CC2420 Power Consumption Measurements on the SPOTs

On the SunSPOT world forums, there was a query regarding the power consumed by the TI CC2420 radio transceiver. The SPOT has quite a bit going on and the power consumption is very dynamic. The only way I could see to get an accurate reading was to isolate the power into the radio chip. There is a ferrite bead, FB1, in series between the switcher and the radio VDD that could be removed and a milliammeter put in its place.


eSPOT main board CC2420 power

We found a working rev 6 eSPOT (s/n 2DA1) and loaded up red-090429 release. Del removed the bottom shield and ferrite bead and connected the test wires. We used a calibrated Agilent 34410A digital multimeter for the readings. This is a free range SPOT with eDEMO board and battery. It was battery powered during the test and the battery was fully charged.

Current testing CC2420


I used a program written by Syntropy for our FCC compliance test. This test can broadcast both modulated direct sequence spread spectrum and unmodulated carrier on channels 11, 18 and 26. The power output of the transmitter can be adjusted between 0dBm to -24dBm. The test receives on channels 11, 18 and 26 and will indicates packet errors in the LEDs.

The CC2420 is a transceiver - either the transmitter is on or the receiver is on but you cannot have both on at the same time. When the SPOT is active (not in deep sleep) the CC2420 draws 0.44ma without either transmitter or receiver enabled.

The receiver drew 18.57ma (ch11), 18.49ma (ch18) and 18.61ma (ch26) without a nearby transmission. The receive current drops about 30uA when receiving packets from a nearby transmitter. It did not vary noticeably if the packets were sent at low or high signal levels.

Transmit power drew at full output power modulated 18.24ma (ch11), 18.18ma (ch18) and 18.05ma (ch26). At full power unmodulated carrier, it consumed 18.04ma (ch11), 17.98ma (ch18) and 15.54ma (ch26). The higher power setting of ch26 is forced to a lower power output to be compliant with FCC emission requirements for the ISM band. The following is a graph of the current versus RF output power. There was very little variation switching between channels.

CC2420 transmit power


The measured transmit current of 18.24ma was higher by 0.82ma than the typical specification rating of 17.4ma. The measured receive current of 18.57ma was lower by 1.13ma than the specified typical of 19.7ma. The idle mode was slightly higher by 14uA with 440ua measured and 426uA specified.

There were minor rapid fluctuations of power during the test. The transmit power would fluctuate about 20-30uA and the receive current fluctuated <7uA (not including the variation caused by nearby transmitter). The values measured were average values over these fluctuations.

If there are other power measurements on the radio that need to be done, let me know. I'll keep this modified SPOT around for that.


Comments:

Bob:
In some work I've been doing on 802.15.4 and 802.11 sensor nodes, I find that the actual energy to send a packet is a small proportion of the total energy spent. Do you have the capability to put a 1-ohm resistor in there and put a scope on it, so you can watch the whole cycle (i.e. WAKE - DO SOMETHING - FORM PACKET - CCA - TRANSMIT DATA - GET ACK - GO BACK TO SLEEP) and estimate total energy consumption per wakeup? Thanks.

Posted by Daniel M. Dobkin on May 21, 2009 at 09:38 AM PDT #

Hello Sir,
Am working on energy consumption by different Chips in sleep, switching, tranmitting and reception. Sir could you please tell me value/energy/current required by following parameter of the CC2420
1. BitRate
2. Preamble size
3. potRx
4. potTx
5. potS1
Switching Times
6. Delay off listen
7. Delay off send
8. Delay Listen Send
9. Delay send off
Switching Energy
10.Energy off Listen
11. Energy Off send
12. Energy Listen send
13. Energy Listen off
14. Energy send Listen
15 Energy Send off

I would be highly obliged.
Thanks

Posted by Monica on May 21, 2009 at 05:49 PM PDT #

Hi Daniel and Monica,

Sorry for the delayed response, I was looking into for a way to do this.

After I did this blog entry, I sent my test SPOT to a University in Europe and don't have a test setup anymore. It looks like a special program would need to be written for the test. Do either of you have this programmed?

A few thoughts:
A 1 ohm resistor will have an 18mV signal for 18ma transmit/receive power, 20uV for 20uA fluctuations. My scope goes down to 20mV/div. You can increase the current sense resistance to a point but the voltage drop may impact the operation. I might use a 10 ohms which would be 180mV for transmit/receive with 200uV fluctuations.

Posted by Bob Alkire on May 30, 2009 at 08:30 PM PDT #

Hi,

I need to measure power consumption of CC2420 for different temperature range. The method which is give above requires programming in syntropy which i dont know how to do.

Could you please tell me how to do measure of power consumption by CC2420 in easier way or the way which involves measuring current, so that power could be calculated using (P=V\*I)or some other way ?

Posted by sunit verma on September 15, 2010 at 03:23 PM PDT #

I would like to find the power consumption for different transmit powers as well. The datasheet mentions the current consumptions. It also mentions the operating voltage to be between 2.1 and 3.6V. Any ideas if this operating voltage is constant for the different transmit powers?

Posted by D. Plets on January 06, 2011 at 10:58 PM PST #

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