AD9518-3/PCBZ Analog Devices Inc, AD9518-3/PCBZ Datasheet - Page 22
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AD9518-3/PCBZ
Manufacturer Part Number
AD9518-3/PCBZ
Description
BOARD EVAL FOR AD9518-3
Manufacturer
Analog Devices Inc
Specifications of AD9518-3/PCBZ
Main Purpose
Timing, Clock Generator
Utilized Ic / Part
AD9518-3
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
AD9518-3
THEORY OF OPERATION
OPERATIONAL CONFIGURATIONS
The AD9518 can be configured in several ways. These
configurations must be set up by loading the control registers
(see Table 41 and Table 42 through Table 48). Each section
or function must be individually programmed by setting the
appropriate bits in the corresponding control register or registers.
High Frequency Clock Distribution—CLK or External
VCO >1600 MHz
The AD9518 power-up default configuration has the PLL
powered off and the routing of the input set so that the
CLK/ CLK input is connected to the distribution section
through the VCO divider (divide-by-2/divide-by-3/divide-by-4/
divide-by-5/divide-by-6). This is a distribution-only mode that
allows for an external input up to 2.4 GHz (see Table 3). The
maximum frequency that can be applied to the channel dividers
is 1600 MHz; therefore, higher input frequencies must be divided
down before reaching the channel dividers. This input routing
can also be used for lower input frequencies, but the minimum
divide is 2 before the channel dividers.
When the PLL is enabled, this routing also allows the use of the
PLL with an external VCO or VCXO with a frequency less than
2400 MHz. In this configuration, the internal VCO is not used
and is powered off. The external VCO/VCXO feeds directly into
the prescaler.
The register settings shown in Table 20 are the default values
of these registers at power-up or after a reset operation. If the
contents of the registers are altered by prior programming after
power-up or reset, these registers may also be set intentionally
to these values.
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Table 20. Default Settings of Some PLL Registers
Register
0x10<1:0> = 01b
0x1E0<2:0> = 010b
0x1E1<0> = 0b
0x1E1<1> = 0b
When using the internal PLL with an external VCO, the PLL
must be turned on.
Table 21. Settings When Using an External VCO
Register
0x10 to 0x1E
0x1E1<1> = 0b
An external VCO requires an external loop filter that must be
connected between CP and the tuning pin of the VCO. This
loop filter determines the loop bandwidth and stability of the
PLL. Make sure to select the proper PFD polarity for the VCO
being used.
Table 22. Setting the PFD Polarity
Register
0x10<7> = 0b
0x10<7> = 1b
Function
PLL normal operation (PLL on)
PLL settings; select and enable a reference
input; set R, N (P, A, B), PFD polarity, and I
according to the intended loop configuration
Function
Set VCO divider = 4
Use the VCO divider
CLK selected as the source
Function
PFD polarity positive (higher control
voltage produces higher frequency)
PFD polarity negative (higher control
voltage produces lower frequency)
PLL asynchronous power-down (PLL off )
CP