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.

[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.