MRF24WB0MB datasheet(13/38 Pages) MICROCHIP

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DS70632C-page 13

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

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).

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).

Note 1: See Section 2.2, Power-On Sequence.

Off

Hibernate

Standby

RX On

TX On

Sleep

200 µs

10 µs

Note 1

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