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Texas Instruments Incorporated
Low-Power RF
Using the CC2430 and TIMAC for low-power
wireless sensor applications: A power-
consumption study
By Zin Thein Kyaw, Field Applications Engineer
and Chris Sen, Senior Software Engineer
Introduction
This article presents a power-consumption analysis of
devices in a beacon-enabled IEEE 802.15.4[1] network and
describes how to achieve the lowest power consumption
with TIMAC software. Network configuration parameters
are identified, and power consumption is measured on a
CC2430EM module against the theoretical maximum.
Customers of beacon-enabled Medium Access Control
(MAC) networks can use this article to select the most
efficient parameters for optimal battery life and an
acceptable data rate.
The test measurement and setup from Reference 2 have
been used to measure the power consumption of devices
studied in this article. It is assumed that the reader has
some basic understanding of IEEE 802.15.4 concepts and
terminology.
Network configuration
The designer of any wireless sensor application that has to
meet stringent battery-life requirements will have to pay
attention to the on-time duty cycle of the device. There is
a constant trade-off between battery life and duty cycle;
therefore, the goal is to minimize the on duty cycle in
order to maximize battery life.
Two network configuration parameters are essential to
determining the duty cycle of any device: the beacon
order (BO) and the superframe order (SO). BO deter-
mines how often the beacon is broadcasted; SO deter-
mines the on-time duration within the superframe struc-
ture. For this study, we have configured a network that
supports a BO equal to 7 and an SO equal to 0. Both para-
meters essentially dictate the battery life of each device in
the network.
The following sections explain how this network config-
uration affects the power consumption of the coordinator,
or full-function device (FFD), and the reduced-function
device (RFD).
FFD configuration
Nominally, the FFD will be awake for only a period of time
during every beacon interval (BI), then go back to sleep if
it has nothing else to do. Using a BO of 7, we can calculate
the BI to be 1.966 seconds:
BI = aBaseSuperframeDuration × 2 BO symbols,
where aBaseSuperframeDuration is 960 µs and each sym-
bol is 16 µs. The data can be exchanged only immediately
after a beacon, so the BI is also an approximate data-
response time when a device is requesting data exchange.
The next step is to determine the superframe duration
(SD), which determines how long the device is awake dur-
ing the contention access period (CAP). For an SO of 0,
the SD is approximately 15 ms:
SD = aBaseSuperframeDuration × 2 SO symbols.
An SO of 0 was selected to minimize the ON time for
the device during the CAP. The SO can be increased to
allow more packets to be transferred during the CAP at
the expense of higher power consumption.
RFD configuration
The RFD is typically a sensor device. For example, a tem-
perature sensor can be configured to report temperature
data to the FFD once a minute. The RFD wakes up only
when it has to transmit its payload to the FFD. The sensor
device will typically have a more stringent power-
consumption requirement than the FFD, so it cannot be
awake for every BI or the battery will be drained very
quickly.
The periodic report interval is accomplished at the
application layer by starting an application software timer
expiring at the desired interval. When the RFD is awake, it
generates an MLME-SYNC.request primitive with the
TrackBeacon parameter turned off. This will trigger a one-
time SYNC request so that the sensor can receive the bea-
con from the FFD, transmit the payload data, then go
back to sleep. The data is assumed to be around 50 bytes.
The application software timer can be configured to match
the application’s throughput and power-consumption
requirements.
17
Analog Applications Journal
2Q 2008
High-Performance Analog Products
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Low-Power RF
Texas Instruments Incorporated
Power-consumption analysis
FFD power consumption
Figure 1 shows a power-profile scope plot of the FFD at
every BI.
Total time on = 18.87 ms
Total time in low-power mode
= 1.966 s – 18.87 ms = 1966 ms – 18.87 ms = 1947.13 ms
Current consumption during low-power mode (CC2430
PM2) = 0.0005 mA × 1947.13 ms = 0.973565 mA ms
FFD power-consumption calculation
The measurement of the voltage drop across a series resis-
tor results in a voltage plot that relates to calculated cur-
rent levels over various time intervals. Except for using a
13.3-
Total inactive + active power consumption
457 58
00000
.
mA ms
i
-4
=
=
1.27
×
10
mAh drawn per BI
resistor, the test
setup in Reference 2 is used here as well as for the calcu-
lations for current consumption during each interval. The
capture is marked with 6 different intervals.
