IRC48M clock to output pin? What happens if voltage is lower than 2.7 V?

[andrejnastran]

Hello there.

Little help needed. I need high frequency output on my low power project. I'm using MKL03Z32VFK4 MCU. Is there way  to output IRC48M to a pin when VDD voltage is lower than 2.7 V (I'm using CR2032 battery)

Datasheet says that:

Page 179: IRC48M clock (IRC48M clock can be output to PAD only when chip VDD is 2.7-3.6 V)

https://www.nxp.com/docs/en/reference-manual/KL03P24M48SF0RM.pdf  

What happens if voltage is below 2.7 V? Usable voltage range of CR3032 is about from 3.4 V down to 2.4 V

[andrejnastran]

bmwhui‌ thank you so much. If you already tested it I have additional question:  How much is VDD supply used on scope and how much peak to peak is signal from CLKOUT pin?

I also tried it and it works down to 1.65 V. Maybe is really doucment issue - I hope.

    SIM->SOPT2 = SIM_SOPT2_CLKOUTSEL(7) ;          // Selects the IRC48M clock output on the CLKOUT pin.
    CLOCK_EnableClock(kCLOCK_PortA);                      // PORTA clock enable
    PORT_SetPinMux(PORTA, 12U, kPORT_MuxAlt5);    // Set PTA12 to CLOCKOUT

Is code correct? And signal is pretty weak - probably cause is oscilloscope internal resistance.

I'm migrating form Microchip PIC used in this product: PlantRay - Smart plant watering reminder 

Thank you,

Andrej

[Hui_Ma]

Hi Andrej,

Your test code is correct.

I check that info with Kinetis product team, the document mentioned chip VDD range 2.7V-3.6V is a suggested voltage range, which guarantee the output IRC48M clock accuracy for full temperature range.

While, customer still could low down the VDD voltage, while the output IRC48M clock accuracy could not be guaranteed in below datasheet description range:

So, customer need to evaluate the 48MHz clock signal clock accuracy in product application whole temperature range.

I don't have the test equipments to do that test. Sorry for that.

Thank you for the attention.

best regards,

Mike

[Hui_Ma · Accepted solution]

Hi

I had done a test with FRDM-KL03Z board.

The IRC48M clock still could be output at CLKOUT pin when KL03 VDD drop below 2.7V.

I test the KL03 VDD with voltage at 1.74V, the CLKOUT also output the IRC48M clock.

I think that should be a document issue.

I will check with Kinetis product team to fix it.

best regards,

Mike