There are four 24-bit registers in the ADF4153/4 and seven such registers in the ADF4251/2. In this
calculator, each of the four registers is illustrated with field
labels and user inputs corresponding to the bit fields in the
real device. The width of the labels and elements is in proportion
to the bit field widths: a togglebox is used for 1-bit fields,
appropriately-sized pulldown menus for 2-16 choice fields, and
numerical text boxes for fields longer than 4 bits.
Changing the state of a bit field
recomputes the combined register value, expressed in hex, in a text
box located to the right of each register. Conversely, changing the
hex value in this box updates the individual bit fields that
compose the register.
The counter fields can be automatically computed from user
specifications for reference frequency, VCO frequency and channel
spacing (top left). Internal frequency limits are checked which
depend on the part and supply voltage (top center). When changing
channel spacing, R-counter or prescaler values, the calculator
attempts to preserve the VCO frequency, however, due to precision
of the various counters, the frequency will tend to drift
slightly. The prescaler may be adjusted to keep the VCO and channel spacing targets.
RSET can be calculated from a maximum desired
charge-pump current, ICP MAX, or the maximum current
can be found for a given RSET. These fields are
independent of the other calculator fields.
There is a dual-mode display at the bottom of the calculator which displays either bit-field help or shows a block diagram. Click on "Help" to the left of this display to select a help text field, and "Diagram" to show a block diagram of the ADF4153/4 or ADF4251/2. Help for most bitfields is available by clicking on the
field title, and is shown in yellow in the bottom display with the field title similarly highlighted. When in block diagram mode, many of the blocks are selectable and will highlight when clicked, along with the corresponding register bitfield.