• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 21 subscribers
  • Views 316 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CDCEL913 doesn't clock from LVCMOS

deepintheforest
Prodigy 90 points
Other Parts Discussed in Thread: CDCEL913

We have a CDCEL913PW
   powered with 1.8V throughout,
   and feed with a 27MHz LVCMOS clock

One of the outputs feeds a processor main clock,
  which will be used to program this CDCEL913
  during first-time operation after manufacturing of the Board.

The un-programmed chip has a factory default setting
   where the input stages are configured for XTAL operation.

To my great surprise it turned out the input stage of the CDCEL913
  doesn't reliable clock when feed with a 1V8 LVCMOS signal,
  when it is still in its factory default setting for XTAL operation.
This means we have a deadlock and can't first-time program the CDCEL913
  after manufacturing. (where we would switch over to LVCMOS configuration)

I've troubles to understand this situation, that is
  I can't imagine what sort of input stages have been used,
  which won't clock in face of a full swing 1.8V rectangle.

I'd ask you to shed some light on this issue,
   and I'd recommend to add a warning to the data-sheet concerning this issue.

Thanks

  • 0
    TI__Expert 3985 points

    Hi,

    let me first try to figure out the situation. You have on your board a default-programmed CDCEL913. One of its output is used to clock a processor which will be used to transfer your desired setting to the CDCEL913. Is this right?

    As you mention the device is the default setting accepts only XTAL input. Under this configuration the device will generate an in-spec output clock only if a XTAL input is available. If you feed an LVCMOS while the CDCEL913 is in XTAL input mode we can not guarantee the output clock performance.

    There is no deadlock in the device.

    You should either ask for pre-programmed TI part or add an I2C interface generator (FPGA, or similar) which program the CDCEL913 in LVCMOS input configuration.

    Thanks and best regards,

    Leandro

  • 0 in reply to Leandro_z
    Prodigy 90 points

    Hello Leandro,

    > let me first try to figure out the situation. You have on your board a default-programmed CDCEL913. One of its output is used to clock
    > a processor which will be used to transfer your desired setting to the CDCEL913. Is this right?

    Thats correct,

    > As you mention the device is the default setting accepts only XTAL input. Under this configuration the device will generate an in-spec
    > output clock only if a XTAL input is available. If you feed an LVCMOS while the CDCEL913 is in XTAL input mode we can not guarantee
    > the output clock performance.

    You confirm my speculation, Thanks.

    > There is no deadlock in the device.
    >
    > You should either ask for pre-programmed TI part or add an I2C interface generator (FPGA, or similar) which program the CDCEL913 in
    > LVCMOS input configuration.

    These "solutions" are obvious,
       and of course I would have considered this during Design of the Board,
       if I had knewn of this surprising deficiency.
    It simply didn't occur to me,
       because I've never seen such a behaviour the last two decades.

    Thank You for your confirmation,
      I consider this issue `Closed'