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The OSC0 feedback register on TMDSSK3358

Nomo
Guru 16800 points

Hello,

Is R216 on TMDSSK3358 for the feedback register?
Because the register is DNI, R216 doesn't work.
However the register should be connected to the right of R213.

Best Regards.

Nomoto

  • 0
    TI__Guru**** 393215 points

    Hi Nomoto-san,

    The Starter Kit schematics are quite old. R216 is supposed to be populated if the crystal doesn't have a parallel resistor inside. However most manufacturers nowadays build in these resistors in their crystals. You are correct about the position of R216, it should be on the other side of R213.

  • 0 in reply to Biser Gatchev-XID
    TI__Guru 62855 points

    Both AM335x oscillators have an internal feedback resistor that can be enabled or disabled.  So in most cases an external feedback resistor is not needed.  However, we have normally recommended customers provide an option to add the feedback resistor on pre-production PCBs until they have characterized their system performance across all use case conditions with the actual crystal circuits planned for their production system.  We also recommend pre-production PCBs include a series damping resistor on the oscillator output for the same reason.  A 0-ohm resistor would be installed initially and in most cases it can be remove in production systems.  Please refer to the clocking section of the AM335x data sheet for recommended crystal circuits.

    Regards,
    Paul