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ADF4360-2 Vtune Voltage


Can Vtune voltage vary with different populations of ADF4360-2 for the same circuit board?

We have a Modulated RF signal from the DAC (AD9705BCPZ) that feeds into Vtune along with the Charge Pump (CP) Output.

Typically the Modulation shift of the DAC from the carrier frequency for all our previous board assemblies were set between 60 and 65 for a Vtune voltage of 1.5V.

With the latest set of assemblies the Vtune voltage output is now 2.0V and to get the frequency we need we've got to set the Modulation shift of the DAC from the carrier frequency to 85 so as to get the correct frequency output from the VCO.

Is it typically for the part to have such a  large change in its voltage to frequency slope. I am particularly interested in a more detailed explanation and understanding or figure 14 of the datasheet between 1900MHz and 2000MHz. We use the divide by 2 option of the ADF4360-2.


  • Hello,

    The internal VCO is constructed such that Vtune values  between 1.4 and 2.4, do not go to the extreme edges of the band, so whether your Vtune is at middle of the band or the edge is not an issue , you will get equally  equivalent datasheet performance over the Vtune voltage range of 1.4Volts to 2.5Volts. The band select calibration that occurs when you power up / change channels ensures that the band selected places the Vtune within the specified range.

    Designing for a specific Vtune / o/p frequency will be difficult, as you will get part variation between lots , which will vary the Vtune, and this is what is happening in this case.

    For an external VCO, yes you should keep the Vtune close  to the centre of the VCO where possible , however when you compare to our internal VCO with overlapping bands, the centre point of the external VCO is equivalent to the centre band of the 8 overlapping bands as shown in fig 14.

    I hope this helps,



  • Hi,

    Thanks for your email and response. This is helpful.

    We understand the variation in Vtune voltage and keeping it in the center of the band but we still don’t understand the steep slope change (Figure 14 Voltage Vs frequency). Any thoughts on that?

    The Modulated DAC output controls the Vtune voltage in our design, so should we expect such large variations in Vtune and account for that in our DAC settings (65 to 85?) that's a 30% change.



  • Hello Behlul,

    I am sending you an email in order to get more detail on your scheamtics and application, regards, Brigid

    ( PS: we can close this discussion on EZ)

  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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