Current Consumption in deep sleep mode: when the voltage goes below 1.5V current starts peaking to 300µA.

[Naveed]

Hi,

I am using nRF52832 board with the SDK version nRF5_SDK_15.3.0 and soft device S132.

I have implemented the POF(power fail comparator) to generate event when the event is set to the threshold 2V. I am successfully able to generate the event for the set threshold 2V.

When the event(NRF_EVT_POWER_FAILURE_WARNING) is generated, I am putting my device into the deep sleep mode. I have disabled all the configuration such as(GPIO's, GPIOTE, SPI and Flash) before calling the System OFF function as shown below.

void pof_sleep_mode_enter(void)
{
    uint32_t err_code = bsp_indication_set(BSP_INDICATE_IDLE);
    APP_ERROR_CHECK(err_code);
    // Disconnect all the GPIO's
   disableGPIOs();
   nrf_gpio_cfg_input(24,NRF_GPIO_PIN_NOPULL);//INT
   nrf_gpio_cfg_input(23,NRF_GPIO_PIN_NOPULL);//INT
   nrf_gpio_cfg_input(13,NRF_GPIO_PIN_NOPULL);//INT
   nrf_gpio_input_disconnect(24);
   nrf_gpio_input_disconnect(23);
   nrf_gpio_input_disconnect(13);
   nrfx_gpiote_uninit();
   flash_uninit();
   spi_uninit();
   /* Sleep mode */
   err_code = sd_power_system_off();
   APP_ERROR_CHECK(err_code);
} 

Given in the data sheet. 

The device can be put into System OFF mode using the POWER register interface. When in System OFF mode, the device can be woken up through one of the following signals:

1. The DETECT signal, optionally generated by the GPIO peripheral
2. The ANADETECT signal, optionally generated by the LPCOMP module
3. The SENSE signal, optionally generated by the NFC module to “wake-on-field”
4. A reset

Before entering System OFF mode, the user must make sure that all on-going EasyDMA transactions have been completed. This is usually accomplished by making sure that the EasyDMA enabled peripheral is not active when entering System OFF.

Observation:

After the voltage drops below the set threshold I can see the current consumption is around 3µA in the deep sleep mode and it start increasing slowly for the same threshold voltage 2V. But when the voltage drops below 1.4V to 0.9V there is a sudden peak in the current consumption around 200µA-300µA. What might be the reason for this behavior?

Is the device getting wakeup here again by any means? signals mentioned in the datasheet above? 

I don't want to wakeup my device by any signals, It should only be wakeup if the voltage is above the given threshold.

Can you please help me to understand what might be the reason for current consumption even if the device is put into deep sleep mode sd_power_system_off(). Am I missing something here in the configuration? Do I need add anything in the code?

Regards,

Naveed

[Turbo J]

At some point you will trigger a low voltage POR. Its not possible to operate the µC properly when voltage drops too low - back to the drawing board, you probably need to change the schematic.

See also V_BOR,OFF in the POWER section with electrical specs.

[Naveed]

Hi,

Thankyou for your quick response.

The data sheet states that a nominal voltage of 3V and a range of Min=1.7V to Max=3.6V are the recommended operating voltages.

Observed current readings are attached in the image below. For the defined threshold voltage VPOF=2V.

1. When the voltage is at 2.4V, I can see the constant oscillation here (from low 4µA to high 18µA). What could be causing the device to act in this way?

2. When the voltage hits the threshold voltage 2V current dropped to around nearly 3µA and device is put into the deep sleep mode(sd_power_system_off()). We can observe from the graph that the current reading increases progressively from 3µA to 49µA (and even up to 100µA).What might be the reason behind this device's behavior?

3. Is the device coming out of the deep sleep mode? Am I missing any configuration here before putting the device into deep sleep mode?

Can you please help me to understand what might be the reason for current consumption even if the device is put into deep sleep mode at 2V and the constant oscillations at 2.4V in the operating condition.

Regards,

Naveed

[Vidar Berg]

Hi Naveed,

The regulator will enter the auto-controlled refresh mode when in ultra low power mode ( Auto controlled refresh mode ), and I suspect you may be observing re-charging spikes. The current consumption should be around 0.6 uA in system OFF, which is well below what you are currently measuring. Is it possible that the sample rate in your measurement setup is too low to properly measure the spikes resulting in aliasing? The system OFF current should be measurable with a multimeter. 

[Naveed]

Hi,

Thankyou for your response.

I understood that the device is entering into refresh mode when in ultra low power mode by observing re-charging spikes in the graph (Box1 in the graph).

You said that, when the system is off, the current consumption should be about 0.6µA, yet in my situation, as shown in the graph (Box2, to be exact), this is not the case.

I'm using a Joule scope to measure the voltage and current values accurately. I still didn't find the answer for this.

1. When the voltage hits the threshold voltage 2V current dropped to around nearly 3µA and device is put into the deep sleep mode(sd_power_system_off()). We can observe from the graph that the current reading increases progressively from 3µA to 49µA (and even up to 100µA).What might be the reason behind this device's behavior?

2. Is the device coming out of the deep sleep mode? Am I missing any configuration here before putting the device into deep sleep mode?

Can you please help me to understand what might be the reason for current consumption even if the device is put into deep sleep mode at 2V.

Regard,

Naveed

[Vidar Berg]

Hi Naveed, please try with the system_off_pca10040.hex file I posted here:  current consumption is very high during sleep off mode in nrf52832 and see if you get the same result. I can't think of anything which can explain the gradual increase in power consumption as you observing.

Regards,

Vidar