Shutdown Routine State; Emergency Shutdown State; Inrush Currents; Figure 4: Inrush Model - Sierra Wireless MC5720 Hardware Integration Manual

P C I E x p r e s s M i n i C a r d H a r d wa r e I n t e g r a t i o n G u i d e

SHUTDOWN ROUTINE state

In this state, the EM has received a request from the host to power down and is
completing its active tasks and initiating the shutdown routine. At the completion
of the shutdown routine, the EM drives its OFF signal high and completely
powers down. To keep the EM powered down, the host should keep ON/OFF de-
asserted.

EMERGENCY SHUTDOWN state

In this state, the EM has detected a critically high or critically low battery supply
and sets an internal timer of 15 sec. If the host sends a shutdown request prior to
the expiration of the timer, the EM enters the shutdown routine state. If the timer
expires prior to the host shutdown command, the module automatically enters the
shutdown routine. If the host fails to assert ON/OFF throughout the EM
automatic shutdown routine, an unintentional power-down/power-up cycle may
occur.

Inrush currents

There are two power events that cause large inrush currents from the host supply
to the EM on the power pins.
One event is the application of the supply to the host. This occurs when the
supply is enabled. This event charges the input decoupling capacitors on the EM
power rail.
Figure 4 shows a model of this event.

Figure 4: Inrush model

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Note: For the duration of the shutdown routine, the EM asserts
the VCC_RADIO signal. Only upon actual power-down does the
EM de-assert its VCC_RADIO signal.
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