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MSP430F1232: Crystal circuit

Sh.Sasaki
Guru 13625 points
Part Number: MSP430F1232

Hi, 

The customer got an error that the crystal did not oscillate in one of the 1000 mass-produced units.

They design the crystal connection as follows:

They solved the problem by adding a 15pF capacitor between the Xout terminal and GND on the board where this crystal does not oscillate.

The crystals they are using are:
https://www.sii.co.jp/en/quartz/datasheets/smd/ssp-t7-f/

Does this mean that the load capacity built into the MSP430 is not enough for this individual?

They have been matched tested by the Xtal vendor.

I want to know why adding 15pF improves the problem.

Best regards,
Sasaki

  • 0
    TI__Mastermind 20035 points

    Hi Sasaki

    I will check in detailed  and reply to you later

  • 0
    TI__Mastermind 20035 points

    Hi Sasaki

    Usually, several pF load capacitors is needed on 32KHz crystal.

    Please find application notes as the reference

  • 0 in reply to Xiaodong LI
    Guru 13625 points

    Hi Li-san,

    Thank you for your support.

    I checked it.

    The documentation says "MSP430x1xx: 6 pF (fixed effective capacitance with 12 pF per pin), external capacitors are not recommended"

    I want to know why my customer solved the problem by adding a 15pF capacitor 

    Best regards,
    Sasaki

  • 0 in reply to Sh.Sasaki
    TI__Mastermind 20035 points

    Hi Sasaki

    Thanks for your reminding!

    I have checked the following parameter between MSP request with the crystal spec

    • Crystal's required effective load capacitance (for 32-kHz crystals, typically 6 pF to 15 pF)；
    • Crystal's ESR (for 32-kHz crystals, typically 30 kΩto 100 kΩ)
    • Tolerance (typically 5 ppm to 30 ppm)

    I think the crystal should be suitable on used on MSP device

    So far, I don't have idea on the reason to solved the problem by adding a 15pF capacitor

    On possile point of this question is about the PCB desig of crystal.

    On "3. PCB Design Considerations" section, you can see crystal working is related with PCB design as well

    Could you please hlep to share the sreenshot of this part of user's PCB design?

    I want to review with our team and try to find some thread.

    Thanks

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