Low power beacon

[agishii]

Hello,

I am making a low-power beacon.

I am using NRf52832 module with external crystal. No extra device.

I use SDK 14.2.0, because it's much easier than 15.3 for making a broadcaster system.

When I compile and load the sample of "ble_app_beacon", a current of 40 mA 3.5uS flows periodically. I attached the screen shot as below.

This current flows at 200uS intervals during the transmission of radio waves.

What is this for? How can I stop the current consumption?

I set logging stopped. Disable LED. Set external xtal as " NRF_SDH_CLOCK_LF_SRC 1".

[Turbo J]

What is your power source?

Ar CR2032 or similar coin cell with high internal resistance needs reservoir capacitors (around 100µF, more is better).

Otherwise the voltage drops significantly every time the NRF chip turns on CPU or radio peripherial, since the battery cannot follow these fast current changes.

Do you use the integrated DCDC switching mode regulator? If yes, these spikes might just be the DCDC startup shortly before the radio event. But that is just a wild guess at this point...

[agishii]

Hello Turbo,

Thank you for reply. You know a lot about battery-powered circuits.

Looking at your answer, I momentarily thought it was DCDC power. But, I am using DCDC via LiPo, but the current measurement is between DCDC and BLE. So, I think that this 200uS cycle current consumption is used in BLE.

[haakonsh]

I think your measurements are off by a factor of 10x to high. 

The TX current will be ~60mA with respect to the 40mA spikes, which fits well with ~6mA TX current of the radio with DCDC enable and transmitting at 0dBm. 
See ITX,0dBM,DCDC in Radio current consumption (Transmitter). 


If that's the case then those 40mA spikes would be ~4mA, which fits well with the CPU run current of ~4mA with DCDC enabled. 
See IDDFLASHCACHEDCDC in CPU performance.

What's the resistance of the series resistor you're using for the measurements? 

[agishii]

Hello, 

This has been resolved. After all, it was caused by DCDC switch noise. In the case of CR2032 + 100uF or AAA alkaline battery, no noise appeared. Thank you for your cooperation.

When using a LiPo battery or AC adapter, noise occurs when the power source voltage is significantly different from the target voltage.

Below is using AAA battery.