Strange current spikes in nRF52 with RTC only

RE: Strange current spikes in nRF52 with RTC only

Mateusz Gancarczyk — Fri, 28 Jul 2017 08:43:39 GMT

It looks like you right. It's from power supply working in ref refresh mode. The spikes interval are 22ms, amplitude 35uA and rising edge ~25uS:

BTW: yes, my mistakes. In RTC prescaler shoudl be 32.

RE: Strange current spikes in nRF52 with RTC only

MartinBL — Fri, 28 Jul 2017 07:26:39 GMT

Hi,

Those short spikes are probably due to the nRF52's power supply working in ref refresh mode. Here is a quote from the current measurement guide:

The nRF52 power supply uses auto-controlled refresh modes to maximize efficiency. What this basically means is that a capacitor is recharged regularly to provide power to the chip. The recharge off the capacitor happens during a very short time interval, and results in a high frequency peak in current. This peak is measured to be about 10 - 15 us long. In order to get the correct average current during these peaks, a sampling frequency corresponding to half the peak length is required. This results in a minimum frequency of 200k samples per second (1 sample every 5 us).

BTW, aren't your RTC intervals closer to ~650ms? With a prescaler of 64 and a compare register value of MEASURMENT_TIME_MS = 333, you will get a f_RTC 32.768 / (64 + 1) = ~504 and hence, an interval of 333/504 = ~660ms.

RE: Strange current spikes in nRF52 with RTC only

Shahrear — Fri, 28 Jul 2017 05:00:46 GMT

Run a while loop with 1ms delay and test the power supply again. change the loop delay time and looks for spike. if spike vary depends on loop time it will be power supply's fault.

RE: Strange current spikes in nRF52 with RTC only

Mateusz Gancarczyk — Thu, 27 Jul 2017 20:23:17 GMT

It's from power supply directly for nRF52. I've use BL652-SA-01 module, so I measure current between pin VCC and GND.

RE: Strange current spikes in nRF52 with RTC only

Shahrear — Thu, 27 Jul 2017 19:17:47 GMT

Need more details.. this spikes across which pin?