High current consumption offset when using internal RC oscillator as compared to crystal oscillator for low frequency clock.

[Kiara Navarro]

Describe the bug

When trying to sleep core on NRF52805 using low frequency internal rc oscillator, average current consumption is ~189.50 uA while when using external crystal oscillator, average current consumption is ~ 8 uA. 

I can't provide actual application code that I'm running, however, the only difference at Kconfig level it's whether to decide which low frequency crystal is used. I tried to get into the errata section to find out if it was something related to it but it doesn't. Also, I do not have UART enabled, and verification have been made to confirm that there is no GPIO line floating. 

How to reproduce

Chip model: NRF52805 CAAA

os: Linux / GNU

sdk-nrf tag: v1.5.1, v1.4.0

Microcontroller is using System ON and DC-DC is enabled

• Use internal rc crystal oscillator
  • remove extra capacitors and crystal connected to xtal pins
  • leave extra capacitors and crystal connected to xtal pins
• Measure current consumption going into NRF52805
• prj.conf:
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    CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y

    CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n

    CONFIG_CLOCK_CONTROL_NRF_K32SRC_SYNTH=n

    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
    CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n
    CONFIG_CLOCK_CONTROL_NRF_K32SRC_SYNTH=n

• Extra configurations:
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    CONFIG_CLOCK_CONTROL_NRF_CALIBRATION_LF_ALWAYS_ON=n

    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    CONFIG_CLOCK_CONTROL_NRF_CALIBRATION_LF_ALWAYS_ON=n

• When device sleeps and debugger is connected these are the register values:
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    Fields in CLOCK > LFCLKSTAT:

    SRC: RC 32.768 kHz RC oscillator - Source of LFCLK

    STATE: Running LFCLK running - LFCLK state

    Fields in CLOCK > HFCLKSTAT:

    SRC: RC 64 MHz internal oscillator (HFINT) - Source of HFCLK

    STATE: Running HFCLK running - HFCLK state

    Fields in CLOCK > LFCLKSRC:

    SRC: RC 32.768 kHz RC oscillator - Clock source

    Fields in CLOCK > HFCLKSTAT:

    SRC: RC 64 MHz internal oscillator (HFINT) - Source of HFCLK

    STATE: Running HFCLK running - HFCLK state

    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    Fields in CLOCK > LFCLKSTAT:
    SRC: RC 32.768 kHz RC oscillator - Source of LFCLK
    STATE: Running LFCLK running - LFCLK state
    Fields in CLOCK > HFCLKSTAT:
    SRC: RC 64 MHz internal oscillator (HFINT) - Source of HFCLK
    STATE: Running HFCLK running - HFCLK state
    Fields in CLOCK > LFCLKSRC:
    SRC: RC 32.768 kHz RC oscillator - Clock source
    Fields in CLOCK > HFCLKSTAT:
    SRC: RC 64 MHz internal oscillator (HFINT) - Source of HFCLK
    STATE: Running HFCLK running - HFCLK state

One way to quickly reproduce the behavior it's modifying system off sample on zephyr samples: 

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/*

* Copyright (c) 2019 Nordic Semiconductor ASA

*

* SPDX-License-Identifier: Apache-2.0

*/

#include <stdio.h>

#include <zephyr.h>

#include <device.h>

#include <init.h>

#include <power/power.h>

#include <hal/nrf_gpio.h>

#define CONSOLE_LABEL DT_LABEL(DT_CHOSEN(zephyr_console))

/* Prevent deep sleep (system off) from being entered on long timeouts

* or `K_FOREVER` due to the default residency policy.

*

* This has to be done before anything tries to sleep, which means

* before the threading system starts up between PRE_KERNEL_2 and

* POST_KERNEL. Do it at the start of PRE_KERNEL_2.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

/*
 * Copyright (c) 2019 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <stdio.h>
#include <zephyr.h>
#include <device.h>
#include <init.h>
#include <power/power.h>
#include <hal/nrf_gpio.h>

#define CONSOLE_LABEL DT_LABEL(DT_CHOSEN(zephyr_console))

/* Prevent deep sleep (system off) from being entered on long timeouts
 * or `K_FOREVER` due to the default residency policy.
 *
 * This has to be done before anything tries to sleep, which means
 * before the threading system starts up between PRE_KERNEL_2 and
 * POST_KERNEL.  Do it at the start of PRE_KERNEL_2.
 */
static int disable_ds_1(const struct device *dev)
{
	ARG_UNUSED(dev);

	pm_ctrl_disable_state(POWER_STATE_DEEP_SLEEP_1);
	return 0;
}

SYS_INIT(disable_ds_1, PRE_KERNEL_2, 0);

void main(void)
{
	int rc;
	uint8_t i;
	const struct device *all_devices;
	static volatile uint16_t devices_count;
	devices_count = z_device_get_all_static(&all_devices);

	for(i = 0; i < devices_count; ++i)
	{
		rc = device_set_power_state(&(all_devices[i]), DEVICE_PM_LOW_POWER_STATE, 0, 0);
	}
	k_sleep(K_MSEC(1000000));

	printk("ERROR: System off failed\n");
	while (true) {
		/* spin to avoid fall-off behavior */
	}
}

Expected behavior

To have similar results on current consumption as when using external crystal oscillator with slightly offset.