AD9520-4/PCBZ View Datasheet(PDF) - Analog Devices
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Description
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AD9520-4/PCBZ Datasheet PDF : 84 Pages
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AD9520-4
Mode 1: Clock Distribution or External VCO <1600 MHz
When the external clock source to be distributed or the external
VCO/VCXO is <1600 MHz, a configuration that bypasses the
VCO divider can be used. This is the only difference from Mode 2.
Bypassing the VCO divider limits the frequency of the clock
source to <1600 MHz (due to the maximum input frequency
allowed at the channel dividers).
Configuration and Register Settings
For clock distribution applications where the external clock is
<1600 MHz, the register settings shown in Table 23 should be used.
Table 23. Settings for Clock Distribution < 1600 MHz
Register
Description
0x010[1:0] = 01b
PLL asynchronous power-down (PLL off )
0x1E1[0] = 1b
Bypass the VCO divider as source for
distribution section
0x1E1[1] = 0b
CLK selected as the source
When using the internal PLL with an external VCO < 1600 MHz,
the PLL must be turned on.
Table 24. Settings for Using Internal PLL with External VCO
< 1600 MHz
Register
Description
0x1E1[0] = 1b
Bypass the VCO divider as source for
distribution section
0x010[1:0] = 00b
PLL normal operation (PLL on) along
with other appropriate PLL settings in
0x010 to 0x01E
An external VCO/VCXO requires an external loop filter that
must be connected between CP and the tuning pin of the VCO/
VCXO. This loop filter determines the loop bandwidth and stability
of the PLL. Make sure to select the proper PFD polarity for the
VCO/VCXO being used.
Table 25. Setting the PFD Polarity
Register
Description
0x010[7] = 0
PFD polarity positive (higher control voltage
produces higher frequency)
0x010[7] = 1
PFD polarity negative (higher control voltage
produces lower frequency)
Rev. 0 | Page 30 of 84
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