LMX2430 National Semiconductor Corporation, LMX2430 Datasheet - Page 42

• Manufacturer Part Number: LMX2430
• Description: Pllatinum Dual High Frequency Synthesizer For Rf Personal Communications
• Manufacturer: National Semiconductor Corporation

www.national.com
Reg
R2
2.0 Programming Description
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.
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.
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]
23
0
4095
22
0
…
0
1
2
3
4
Control Bit
RF_PD
21
0
20
0
19
0
Automatic Fastlock
Automatic Fastlock
FastLock Mode
Manual Fastlock
18
Register Location
Disabled
Disabled
Disabled
0
Enabled
Enabled
Enabled
…
17
0
R1[23]
16
0
15
0
DATA[20:0] FIELD
14
(Continued)
RF Powerdown
Fastlock Period
[PFD Events]
13
Description
4095
N/A
N/A
N/A
N/A
…
4
12
42
11
10
General Purpose.
High Impedance State
General Purpose.
Logic LOW State
General Purpose.
Logic LOW State
General Purpose.
Logic HIGH State
FastLock.
Logic LOW State.
Switches to High
Impedance after 4 PFD
events
FastLock.
Logic LOW State.
Switches to High
Impedance after 4095
PFD events
RF PLL Active
RF_TOC[11:0]
Functionality/ State
9
FLoutRF Pin
8
0
…
7
Function
6
RF PLL Powerdown
5
I
controlled by R0[19]
I
I
controlled by R0[19]
I
controlled by R0[19]
I
Switches to 1 mA after
4 PFD events
I
Switches to 1 mA after
4095 PFD events
CPoutRF
CPoutRF
CPoutRF
CPoutRF
CPoutRF
CPoutRF
I
CPoutRF
4
1
magnitude
= 4 mA
magnitude
magnitude
= 4 mA
= 4 mA
3
Magnitude
…
2
0
ADDRESS
FIELD
[2:0]
1
1
0
0