AD9548BCPZ Analog Devices Inc, AD9548BCPZ Datasheet - Page 29

• Manufacturer Part Number: AD9548BCPZ
• Description: IC CLOCK GEN/SYNCHRONIZR 88LFCSP
• Manufacturer: Analog Devices Inc

Specifications of AD9548BCPZ

• Input: *
• Output: *
• Frequency - Max: *
• Voltage - Supply: *
• Operating Temperature: *
• Mounting Type: Surface Mount
• Package / Case: 88-LFCSP
• Frequency-max: *
• Clock Ic Type: Clock Synthesizer
• Ic Interface Type: Serial
• Frequency: 1GHz
• No. Of Outputs: 4
• No. Of Multipliers / Dividers: 4
• Supply Current: 190mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MSB of each nibble is the manual profile bit, whereas the
three LSBs of each nibble identify one of the eight profiles (0 to
7). A Logic 1 for the manual profile bit assigns the associated
reference to the profile identified by the three LSBs of the nibble.
A Logic 0 for the manual profile bit configures the associated
reference for automatic reference-to-profile assignment (the
three LSBs are ignored in this case). Note that references
configured for automatic reference-to-profile assignment
require activation (see the Reference-to-Profile Assignment
State Machine section).
Reference-to-Profile Assignment State Machine
The functional flexibility of the AD9548 resides in the way that
it assigns a particular input reference to one of the eight
reference profiles. The reference-to-profile assignment state
machine effectively builds a reference-to-profile table that maps
the index of each input reference to a profile (see Table 22).
Each entry in the profile column consists of a profile number
(0 to 7) or a null value. A null value appears when a reference-
to-profile assignment does not exist for a particular reference
input (following a reset, for example). The information in
Table 22 appears in the register map (Register 0D0C to Register
0D13) so that the user has access to the reference-to-profile
assignments on a real-time basis. Register 0D0C contains the
information for REF A, Register 0D0D contains the inform-
ation for REF AA, and so on to Register 0D13 for REF DD. Bit 7
of each register is the null indicator for that particular reference.
If Bit 7 = 0, then the profile assignment for that particular
reference is null. If Bit 7 = 1, then that particular reference is
assigned to the profile (0 to 7) identified by Bits[6:4]. Note that
Bits[6:4] are meaningless unless Bit 7 = 1.
Table 22. Reference-to-Profile Table
Reference
Input
A
AA
B
BB
C
CC
D
DD
Following a reset, the reference-to-profile assignment state
machine is inactive to avoid improperly assigning a reference to
a profile before the system clock stabilizes. The reason is that
the state machine relies on accurate information from the
reference monitors, which, in turn, rely on a stable system clock.
Because the reference-to-profile assignment state machine is
inactive at power-up, the user must initiate it manually by
writing to the reference profile detect register (Address 0A0D).
The state machine activates immediately, unless the system
clock is not stabilized, in which case, activation occurs upon
Reference
Index
0
1
2
3
4
5
6
7
Profile
Profile number (or null value)
Profile number (or null value)
Profile number (or null value)
Profile number (or null value)
Profile number (or null value)
Profile number (or null value)
Profile number (or null value)
Profile number (or null value)
Rev. A | Page 29 of 112
expiration of the system clock stability timer. Note that
initialization of the state machine is on a per-reference basis.
That is, each reference input is associated with an independent
initialization control bit.
Once initialized for processing a reference, the state machine
continuously monitors that reference until the occurrence of a
device reset. This is true even when the user programs a
reference for manual profile selection, in which case, the state
machine associated with that particular reference operates with
its activity masked. The masked background activity allows for
seamless operation if the user subsequently reprograms the
reference for automatic profile selection.
Reference-to-Profile Assignment
When a reference is programmed for manual profile assignment
(see Register 0503 to Register 0506), the reference-to-profile
assignment state machine simply puts the programmed manual
profile number into the profile column of the reference-to-
profile table (see Table 22) in the row associated with the appro-
priate reference. However, when the user programs a reference
for automatic profile assignment, the state machine must figure
out which profile to assign to the reference.
As long as a null entry appears in the reference-to-profile table
for a particular input reference, the validation logic for that
reference enters a period estimation mode. Note that a null
entry is the default state following a reset, but it also occurs
when a reference redetect timer expires. The period estimation
mode enables the validation logic to make a blind estimate of
the period of the input reference with a tolerance of 0.1%. The
validation logic remains in the period estimation mode until it
successfully estimates the reference period.
Upon a successful reference period measurement by the
validation logic, the state machine compares the measured
period to the nominal reference period programmed into each
of the eight profiles. The state machine assigns the reference to
the profile with the closest match to the measured period. If
more than one profile exactly matches the reference period,
then the state machine chooses the profile with the lowest
numeric index. For example, if the reference period in both
Profile 3 and Profile 5 matches the measured period, then
Profile 3 is given the assignment.
To safeguard against making a poor reference-to-profile
assignment, the state machine ensures that the measured
reference period is within 6.25% of the nominal reference
period that appears in the closest match profile. Otherwise, the
state machine does not make a profile assignment and leaves
the null entry in the reference-to-profile table.
As long as there are input references programmed for automatic
profile assignment, and for which the profile assignment is null,
the state machine continues to cycle through those references
searching for a profile match. Furthermore, unless an input
reference is assigned to a profile, it is considered invalid and
excluded as a candidate for a reference switchover.
AD9548