HMC735 biasing question

I'm using the HMC735LP5E VCO with a divide-by-4 divider and noticed that the Electrical Specifications shown above the table on page indicates that bias for Vcc (Amp) is required. I see connections on the evaluation board for Vcc (Amp) but not in the functional block diagram for the part or in the pin descriptions. What's going on?   

Also, is there a bias sequence I should use on this part?

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  • 0
    •  Analog Employees 
    on Dec 21, 2017 11:57 PM

    This evaluation board is used across multiple models, some of which have an additional amplifier to boost the RFOUT /2 power (e.g. HMC632), this is not the case for the HMC735 however. The DS clearly has an error as it seems to indicate that  bias is required for a Vcc (Amp) in the Electrical Specifications. The functional block diagram correctly shows that there is no Vcc (Amp) connection and the applications circuit at the end of the datasheet shows that although it's connected to the Vcc (Amp) terminal it will remain floating. There is no internal connection on pin 7 of the HMC735.

     

    HMC735 Eval board (110225-3) biasing should be as follows:

     

    Vcc(RF) – pin 21 = 5.0Vdc – although I don’t believe there is a true power up sequence it would be best to apply Vcc(RF) first so that the input of the divider has a signal at power up.

          In general, some dividers will oscillate without an input signal – not sure if this one will or not. Typically the oscillation       doesn’t result in any damage but if we can avoid it that would be best.

     

    Vcc (Dig) – pin 6 = 5.0Vdc

     

    Vcc (Amp) – No Connection.

     

    Best Regards,

    Marty

Reply
  • 0
    •  Analog Employees 
    on Dec 21, 2017 11:57 PM

    This evaluation board is used across multiple models, some of which have an additional amplifier to boost the RFOUT /2 power (e.g. HMC632), this is not the case for the HMC735 however. The DS clearly has an error as it seems to indicate that  bias is required for a Vcc (Amp) in the Electrical Specifications. The functional block diagram correctly shows that there is no Vcc (Amp) connection and the applications circuit at the end of the datasheet shows that although it's connected to the Vcc (Amp) terminal it will remain floating. There is no internal connection on pin 7 of the HMC735.

     

    HMC735 Eval board (110225-3) biasing should be as follows:

     

    Vcc(RF) – pin 21 = 5.0Vdc – although I don’t believe there is a true power up sequence it would be best to apply Vcc(RF) first so that the input of the divider has a signal at power up.

          In general, some dividers will oscillate without an input signal – not sure if this one will or not. Typically the oscillation       doesn’t result in any damage but if we can avoid it that would be best.

     

    Vcc (Dig) – pin 6 = 5.0Vdc

     

    Vcc (Amp) – No Connection.

     

    Best Regards,

    Marty

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