Power Consumption Spike

[Vala]

Hi all,

I have seen thread related to this question such as this and this and I am aware that spikes happen due the automatically controlled refreshing mode of the DCDC. But I saw these spikes even before enabling the DCDC, after including the __WFE in the advertisement phase. So the question:

1- Can the spikes be related to LDO?

2- I see the same spikes also after enabling the DCDC. Are these actually related to the refreshing mode?

The spikes are happenning almost every 10ms. The sampling rate of the osciloscope is 500 ksps, so it is high enough to see all the spikes.

UPDATE: I see the spikes even after putting the MCU is the system off mode using NRF_POWER->SYSTEMOFF = 1;

[Stian Røed Hafskjold]

Yes, both the LDO and DCDC can operate in refresh mode. Actually, when DCDC is enabled it is still only started when it is more efficient than the LDO. Since the DCDC is drawing a constant base current, the LDO is always more efficient when the chip is in __WFE (nothing else running). Thus, what you see in your plots are LDO in refresh mode, even if you have enabled DCDC.

[Vala]

Thanks for your answer. I have two questions:

1- When I enabled the DCDC I noticed that the power consumption (in the exact frame that I uploaded the image of) is reduced about 0.3mA. Doesn't it mean that DCDC is taking the control? Beside the BLE advertisement in this frame of measurement, the CPU also wakes up every 50ms to control some LEDs. 2- What about when the CPU is in system off mode? Should there still be these spike at that time? Should I disable anything before it?

[Stian Røed Hafskjold]

1. If DCDC is enabled, the DCDC will start when needed. In your plot you have the radio events, and since these draw a lot of current the DCDC will be more efficient and start up. It switches to DCDC before the radio event and back to LDO after the radio event. Same thing when CPU is running. DCDC when CPU wakes up and LDO when it goes back to WFE. If DCDC is disabled, it will use the LDO all the time and consume more current during the radio events, hence the 0.3mA extra current.

2. In System OFF mode the regulator will operate in the same LDO low power mode (refresh mode) as when it is in System ON IDLE (WFE). So you will also see spikes in System OFF, but with a longer interval.

[Vala]

Thanks for the clear answer Stian.