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LMX2485E: Ftest/LD detail

KANJI SHIBATANI
Mastermind 6205 points

Part Number: LMX2485E
Other Parts Discussed in Thread: LMX2485, LMX2581

Hello

My customer had been used Fujiutsu MB15F72UL but EOL.

What customer want to do is, input frequency is 50MHz~1300MHz and divide it , digital (CMOS/TTL) output  of that.

For example, inpyut 450MHz, divide 9,  digital output is 50MHz.

  

LMX2485E can accept 50MHz~1300MHz, and it have RF N divider( 8/9 Or 16/17/20/21) and ..Ftest/LD pin...

Anyway, does Ftest/LD can do that?

 

Please advise

 

 

 

 

  • 0
    Mastermind 6205 points

    Dear Sirs,

    Please discard this question.

    I understood LMX2485E can not have RF N divider output  from  Ftest/LD.

    Thank you

  • 0 in reply to KANJI SHIBATANI
    TI__Expert 8625 points
    Kanji,

    You can output RF N divider output from Ftest/LD. If you see in the programming options for the MUX, at setting MUX[3:0] = 15, it is RF N divider divided by 2. Let me know if that is what you're looking for. Thanks!

    Regards,

    Brian Wang
  • 0 in reply to Brian Wang
    Mastermind 6205 points

    Dear Brian-san,

    Thank you for your answer!!

    It was so helpfully.

    I will try again  to replace MB15F72UL with LMX2485E

    Please let me know again.

     

    Q1 

    I could not find the path  from RF N divider to Ftest/LD in the LMX2485 data sheet block diagram, but this path exists as you mention MUX[3:0]=15?

    ( My understanding in attached ppt correct?)

    Q2 

    As I mentioned ,Customer’s goal is, Input FinRF=50~1.3GHz, get digital output from Ftest =FinRF/384. ( I said FinRF/9, but

    please let me correct)

    Use LMX2581 just as divider. For example, if input was 450MHz, customer hope to get digital output  1/384=1.171875MHz.

    Backward of LMX2485E is MPU.

    Anyway, the value which customer can select for RF_N  is, 31~1023 Or 55~2039 in data sheet P26 Table15/Table 16?   

    Also, Is there minimum/mximum frequency for Ftest/LD pin?

    ( In case there are restriction, I ask customer to use D-FF after LXM2485E)

     

    Best Regards

    LMX2485_replace from MB15F72UL.pptx

     

     

     

     

     

  • 0 in reply to KANJI SHIBATANI
    TI__Expert 8625 points
    Hi Kanji,

    for Q1: your power point slide is correct. The diagram in the datasheet does not show all the paths to Ftest/LD. all the ones described in the register section exists.
    for Q2: Yes. you can do FinRF=450MHz, then RF_N=192, then you program the Ftest/LD MUX to route RF N Divider divided by 2. This will output 450MHz / 192 / 2 = 1.171875MHz at the Ftest/LD pin.

    Regards,

    Brian Wang
  • 0 in reply to Brian Wang
    Mastermind 6205 points

    Dear Brian san,

     

    Thank you for your answer quickly!!

    Customer think LMX2485E is the best choice for replacing from MB15F72UL.

    I will have another post about evaluation borad, but thank you for your support.

     

    Thank you again