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LMX2595: LXM2595

singam vamshi krishna
Intellectual 775 points
Part Number: LMX2595
Other Parts Discussed in Thread: LMX2594EVM, , TIDA-01410, TICSPRO-SW

Hello.

I have few queries regarding LMX2595.

1) The lock time of LMX2595 is calculated by using PLLatinum sim tool. But for the frequencies higher than 15GHz what could be the lock time. I mean once the VCO frequency is doubled what is the effect on lock time.  

2) While programming LMX2595 it is recommended to transfer MSB first. Now in that case lets consider I need to transfer 0X00251C. So, Should I program to transfer 1C at the beginning.

3) I am trying to replicate the design with eliminating the additional connectors. Any PCB guidelines and gerber files for reference.

4) The output power level at high frequencies is very less. Is it desirable to use a Low Noise Amplifier at the output of LMX2595 to attain the desired power level. 

Thanks in Advance.

  • 0
    TI__Genius 11900 points

    Hello Singam,

    1. The doubler is not part of the loop, and should not play a role in the lock time.
    2. 0x00251C => programming data 0x251C into register R0. 0x251C = 0010 0101 0001 1100 in binary. You must program D15 = 0, D14 = 0 , D13 = 1, D12 = 0 ... D3 = 1, D2 = 1, D1 = 0, D0 = 0. Refer to "Figure 1. Serial Data Input Timing Diagram" of the datasheet as well.
    3. The LMX2595EVM or LMX2594EVM altium and gerber files can be found on the product folders.
    4. The output power varies with frequency as well as the trace matching and trace lengths. To get the best output power the traces on the PCB can be made smaller. TIDA-01410 is optimized better for short traces and better output power.

    Thanks,

    Vibhu

     

  • 0 in reply to Vibhu Vanjari
    Intellectual 775 points

    That's Fine.

    1) I accept that the doubler is not part of the loop, But there is effect on lock time once the frequency is doubled. The reason I am calculating this is that In my application I am enabling VCO Doubler, so for the frequencies that are doubled will have any effect on lock time. Specifically speaking the lock time at 8GHz will not be same for 16GHz?? Is that so.. 

    2) But while programming do I need to transfer as binary format. I mean the Hex format is to be converted into Binary before transferring from master to slave device (LMX2595)?? Moreover As you have mentioned earlier that only 0x251C is converted in to binary which comes around 16-bits. But in general a total of 24-bits is to be transferred??

    Thanks for your patience reply. 

  • 0 in reply to singam vamshi krishna
    TI__Genius 11900 points

    Hello Singam,

    1. Yes, you are correct the lock time will not be the same. There will be a difference in the analog settling time. However this will vary case by case and depends on what frequency you are starting from as well. Your best bet to get an accurate estimate of the lock time is by using the https://www.ti.com/tool/PLLATINUMSIM-SW tool.
    2. You will program the device using SPI, so naturally you will need to send one bit on SDI at a time clocked by the SCK. Yes, if you look at the timing diagram you will see that you need to write a bit to inidicate read or write, a 7-bit address and a 16-bit register. So I believe 24-bits is correct.

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Intellectual 775 points

    Thanks for the reply.

    1) It is recommended by TI that before loading the all the registers RESET should be applied. May I know is there any specific register to RESET or else do I need to load all the registers with zeros.

    2)  How a particular set of register value performs the desired operation. I mean  how exactly are these register values calculated and extracted from TICS pro GUI. Could you please let me know what is the background operation.

    Thanks in Advance

  • 0 in reply to singam vamshi krishna
    TI__Genius 11900 points

    Hello Singam,

    The RESET is a particular register. In the LMX2595  this is R0[1] (register 0 bit 1).

    All the register functions and instructions on what to set each register to are provided in the datasheet starting page 48. Register settings can also be exported from TICSPRO-SW.

    Thanks,

    Vibhu