Datasheet

Data Sheet AD9557
Rev. B | Page 71 of 92
Table 60. History Accumulation Timer
Address Bits Bit Name Description
0x0314
[7:0] History accumulation timer (ms) History accumulation timer bits[7:0].
Default: 0x0A. For Register 0x0314 and Register 0x0315, 0x000A = 10 ms.
Maximum is 65 sec. This register controls the amount of tuning word averaging used to
determine the tuning word used in holdover. Never program a timer value of zero.
The default value is 0x000A = 10 decimal, which equates to 10 ms.
0x0315
[7:0] History accumulation timer bits[15:8].
Default: 0x00.
Table 61. History Mode
Address Bits Bit Name Description
0x0316
[7:5] Reserved Reserved.
4
Single sample fallback Controls holdover history. If tuning word history is not available for the reference
that was active just prior to holdover, then:
0 (default) = uses the free run frequency tuning word register value.
1 = uses the last tuning word from the DPLL.
3
Persistent history Controls holdover history initialization. When switching to a new reference:
0 (default) = clear the tuning word history.
1 = retain the previous tuning word history.
[2:0]
Incremental average
History mode value from 0 to 7 (default: 0).
When set to non-zero, causes the first history accumulation to update prior to the
first complete averaging period. After the first full interval, updates occur only at the
full period.
0 (default) = update only after the full interval has elapsed.
1 = update at 1/2 the full interval.
2 = update at 1/4 and 1/2 of the full interval.
3 = update at 1/8, 1/4, and 1/2 of the full interval.
...
7 = update at 1/256, 1/128, 1/64, 1/32, 1/16, 1/8, 1/4, and 1/2 of the full interval.
Table 62. Base Digital Loop Filter with High Phase Margin (PM = 88.5°, BW = 0.1 Hz, Third Pole Frequency = 10 Hz, N1 = 1)
1
Address
Bits
Bit Name
Description
0x0317 [7:0] HPM Alpha-0 linear Alpha-0 coefficient linear bits[7:0].
Default: 0x8C
0x0318
[7:0] Alpha-0 coefficient linear bits[15:8]
0x0319
7 Reserved Reserved
[6:0] HPM Alpha-1 exponent Alpha-1 coefficient exponent bits[6:0]
0x031A
[7:0] HPM Beta-0 linear Beta-0 coefficient linear bits[7:0]
0x031B
[7:0] Beta-0 coefficient linear bits[15:8]
0x031C
7
Reserved
Reserved
[6:0] HPM Beta-1 exponent Beta-1 coefficient exponent bits[6:0]
0x031D
[7:0] HPM Gamma-0 linear Gamma-0 coefficient linear bits[7:0]
0x031E
[7:0]
Gamma-0 coefficient linear bits[15:8]
0x031F 7 Reserved Reserved
[6:0] HPM Gamma-1 exponent Gamma-1 coefficient exponent bits[6:0]
0x0320 [7:0] HPM Delta-0 linear Delta-0 coefficient linear bits[7:0]
0x0321
[7:0] Delta-0 coefficient linear bits[15:8]
0x0322
7 Reserved Reserved
[6:0] HPM Delta-1 exponent Delta-1 coefficient exponent bits[6:0]
1
Note that the base digital loop filter coefficients (α, β, γ, and δ) have the following general form: x(2y), where x is the linear component and y is the exponential
component of the coefficient. The value of the linear component (x) constitutes a fraction, where 0 ≤ x ≤ 1. The exponential component (y) is a signed integer.