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ADF5610 Register settings

Category: Datasheet/Specs
Product Number: ADF5610


Customer issue is: reference is connected (in this case 50MHz) everything works fine… the PLL locks everything is happy. When the unit is powered up with the reference disconnected, or off, the PLL will not lock when the reference is applied.

Now, while fiddling around with the registers trying to understand them, especially reg 5, if comment out those lines, basically leaving it to defaults, the PLL works in both cases. 50 MHz present or absent during power up the PLL locks when the reference is turned on.

The datasheet is a bit cryptic on the VCO subsystem register controlled by Register 5… need some help in decoding them and understanding why they cause this behavior.

Here’s one example of the register sets the customer is  using with the ADF5610…

  0x01000003,  //   Register 0x01 = 03

  0x02000001,  //   Register 0x02 = 01      (R)

  0x05000390,  //   Register 0x05 = 0390    (VCO Subsystem)

  0x05003E08,  //   Register 0x05 = 3E08    (VCO Subsystem)

  0x05000000,  //   Register 0x05 = 00      (VCO Subsystem)

  0x06002F4A,  //   Register 0x06 = 02F4A

  0x0700094D,  //   Register 0x07 = 094D

  0x08C9BEFF,  //   Register 0x08 = C9BEFF  (d, bit19=1)

  0x095B7FFF,  //   Register 0x09 = 5B7FFF

  0x0A002047,  //   Register 0x0A = 2047

  0x0B0F8061,  //   Register 0x0B = F8061

  0x0F000081,  //   Register 0x0F = 0081

  0x03000042,  //   Register 0x03 = 42      (Ni) 42   << Change this for  >>

  0x04600000   //   Register 0x04 = 600000  (Nf) 46   << BS1 & BS2 float>>

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  • Hi,

    If the reference is disconnected when running autocalibration we don't expect the part to lock after the reference is applied. The reference must be connected. 

    The datasheet is a bit cryptic on the VCO subsystem register controlled by Register 5… need some help in decoding them and understanding why they cause this behavior.

    Do you have any specific question about the VCO subsystem registers?

  • Thanks for the response.

    Customer needs better understanding of function and effects and settings of registers 0 and register 2. Please let me know if there are any reference material to address the customer's inquiries. Thanks. 

  • Hi,

    Reg 0 is used when using manual calibration (by-passing autocalibration). If the user has previously performed an autocal. on the part and read back the bands used for particular frequencies, they can then disable autocal, and manually write the band before changing frequency. This allows faster lock time. Bands from 0 to 255 are selectable. 

    Reg 2 is used to set the divider value on the P/N divider outputs. As well as to disable the differential output buffer. 

    When writing to the VCO subsystem, the user must perform a write to reg 0 last. 

    Regards,

    Kieran 

  • Hi,

    Our customer has the following comments:

    ....the list I included shows the order of writes (see below). I still don’t understand how this can keep the PLL from locking if powered up with the reference absent… this is my main problem.

    0x05000390,  //   Register 5 = 0x0390    (VCO Subsystem reg 0x02)

      0x05003E08,  //   Register 5 = 0x3E08    (VCO Subsystem reg 0x01)

      0x05000000,  //   Register 5 = 0x00      (VCO Subsystem reg 0x00)

  • The reason it does not work with the reference absent is that the part needs to have the reference present in order to perform an autocalibration to select the correct subband of operation for the frequency. If the part does not know what reference is used, it can not select the correct band. The autocalibration routine is documented on page 20 of the datasheet

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  • The reason it does not work with the reference absent is that the part needs to have the reference present in order to perform an autocalibration to select the correct subband of operation for the frequency. If the part does not know what reference is used, it can not select the correct band. The autocalibration routine is documented on page 20 of the datasheet

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