• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 21 subscribers
  • Views 4401 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LMK04828: What is HSDS interface and compatibility with CML

Jade Goo
Intellectual 1940 points
Part Number: LMK04828

Hi Team,

LMK04828 can use "HSDS" interface for output.
What is "HSDS"? And possible compatibility with CML?
Thank you.

Best Regards,
Jade

  • 0
    TI__Mastermind 28530 points

    HSDS is high swing differential signal.  It is like LVDS but with higher swing.

    Anytime differential signaling is considered for AC coupling, it's ability to be used will depend upon the swing.  Typically measured as Vod/Vid as the difference between the inverting and non-inverting pins.  Note when using AC coupling with HSDS on LMK0482x, if the load is not on the driver side of the termination, place a 560 ohm shunt resistor close to the output pins to provide a DC current path for the output driver.

    Anytime differential signaling is considered for DC coupling, in addition to swing, the common mode must be considered.  For HSDS 8 mA it is approximately 1.64 V.  Please refer to datasheet page 20 of LMK04828 datasheet (SNAS605) for more info on  the various  HSDS modes.  For example there are three amplitude swing levels of HSDS, 6 mA, 8 mA, and 10 mA.

    HSDS may be compatible with CML, again  it depends upon the specs of the CML input.  CML input levels vary and the datasheet must be referred to.

    73,
    Timothy

  • 0 in reply to Timothy T
    Prodigy 80 points

    Hi Timothy,

    I understand from your comment that when AC coupling is used with HSDS ouptut drivers, a shunt resistor (560 ohm) should be placed before coupling. Is following calculation is true and feasible?

    For example if it is HSDS 8mA driver then there will be 8mA*560 = 4480mV voltage difference between positive and negative pins. However IC is supplied with 3.3V so I think there will be some problem?

    What is the point that I missed, can you explain?

    Best Regards,

    Mustafa

  • 0 in reply to Mustafa Dursun
    TI__Mastermind 28530 points

    Hello Mustafa,

    That 560 ohm will be in parallel with a 100 ohm.  So the swing is theoretically Vod = 84.84 ohm * 8 mA = 679 mV.

    By having HSDS Output --> Transmission Line --> 100 ohm termination --> DC blocking caps --> Target device.  You can get closer to the Vod = 800 mV.

    Note the Vpp differential is 2* Vod.

    73,
    Timothy