BCM43455 Preliminary Data Sheet
Power-Off Shutdown
Each resource is in one of four states:
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•
•
•
enabled
disabled
transition_on
transition_off
The timer contains 0 when the resource is enabled or disabled and a non-zero value in the transition states. The
timer is loaded with the time_on or time_off value of the resource when the PMU determines that the resource
must be enabled or disabled. That timer decrements on each 32.768 kHz PMU clock. When it reaches 0, the
state changes from transition_off to disabled or transition_on to enabled. If the time_on value is 0, the resource
can transition immediately from disabled to enabled. Similarly, a time_off value of 0 indicates that the resource
can transition immediately from enabled to disabled. The terms enable sequence and disable sequence refer
to either the immediate transition or the timer load-decrement sequence.
During each clock cycle, the PMU sequencer performs the following actions:
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•
Computes the required resource set based on requests and the resource dependency table.
Decrements all timers whose values are non zero. If a timer reaches 0, the PMU clears the
ResourcePending bit for the resource and inverts the ResourceState bit.
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•
•
Compares the request with the current resource status and determines which resources must be enabled
or disabled.
Initiates a disable sequence for each resource that is enabled, no longer being requested, and has no
powered up dependents.
Initiates an enable sequence for each resource that is disabled, is being requested, and has all of its
dependencies enabled.
Power-Off Shutdown
The BCM43455 provides a low-power shutdown feature that allows the device to be turned off while the host,
and any other devices in the system, remain operational. When the BCM43455 is not needed in the system,
VDDIO_RF and VDDC are shut down while VDDIO remains powered. This allows the BCM43455 to be
effectively off while keeping the I/O pins powered so that they do not draw extra current from any other devices
connected to the I/O.
During a low-power shutdown state, provided VDDIO remains applied to the BCM43455, all outputs are
tristated, and most inputs signals are disabled. Input voltages must remain within the limits defined for normal
operation. This is done to prevent current paths or create loading on any digital signals in the system, and
enables the BCM43455 to be fully integrated in an embedded device and take full advantage of the lowest
power-savings modes.
When the BCM43455 is powered on from this state, it is the same as a normal power-up and the device does
not retain any information about its state from before it was powered down.
Broadcom®
November 5, 2015 • 43455-DS109-R
Page 27
BROADCOM CONFIDENTIAL
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