LMX2505
PLLatinum™ Dual Frequency Synthesizer System
with Integrated VCOs
General Description
Features
LMX2505 is a highly integrated, high performance, low
power frequency synthesizer system optimized for dualband Japan PDC mobile handsets. Using a proprietary digital phase locked loop technique, LMX2505 generates very
stable, low noise local oscillator signals for up and down
conversion in wireless communications devices.
n Small Size
5.0 mm X 5.0 mm X 0.75 mm 28-Pin LLP Package
n RF Synthesizer System
Two Integrated VCOs
Integrated Loop Filter
Low Spurious, Low Phase Noise Fractional-N RF PLL
Based on 10-Bit Delta Sigma Modulator
Frequency Resolution Down to 20 kHz
n Supports Various Reference Frequencies
12.6/14.4/25.2/26.0 MHz
n Fast Lock Time: 300 µs
n Low Current Consumption
10 mA at 2.8 V in PDC800 Mode
n 2.5 V to 3.3 V Operation
n Digital Filtered Lock Detect Output
n Hardware and Software Power Down Control
LMX2505 includes dual voltage controlled oscillators (VCOs)
for the upper and lower Japan PDC frequency bands, a loop
filter, and a fractional-N RF PLL based on a delta sigma
modulator. In concert these blocks form a closed loop RF
synthesizer system. The RF synthesizer system supports
two frequency bands: PDC1500 and PDC800.
Serial data is transferred to the device via a three-wire
MICROWIRE interface (DATA, LE, CLK).
Operating supply voltage ranges from 2.5 V to 3.3 V.
LMX2505 features low current consumption: 10 mA at 2.8 V
when operating in the PDC800 mode.
LMX2505 is available in a 28-pin leadless leadframe package (LLP).
Applications
n Japan PDC Systems at 800 MHz and 1500 MHz
Frequency Bands.
Functional Block Diagram
20067107
FastLock™ is a trademark of National Semiconductor Corporation.
TRI-STATE ® is a registered trademark of National Semiconductor Corporation.
PLLatinum™ is a trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation
DS200671
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LMX2505 PLLatinum Dual Frequency Synthesizer System with Integrated VCOs
April 2004
LMX2505
Connection Diagram
28-Pin 5x5 LLP (LQ) Package
20067102
NOTE: Analog ground connected through exposed die attached pad.
Pin Descriptions
Pin Number
Name
I/O
1
OSCin
I
2
GND
—
Ground for digital circuitry
3
VDD
—
Supply voltage for analog circuitry
4
GND
—
Ground for analog circuitry
5
NC
—
Do not connect to any node on the printed circuit board.
6
NC
—
Do not connect to any node on the printed circuit board.
7
VDD
—
Supply voltage for RF analog circuitry
8
NC
—
Do not connect to any node on the printed circuit board.
9
L1
—
RF2 VCO tank pin. An external inductor is required between pins
L1 and L2 to set the resonant frequency of RF2 VCO (PDC800).
10
L2
—
RF2 VCO tank pin. An external inductor is required between pins
L1 and L2 to set the resonant frequency of RF2 VCO (PDC800).
11
NC
—
Do not connect to any node on the printed circuit board.
12
NC
—
Do not connect to any node on the printed circuit board.
13
VDD
—
Supply voltage for RF analog circuitry
14
RF1out
O
RF output of RF1 VCO for PDC1500
15
VDD
—
Supply voltage for RF analog circuitry
16
RF2out
O
RF output of RF2 VCO for PDC800
17
VDD
—
Supply voltage for analog circuitry
18
GND
—
Ground for digital circuitry
19
VCC
—
Supply voltage for digital circuitry
20
GND
—
Ground for digital circuitry
21
VCC
—
Supply voltage for digital circuitry
22
LE
I
MICROWIRE Latch Enable
23
DATA
I
MICROWIRE Data
24
CLK
I
MICROWIRE Clock
25
CE
I
Chip enable control pin
26
BS
I
Band select control pin
27
LD
O
Lock detect pin
28
VCC
—
Supply voltage for digital circuitry
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Description
Reference frequency input
2
Part Number
RF1 Min.
(MHz)
LMX2505LQX1321
1270.22
RF1 Max. RF1
(MHz)
Center
(MHz)
~
1394.95
1321
LMX2505LQ1321
1270.22
1394.95
~1321
RF2 Min. RF2 Max.
(MHz)
(MHz)
Package
Marking
Supplied As
633.15
768.0
25051321
4500 units on
tape and reel
633.15
768.0
25051321
1000 units on
tape and reel
Part Number Description
20067103
Typical Application Circuit
(Note 1)
20067104
Note 1: Refer to RF2 VCO Tuning Range vs. External Inductance plot to aid in selecting the appropriate external inductance, PCB trace and L1, for the desired
frequency range.
