Standby current consumption waiting for connection

[Matt Brown]

I'm trying to evaluate a Nordic BLE module for a new battery powered project while waiting to establish a connection to a base station device. It seems like your lowest powered devices might be something like the nRF52805, though if you want to suggest a different part I would be willing to look at it.

I believe the best description of the mode I want to use the device in is that primarily the module will be in sleep mode and perhaps once a second will wake and listen for incoming packets from the base station for a short period before turning back off. I'm trying to characterize what this power draw might look like and am just looking for some help with some of the timing characteristics or anything else I may not be aware of. 

If I understand the datasheet correct, in sleep mode with RAM retention, the device might draw 1.4uA (per Ion_ramon_rtc) while waiting to wake from RTC. Then perhaps once a second would wake and be in receive mode drawing 7.6mA (per Is2), so the total power draw per second might look like a superposition of those two power draw. If the receive time is as short as 50ms, for that time, it would draw 7.6mA and for the other 950ms, it would draw 1.4uA. 

My question is threefold.

1) Would a scheme like this accurate estimate the power draw of this device?

2) Could you suggest a timing period that might portray a real world use case similar to this one? (BLE transmission periods are somewhat new to me)

3) Is there already a characterized power number that more accurately gives this sort of information or anything else you'd recommend I consider.

Thanks in advance,

Matt Brown

[ovrebekk]

Hi Matt

We provide an online power profiler for the nRF52 series which should answer most of your questions. You can choose a chip in the nRF52 series, and see average current consumption and battery life in various Bluetooth scenarios such as advertising and connected mode. 

The scenario you describe is basically a low duty cycle advertising scenario, where you wake up at a regular interval (between 20ms to 10 seconds), send an advertise packet, and wait for a scan or connection request from a nearby BLE central device. With the profiler you can experiment with different wakeup intervals, TX output power, payload bytes etc and see how it affects average current. 

Please note there is no nRF52805 option in the power profiler, but the nRF52810 has essentially identical current consumption numbers and you can use this instead. 

Best regards
Torbjørn