AD9516-5PCBZ datasheet(30/76 Pages) AD

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AD9516-5

Rev. A | Page 30 of 76

Automatic revertive switchover relies on the REFMON pin to

indicate when REF1 disappears. By programming Register 0x01B =

0xF7 and Register 0x01C = 0x26, the REFMON pin is programmed

to be high when REF1 is invalid, which commands the switch to

REF2. When REF1 is valid again, the REFMON pin goes low, and

the part again locks to REF1. The STATUS pin can also be used

for this function, and REF2 can be used as the preferred reference.

A switchover deglitch feature ensures that the PLL does not receive

rising edges that are far out of alignment with the newly selected

reference. Automatic nonrevertive switching is not supported.

Reference Divider R

The reference inputs are routed to the reference divider, R.

R (a 14-bit counter) can be set to any value from 0 to 16,383 by

writing to Register 0x011 and Register 0x012. (Both R = 0 and

R = 1 give divide-by-1.) The output of the R divider goes to one

of the PFD inputs to be compared with the VCO frequency divided

by the N divider. The frequency applied to the PFD must not

exceed the maximum allowable frequency, which depends on

the antibacklash pulse setting (see Table 2).

The R counter has its own reset. The R counter can be reset via

the shared reset bit of the R, A, and B counters. It can also be

reset by a SYNC operation.

VCXO/VCO Feedback Divider N—P, A, B

The N divider is a combination of a prescaler (P) and two

counters, A and B. The total divider value is

N = (P × B) + A

where P can be 2, 4, 8, 16, or 32.

Prescaler

The prescaler of the AD9516 allows for two modes of operation:

a fixed divide (FD) mode of 1, 2, or 3, and a dual modulus (DM)

mode where the prescaler divides by P and (P + 1) {2 and 3, 4

and 5, 8 and 9, 16 and 17, or 32 and 33}. The prescaler modes

of operation are given in Table 49, Register 0x016[2:0]. Not all

modes are available at all frequencies (see Table 2).

When operating the AD9516 in dual modulus mode, P/(P + 1),

the equation used to relate the input reference frequency to the

VCO output frequency is

fVCO = (fREF/R) × (P × B + A) = fREF × N/R

However, when operating the prescaler in FD Mode 1,

FD Mode 2, or FD Mode 3, the A counter is not used (A = 0)

and the equation simplifies to

fVCO = (fREF/R) × (P × B) = fREF × N/R

When A = 0, the divide is a fixed divide of P = 2, 4, 8, 16, or 32,

in which case, the previous equation also applies.

By using combinations of DM and FD modes, the AD9516

can achieve values of N all the way down to N = 1 and up to N =

26,2175. Table 24 shows how a 10 MHz reference input can be

locked to any integer multiple of N.

Table 24. Using a 10 MHz Reference to Generate Different VCO Frequencies

fREF (MHz)

fVCO (MHz)

Mode

Conditions/Comments

P = 1, B = 1 (A and B counters are bypassed).

P = 2, B = 1 (A and B counters are bypassed).

A counter is bypassed.

Maximum frequency into prescaler in P = 2/3 mode is 200 MHz.

If N = 7 or N = 11 is desired for prescaler input frequency of 200 MHz

to 300 MHz, use P = 1, and N = 7 or 11, respectively.

150

1500

151

1510

151

1510

200

2000

270

2700

P = 8 is not allowed (2700 ÷ 8 > 300 MHz).

P = 32 is not allowed (A > B not allowed).

2710

P = 32, A = 22, B = 84.

P = 16 is also permitted.

1 X = don’t care.

AD9516-5PCBZ Datasheet(PDF) 30 Page - Analog Devices

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