NRF52832/52810 System OFF wakeup issue

[bevis]

Hi:

I test the system off mode, I attached a micro vibration sensor. Pulse generated when shaking as follow.

the button config is BSP example default(toggle) ,  i try to use  NRF_GPIO_PIN_PULLUP/NRF_GPIO_PIN_PULLDOWN/ NRF_GPIO_PIN_NOPULL ang BUTTONS_ACTIVE_STATE  One-to-one matching for test. and found when the input is high on hold or low on hold，the system always wakeup. it is true ???? 

[Einar Thorsrud]

Hi,

I did not fully understand the question, so please elaborate and ask again if the following does not answer it.

The GPIO sense mechanism can be used as a wake up source from system off mode, and it can detect either a high or a low level. This pulse can be quite short (exactly how short is not documented) and wake up the device from system off. So if you have a bit of noise on the input, then this will typically wake up the system.

[bevis]

As you said, the voltage between Rser and Rpull is logical low level < 0.7*VDD = 2.1. I'm adjusting 1.7V. When shake the vibration sensor, GPIO can detect the rising edge pulse to 1.7V - > 3V, because I set GPIO as the pull-up input. Because of setting up pull-up input, Rpull and GND generate a 100-200ua leakage current. This is very troublesome when it comes to system off. By the way, the sensor is also connected to GND.

[Einar Thorsrud]

I see. As mentioned, the nRF GPIO input is high impedance (unless you count the optional pull resistor, which is ~13 kΩ), so it is up to you to design a circuit that provided valid logic levels to the nRF.

[bevis]

I have tried 10K, voltage is 1.7V, shaking can produce 1.7V - > 3V rising edge pulse, but when the sensor is still off, leakage is about 200 ua. When I increase to 100K, voltage is 2.6V, shaking can produce 2.6 - > 3V rising edge, although the leakage current is reduced to 100ua, setting high sense at this time will lead to no access to s. System off, if sense low is set, the system will not wake up. Was the system off designed without considering that some sensors were on?Because this sensor is always on, it causes the leakage of the pull-up input. I changed to turn on mode when dormant 1.9ua, but the wake-up conditions I still need to induction logic level pulse, or to face the leakage problem, I do not know how to deal with now.

[Einar Thorsrud]

Hi,

The internal pull resistor is optional. You can disable it if you like, and in that case, the input is high impedance (virtually no leakage). So, it is entirely up to you to design the HW to match your needs.

[bevis]

What should we do? Are you talking about the high impedance state as pull-down input or something else? On the other hand, if I take an external pull-up input, in order to trigger the edge, my MCU must set no pull or pull down.

[Einar Thorsrud]

Hi,

The key thing is that the nRF GPIO can be configured with internal pull-up, pull-down or no pull resistor at all. This gives you full flexibility, so it is all up to you to design this. Please refer to my post from yesterday for suggestions about how you can do it.