Kinetis KLx RTC_CLKOUT / RTC_CLKIN

[carlnormansuret]

Hi all,

We have an application with 2 Kinetis KL series processors (MKL03Z8VFG4 and MKL27Z128VFM4). I need to run them in super low power sleep mode with the RTC running. We basically want the RTC on one clocking the other in super low power mode.

Will running the KL27 with the 32Khz xtal then connecting the RTC_CLKOUT to the RTC_CLKIN on my KL03 allow them to both run in the lowest power mode? Or do they both need 32Khz xtals to achieve the extremely low power I require?

[mjbcswitzerland]

Hi

See http://www.utasker.com/kinetis/KL_RTC.html

For fullest flexibility you can use a very low power 32kHz oscillator connected to RTC_CLK of each chip (it may also give lower power consumption if it is of highest quality).
You may also be able to use a 32kHz crystal on one of the chip's EXTAL0/XTAL0 and connect the XTAL0 to the RTC_CLK of the other - you will however need to check that the signal is suitable (its amplitude etc.). Although it may be possible to connect XTAL0 from one to EXTAL0 of the other I think that the RTC_CLK input is still the most suitable since it will allow the second chip to power down its oscillator logic in low leakage mode.

Using RTC_CLKOUT will probably increase consumption at the KL27 a bit and is not possible in all low leakage modes, but would be a "clean" method if you can accept the low leakage mode restriction it applies.

For LLWU/alarms see also http://www.utasker.com/kinetis/LLWU.html

Regards

Mark

[carlnormansuret]

Thanks mark,

I guess for my application I can run the KL27 with external 32Khz xtal, and the KL03 can clock its RTC from LPO, only the larger processor needs to be accurate. The KL03 is literally a programmable external watchdog monitoring the entire system. 

Ill go off an test the LPO and see if thats ok, and make sure the KL27 will wake up from hardware interrupts while in low power mode clocking its RTC.

[kerryzhou]

Hi Carl Norman,

    What the low power mode you want to using?

   VLLS3, VLLS1 or VLLS0?

 From the reference manual Table 7-2. Module operation in low power modes, you can find the OSC can work in VLLS1/3 if the crystal is below 16Mhz, but VLLS0 is OFF.

RTC in VLLS0, the only clocking option is from RTC_CLKIN.

Please read the table at first, then decide which clock you can use.

If you still have question, please let me know!

Have a great day,
Kerry

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[carlnormansuret]

Hi,

I have two requirements

For my KL27

Wake up from single pin input or RTC periodic alarm

- GPIO outputs need to be set in certain states to stop leakage current on external circuits (bias things off or on)
- Inputs need to have some pull ups to stop some external leakage but do not need to wake it up.

- RTC needs to run from external 32.Xkhz xtal with programmed wake up time

- 3 GPIO inputs needs to be able to wake up the chip (the KL03 can wake it up, or, my other hardware trips the other input)

- Lots of modules are enabled (1 x UART, 2 x LPUART's, I2C, SPI) so I guess I need to somehow disable / unlock these for minimal power

- I guess I need to disable unused GPIO

- I need the entire RAM retained

- I need to exit into the same state (no reset)

For my KL03

- Same as above but using LPO to run the RTC with periodic wake up, or maybe just LPTMR as might be ok, as long as I can wake it up at some interval..

My goal is under 3uA each processor

From my reading so far I think i need to enter LLS3 , VLLS3 requires reset which makes it to complex for my RToS. I just need to work out if how I manage the GPIO before entering and also UART/LPUART/SPI/I2C so that the current is minimal.

[kerryzhou]

Hi Carl Norman,

    If you don't want to get the wake up reset, you can't use the VLLSx mode, all VLLSx mode will be wake up reset.

    1.KL03 don't have LLS mode, may be you can choose VLPS, but add RTC, the current consumption may higher than 3uA.

2. KL27 don't have LLS3, just have LLS mode.But the power consumption also may higher than 3uA with RTC, and all other module is disabled.

So, you can consider to use the VLLS3. VLLS3 wake up is reset, but the RAM retains in the hardware.

Have a great day,
Kerry

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[carlnormansuret]

It does not matter if its more current, my target is 3uA per processor, but i can handle 10uA per processor really, (20uA total)... 

I think I can run the KL03 in VLPS with LPO and use the LPTMR to wake up and get around 6uA? This wont require any reset logic to be handled, it can just stop and wake up and continue?

KL27 looks ok to run in LLS mode with RTC and external 32Khz xtal? Should be under 5uA?

This will take my total power to around 10uA which is fine, I can handle up to 20uA to meet the project requirements.

[kerryzhou]

Hi Carl Norman,

1. KL03 VLPS

yes, you use the LPTMR to wake up, the power consumption will below 6uA, I have test it on our FRDM-KL03 board with KSDK2.0.

After VLPS wake up, the code will continue to work below the point where enter the VLPS, it is not reset.

2. KL27 in LLS mode

Yes, it also can under 5uA.

You can use it, now the low power mode is determined on your side.

Wish it helps you!

Have a great day,
Kerry

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