Power Supply - SimCom SIM548C HD V1.01 Hardware Design

SIM548C Hardware Design
only parts of AT commands can be available.
GHOST Mode GHOST mode means off and charging mode. In this mode, the module can not
(Charge-only be registered to GSM network and only limited AT commands can be
mode) accessible, the following way will launch GHOST mode:
Charge mode Start charging while the module is in normal mode (including: SLEEP, IDLE,
during normal TALK, GPRS IDLE and GPRS DATA)
operation

3.3 Power supply

The power supply of SIM548C GSM part 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
rise 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 100µF, 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 (0.1 µF to 1µF) ceramic in parallel, which is
illustrated as following figure. The capacitors should put as close as possible to the module VBAT
pins.
SIM548C_HD_V1.01
From POWER DOWN mode: Connect charger to the module's VCHG pin,
and battery is present while the module is power down.
From Normal mode: Connect charger to the module's VCHG pin, and
battery is present, then power down the module by "AT+CPOWD＝1"
Figure 2: Reference circuit of the VBAT input
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09.05.2008