AD9858SLASHFDPCB datasheet(23/32 Pages) AD

23 / 32 page

AD9858

Rev. C | Page 23 of 32

Address

(MSB)

(LSB)

Default

Name

Ser

Par

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value

Profile

Phase

Offset

Word 2

(POW2)

0x08

0x1A

Phase Offset Word 2[7:0]

0x1B

Not used

Phase Offset Word 2[13:8]

Frequency

Tuning

Word 3

(FTW3)

0x09

0x1C

Frequency Tuning Word 3[7:0]

0x1D

Frequency Tuning Word 3[15:8]

0x1E

Frequency Tuning Word 3[23:16]

0x1F

Frequency Tuning Word 3[31:24]

Phase

Offset

Word 3

(POW3)

0x0A

0x20

Phase Offset Word 3[7:0]

0x21

Not used

Phase Offset Word 3[13:8]

Reserved

0x0B

0x22

Reserved, do not write, leave at 0xFF

0xFE

N/A

0x23

Reserved, do not write, leave at 0xFF

0xFF

N/A

Control Function Register (CFR)

The CFR comprises four bytes. CFR is used to control the

various functions, features, and modes of the AD9858. The

functionality of each bit follows. Note that the register bits are

identified according to their serial register bit locations beginning

with the most significant bit.

CFR[31:30]: Frequency Detect Mode Charge Pump Current

These bits are used to set the scale factor for the frequency

detect mode charge pump output current (see Table 7). The

charge pump delivers the scaled output current when the

control logic forces the charge pump into its frequency detect

operating mode. The charge pump’s baseline output current

(ICP0) is determined by the external CPISET resistor and is

given by

ICP0 = 1.24/CPISET

The recommended nominal value of the CPISET resistor is

2.4 kΩ, which yields a baseline current of 500 μA.

Table 7.

CFR[31:30]

Frequency Detect Mode

Charge Pump Scale Value

Notes

IOUT = 0 (default)

IOUT = 20 × ICP0

IOUT = 40 × ICP0

IOUT = 60 × ICP0

CFR[29:27]: Final Closed-Loop Mode Charge Pump

Current

These bits are used to set the scale factor for the final closed-

loop mode charge pump output current (see Table 8). The

charge pump delivers the scaled output current when the control

logic forces the charge pump into its final closed-loop mode.

Table 8.

CFR[29:27]

Final Closed-Loop Mode

Charge Pump Scale Value

Notes

0xx

IOUT = 0 (default)

100

IOUT = ICP0

101

IOUT = 2 × ICP0

110

IOUT = 3 × ICP0

111

IOUT = 4 × ICP0

CFR[26:24]: Wide Closed-Loop Mode Charge Pump

Current

These bits are used to set the scale factor for the wide closed-

loop charge pump output current (see Table 9). The charge

pump delivers the scaled output current when the control logic

forces the charge pump into its wide closed-loop operating mode.

Table 9.

CFR[26:24]

Wide Closed-Loop Mode

Charge Pump Scale Value

Notes

000

IOUT = 0 (default)

001

IOUT = 2 × ICP0

010

IOUT = 4 × ICP0

011

IOUT = 6 × ICP0

100

IOUT = 8 × ICP0

101

IOUT = 10 × ICP0

110

IOUT = 12 × ICP0

111

IOUT = 14 × ICP0

CFR[23]: Auto Clear Frequency Accumulator Bit

When CFR[23] = 0 (default), a new delta frequency word is

applied to the input of the accumulator and added to the

currently stored value.

When CFR[23] = 1, this bit automatically synchronously clears

(loads zeros into) the frequency accumulator for one cycle upon

reception of the FUD sequence indicator.

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