3
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LMX2505
Ordering Information
LMX2505
Absolute Maximum Ratings (Notes 2, 3,
Recommended Operating
Conditions
4)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Parameter
Symbol
Supply Voltage
VCC, VDD -0.5 to 3.6
V
Voltage on any pin
to GND
VI
V
Storage Temperature TSTG
Range
Ratings
-0.3 to VDD+0.3
V
-65 to 150
˚C
Symbol
Min Typ Max Unit
Ambient Temperature
TA
-30 25
Supply Voltage (to GND) VCC, VDD 2.5
Units
-0.3 to VCC+0.3
Parameter
85
˚C
3.3
V
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to
the device may occur. Recommended Operating Conditions indicate conditions for which the device is intended to be functional, but do not guarantee
specific performance limits. For guaranteed specifications and test conditions, refer to the Electrical Characteristics section. The guaranteed specifications apply only for the conditions listed.
Note 3: This device is a high performance RF integrated circuit with an ESD
rating < 2 kV and is ESD sensitive. Handling and assembly of this device
should be done at ESD protected workstations.
Note 4: GND = 0 V.
Electrical Characteristics (VIN = 2.8 V, refer to Typical Application Circuit; Limits in standard typeface are
for TA = 25 ˚C; Limits in boldface type apply over the operating temperature range from -20 ˚C ≤ TA ≤ 75 ˚C unless otherwise noted.)
Symbol
Parameter
Condition
Min
Typ
Max
Units
OB_CRL [1:0] = 11
11.5
13.0
13.3
mA
OB_CRL [1:0] = 00
10.0
11.5
11.8
mA
OB_CRL [1:0] = 11
16.0
17.5
17.8
mA
OB_CRL [1:0] = 00
14.2
15.6
15.9
mA
20
µA
14.4
26.0
MHz
0.5
VCC
Vp-p
1394.95
MHz
ICC PARAMETERS
ICC + IDD
ICC + IDD
IPD
Supply Current (Note 5)
Supply Current (Note 6)
Power Down Current
CE = LOW or
RF_PD = 1
REFERENCE OSCILLATOR PARAMETERS
fOSCin
Reference Oscillator Input Frequency 12.6/14.4/25.2/26.0 MHz are
(Note 7)
supported.
VOSCin
Reference Oscillator Input Sensitivity
12.6
RF1 VCO for PDC1500
fRF1out
Frequency Range (Note 8)
RF1 VCO for PDC1500
PRF1out
Output Power
OB_CRL [1:0] = 11
-5
-2
1
dBm
OB_CRL [1:0] = 10
-7
-4
-1
dBm
Lock Time
1270.22
OB_CRL [1:0] = 01
-10
-7
-4
dBm
OB_CRL [1:0] = 00
-13
-10
-7
dBm
Full frequency span within
each band in High Speed
Mode.
300
(Note 9)
µs
Between bands High Speed
Mode.
300
(Note 9)
µs
Full frequency span within
each band in Normal Mode.
500
(Note 9)
µs
375
(Note 10)
µs
500
(Note 9)
µs
400
(Note 10)
µs
Between bands in Normal
Mode.
RMS Phase Error
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1.3
4
degrees
Symbol
Parameter
Condition
Min
Typ
Max
Units
@ 25 kHz offset
-95
-93
-91
dBc/Hz
@ 50 kHz offset
-106
-103
-101
dBc/Hz
@ 100 kHz offset
-115
-113
-111
dBc/Hz
-135
-133
dBc/Hz
2nd Harmonic Suppression
-25
dBc
3rd Harmonic Suppression
-20
dBc
-45
dBc
@ 25 kHz
-60
dBc
@
-69
dBc
-75
dBc
RF1 VCO for PDC1500
L(f)RF1out
Phase Noise when RF1 VCO for
PDC1500 is activated in Normal
Mode.
@ 1 MHz offset
Spurious Tones
@ ≤ 25 kHz offset
@
< offset ≤ 50 kHz
50 kHz < offset ≤ 100 kHz
offset > 100 kHz
RF2 VCO for PDC800
fRF2out
Frequency Range (Note 8)
RF2 VCO for PDC800
768
MHz
PRF2out
Output Power
OB_CRL [1:0] = 11
-6
-3
0
dBm
OB_CRL [1:0] = 10
-9
-6
-3
dBm
Lock Time
633.15
OB_CRL [1:0] = 01
-11
-8
-5
dBm
OB_CRL [1:0] = 00
-15
-12
-9
dBm
Full frequency span within
each band in High Speed
Mode.
300
(Note 9)
µs
Between bands High Speed
Mode.
300
(Note 9)
µs
Full frequency span within
each band in Normal Mode.
500
(Note 9)
µs
375
(Note 10)
µs
500
(Note 9)
µs
400
(Note 10)
µs
Between bands in Normal
Mode.
L(f)RF2out
RMS Phase Error
1.3
@ 25 kHz offset
Phase Noise when RF2 VCO for
PDC800 is activated in Normal Mode.
