LMX2430 datasheet(42/49 Pages) NSC

42 / 49 page

2.0 Programming Description (Continued)

2.5.4 RF_PD - RF Synthesizer Powerdown (R1[23])

The RF_PD bit is used to switch the RF PLL between a powered up and powered down mode.

Furthermore, the RF_PD bit operates in conjuction with the RF_CPT bit to set a synchronous or an asynchronous powerdown

mode. Refer to Section 2.4.4 for more details on how to program the RF_CPT bit.

Control Bit

Description

Function

RF_PD

R1[23]

RF Powerdown

RF PLL Active

RF PLL Powerdown

2.6 R2 REGISTER

The R2 Register contains the RF_TOC control word. The RF_TOC is used to setup the RF syhnthesizer’s Fastlock circuitry. The

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

Reg

9876543210

DATA[20:0] FIELD

ADDRESS

[2:0]

FIELD

000000000

RF_TOC[11:0]

2.6.1 RF_TOC[0:11] - RF Synthesizer Timeout Counter (R2[14:3])

The FLoutRF pin can be configured as a general purpose CMOS TRI-STATE output or as a Fastlock output by programming the

RF_TOC appropriately. When the RF_TOC is programmed from 0 to 3, Automatic Fastlock is disabled, and the FLoutRF pin is

either configured as a general purpose CMOS TRI-STATE output or Manual Fastlock is enabled. When the RF_TOC is

programmed to 0, the FLoutRF pin will be in TRI-STATE (high impedance) mode. The charge pump current is then the value

specified by RF_CPG (R0[19]). When the RF_TOC is programmed to 1, the FLoutRF pin is pulled to a LOW state. The charge

pump current is then set to a HIGH gain state (RF_CPG bit = 1). This condition is known as the Manual Fastlock. When the

RF_TOC is programmed to 2, the FLout_RF pin will again be pulled to a LOW state, but this time the charge pump current is the

value specified by RF_CPG (R0[19]). When the RF_TOC is programmed to 3, the FLoutRF pin is pulled to a HIGH state. Again,

the charge pump current is the value specified by RF_CPG (R0[19]). When the RF_TOC is programmed from 4 to 4095, Fastlock

is enabled and the FLoutRF pin is pulled to a LOW state. Fastlock will time-out after the specified number of PFD events. At this

time, the FLoutRF pin will switch to TRI-STATE (high impedance) mode. The value programmed into RF_TOC represents the

number of PFD events that the RF synthesizer will spend in the Fastlock state. Note that any write to the RF_TOC requires a PFD

event on the RF synthesizer to latch the contents. This means that writes to the RF_TOC take effect synchronously with the next

PFD event.

RF_TOC[11:0]

FastLock Mode

Fastlock Period

[PFD Events]

FLoutRF Pin

Functionality/ State

CPoutRF Magnitude

Disabled

N/A

General Purpose.

High Impedance State

CPoutRF magnitude

controlled by R0[19]

Enabled

Manual Fastlock

N/A

General Purpose.

Logic LOW State

CPoutRF =4 mA

Disabled

N/A

General Purpose.

Logic LOW State

CPoutRF magnitude

controlled by R0[19]

Disabled

N/A

General Purpose.

Logic HIGH State

CPoutRF magnitude

controlled by R0[19]

Enabled

Automatic Fastlock

FastLock.

Logic LOW State.

Switches to High

Impedance after 4 PFD

events

CPoutRF =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

CPoutRF =4 mA

Switches to 1 mA after

4095 PFD events

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