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LMK1C1104: Rout design question

Jim Tsai
Expert 4470 points
Part Number: LMK1C1104

Hi,

I would like to check the spec of output impedance. Is Rout (50ohm) embedded in output of buffer or it is required for measurement only? And do you know the driving capability of 1104? Many thanks.

  • 0
    TI__Genius 9250 points

    Hi Jim,

    Rout is embedded in the output so we don't need any external Rs resistor to match the 50 ohm trace impedance. 

    Based on above, currently datasheet specify VOH and VOL values at 1mA drive current. 

    Figure 8-2. indicates that measurements were taken with outputs terminated with 50 ohm to VDD/2.

    One of the figure in datasheet shows that we can drive VDD/2 with 100 ohm to ground and  VDD.

    So based on this circuit, we can calculate the drive current to as shown below:

    We can also drive 50 ohm to ground that would result in 33mA drive current but I would consider the number of outputs, ambient temperature and junction temperature in consideration. Because we can run into issue if the junction temperature gets to maximum values. It would also consume a lot of power.

    Best,

    Asim

  • 0 in reply to Asim Khan
    TI__Expert 4470 points

    Hi Khan,

    Do we have any P2P deice with LMK1C1104PWR and without Rout embedded?

  • 0 in reply to Jim Tsai
    TI__Expert 4470 points

    Hi Khan,

    Add more information, customer encounter to the clock (50MHz) rising time issue if CLK BUF has embedded Rout for their application.

  • 0 in reply to Jim Tsai
    TI__Genius 9250 points

    Hi Jim, 

    Can you give a little more information about this rise time issue. We can use CDCV304 which doesn't have 50ohm impedance. Its roughly around 25 ohm by looking at the I/V curves.

    Best,

    Asim