Design

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 SIM900A 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 SIM900A VBAT pins. The following figure is the recommended circuit.

VBAT

+

CA

CB

SIM900_HD_V1.01

Figure 3: Reference circuit of the VBAT input

21

26.12.2009

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