RE: NRF51822 : is that a normal power consumption

Stian Røed Hafskjold — Mon, 07 Nov 2016 14:50:37 GMT

Yes, that is correct. You can reduce the consumption a bit by choosing a PWM frequency that allows the TIMER module to use the 1MHz peripheral clock instead.

RE: NRF51822 : is that a normal power consumption

julienh — Thu, 03 Nov 2016 17:02:22 GMT

Thank you for this theorical consumption study.

In my case, the PWM is updated each second and is always on so I will have 500uA power consumption in continue right?

RE: NRF51822 : is that a normal power consumption

Stian Røed Hafskjold — Tue, 01 Nov 2016 15:54:25 GMT

PWM
Since the nRF51 doesn't have a PWM module, the PWM library uses a TIMER to toggle a GPIO according to the PWM frequency. The TIMER module requests the HFCLK. Since you are using BLE/SoftDevice, you already have a HF crystal on your board. So then the PWM timer will be using the HF crystal.

Run currents for PWM (timer and 16mHz crystal):

I_TIMER + I_X16M = 30uA + 470uA = 500uA

BLE
The base current when running the SoftDevice consists of System ON base current, LFCLK run current and RTC run current. Then you have the radio and CPU usage every adv/con interval, this varies with the adv/con parameters you specify. The numbers below are based advertising with 0dBm TX power and full payload (31 byte)

Base current:
I_ON,32k + I_X32k + I_RTC = 3.8uA + 0.7uA + 0.1uA = 4.6uA

Total charge for one advertising event, 0dBm, 31 byte (includes radio and CPU):
27uC

1200 ms advertising + base current gives an average current of:
27uC / 1200 ms + 4.6uA = 27,1 uA

So to sum up, average current during advertising with PWM library running is 500uA + 27uA

When not using PWM, the HFCLK will only be active during the BLE event (about 4 ms), and will reduce the average current significantly.

I would say that the CPU time used to update the PWM is so small that the current is negligible compared to the other currents.