MRF24WB0MA_13 Datasheet, PDF (13/38 Pages) Microchip Technology – MRF24WB0MA/MRF24WB0MB Data Sheet 2.4 GHz IEEE 802.11b™

MRF24WB0MA/MRF24WB0MB
2.3 Power States
The MRF24WB0MA/MRF24WB0MB has the following
power states: Hibernate, Sleep and Active (two sub-
states), as shown in Figure 2.4. The selection of power
state affects system behavior, and overall power con-
sumption or battery life. Addition to that there is one
“Standby” state that is not user-controlled.
FIGURE 2-3:
MRF24WB0MA/MRF24WB0MB POWER-STATE DIAGRAM
Off
Hibernate
Note 1
Note 1
Standby
RX On
10 µs
TX On
200 µs
200 µs
Note 1: See Section 2.2, Power-On Sequence.
2.3.1 HIBERNATE STATE
An “Off” state is defined as no power applied to the
device. The Hibernate mode is the closest to controlled
off that the module can approach. It is controlled
through the HIBERNATE pin (high input puts the
module into Hibernate). When in Hibernate, the module
only consumes leakage current, but does not maintain
state. Hibernate has to be fully controlled by the PIC
MCU and requires the TCP/IP stack to restart on an
awake.
The module contains about 70µF of internal bulk
capacitance. Supplies should be provisioned to supply
sufficient charge on release of hibernate for required
start time or sufficient delay must be provided in
software after hibernate release and before Reset
release.
This state provides the best battery life for embedded
products. Entering Hibernate for intervals of less than
30 seconds is not likely to save power. Battery life
expectation can be more than a year for devices
operating on AA cells that is in Hibernate except to
wake up every hour for a small data transfer (<500
Bytes).
Sleep
2.3.2 SLEEP STATE
The Sleep state is a low power dynamic state that
implements the 802.11 Power Save feature. In this
mode, if enabled, the module will enter Power Save
mode when all activity is complete.
The module will wake autonomously to any PIC
intervention to check DTIM beacons from the Access
Point (AP). If any traffic is listed as queued for the
module, then it will awaken and get the data from the
AP on the next possible opportunity. When data is
acquired, the module will interrupt the PIC
microcontroller on a normal “data available” indication.
If no data is available on a DTIM check, the module
reenters the Power Save state until the next DTIM. The
DTIM interval is programmed at the AP. This state can
provide “as if on” behavior of the radio with a significant
power savings versus “always on”. The battery life
expectation of this mode is several days to several
weeks. This mode is characterized by a very-low
latency (as low as 200 mS) to begin data transfer from
the low-power state.
2.3.3 ACTIVE STATE
The Active state is identified as one of the two states
where the radio circuitry is fully on. The two active
states are the Receive state (RX ON) and Transmit
state (TX ON).
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DS70632C-page 13