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AM3352: VSS_OSC and VSS_RTC connection

Kanae
Guru 10295 points

Part Number: AM3352


Hi Sitara support team,

About the Workaround for Errata Advisory 1.0.30,
"Connect the VSS_OSC and VSS_RTC terminals and respective crystal circuit
component grounds directly to the nearest PCB digital ground..."

Q1. Are there reccomended pattern length and impedance value?

Q2. Is there possibility that the internal clock has the influence of such as the noise of the external 25MHz clock?

Best regards,
Kanae

  • 0
    TI__Guru**** 393215 points
    Hi,

    Q1. No, these pins should simply be connected to the common GND plane.
    Q2. Yes, external clock noise can influence internal clocks.
  • 0 in reply to Biser Gatchev-XID
    Guru 10295 points
    Hi,
    Thank you fr your quick reply.
    Could I confirm your answers to make me understand them?

    Q1. The references of connections are only on AM335x's datasheet; 6.2.2 Input Clock Requirements.
    We sould just follow the datasheet, right?

    Q2. The influence of internal clock is much less than the external clock noise influence, but still there.
    However, the noise from the oscillator may be filtered by the internal clock structures, right?

    I appreciate your support.
    Best refards,
    Kanae
  • 0 in reply to Biser Gatchev-XID
    Guru 10295 points
    Thank you for quick reply, Biser.
    I would like to confirm your answers to make me understand them.

    Q1. This connections are just refer to datasheet of AM335x; 6.2.2 Input Clock Requirements, right?
    Q2. The influence of internal clock noise is much less than the external clock noise' s influence, right?

    I appreciate your supports.
    Best Regards,
    Kanae
  • 0 in reply to Kanae
    TI__Guru**** 393215 points
    Q1. Correct. Latest datasheets have the correct information and Errata Advisory 1.0.30 does not concern them.
    Q2. I don't understand this. Influence on what?
  • 0 in reply to Biser Gatchev-XID
    Guru 10295 points


    Thank you for your reply.
    I'm sorry I didn't explain it enough.

    As for "Influence", the noise on 25MHz external clock makes one cycle to be more than 50 MHz,
    and AM335x cannot work normally, because the input frequency specification is exceeded.
    This influence of noise for the internal clock is much less than influence of noise for the external clock, right?

    Best regards,
    Kanae

  • 0 in reply to Kanae
    TI__Guru**** 393215 points
    The internal clocking structure is very complex and it's practically impossible to determine how it will be influenced by external clock noise. Maximum effort must be taken to provide noise-free external clock to the device.
  • 0 in reply to Biser Gatchev-XID
    Guru 10295 points
    Thank you for quick reply.
    I understand that the external clock noise must be eliminate as much as I can.
    I also refer this post.
    e2e.ti.com/.../490351

    Best regards,
    Kanae