Prototype using MC9S12XEP100 based on VB9S12XEP100

[danielflor]

Hello,

I'm designing a prototype that uses the MC9S12XEP100 microcontroller and  I'm taking as an example the EVB9S12XEP100 evaluation board. The following questions have arisen.

1) Regarding decoupling capacitors, I used the information present in the datasheet, mainly in the Appendix C PCB Layout Guidelines. Analyzing the EVB9S12XEP100 board, I found that 10uF polarized capacitors are used together with the decoupling capacitors, however, I did not find reference to these 10uF capacitors in the MC9S12XEP100 datasheet.

2) The VDPLL, VDD, VDDF pins have 220nF decoupling capacitors to earth, however. Since the EVB9S12XEP100 evaluation board makes them available externally, I would like to know if there is a need to connect these pins to an external voltage source .

3) Regarding the ocylator circuit, I noticed that, on the EVB9S12XEP100 card, there are two circuits, one of them uses full swing Pierce (FSP) with crystal and the other uses a clock generator. Is there any reason to use the external clock instead of a higher frequency oscillator?

With my best regards,

Daniel.

[danielmartynek · Accepted solution]

Hello Daniel,

1.
You can refer to this application note:
AN3262 Designing Hardware for the MC9S12X D-Family

2.
No, these are outputs not inputs of the internal voltage regulator.

3.

It is an addition option, if you need to use an external oscillator for some reasons.

Regards,

Daniel

[danielflor]

Thank you, Daniel, This document AN3262 will be very useful. But I still have another doubt, on the EVB9S12XEP100, there is a inductor of 10uH between VDD and VDDA, I guess it is there to remove high frequency components of the digital circuitry and separate them of the analog circuitry, but I didn't find any mention about it on the related documents.

So, I would like to know if is mandatory to have this inductor or in which cases it is recommended.

With my best regards,
Daniel

[danielmartynek]

Hello Daniel,

Yes, it can help to decouple the analog circuit but this is not required.

It was discussed, for example, here:

ACD Reference Voltages 

https://community.nxp.com/thread/476060 

BR, Daniel