Start-up power consumption / nRF51-DK - PCA10005

[Michael]

Hi,

I've got a question about the startup-process and power consumption using BLE&Advertising (sample code: nrf51-ble-tutorial-advertising)

I've got the "new" nrf51-DK and the "old" nRF51822-Development-Kit, compiled the code with Keil and flashed it on both devices (nRF51-DK Board and PCA10005). Then I've done some initial measurements about the power consumtion during start-up and advertising.

What I've noticed:

• comparing the current measurement of the nrf51-DK and PCA10005 (center and right on the picture), it seems like the nrf51-DK is going in sleep mode right away, while the PCA10005 draws 1mA for 400ms. So my first question is if anyone can explain this different behavior (although it's the same code) ?
• Also, I want to understand what happens between 400-470ms after power reset (marked orange in the picture) where the MCU draws about 1mA. My first guess is that it's due to the initialisation of the radio, right ?
• using the nRF51-DK& measuring the input current at the "External supply pins" (left on the picture), there is a huge input current of 80mA over 42ms. As this peak isn't measurable at the "nRF current measurement pins" (where you measure only the current of the nRF51422 MCU itself as I undestand), I think the 80mA are drawn by other electronics on the board (maybe the Segger MCU ?). Is there any jumper or "solder bridge" where I can disable all other electronics on the board and use only the nRF51422 ?

Best regards.

Measurements:

PS: Some background of my application: I want to build a proof-of-concept "energy self-sufficient" sensor which charges a capacitor over a few minutes and then starts the microcontroller with BLE. So a low start-up energy is important as the capacitor has to store nearly all energy to start the microcontroller and power it while advertising, as the energy source can power the microcontroller only in sleep mode (plus charge the capacitor a little bit).

[Stefan Birnir Sverrisson]

Hi Michael

Thank you for your questions and the easy to understand images

I know that when you initialize the softdevice you have to wait for ~400ms for it to finish. The reason is that it takes a long time to start up the low frequency 32kHz crystal. The low frequency crystal is not causing the high current consumption on the second revision chip however, it consumes only ~1uA. 1mA extra current is often the high frequency 16MHz clock to blame, either the crystal or the RC oscillator, it is enabled for some reason. To find out what is going on I have a few questions:

• Are you flashing the same firmware and softdevice for both second and third revision chips?
• What firmware are you using?
• What softdevice are you using?
• Are you using an example from the SDK? If so, which SDK version?

You can see in the compatibility matrix what softdevices and SDKs are compatible with the different nRF51 chip revisions.

What happens if you flash an example from SDK 6.1.0 to the second revision nRF51 board as well as softdevice 7.3.0? do you still see the same current consumption at startup?

It is normal that the Segger chip draws a lot of current. When you measure on the "External supply" pins then you get the combined current consumption of the nRF51 and the Segger chip. Therefore you should always measure current on the "nRF current measurement" pins. There is no option to turn of everything else on the board. If that option would be available, you would measure the same current consumption on the "external supply" pins and the "nRF current measurment" pins.

[Jay Tyzzer]

Hi Michael,

In addition to Stefan's questions, can you look at the marking of the Nordic device? This info can be used to determine the rev number using the compatibility matrix Stefan mentioned above. It could be that you are also comparing Rev 1 Silicon vs. Rev 3 silicon. Rev 3 silicon is what is mounted on the nRF51-DK. The Rev 3 silicon's CPU is also lower power then the first 2 revisions of the device.

The DC/DC converter was also "fixed" on the Rev 3 part as well. Just in case you wish to use the DC/DC.

Errata and PAN's are available on the Nordic website on all three revisions of the part. I suggest using the Rev 3 parts. Rev 1 devices are not recommended for new projects and those and the Rev 2 devices will be phased out over time. ~~ Jay