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LMX2492: Set MOD_PIN to reflect

user4107666
Prodigy 220 points
Part Number: LMX2492
Other Parts Discussed in Thread: CODELOADER, USB2ANY

Hi,

I am working with Codeloader 4 to control LMX2492, in repetitive ramp up and ramp down application  

According to the guidelines in the User's Guide SNAU160E–March 2014–Revised October 2017

I've tried to probe mod and trigger1 pin, but the signals are constant low

playing with the tool didn't have impact on the signal,

your support will be appreciated.

Thanks,

Zohar

 

  • 0
    TI__Expert 5370 points
    Dear Zohar,

    Thank you for your interest in LMX2492.

    I recommend you move to TiCS PRO software. You can find the software on ti.com.

    Then to see the output actuve, you need to do 2 things:

    1) set the pin as an output. for example mod_mux==output_mod
    2) set the output as pp for push/pull. look at MOD_PIN==output_pp

    I hope this will fix your problem.

    Regards, Simon.
  • 0 in reply to Simon Damphousse
    Prodigy 220 points

    Thank you for the fast response,

    I've used the TiCS PRO and followed the 2 settings, 

    the Mod is still stacked in zero,

    the LMX it actually being set   in CW or ramping but the triggers all stack and don't response

    please advice,

    Thanks,

    Zohar

  • 0 in reply to user4107666
    TI__Mastermind 28021 points

    Zohar,

    I don't know your exact situation, but let's assume that you have 2 ramps, RAMP0 and RAMP1.  You want MOD to go high during RAMP0 and TRIG1 to go high during RAMP1.

    What you could do is this (not the only way):

    RAMP0_FLAG = FLAG0

    MOD_MUX = Output Flag0 Ramp

    MOD_PIN = Output - PP

    RAMP1_FLAG = FLAG1

    TRIG1_MUX = Output Flag1 Ramp

    TRIG1_PIN = Output - PP

    Regards,
    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 220 points

    Hi Dean,

    It seems so trivial operation and still no response from the triggers,

    I can see the device response to sweep and cw

    I can also see the mode pin toggle ( using the CodeLoader4 Bits/Pins, program pins section by checking and unchecking the mode )

    The mode pin connected with 10K resistor to the usb2any header connector and I probe it with scope, and got no response

    Zohar

  • 0 in reply to user4107666
    TI__Mastermind 28021 points

    Zohar,

    The MUX pin can be either an input or output pin on our device, but the usb2any only can output to this pin.  So on the side of the 10 k resistor to the usb2any, the voltage should follow whatever state the MOD pin is checked in TICSPro in the User Controls tab.

     Now on the other side of the 10k resistor, this is the LMX2492.  If the LMX2492 is set to an input, then one would expect it to roughly track the usb2any voltage.  But if the LMX2492 MOD pin is set to output, then one would expect it to track the LMX2492.

    Looking at the EVM instructions, I see R71 is 10 k and is typically assembled.  If you probe where the test point should be (not the USB2ANY side), then this should be a direct connection to the actual chip output.

    As a diagnostic, have you tried just manually toggling the MOD pin?  In other words, try this:

    Set MOD_MUX = GND

    Toggle MOD_PIN between "Output - PP" and "Inverted Output - PP".  You should be able to see the voltage change.  

    Regards,

    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 220 points

    Hi Dean,

    Thanks for the tip, you just nail it down.

    I've probed the pin from the connector side and saw no trigger.

    probing the mod pin from the LMX side and it appear. (I am checking why it is with DC offset)

    can I remove the 10K series resistor from the MOD pin to the USB2ANY?

    Thanks,

    Zohar

  • 0 in reply to user4107666
    Prodigy 220 points
    Hi Dean,

    I made some progress and programmed ramp up and down 80Mhz LFM in 10us cycle

    I assigned the output flag0 ramp to the mod pin and noticed that the p-p of the mod pin trigger is 400mv

    when I changed the cycle time to 100us the mod pin trigger measured was 2.5V

    doe's it mean that the lmx loop filter need to be widen.... else .....

    thanks,

    Zohar
  • 0 in reply to user4107666
    Prodigy 220 points
    Hi Dean,

    short question in a raw,

    what is the minimum trigger width?

    the ramp test design is
    5800Mhz to 5880Mhz in 4.2us
    5880Mhz at 0.8us
    5880Mhz to 5800Mhz in 4.2us
    5800Mhz at 0.8us

    Is such scenario feasible?

    Thanks,

    Zohar
  • 0 in reply to user4107666
    TI__Guru** 110680 points
    Hi Zohar,

    This is an exceptionally fast ramping. In theory, the loop bandwidth has to be greater than 1MHz.
    Would you also provide the .tcs file of TICS Pro? This will help us understand your configuration in no time.
  • 0 in reply to Noel Fung
    Prodigy 220 points

    Hi Noel,

    Can you please explain how you derived 1MHz BW?

    Thanks very much!

  • 0 in reply to user4107666
    TI__Guru** 110680 points
    Hi Zohar,

    Analog loop lock time is approx. equal to 4/loop bandwidth. If the loop bandwidth is 1MHz, then the lock time is about 4µs.
  • 0 in reply to Noel Fung
    Prodigy 220 points

    Hi Dean,

    My application requires LMX2492 configuration with the following parameters

    1. The ramp start frequency is 5800Mhz up to 5880Mhz in 0.8us

    2. The pulse width is 0.3us repeated at interval of 10us - the pulse width wrap 30Mhz chirp out of 80Mhz ramp

    3. The chirp ramp returned4.4.2444f4.4.2 back to its starting point every 10Us using 4 segments ( stay low, ramp up, stay up, ramp down )

    4. I've used the PLLatinium utility to calculate a loop bandwidth of 2MHZ

    The measurement showed 40Mhz BW instead of 80Mhz BW ( several iteration tested with the same results)

    Please advice

     

    Attached 3 files 

    1. Code loader .mac ( this ramp configuration worked in my environment )

    2. Tics Pro  .tics ( same as Code loader, however doesn't work )

    3. PLLatinum .sim 

    lmx.zip

    Thanks,

    Zohar

  • 0 in reply to user4107666
    TI__Guru** 110680 points
    Hi Zohar,

    the analog lock time of a pll is approx. equal to 4 / LBW.
    If LBW is 1kHz, the lock time is about 4ms.
    Now you want 4us lock time, that implies the LBW has to be around 1MHz.