LMX2430 datasheet(46/49 Pages) NSC

46 / 49 page

2.0 Programming Description (Continued)

2.9 R5 REGISTER

The R5 Register contains the IF_TOC control word. The IF_TOC is used to setup the IF syhnthesizer’s Fastlock circuitry. The

IF_TOC is a 12-bit binary counter programmable from 0 to 4095.

Reg

9876543210

DATA[20:0] FIELD

ADDRESS

[2:0]

FIELD

000000000

IF_TOC[11:0]

2.9.1 IF_TOC[0:11] - IF Synthesizer Timeout Counter (R5[14:3])

The OSCout/ FLoutIF pin can be configured as a general purpose CMOS TRI-STATE output or as a Fastlock output by

programming the IF_TOC appropriately. When the IF_TOC is programmed from 0 to 3, Automatic Fastlock is disabled, and the

OSCout/ FLoutIF pin is configured as a general purpose CMOS TRI-STATE output or Manual Fastlock is enabled. When the

IF_TOC is programmed to 0, the OSCout/ FLoutIF pin will be in TRI-STATE (high impedance) mode. The charge pump current

is then the value specified by IF_CPG (R3[19]). When the IF_TOC is programmed to 1, the OSCout/ FLoutIF pin is pulled to a

LOW state. The charge pump current is then set to a HIGH gain state (IF_CPG bit = 1). This condition is known as the Manual

Fastlock. When the IF_TOC is programmed to 2, the OSCout/ FLout_IF pin will again be pulled to a LOW state, but this time the

charge pump current is the value specified by IF_CPG (R3[19]). When the IF_TOC is programmed to 3, the OSCout/ FLoutIF pin

is pulled to a HIGH state. Again, the charge pump current is the value specified by IF_CPG (R3[19]). When the IF_TOC is

programmed from 4 to 4095, Fastlock is enabled and the OSCout/ FLoutIF pin is pulled to a LOW state. Fastlock will time-out after

the specified number of PFD events. At this time, the OSCout/ FLoutIF pin will switch to TRI-STATE (high impedance) mode. The

value programmed into IF_TOC represents the number of PFD events that the IF synthesizer will spend in the Fastlock state.

Note that any write to the IF_TOC requires a PFD event on the IF synthesizer to latch the contents. This means that writes to the

IF_TOC take effect synchronously with the next PFD event.

IF_TOC[11:0]

FastLock Mode

Fastlock Period

[PFD Events]

OSCout/ FLoutIF Pin

Functionality/ State

CPoutIF Magnitude

Disabled

N/A

General Purpose.

High Impedance State

CPoutIF magnitude

controlled by R3[19]

Enabled

Manual Fastlock

N/A

General Purpose.

Logic LOW State

CPoutIF =4 mA

Disabled

N/A

General Purpose.

Logic LOW State

CPoutIF magnitude

controlled by R3[19]

Disabled

N/A

General Purpose.

Logic HIGH State

CPoutIF magnitude

controlled by R3[19]

Enabled

Automatic Fastlock

FastLock.

Logic LOW State.

Switches to High

Impedance after 4 PFD

events

CPoutIF =4 mA

Switches to 1 mA after

4 PFD events

…

………

…

4095

Enabled

Automatic Fastlock

4095

FastLock.

Logic LOW State.

Switches to High

Impedance after 4095

PFD events

CPoutIF =4 mA

Switches to 1 mA after

4095 PFD events

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