High current consumption (2mA) in SystemOn and SystemOff Sleep (SDK16, no Softdevice) with some other peripherals.

RE: High current consumption (2mA) in SystemOn and SystemOff Sleep (SDK16, no Softdevice) with some other peripherals.

jhennrich — Fri, 15 May 2020 16:43:16 GMT

Thanks, that fixed it! I configured all /CS as output high and the overall current drain decreased to 11uA. That is already low enough for me, but when I have time I will do some calculations what all ICs in standby, the external voltage regulator and the voltage dividers *should* drain.

Another small mistake I made (just in case someone else reads this and has the same problem) at first was setting the /CS to output/high right after sending the standby command (via SPI) to the accelerometer. A nrf_delay_ms(1) between those commands solved the issue.

Lastly: setting for example the GPIOs connected to the LEDs to output/high or input/disconnected should make no difference I guess? In both cases there should be no current flowing...

RE: High current consumption (2mA) in SystemOn and SystemOff Sleep (SDK16, no Softdevice) with some other peripherals.

Stian Røed Hafskjold — Fri, 15 May 2020 08:25:14 GMT

Hi, the system OFF code you posted will "per definition" consume less than 1 uA.The default reset configuration for GPIOs are 0x2 (input, disconnected buffer), which means that they will not drive any external devices, hence no leakage current. The only leakage sources are pullups/down on SWD, and pull up on nRESET, so if the debugger is disconnected you should be fine. However, If the external devices require non-floating inputs, especially on CS, as hmolesworth mentions, they will probably be in a undefined state, consuming a lot of current if the output from nRF52 is floating.

RE: High current consumption (2mA) in SystemOn and SystemOff Sleep (SDK16, no Softdevice) with some other peripherals.

hmolesworth — Thu, 14 May 2020 22:44:04 GMT

Flash, Mag, pressure and accelerometer /CS signals i/o drive pins must all be configured as outputs and driven high since there are no pull-ups on the board. Without setting the pins they float, and although some SPI devices may have internal pull-ups on /CS most do not. Try and see if that makes a difference .. most likely the flash which always takes most current (/CS can float low if not driven):

"When /CS is brought low, the device will be selected, power consumption will increase to active levels"

The is a further issue with /CS on the flash, it must track rising VCC at first power-on: "The /CS input must track the VCC supply level at power-up and power-down (see “Write Protection” and figure 43). If needed a pull-up resister on /CS can be used to accomplish this."

On first power-on the nRF52 pins are floating and not driven; parasitic and pin capacitive loading will hold the /CS pin low so this should be considered a design flaw on the board.

RE: High current consumption (2mA) in SystemOn and SystemOff Sleep (SDK16, no Softdevice) with some other peripherals.

jhennrich — Thu, 14 May 2020 22:14:14 GMT

To further investigate the problem I wanted to see if the current drain is constant over time or consists of short bursts. For that I measured the current of the minimal example with a scope. I do not have current probes, so I put a 10 Ohm resistor in series to the battery and measured with regular scope probes across the resistor (so in the scope 10mV correspond to 1mA current drain).

For the first three test cases from my original post (1. "while(true) {}", 2. while(true) {__WFE(); }" and 3. "NRF_POWER->SYSTEMOFF=1; while(true) {}" the scope looks the same:

In the scope it looks like the current draw is very constant.