nRF52 battery consumption estimate

[Mufasa1]

Hi guys, I am trying how figure out the the devzone.nordicsemi.com/.../ works or ecuations to estimate the battery life using a central module.

My central device is battery powered and it goes from deep sleep to active each 10mins transmitting a Write to a peripher 20bytes and an indicate to the central 12bytes size. The connection time is about 50ms and the peripheral advertising interval is 20ms.

I am trying to calculate it in the following way:

RF transmitting = 8.1mA RF listening = 6mA

A average RF transmitting/reciving is 7mA per sec using DCDC enabled Sleep mode is 4uA per sec

estimate RF activity = ( 7mA x 0.05s)

Estimate Sleep mode consuption = 4uA x 3600s x 10s)

Estimate consumption = Estimate RF activity + Estimage Sleep mode consumption

Estimate Battery life = battert capacity / estimate cosumption

Is iit a correct way to estimate the battery life?

Thanks.

[Hung Bui]

Hi Mufasa,

Please correct me if I'm wrong. You are trying to measure current consumption for the central, not the peripheral ?

Do you have your peripheral advertising all the time? I have to ask because we need to estimate the time it take for the central to scan and connect to the peripheral.

You have the connection time of 50ms, but we don't know how long would it take to do scanning before the connection.

My suggestion for the calculation is:

Average current consumption = Estimate RF activity in connection (use the online tool for it) *50ms + Estimate RF activity for scanning (7mA) * the time estimated to scan and establish connection + Deep sleep current * 10minute - (50ms + scanning time) / 10 minutes

Note that, to be on the safe side, you should calculate with 70% of battery capacity as most of the time the listed capacity is only for optimized condition.

[Mufasa1]

Hi Hung, Yes, I have a peripheral adverising all the time to the central. The central is the most the time in sleep mode (10mins), wake up start the scan for 100ms if the peripheral is visible it connected, exchange data over BLE (last 50ms) and disconnect to goes to sleep again for 10mins.

There is a RF activity window of 100ms. When the central starts to scann and if the connection happens inside the 100ms.

I would like estimate a CR2032 (240mAh) life

Sleep time: 4uA (measure using a amperimeter)

Sleep duration: 10mins

RF activity/Scann: 7mA (peak measure using a amperimeter)

RF duration: 50ms (sniffing)

After use your ecuation do I have to: BatteryLife =BatteryCapacity /Average current consumption? the results are in hours or seconds?

[Hung Bui]

I forgot to ask if you measured the RTC current to count the time the board in sleep mode ? 4uA is included the RTC or not ? Have you tried to check in the datasheet if 4uA match with what stated there ?

My calculation for your setup would be: We assume it would take 100ms for scanning before the connection can be established, it could be smaller.

Current consumption = (7mAx0.1s + 0.735mA (as in the online calculator for peripheral, similar value can be used for central) 0.05s + 0.004mA(600s-0.15s) )/ 600s = 0.0041215 mA.

The estimated battery life will be 240mAh/0.0041215mA = 58231 h = 2426 days. Given other factors such as temperature, current leakage, self discharge over time, you should use 70% of this estimation, meaning around 1698 days.

You can see that the most important number is the sleeping current, if you can reduce sleeping current you can improve battery life a lot. Next factor is the peak current. I would suggest you to have a look at this interesting article made by one our staff: m.eet.com/.../c0924post.pdf

[Mufasa1]

Awesome Hung, Thanks for the useful help :)

My sleep mode current value (4uA) is a measure using a tester when the device is in sleep mode for 10mins. I am not consideringthe RTC current because I am measuring the consumption direclty in sleep mode. The difficult for me was have a real value when exist a RF activity

[Hung Bui]

How do you wake the chip up every 10 minute ?

To measure the current consumption the more practical way is to use a Power Profiler Kit and measure the DUT over time. Not sure 10 minute period is possible with the kit, but you can measure the RF active time only.