Peak current when BLE-TX/RX and CPU run simultaneously

[Saeed Ghasemi]

Hi!

My question is for the purpose of power calculations for both the nRF52832 and nRF52840 for BLE use only.

I haven't been able to find a reference for this.

I see that the current requirement for the CPU is ~7mA and the BLE TX is at 8.7mA (from memory).

Do these devices TX or RX while the CPU is running, so that the peak current is around ~15mA?

We want to see what to expect when a CR2032 reaches low voltage and the internal resistance gets high. We are concerned about the brown-out-detector getting triggered at these levels and need to know the lowest possible voltage that we can run with on the battery!

Are these two events serialized by the hardware (is the CPU halted when TX or RX) ?

Thanks.

[MartinBL]

Do these devices TX or RX while the CPU is running,

Yes. You need to account for the possibility that the CPU is running while the radio is also active. But make sure you read up on the electrical specs and different ways of optimizing power. If you chose to utilize the internal DCDC regulator and TX at 0 dBm then you are looking at these values:

IRX,1M,DCDC

RX only run current (DCDC, 3V) 1Msps / 1Msps BLE

5.4

mA

ITX,0dBM,DCDC

TX only run current (DCDC, 3V)PRF = 0dBm

5.3

mA

IDDFLASHCACHEDCDC

CPU current, running from flash, cache enabled, DCDC 3V

3.7

mA

Worst case is 9.1 mA with RX and CPU only concurrently.

[Saeed Ghasemi]

Hi MartinBL!

Thank you for the detailed response.

I wonder there is known way of trying to halt the CPU at a specific time to avoid concurrent TX and CPU run, without delaying for too long. (like making a TX and sleeping the CPU for 10 ms. 10 ms being the connection interval.) ?

It could be nice to receive an interrupt 100us before a TX with a TX duration.

[MartinBL]

Hi,

You might look into Radio Notifications. It can be used to figure out when the radio is ramping up. I suppose you can use this to pause whatever tasks the CPU might be doing at the time. 

Here is a relevant (but old) tutorial.