K22_120 : Is it necessary to stop the OSCERCLK (12MHz) going in VLPS MODE ?

[koichisakagami]

Dear community,

We are developing the custom board with MK22FN1M0AVMC12 device.

In the manual (K22P100M120SF5V2RM Rev. 5) Table 7-2. Module operation in low power modes,
it is described that System oscillator specification (at VLPS mode) is
" OSCERCLK max of 4 MHz crystal ".

We use a 12MHz oscillator which is connected to EXTAL0 pin.

[Question]

        When chip is in VLPS mode,
        is it necessary to stop the OSCERCLK via 12MHz oscillator which is connected to EXTAL0 pin ?

        If it is unnecessary to stop the OSCERCLK ,
        we hope to use the LPTMR which is clocking OSCERCLK(12MHz) in order to wake up from VLPS mode.

Best Regards,
Koichi Sakagami

[kerryzhou]

Hi koichi sakagami,

      Just as the reference manual(K22P100M120SF5V2RM.pdf) described, in VLPS mode, the OSC module only support the max of 4Mhz crystal, 12Mhz OSC crystal in VLPS mode won't work any more, but don't worry, in the reference manual page 176, you will get that, actually, the LPTMR still have other source clock:

  You can choose the 1khz LPO, this clock will on in the VLPS mode, normally, we choose this clock source for the LPTMR low power mode wake up.

Wish it helps you!

If you still have question, please contact with me!

Have a great day,

Jingjing

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[koichisakagami]

Dear Jingjing san,

    Thank you for your reply.

    I apologize for my poor explanation.

We use an external OSC but a crystal.

The external OSC is provided with 12MHz clock always.

We don't use internal OSC logic.

So,could you tell us

When chip is in VLPS mode,

is it necessary to stop the 12MHz oscillator which is connected to EXTAL0 pin ?

Best Regards,

Koichi Sakagami

[kerryzhou]

Hi koichi sakagami,

   I got what you mean.

   You can use the 12MHZ oscillator, it has no problem!

  When in VLPS, you still don't need to stop the EXTAL0 pin connection with 12MHZ oscillator, just the OSC module in the K22 won't work, so the according signal OSCERCLK can'e be used.

  Don't worry, when in VLPS, still let the 12Mhz ociallator connect, after wake up, it can be used again!

  When in VLPS, just choose the LPO as the LPTMR clock source.

Wish it helps you!

If you still have question, please contact with me!

Have a great day,

Jingjing

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Note: If this post answers your question, please click the Correct Answer button. Thank you!

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[koichisakagami]

Dear Jingjing san,
Thank you for your answer.

We would like to use an accurate clock for LPTMR in VLPS mode.

In the manual (K22P100M120SF5V2RM Rev. 5) Table 7-2. Module operation in low power modes,
it is described that System oscillator specification (at VLPS mode) is
" OSCERCLK max of 4 MHz crystal ".

Is it impossible to drive the OSCERCLK by 12MHz ociallator clock directly ?
We don't use internal OSC logic.

    Best Regards,
    Koichi Sakagami

[kerryzhou · Accepted solution]

Hi Koichi sakagami,

       You can't use the OSCERCLK by 12Mhz in VLPS directly, this is no doubt!

       If you don't want to use the LPO, because it is not so much accurate as you want, now there has another way, add an 32.768K crystal in EXTAL32,XTAL32, then choose the source of ERCLK32K from RTC oscillator, the LPTMR also can choose ERCLK32K as the clock source.

Wish it helps you!

If you still have question, please contact with me!

Have a great day,

Jingjing

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Note: If this post answers your question, please click the Correct Answer button. Thank you!

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[koichisakagami]

Dear Jingjing san,

Thank you very much for your information.

We consider our design with your advice and information.

Best Regards,

Koichi Sakagami