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CDCE913: Power up with no input clock produces unstable output even after input clock applied

Prodigy 40 points

Replies: 3

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Part Number: CDCE913

We are using the CDCE913 to generate a 27MHz output from a 10MHz input. The 10MHz comes from a GPS receiver and what we are finding is that if the 10MHz is not connected when the unit powers up and the 10MHz is connected afterwards the CDCE913 is producing unstable clocks. We have tried reprogramming the CDCE913 when in this state and it does not change. Have tried setting the PWDN bit and putting the dividers into reset and then reprogramming but it is still stuck in this state. Only a power cycle (with the 10MHz attached)will recover it to producing a stable 27MHz. We are not using any of the spread spectrum options.

  • Genius 11260 points

    Hi Gary,

    Can you try writing all registers after the reference is connected?

    Regards,
    Hao

    Clock and Timing Systems & Applications

    To view training videos on Clock and Timing Solutions please visit  TI Precision Labs ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

  • In reply to Hao Z:

    Yes this is what I have tried. And have tried putting setting the PWDN bit first before reprogramming and still get the unstable clocks.

  • Genius 11260 points

    In reply to Gary Morrison:

    Hi Gary,

    Normally all you need to do is to trigger a PLL re-calibration. This is typically done by a recal bit, a software reset bit or a PDN/RESETN pin. Unfortunately I didn't find any register or pin that can trigger a recal.

    Right now the only other way that I can think of is to change the PLL feedback divider (for example, N divider) to some other value then change it back in order to force a calibration, but I'm not sure if it'll work.

    Regards,
    Hao

    Clock and Timing Systems & Applications

    To view training videos on Clock and Timing Solutions please visit  TI Precision Labs ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

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