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DLPC300 input clock and reset

Other Parts Discussed in Thread: DLPC300

Hi,

Instead of using external crystal or oscillator, we want to use the FPGA to generate the input clock for DLPC300. The RESET is controlled by FPGA as well. 

Due to limitation of the PLL, we cannot generate 16.667Mhz, but the closest is 16.384Mhz. From DLPC300 datasheet, there is an internal PLL to generate other clocks from the 16.667Mhz input. I'm curious if there will be any timing implications with a slightly reduced input clock? 

I understand the RESET should be released after input clock and power rails are stable. Is there any delay requirements between them?

Thank you,

William

  • I'll move this to the appropriate forum...

  • William,

    Using a clock input of 16.384MHz is outside the recommended operating range of 16.667MHz +/- 200ppm and is not work. Can your FPGA generate 8.333 MHz? Is there a reason other than BOM cost and board space not to use a crystal or oscillator at the spec'd frequency?


    Regards,

    Kevin

  • Hi Kevin,

    Thanks for the reply. We are trying to save the board space mostly. I'm checking to see if I can generate 8.333Mhz. May I ask why?

    It is a possible alternatives if I can find a crystal with small enough footprint. The LightCrafter eval driver board BOM (http://www.ti.com/tool/DLPLIGHTCRAFTER) used TXC 8Z xtal for DLPC300. This xtal has a small footprinit 2.5x2mm, but it's max ESR is 100ohm, which exceeds the DLPC300 spec of 80ohm. There are crystals that meets all the spec, but in larger footprint 3.2x2.5mm. Can you please confirm the DLPC300 drives xtal with ESR=100ohm?

    Thanks,

    William

  • William,

    The DLPC300 should be able to use an 8.333MHz crystal if a pullup is added to the OUTPUT_TRIGGER pin (N9). This is undocumented in the DLPC300 datasheet - it is also untested. Please discuss further with TI if you want to go this route.

    We've not tested a crystal with ESR > 80ohm. Also, I do not know of a crystal smaller than the 3.2x2.5mm that will meet the DLPC300 requirements but, is has been a while since I looked. Would you consider an oscillator? Abracon makes a 2x2.5mm oscillator the link is:
    http://www.abracon.com/Oscillators/ASDMB.pdf

    Regards,
    Kevin
  • Thanks for the suggestion. I wasn't able to find any xtal smaller than 3.2x2.5mm that meets the requirements either. MEMS Oscillators offer high performance in small size. I will take a look at SiT8008 - they offer 2.0x1.6mm!

    Generating 8.333Mhz from FPGA is unlikely or not as straight-forward. So I'm looking at a different FPGA frequency source.

    - Do I follow the oscillator connection to DLPC300 when using clock from FPGA?
    - Any requirement of Trise/fall from DPLC300 side?

    Thanks,
    William