topic Re: TWR-K65F180M OSC_CR Register in Kinetis Microcontrollers

TWR-K65F180M OSC_CR Register

Mike_d — Thu, 13 Oct 2016 19:15:00 GMT

Hello,

I was wondering about the load capacitance for the 1600084 Pericom crystal on the board. According to the datasheet the calibration load capacitance is 15pF. The settings in the tower examples have the internal load capacitors disabled. Shouldn't the internal load capacitors be set to match?

Regards,

-Mike

Re: TWR-K65F180M OSC_CR Register

kerryzhou — Mon, 17 Oct 2016 08:08:19 GMT

Hi Michael del Busto,

About this question, I am checking it with our according department now, and wait for the reply.

After I get the reply, I will let you know ASAP, please wait patiently.

Thanks a lot for your understanding.

Have a great day,
Kerry

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Re: TWR-K65F180M OSC_CR Register

kerryzhou — Wed, 19 Oct 2016 04:08:57 GMT

Hi Michael del Busto,

According to the reference manual:

When use Connection1, it is better to use the internal load capacitors.

The tower code didn't enable the internal load capacitors and it also works ok, because the cap loading also include stray capacitance for PCB layout, 16MHz can start up with that level of stray capacitance.

So, it would be better to use internal caps and customer need to check with their own board for which cap value to use, possibly with some board simulation to include PCB layout stray capacitance.

Wish it helps you!

Have a great day,
Kerry

Re: TWR-K65F180M OSC_CR Register

Mike_d — Wed, 19 Oct 2016 16:27:35 GMT

Hi Kerry,

When selecting the internal load capacitors is it assigning that capacitance value on either side of the crystal or is the value selected the load capacitance applied?

e.g. CLoad = (Cx * Cy) / (Cx + Cy ) + Cstray

Regards,

-Mike

Re: TWR-K65F180M OSC_CR Register

kerryzhou — Thu, 20 Oct 2016 02:43:50 GMT

Hi Mike,

The internal capacitance value on both side of the crystal, and connect to ground.

Just like Figure 28-4, Cx=Cy= internal capacitance.

Cload= Cx_internal+Cstray=Cy_internal+Cstray

Wish it helps you!

Have a great day,
Kerry