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LMK3H0102: Design Question and replace the CDCI6214RGET device

Part Number: LMK3H0102
Other Parts Discussed in Thread: SK-AM68, AM68A, , , CDCI6214

Tool/software:

Dear All,

we are designing with AM68A and want to replace CDCI6214RGET ( SK-AM68 EVM) with LMK3H0102 or LMK3H0102-q1 and have some questions:

1) Do you recommend LMK3H0102 or LMK3H0102-q1 over CDCI6214RGET for PCIe input clock?

2) When in I2C mode the default values are loaded from OTP PAGE 0 as per DS

Eg Out0 is 100MHz 100hm LP-HCSL and it is disabled

-> We want this clock to be enabled upon start-up , can we pull the OE0 pin to low so that the output is enabled?

OR do we need also to toggle the EN bit in register in order to enable the CLK out?

-> is there a way that the clk output will be enabled upon start-up in I2C mode?

3) It is stated in DS that LP-HCSL output have 50OHm termination to GND in booth devices, nevertheless on on AM68A evm the output have 33Ohm series termination and additional 50Ohm to gnd termination , please can you explain why external termination if a internal is available?

Best Regards,

d.

  • D,

    1. I would recommend using the LMK3H0102 devices over the CDCI6214 for PCIe applications.
    2. The OE pin (Pin 1 on LMK3H0102, both Pins 1 & 2 on LMK3H0102-Q1) can be pulled low for the outputs to be enabled by default on startup. The Enable bits are already set in I2C, both the enable bits and the pin states are required for the outputs to be enabled.
    3. Series resistors can be added to best match with the trace impedance. An example of this is provided in the CDCI6214 datasheet:


      The CDCI6214, being HCSL rather than LP-HCSL, requires the external 50-Ohms to GND.
      The LMK3H0102(-Q1) does not require either of these resistors, and should not have them.

    Thanks,

    Kadeem

  • Dear Samuel,

    thank you for the replay.

    From Ds it it stated the OE(LMK3H0102) must be low and OUT0_EN/OUT1_EN must be "1" to enable output on start-up

    so if i put pull-down on OE pin it is not enough to output be enabled on start-up because the default value in register is "0"

    So that means we need to do  I2C set the register in order to enable the output on every start up is that correct?

    similar is for LMK3H0102-Q1

    How can we set-up the device that on start-up clock is enabled without using I2C to set registers?

    Best Regards,

    d.

  • D,

    We are working on updating the datasheet to reflect the correct register settings for the default LMK3H0102V33RERR orderable device. The default for this part number/configuration will have the OUT0_EN and OUT1_EN bits set to a '1'.

    Thanks,
    Kadeem