Power Supply Pins On The Board-To-Board Connector; Minimizing Power Losses; Monitoring Power Supply; Power Up And Down Scenarios - SimCom SIM548C HD V1.01 Hardware Design

SIM548C Hardware Design

3.3.1 Power supply pins on the board-to-board connector

Four VBAT pins of the board-to-board connector are dedicated to connect the supply voltage. The
VCHG pin serves as control signal for charging a Li-Ion battery. VRTC pin can be used to back
up the RTC.

3.3.2 Minimizing power losses

Please pay special attention to the supply power when you are designing your applications. Please
make sure that the input voltage will never drop below 3.4V even in a transmitting burst during
which the current consumption may rise up to 2A. If the power voltage drops below 3.4V, the
module may be switched off. So the impedance from extern power supply to module VBAT pins
should be as low as possible. When using a battery, you should also take the impedance of the
battery pack, the battery connector and PCB track on the host board into account. The PCB traces
from the VBAT pins of connector to the power source must be wide enough to ensure less voltage
drops occur in the transmitting burst mode.

3.3.3 Monitoring power supply

To monitor the supply voltage, you can use the "AT+CBC" command which include three
parameters: charging status, voltage percentage and voltage value (in mV). It returns charge state、
the battery voltage 1-100 percent of capacity and actual value measured at VBAT and GND.
The voltage is continuously measured at intervals depending on the operating mode. The
displayed voltage (in mV) is averaged over the last measuring period before the AT+CBC
command is executed.
For details please refer to document [1]

3.4 Power up and down scenarios

3.4.1 Turn on the GSM part

The GSM part of SIM548C can be turned on by various ways, which are described in following
chapters:
Via PWRKEY pin: starts normal operating mode;
Via VCHG pin: starts GHOST modes;
Via RTC interrupt: starts ALARM modes
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09.05.2008