Em Power State Transitions; Disconnected State; Off State; Normal State - Sierra Wireless MC5720 Hardware Integration Manual

EM power state transitions

Figure 3 shows how the EM transitions between power states. Each power state
is described in the sections that follow.

Figure 3: Power state transition diagram

DISCONNECTED state

This power state occurs when the host power supply is disconnected from the
EM. In this state, all voltages associated with the EM are at 0 V and the host may
or may not be powered off. If the host and the EM share the same battery power
rail, then both the host and EM unit are powered off in this state. If the host
controls the connection between the EM and the battery power, the host can put
the EM into the disconnected state by cutting power to it.

OFF state

In this power state, the host is powered up and the EM is powered down. The EM
unit defaults to the OFF state when VBATT is first applied in the absence of
ON/OFF control. The host keeps the EM powered off by de-asserting the
ON/OFF signal.
Current draw in this mode is an absolute minimum (not more than 50 µA).

NORMAL state

This is the active state of the EM. The EM is fully powered and capable of
placing and receiving phone calls on the CDMA network. All functional
interfaces to the module are enabled (audio, MIO, serial, and, when used, USB).
VCC_RADIO is driven high by the module at 2. 5~3.0 V, indicating full power
status.

LOW BATTERY state

The EM has detected a low battery condition (VBATT <= 3.4 V) and requests
shutdown from the host via UART messaging. The EM carries on its regular
tasks.
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Note: In this state, the VCC_RADIO signal is 0 V out of the EM.
To minimize current leakage and prevent unintentional partial
power-up of the EM, the host should not drive any outputs to the
module at a voltage exceeding VCC_RADIO.
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