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LMX2581 RFin ⇒ RFout

cafain
Mastermind 6365 points
Other Parts Discussed in Thread: LMX2581

Hi

LMX2581

Input 150MHz clock from RFin, Can you output the 150MHz to RFoutA as it is? (RFin 150MHz ⇒ RFoutA 150MHz)

following register setting OUTA_MUX : "2" MODE[1:0]: "1" (PLL Only Mode)

I am aware that the specifications of RFin is 0.5 ~ 2.2GHz.
I think that is only through to RFout from RFin, and not affect the frequency limit of 0.5GHz, but how might it be?

Best regards

  • 0
    TI__Mastermind 27581 points

    Cafain,

    The spec is 500 MHz min, so that is the specification that we guarantee.   We chos this due to test capability and also because the prescalers become to be an issue for lower frequencies.   We have no test data and the guaranteed lower limit of 500 MHz does impact.

    The issue for the high frequency input pin at lower frequecies is that any noise riding on the signal can cause a miscount.  If you put in a square wave, then this has a much higher slew rate and probably will work.

    You might also want to use "MODE=3".  We call this reserved in the datasheet, but this is the fin pin straight to the outputs.

    If you do this with a square wave, it probably will work, but because we have no test capability, the guarantee is down to 500 MHz, so I can not guarantee this performance below 500 MHz input.

     

    Regards,

    Dean

  • 0 in reply to Dean Banerjee
    Mastermind 6365 points

    Hi Dean

    It is gratitude at kind support.

    He understood that the input which is less than 500 MHz could not be guaranteed.

    Please let me ask one more.

    Specified is Datasheet(SNAS601G) page7  "fRIN".

    "OUTA_PD=OUTB_PD=1(Power-Down)" is written on the "TEST CONDITIONS" .

    When it sets to "OUTA_PD=OUTB_PD=0"(Power-Up), does the specification of a fRin have a difference?

    Regards,

    Cafain