Comsumption
(mA • ms)
Ω
sense resistor in place of the 10-
Ω
36
ms/h
1.27 × 10 -4 mAh drawn per BI × 30 BI/min × 60 min/h
= 0.22879 mA
If we assume that two AA batteries with 3100-mAh true
capacity are used, then
31 mAh
22879 mA
00
1. Start-up sequence:
5 mA
×
0.34 ms
= 1.70
=
13549 h
=
564 days
=
1.5 years.
2. MCU on:
12 mA × 2.5 ms
= 30.00
0.
3. Radio on, Tx mode:
27 mA
×
0.83 ms
= 22.41
4. Radio on, Rx mode:
27 mA × 14.75 ms
= 398.25
5. MCU on:
12 mA
×
0.25 ms
= 3.00
6. Shutdown sequence:
5 mA × 0.2 ms
= 1.25
Total active power consumption
= 456.61
Figure 1. Power profile of FFD
4
3
5
2
6
1
Time (2.5 ms/div)
18
Analog Applications Journal
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2Q 2008
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Texas Instruments Incorporated
Low-Power RF
RFD power consumption
Figure 2 shows a power-profile scope plot of the RFD
during the SYNC request and data-transmission phase.
The data payload length is 50 bytes.
RFD power-consumption calculation
The measurement of the voltage drop across a series
resistor results in a voltage plot that relates to calculated
current levels over various time intervals. Except for using
a 13.3- Ω sense resistor in place of the 10- Ω resistor, the
test setup in Reference 2 is used here as well as for the
calculations for current consumption during each interval.
The capture is marked with 9 different intervals.
Comsumption
(mA ms)
Total time on = 29.54 ms
Total time in low-power mode
= 1 min – 29.54 ms = 60000 ms – 29.54 ms
= 59970.46 ms
Current consumption during low-power mode (CC2430
PM2) = 0.0005 mA × 59970.46 ms = 29.98523 mA ms
Total inactive + active power consumption
514 69 mA ms
36
.
i
−
4
=
=
1.43
×
10
mAh drawn per min
00000
ms/h
1.43 × 10 -4 mAh/datagram × 1 datagram/min × 60 min/h
= 0.008578 mA
If we assume that two AA batteries with 3100-mAh true
capacity are used, then
5 mA × 0.34 ms
1. Start-up sequence:
= 1.70
2. MCU on:
12 mA × 10 ms
= 120.00
00
000
31
mAh
8578 mA
27 mA × 4 ms
3. Radio on, Rx mode:
= 108.00
=
361389 h
=
15057 days
=
41 years
.
.
4. MCU on:
12 mA × 2 ms
= 24.00
This far exceeds the shelf life of the AA battery.
27 mA × 2 ms
5. Radio on, Rx mode:
= 54.00
6. Radio on, Tx mode:
27 mA × 2 ms
= 54.00
If we assume that a coin-cell battery with 50-mAh true
capacity is used, then
7. Radio on, Rx mode, listen
for acknowledgment:
27 mA × 1 ms
= 27.00
5 mAh
0.008578 mA
0
=
5828 h
=
242 days
.
12 mA × 8 ms
8. MCU on:
= 96.00
9. Shutdown sequence:
5 mA × 0.2 ms
= 1.00
Conclusion
This article has provided a power-consumption analysis for
CC2430-based devices in a beacon-enabled network run-
ning TIMAC software, for a
given set of network configu-
ration parameters. The analy-
sis shows that the stringent
battery-life requirements for
sensor applications can be
easily met.
References
1. IEEE Standard 802.15.4-
2003.
2. B. Selvig, “Measuring Power
Consumption with
CC2430 & Z-Stack,”
Application Note AN053
TI lit. number . . . .swra144
Total active power consumption
= 484.70
Figure 2. Power profile of RFD
3
4
5
67
8
2
9
1
Time (2.5 ms/div)
19
Analog Applications Journal
2Q 2008
High-Performance Analog Products
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