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DS92LV2421 75MHz clock rate limit

Ed Walker
Prodigy 5 points
Other Parts Discussed in Thread: DS92LV2421, DS92LV2422, DS90UB925Q-Q1

We would like to use the DS92LV2421 to create a serial DVI stream to send over fiber.
The datasheet states a 75MHz clock rate maximum.
We need about 77MHz.

The Spread Spectrum spec at 75MHz is 35kHz with a +-2% fdev.
Is the +-2% fdev considered to be 2% of 75MHz?

If so then +2% of 75MHz is 76.5MHz.
I do not intend to use spread spectrum, thus can I run my clock up to 76.5MHz?

I really want 77MHz, just 500kHz more.
Can you comment on the performance of the DS92LV2421 with a 77MHz clock?

Thank you.

  • 0
    Prodigy 5 points
    And we would like to use the DS92LV2422 on the other end to deserialize with a 77MHz clock rate.
  • 0
    TI__Mastermind 29655 points
    Hi Ed,

    The DS92LV2421/22 cannot be used above the datasheet specification of 75 MHz. This is because the PLL internal to the serializer and deserializer are designed to function within the 10-75 MHz specification. Since 77 MHz is relatively close to the 75 MHz maximum, it is possible that the PLL may be able to lock to the incoming 77 MHz clock signal, but none of our parts are tested to work at rates beyond the datasheet, so the DS92LV2421 will be unable to support this rate.

    Regarding the comment about SSC (spread spectrum clocking), you are correct that the serializer max spread is +/-2%, thereby getting you to a maximum of 76.5 MHz. However, this does not necessarily mean that the IC will function correctly if the clock is sustained above 75 MHz. When SSC is used, the frequency only briefly reaches 76.5 MHz while remaining centered on 75 MHz.

    Thus, the IC MAY work at 77 MHz, but TI will not guarantee or support operation of this product outside its specs. I suggest you try an FPD-Link III that can work with that rate, like the DS90UB925Q-Q1/926Q-Q1.

    Thanks,

    Michael