• State TI Thinks Resolved
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 21 views
  • Users 0 members are here
Support feedback
Options
Options
Related

Original question:

LMK04808BEVAL: Using LMK04808 in single-loop mode (PLL2, internal VCO)

LMK04803: About 0-Delay Single PLL mode feedmux

APPLO ZHANG
Intellectual 515 points
Part Number: LMK04803

Tool/software:

Hi, TI team:

In 0-Delay Single PLL mode, can the output still be used as feedback output if it is turned off?
The detailed settings are shown in the figure below.

By the way, if I need to align the output phases of different channels at different power-ups, is SYNC still required in zero-delay mode? 
Do I need to use the minimum output frequency for feedback?

Thanks!

  

  • 0
    TI__Mastermind 33340 points

    As long as CLKoutX_Y_PD = 0, the divider is still enabled, so the output can still be used as feedback output. In other words, the value of CLKoutX_TYPE does not impact whether an output can be used as the feedback output.

    Even in zero-delay mode, SYNC is still required to align all the outputs. The microwire programming of each divider causes the divider to be reset internally, and since the microwire logic is not necessarily synchronous to the clock distribution path, each divider phase is effectively randomized after programming the registers. Putting an output in the feedback path constrains the possible phases of that output with respect to the input, but not necessarily with respect to the other outputs. Fortunately, LMK0480x devices have a useful feature called Qualified SYNC, which allows the feedback clock to be used as a re-timer for the SYNC signal. Section 8.3.9.3.5.4 of the datasheet provides an example.