RTC standby mode

[Afeefah]

Hi NXP team,

we are currently using the RTC PCF85263A in our device with IMX6ULL as host processor, we have observed that the RTC consumes around 10mA during normal operation and also when our device is put to sleep mode the RTC consumes the same , default current value is around 10mA. we would like to reduce the current consumed by RTC during this mode for our application. Are there any low power mode that the RTC can be put to in order to consume minimum current. Is there any mechanism to put RTC to sleep? How to check the minimum current consumption by RTC in standby mode?

Thank you

[Dhruvit]

Hi @Afeefah,

I hope you are doing well.

->One can put PCF into 2 modes, Stop mode and standby mode.
->A low drive mode is available for low-series resistance quartz. This reduces the current consumption.

->i.MX6 will enter stop mode, the difference between standby and mem mode is: in mem mode, the ARM core's power will be gated and DDR IO will be floated, mem mode is the most power-saving mode, named deep sleep mode(DSM).
->One can make Linux enter suspend by "echo mem > /sys/power/state", or "echo standby > /sys/power/state", to wake up the system from suspend, you can use RTC wake up or power key. 

For example, "echo +3 > /sys/class/rtc/rtc0/wakealarm", the system will auto resume 3 seconds after suspend.

->Please use a multimeter to measure the current draw on the RTC's VDD pin.

Please refer to the below documents for in-depth details.
https://www.nxp.com/docs/en/data-sheet/PCF85263A.pdf

I hope this helps!

Thanks & Regards,

Dhruvit Vasavada

[Afeefah]

Hi @Dhruvit 

Thanks for the reply.

We are aware of the steps to put iMX6ULL in sleep mode.

• We have put iMX6ULL device in sleep mode with wakeup interrupt other than RTC.
• In the above case RTC is consuming same power as of normal mode.

Is there any mechanism to put RTC in low power mode while iMX6ULL device going to sleep mode with an interrupt.

Thanks & Regards,

Afeefah Fathima

[Dhruvit]

Hi @Afeefah,

I hope you are doing well.

Please correct my understanding if wrong.
While i.MX6ULL is going into sleep mode, RTC should be used as a wake-up alarm, right?

If, Yes.
The below example sets the timeout (in Sec) to wake up from standby/suspend mode.
echo +(Seconds) > /sys/class/rtc/rtc1/wakealarm

Thanks & Regards,
Dhruvit Vasavada

[Afeefah]

Hi @Dhruvit 

'While i.MX6ULL is going into sleep mode, RTC should be used as a wake-up alarm, right?'

No, we want to make the RTC to go into sleep mode. Is there any settings for this.

Regards

Afeefah Fathima

[Dhruvit · Accepted solution]

Hello @Afeefah 

I hope you are doing well.

"No, we want to make the RTC to go into sleep mode. Is there any settings for this."
->The PCF85263A has two-time mode register sets, one for the real-time clock mode and one for the stopwatch clock mode. The access to these registers can be switched by the RTCM bit in the Function control register.

There is no mention of sleep mode.

For more details please refer to the datasheet.
https://www.nxp.com/docs/en/data-sheet/PCF85263A.pdf

Thanks & Regards,

Dhruvit Vasavada