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LMX2594: Burst mode

Christer Andersson
Intellectual 290 points

Part Number: LMX2594

Hi,

Can you please explain burst mode. There is very little information in the datasheet.

What I'm basically looking for is if bust mode is the same thing as automatic ramping mode, but that it disables automatic ramping after a certain number of ramps are completed.

In more detail I want to output a triangle wave (i.e. 2 ramp segments, using both RAMP0 and RAMP1) and also use the RAMP_LIMITS_HIGH/LOW to flatten the peaks and valleys to shape the triangle wave. In one burst I would typically like to output 300 triangles.

Is this possible to do this by:

  • Program the ramp segments in the same way as would be done in automatic ramping mode
  • RAMP_BURST_COUNT = 300 (or should it be 600 as there are 2 ramp segments per triangle/period?)
  • RAMP_BURST_TRIG = 0 (this is called "Ramp transition" in the datasheet, is this the same as counter timeout of each ramp segment?)
  • RAMP_BURST_EN = 1
  • RAMP_EN = 1

Thanks,

Christer

  • 0
    TI__Mastermind 28031 points

    Crister,

    When using ramping with the LMX2594, I first want to make it clear that there is a limit to how far the VCO can ramp without recalibrating.  I lead with this because for some it is a showstopper, but for others, it is OK.  See attached document.  You may also find the TICSPro GUI helpful in this.

    2654.LMX2594 Calibration Free Ramping.pdf

    • RAMP_BURST_COUNT = 300 (or should it be 600 as there are 2 ramp segments per triangle/period?)
    • RAMP_BURST_TRIG = 0 (this is called "Ramp transition" in the datasheet, is this the same as counter timeout of each ramp segment?)
    • RAMP_BURST_EN = 1
    • RAMP_EN = 1

    Now, in regards to these programmable fields:

    RAMP_BURST_COUNT:

    After this event, the ramp is triggered.  You can choose "Ramp Transition", "Trigger A", or "Trigger B"  (I know TICSPro shows "Trigger C", but this makes no sense.  So if you choose "Ramp Transition", then if you have two ramps, you would set to 600

    RAMP_BURST_TRIG:

    This is the event that triggers the next count of the burst.  So if you set to 0, the action of the timoeout counter running to zero increments the count.  If you want to use one of the RAMP_CLK or RAMP_DIR pins to trigger, you could do this by defining this as Trigger A or Trigger B and setting to these triggers.

    RAMP_BURST_EN:

    By setting this equal to 1, this means that the RAMP_BURST_COUNT is run, otherwise the mode is ignored.

    RAMP_EN=1:

    The action of programming register R0 with RAMP_EN=1 starts the ramping.  However, if RAMP_BURST_EN=1, then this bit gets cleared to 0 after the burst count is finished.

    Regards,

    Dean