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LMK04832: question about SPI circuit

Shinichi Inoue
Guru 21666 points
Part Number: LMK04832
Other Parts Discussed in Thread: LMK04828,

Dear Specialists,

My customer is considering LMK04832 and LMK04828, he has a question.

I would be grateful if you could advise.

---

.LMK04832 / LMK04828B,


About SPI used in register control SDIO is a bidirectional buffer.

When connecting to the master side, is it not necessary to put series resistance in the transmission line?

(Since half duplex = quasi two-way communication)

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I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    Guru 21666 points
    Dear Specialists,

    My customer is considering LMK04832 and LMK04828, he has a question.

    I would be grateful if you could advise.

    ---

    Regarding LMK04832 / LMK 04828B,

    Is it ok to recognize that all clocks are forcibly synchronized by driving the SYNC pin?

    ---

    I appreciate your great help in advance.

    Best regards,

    Shinichi
  • 0 in reply to Shinichi Inoue
    TI__Mastermind 28550 points
    Hello Shinichi,

    It is not strictly necessary to put a resistor on the SPI line. However it is recommended to place some series resistance, say ~33 ohms to provide a source termination for the CMOS output, otherwise there could be large ringing depending on your design and output driver. Also, before the LMK04832/28 drives the SPI line, you would want to set the master output to an input so it is no longer driving the line or if the master output is using an open drain output type output, be sure the master is outputting high so the LMK can then drive the bus.

    When asserting the SYNC pin, if the device is programmed to route the SYNC pin through to reset the dividers, all outputs will be held in reset except for /1 outputs which will continue to oscillate. They are always in SYNC because they are the highest frequency. Note that the SYNC pin is close to the VCO, so if there is lots of toggling or noise on the SYNC pin, it can add some momentary noise to the output. I suggest placing an RC filter on the SYNC pin.

    73,
    Timothy
  • 0 in reply to Timothy T
    Guru 21666 points

    Hi Timothy,

    Thank you for your reply.

    I understand it doesn't need a termination resistor.

    I'll share this information with the customer.

    I appreciate your great help.

    Best regards,

    Shinichi