MRF24XA_15 Datasheet, PDF (237/258 Pages) Microchip Technology – Low-Power, 2.4 GHz ISM-Band IEEE 802.15.4™ RF

10.0 BATTERY LIFE OPTIMIZATION
In a battery-operated application, the device only
wakes up when it must transmit or requires to poll for
data. Polling is used for data reception as a means to
synchronize the remotely transmitting node to the
wake-up event in the receiver. Between transmission
and reception the device must be held in Deep Sleep
mode drawing less current than the battery
self-discharge, which is about 1 µA. Register contents
and internal Calibration state are maintained in Deep
Sleep mode for efficient power mode changes. Long
battery life is achieved through low currents in each
state of the device and a series of system features that
contribute to minimize the duration required for transmit
or receive.
The following enhanced features are used to minimize
radio ON time:
• High air-data-rates to minimize the packet
duration
• Automatic, on-the-fly, per frame, air-data-rate
adaptation in the receiver, allowing the transmitter
to select the highest data rate that fits the quality
of the link
• Minimized framing overheads in both the PHY
and the MAC layers
• Minimized ramp-up and turnaround times
• Short, still reliable channel assessment
• Automatically handled TX and RX signal paths
• Inferred destination addressing
On-the-fly, per frame air-data-rate detection is the
capability of the receiver to synchronize to the transmit-
ter data rate without knowing the sender of the frame
and the expected data rate in advance. On-the-fly,
per frame, air-data-rate detection gives the following
advantages:
• Each low-power node can use the highest data
rate allowed by its link quality to save its battery
charge. The evaluation of the link quality requires
MCU interaction.
• Multiple data rates are used within the same net-
work.
As opposed to conventional protocols supporting the
simultaneous use of multiple air-data-rates in the net-
work traffic, the frame header, which encodes the pay-
load data rate, does not use the lowest data rate.
Without this feature either the worst link defines the air-
data-rate that all nodes must use, or each node must
use the lowest data rate for the frame header, which
can severely compromise the throughput and battery
efficiency of the highest rates.
Passive listening, channel assessment and the dura-
tion of the turnaround between transmit and receive
contribute to the power consumption.
MRF24XA
In this regard, MRF24XA excels by minimized TX-to-
RX turnaround durations, fast but reliable channel
assessment and short PLL and AGC ramp-up dura-
tions. Power modes are automatically sequenced
during CSMA sending by the internal state machines of
the device without interaction from the MCU. These
mechanisms can optionally control external PA and
LNA.
The Message Chart in Figure 10-1 illustrates a typical
wake-up cycle:
1. While the low-power device is in Deep Sleep
mode, the coordinator listens to the channel and
buffers any messages addressed to the
low-power node.
2. The low-power node wakes up when must trans-
mit, or periodically to poll the coordinator for any
pending data.
3. First, the low-power node sends a poll
command to the coordinator and any data it
must send.
4. Low-power node can go back to Deep Sleep
mode as soon as it gets an ACK unless the coor-
dinator has buffered pending data. This condi-
tion is indicated in a specific bit field of the
acknowledge frame that the coordinator is
sending.
5. In the case of pending data, the low-power node
may want to turn off the radio for a pre-
determined duration allowing the coordinator to
retrieve the pending data for sending.
6. Finally, the coordinator turns to Receive mode to
get the pending data. On successful reception, it
turns to transmit to send an ACK and returns to
Deep Sleep mode.
7. Time-outs ensure that the low-power node does
not stay powered-up forever in the case when
the coordinator fails to respond in any of the
transactions above.
Figure 10-1 shows that all the radio activities are mini-
mized to immediately return to Deep Sleep mode.
As a result, the average current consumption is
reduced by multiple factors in comparison to the stan-
dard IEEE 802.15.4 operation. The comparison is done
for three corner cases as follows:
• Table 10-1 for polling without pending data
• Table 10-2 for polling with 80 octets pending data
• Table 10-3 for the transmission of 80 octets
A combination of the three cases allow evaluating the
energy budget of complex scenarios. A yearly 10 mAh
is to be added for battery self-discharge and Deep
Sleep mode. Equation 10-1 shows the self discharge
current calculation. The consumption of the MCU and
any sensors, displays must be added.
 2015 Microchip Technology Inc.
Preliminary
DS70005023C-page 237