LMX2430 datasheet(44/49 Pages) NSC

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2.0 Programming Description (Continued)

2.7.3 IF_CPG - IF Synthesizer Charge Pump Current Gain (R3[19])

The IF_CPG bit controls the IF synthesizer’s charge pump gain. Two gain levels are available.

Control Bit

Description

Function

IF_CPG

R3[19]

IF Charge Pump

Current Gain

LOW

1mA

HIGH

4mA

2.7.4 IF_CPT - IF Synthesizer Charge Pump TRI-STATE (R3[20])

The IF_CPT bit allows the charge pump to be switched between a normal operating mode and a high impedance output state.

This happens asynchronously with the change in the IF_CPT bit.

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

mode. Refer to Section 2.8.4 for more details on how to program the IF_PD bit.

Control Bit

Description

Function

IF_CPT

R3[20]

IF Charge Pump

TRI-STATE

IF Charge Pump

Normal Operation

IF Charge Pump

Output in High

Impedance State

2.7.5 IF_RST - IF Synthesizer Counter Reset (R3[21])

The IF_RST bit resets of the IF_A, IF_B and IF_R counters. After removing the reset, the IF_A and IF_B counters resume

counting in close alignment with the IF_R counter. The maximum error is one prescaler cycle.

Control Bit

Description

Function

IF_RST

R3[21]

IF Counter Reset

IF_A, IF_B and IF_R

Normal Operation

IF_A, IF_B and IF_R

Reset

2.8 R4 REGISTER

The R4 register contains the IF_A, IF_B, IF_P, and IF_PD control words. The IF_A and IF_B control words are used to setup the

programmable feedback divider. The detailed descriptions and programming information for each control word is discussed in the

following sections. R4[21] is always set to 0.

Reg

9876543210

DATA[20:0] FIELD

ADDRESS

[2:0]

FIELD

IF_

IF_B[13:0]

IF_A[3:0]

2.8.1 IF_A[3:0] - IF Synthesizer Swallow Counter (A Counter) (R4[6:3])

The IF_A control word is used to setup the IF synthesizer’s A counter. The A counter is a 4-bit swallow counter used in the

programmable feedback divider. The IF_A control word can be programmed to values ranging from 0 to 15.

Divide Ratio

IF_A[3:0]

321

000

•

•••

•

111

LMX2430 Datasheet(PDF) 44 Page - National Semiconductor (TI)

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