LMX2594: Trigger single ramp on external pin

For some reason pasting the image into the post did not work.. attempt number 2:

Hi Dominik,

You have put it automatic ramp mode so whenever RAMP_EN bit is checked, the ramp will get started. 

If you want to have the ramp triggered by RampCLK, use manual ramp mode by checking the RAMP_MANUAL bit.

Ramp limits are not very important, you can make them as shown below to allow for more margin.

Below diagram assumes that the VCO frequency will increment 1MHz every time there is a L-->H transition in RampClk pin. After 10 cycles, you can reverse the direction to make it jump back 10MHz to the original frequency.

Hello Noel,

I'm afraid this would not work for my application. I only want to trigger the start of the automatic ramping, not each individual increment. Then with each rising edge of the RampClk pin, start another ramp (not increment). Is this possible?

Hi Dominik,

I see, please try the followings:

Whenever RAMP_EN is enabled, RAMP0 will start but the frequency remain unchanged. It will not move to RAMP1 until a rising edge at RAMPClk pin is given. After finishing RAMP1, it will switch back to RAMP0 automatically. 

Hello,

Unfortunately, this also does not work.. every pulse of the RampClk pin causes the VCO to continue walking forward from a new start frequency (end of the last ramp). I believe RAMP0 needs to be reset and then it appears to work. However, still not quite how I would like. Ideally, I can allow no more than 5us between ramps, but they must be triggered via the RampClk signal because there is some configuration of other parts down the chain that happens in those 5 us. The Ramp must wait until that configuration is complete. I was hoping that I could set the RAMP0_LEN to 1 so that I could send the RampClk whenever and not be concerned that RAMP0 was still active. When I do this, the system simply ramps continuously. It seems there is some minimum LEN I must uphold. What is this value (it appears to be 2, but it is not mentioned in the datasheet as far as i can tell)?

Also, is it possible to trigger the next ramp while one is still running?

If there is to be a revision of the datasheet, I would recommend expanding the ramping section. In particular, explaining that the Ramp triggers are for transitioning from the END of a ramp to the NEXT ramp. This is quite different from a normal trigger which STARTS something.

Additionally, I've tried tuning the parameters slightly. I would like a ramp from 9500 - 9625 MHz without calibrating mid sweep in 30us. I realize this is quite a long frequency range, but I wanted to evaluate if it would be viable if the temperature was kept stable. I am not quite sure what I am seeing however. Could you explain this behavior? (see image)

Is this what is expected when pushing the VCO beyond the calibration-free range?

Hi Dominik,

My fault, RAMP1 cannot go back to RAMP0 directly because the end frequency is not equal to the start frequency. I modified the setting a little bit, please try it out.

Right, 125MHz calibration-free ramping is likely not possible at this VCO frequency because the Kvco is less than 100MHz/V.