nrf52 > nrf51 power

[Ray]

I have looked around but have been unable to find doc explaining this. If there's something around, I'd truly appreciate a pointer.

I have an existing (solar powered) device that has been built using the nRF51822 + sdkv11 + s130.

In the stable test case that I use to benchmark, the steady-state draw is 0.456mA.

I am trying to upgrade to nRF52832. The hardware works quite well except for power.

My first attempt, of course, was to take the exact same nRF51822+sdkv11+s130 image and to load it onto the nRF52. It works quite well, and the power consumption is comparable or better than the nRF51 hardware.

I need to upgrade to the nRF52 natively, though, because I need the memory and speed. However, when I build the exact same code for nRF52+sdkv11+s132, the power draw is substantially more.

The first problem I ran into, and I just thought I'd let you and others know for posterity, is that in my nrf_drv_config.h I had decided to try easy_dma for the UART. Bad decision. When I turn on uart easy_dma, the current draw is 2.153mA. When I revert to "legacy", the current draw is back to 0.490mA. I am thus not blocked on this, and it's just an FYI that easy_dma represents a power regression.

The blocking issue I've run into, however, is TWI.

On the nRF51+sdkv11+s130, there is little or no power draw overhead by having TWI enabled, or by using it, so long as all devices you try to access actually exist on the bus.

However, on the nRF52+sdkv11+s132, the moment you do your first transfer (which is successful in my case), the power consumption skyrockets by approximately 5mA, and just stays there.

(No, I am not using easy_dma with TWI.)

Does anyone have a pointer to info that might explain this and potentially fix it? My hardware simply doesn't have the budget for 10x the power draw of the nRF51+s130. For now, I'm sticking with using the nRF51+s130 on the nRF52; assistance moving forward would be appreciated.

[Einar Thorsrud]

The current consumption numbers you write are higher than I would expect, even with the known errata. What other chip resources are active when you measure power? Is the CPU active or is the chip in a low power mode? Are you measuring the current consumption of only the chip, or does your measurements also include current consumption of other components on the board?

Are you using GPIOTE? The fact that you see an issue the moment you start the first TWI transfer leads me to think this is due to erratum 89. If that is the case, the following workaround should do the trick:

Turn the TWI off and back on after it has been disabled. To do so, write 0 followed by a 1 to the POWER register (address 0xFFC) of the TWI that needs to be disabled. Reconfiguration of TWI is required before next usage.