nRF51 dongle's current consumption

[Johnson]

I programmed a nRF51 dongle as an ESB receiver using the esb_ptx_prx example code. It sleeps most of the time by calling __WFI() in the while loop.

I used an external 3.3 V power supply to VDD and measure the current consumption. The current was quite constant around 50 mA. Why is the current so high?

On the other hand, the transmitter (also a dongle) only drew 14 mA on average. On the scope, the current was 0 most of the time and peak to 15 mA during transmission.

At first, I thought it was the Segger chip that was drawing the extra current but the transmitter drew the expected amount of current.

[Stefan Birnir Sverrisson]

Hi Johnson

How do you measure current on the nRF51-Dongle? I see no documentation in the nRF51-Dongle User Guide on how to measure current, it is only present in the User Guide for nRF51-DK, which is intended for this purpose. Can you please describe your method on how you measure the current consumption on the nRF51-Dongle.

50mA is more than what the chip should be able to draw. If you have the radio in RX mode it should consume around 13mA. If you have everything else enabled as well, you will normally have around 20mA current consumption, maximum 25mA.

I measure the current consumption of the ESB RX example in nRF51 SDK and get current consumption of 17.3mA, and for the ESB TX example I measure 11.9mA on my nRF51-DK board.

After you flash the chip the current consumption is higher, because the chip is in debug mode. After you power reset the chip it should draw normal current.

For troubleshooting, you may benefit from looking at the current consumption guide, the Troubleshooting section.

[Johnson]

My current measurement method:

1. Powered the dongle using an external 3.3V power supply.
2. +3.3V was attached to the 3.3V pin of the dongle.
3. A 1 Ohm resistor was placed between the power supply ground and the dongle ground.
4. A multimeter was placed across the resistor to measure the DC voltage which translates directly to current.
5. An oscilloscope probe was also placed across the resistor to observe the transient response.

In my first test, dongle A (older one) was programmed as the receiver and dongle B (newer) as the transmitter. Current consumption: Dongle A (receiver): 58 mADC, peak 6 mA. Dongle B (transmitter): 0.03 mADC, peak 14.4 mA.

Then, I swapped them. Dongle A (transmitter): 43 mADC, peak 15.2 mA. Dongle B (receiver): 15 mADC, peak 6.4 mA.

It looks like the older dongle is "leaking current" while the newer one is behaving as expected. In both cases, the LEDs were off by setting the IO pins to high.

In nRF51-DK board, the current measurement pin is only attached to the power line going to the nRF chip which exclude the segger chip. But in the dongle, the same power line goes to both nRF and segger chips. I wonder if the segger chip was the cause. Yes, both dongles were power cycled after programming.

[Stefan Birnir Sverrisson]

Hi Johnson

Thank you for your clarification

Yes, if you measure current directly on the supply, you will be measuring current consumption of both nRF51 and the Segger, which will for sure add something to the current consumption. On the nRF51-DK, there are specific current measurement pins which exclude current going to the Segger chip and the LEDs, they only measure the current used by nRF51.

By old dongle you mean PCA10000? If so, it contains first or second revision nRF51 chip, which is not fully compatible with the latest SDKs. That might be at least partly a reason for the increased current consumption. See the nRF51 compatibility matrix to see what chip revision you have (compare with laser markings on the nRF51 chip) and what nRF51 SDK versions are compatible.

[Johnson]

They are both PCA10031. My apology for not being clear. The older one was purchased early this year and the newer one last month.

[Stefan Birnir Sverrisson]

Hi Johnson

Thank you for your clarification.

All PCA10031 dongles have third revision nRF51 chips, so their current consumption should be approximately the same. This might also be a variation in the Segger chip interface which leads to the higher different current consumption, I am not sure actually. Are the PCA10031 dongles the same version?

Measuring the current consumption on the PCA10031 this way is anyway not valid, since you do not know how much of the current is drawn by the Segger chip. I would recommend to purchase a nRF51-DK board in order to measure current on the nRF51.