LMX2346 National Semiconductor Corporation, LMX2346 Datasheet - Page 22

• Manufacturer Part Number: LMX2346
• Description: Pllatinum? Frequency Synthesizer For Rf Personal Communications
• Manufacturer: National Semiconductor Corporation

www.national.com
1.0 Functional Description
1.9 POWER-DOWN
The LMX2346/7 are power controlled through logical control
of the CE pin in conjunction with programming of the PD
control word. A truth table is provided that describes how the
state of the CE pin and the PD control word set the operating
mode of the device. A complete programming description for
the PD control word is provided in Section 2.3.1.
When the device enters the power-down mode, the oscillator
buffer, RF prescaler, phase detector, and charge pump cir-
cuits are all disabled. The OSC
are all forced to a high impedance state. The reference
divider and feedback divider circuits are disabled and held at
the load point during power-down. When the device is pro-
grammed to normal operation, the oscillator buffer, RF pres-
caler, phase detector, and charge pump circuits are all pow-
ered on. The feedback divider and the reference divider are
2.0 Programming Description
2.1 MICROWIRE INTERFACE
The MICROWIRE interface is comprised of an 18-bit shift register, and two control registers. The shift register consists of a 17-bit
DATA field and a 1-bit address (ADDR) field as shown below. When Latch Enable transitions HIGH, data stored in the shift register
is loaded into either the R or N register depending on the state of the ADDR bit. The data is loaded MSB first. The DATA field
assignments for the R and N registers are shown in Section 2.1.1.
2.1.1 Register Map
2.2 R REGISTER
The R register contains the R_CNTR, CP_TRI, PD_POL, LD_OUT, R_OPT control words. The detailed descriptions and
programming information for each control word is discussed in the following sections.
Register Most Significant Bit
R
N
Register Most Significant Bit
R
CE
0
1
1
1
1
17
17
R_OPT [2:0]
PD[1:0]
R_OPT [2:0]
X
0
1
2
3
16
16
15
15
Power-down (Asynchronous)
Normal Operation
Power-down (Synchronous)
Counter Reset
Power-down (Asynchronous)
14
LD_OUT [1:0] PD_POL
14
LD_OUT [1:0]
IN
Operating Mode
, CP
13
13
O
NB_CNTR [9:0]
, F
IN
MSB
DATA
17
, F
12
(Continued)
12
PD_POL
INB
ADDR
, LD pins
1
0
11
CP_TRI
SHIFT REGISTER BIT LOCATION
11
CP_TRI
Data Field
Data Field
SHIFT REGISTER BIT LOCATION
22
Target Register
R register
N register
held at the load point. This allows the RF Prescaler, feed-
back divider, reference oscillator, and the reference divider
circuitry to reach proper bias levels. After a 1.5 µs delay, the
feedback and reference divider are enabled and they re-
sume counting in “close” alignment (The maximum error is
one prescaler cycle). The MICROWIRE control register re-
mains active and capable of loading and latching in data
while in the power-down mode.
The synchronous power-down function is gated by the
charge pump. When the device is configured for synchro-
nous power-down, the device will enter the power-down
mode upon the completion of the next charge pump pulse
event.
The asynchronous power-down function is NOT gated by the
completion of a charge pump pulse event. When the device
is configured for asynchronous power-down, the part will go
into power down mode immediately.
A counter reset function is provided. When the PD control
word is programmed to Counter Reset, both the feedback
divider and the reference divider are disabled and held at
their load point. When the device is programmed to normal
operation, both the feedback divider and the reference di-
vider are enabled (without a delay) and resume counting in
“close” alignment (The maximum error is one prescaler
cycle).
10
10
9
1
ADDR
9
LSB
8
0
8
7
R_CNTR [9:0]
R_CNTR [9:0]
NA_CNTR [4:0]
7
6
6
5
4
5
4
3
Least Significant Bit
Least Significant Bit
3
2
PD [1:0]
2
1
1
0
ADDR
0
ADDR
1
1
0