AD9557SLASHPCBZ datasheet(71/92 Pages) AD

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Data Sheet

AD9557

Rev. A | Page 71 of 92

Table 60. History Accumulation Timer

Address

Bits

Bit Name

Description

0x0314

[7:0]

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 (ms)

History accumulation timer bits[15:8].

Default: 0x00.

Table 61. History Mode

Address

Bits

Bit Name

Description

[7:5]

Reserved

Reserved.

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.

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.

0x0316

[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]

Alpha-0 coefficient linear bits[7:0].

Default: 0x8C

0x0318

[7:0]

HPM Alpha-0 linear

Alpha-0 coefficient linear bits[15:8]

Reserved

0x0319

[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

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

Reserved

[6:0]

HPM Gamma-1 exponent

Gamma-1 coefficient exponent bits[6:0]

0x0320

[7:0]

Delta-0 coefficient linear bits[7:0]

0x0321

[7:0]

HPM Delta-0 linear

Delta-0 coefficient linear bits[15:8]

0x0322

Reserved

[6:0]

HPM Delta-1 exponent

Delta-1 coefficient exponent bits[6:0]

1Note 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.

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