-95
-93
-91
dBc/Hz
@ 50 kHz offset
-106
-103
-101
dBc/Hz
@ 100 kHz offset
-115
-113
-111
dBc/Hz
-135
-133
dBc/Hz
-25
dBc
@ 1 MHz offset
2nd Harmonic Suppression
3rd Harmonic Suppression
Spurious Tones
@ ≤ 25 kHz offset
@ 25 kHz
@ 50 kHz
@ offset
< offset ≤ 50 kHz
< offset ≤ 100 kHz
> 100 kHz
5
degrees
-20
dBc
-45
dBc
-60
dBc
-69
dBc
-75
dBc
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LMX2505
Electrical Characteristics (VIN = 2.8 V, refer to Typical Application Circuit; Limits in standard typeface are for
TA = 25 ˚C; Limits in boldface type apply over the operating temperature range from -20 ˚C ≤ TA ≤ 75 ˚C unless otherwise
noted.) (Continued)
LMX2505
Electrical Characteristics (VIN = 2.8 V, refer to Typical Application Circuit; Limits in standard typeface are for
TA = 25 ˚C; Limits in boldface type apply over the operating temperature range from -20 ˚C ≤ TA ≤ 75 ˚C unless otherwise
noted.) (Continued)
Symbol
Parameter
Condition
Min
Typ
Max
Units
0.8 VCC
VCC
V
0.8 VDD
VDD
V
-0.3
0.2 VCC
V
-0.3
0.2 VDD
V
DIGITAL INTERFACE (DATA, CLK, LE, LD, CE, BS)
VIH
VIL
High-Level Input Voltage
Low-Level Input Voltage
IIH
High-Level Input Current
-10
10
µA
IIL
Low-Level Input Current
-10
10
µA
Input Capacitance
Rise/Fall Time
VOH
VOL
High-Level Output Voltage
3
pF
30
ns
VCC - 0.4
V
VDD - 0.4
V
Low-Level Output Voltage
Output Capacitance
0.4
V
5
pF
MICROWIRE INTERFACE TIMING
tCS
Data to Clock Set Up Time
50
ns
tCH
Data to Clock Hold Time
10
ns
tCWH
Clock Pulse Width HIGH
50
ns
tCWL
Clock Pulse Width LOW
50
ns
tES
Clock to Latch Enable Set Up Time
50
ns
tEW
Latch Enable Pulse Width
50
ns
Note 5: RF PLL and VCO in PDC800 mode.
Note 6: RF PLL and VCO in PDC1500 mode.
Note 7: The reference frequency must also be programmed using the OSC_FREQ control bit. For other reference frequencies, please contact National
Semiconductor.
Note 8: For other frequency ranges, please contact National Semiconductor.
Note 9: Lock time is defined as the time difference between the beginning of the frequency transition and the point at which the frequency remains within +/-1 kHz
of the final frequency.
Note 10: Lock time is defined as the time difference between the beginning of the frequency transition and the point at which the frequency remains within +/-3 kHz
of the final frequency.
Note 11: All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with TA = 25 ˚C or correlated using
Statistical Quality Control (SQC) methods. All hot and cold limits are guaranteed by correlating the electrical characteristics to process and temperature variations
and applying statistical process control.
Microwire Interface Timing Diagram
20067101
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6
LMX2505
Typical Performance Characteristics
(Note 12)
RF2 VCO Tuning Range vs. External Inductance (Note 13)
VIN = 2.8 V
20067111
Note 12: Typical performance characteristics do not guarantee specific performance limits. For guaranteed specifications, refer to the Electrical Characteristics
section.
Note 13: The frequency range is defined as the difference between the highest frequency and the lowest frequency of a given unit. For a chosen external
inductance, the typical frequency range equals the difference between the Typical Maximum Frequency and the Typical Minimum Frequency. Typical frequency
range may be assumed on any unit with that chosen external inductance, even if the unit has worst case Maximum Frequency or worst case Minimum Frequency.
7
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LMX2505
Functional Description
GENERAL
The LMX2505 is a highly integrated frequency synthesizer
system for Japan PDC wireless communication systems.
The LMX2505 supports dual band operation for 800 MHz
and 1500 MHz.
20067110
where Ctotal is the total capacitance of the VCO, including
the parasitic capacitance and the nominal self-tuning capacitance. Note, the external inductance consists of the PCB
traces and lumped element inductor. The output frequency
tuning range can be optimized for the specific application by
selecting the appropriate external inductance. Refer to RF2
VCO Tuning Range vs. External Inductance plot to aid in
selecting the appropriate external inductance. Care should
be taken to ensure proper frequency coverage when choosing the tolerance of the lumped element inductor. For the
1500 MHz band, the internal bonding-wires provide the necessary inductance to set the VCO center frequency.
The LMX2505 includes all functional blocks for the RF PLL
including RF VCOs, frequency dividers, PFDs, and loop
filters. Only external passive elements for the RF2 VCO tank
and supply bypassing are required to complete the RF synthesizer.
The LMX2505 uses a patent pending Fractional-N synthesizer architecture based on a delta sigma modulator to support fine frequency resolution. Four of the most common
reference frequencies for PDC applications, 12.6 MHz, 14.4
MHz, 25.2 MHz and 26.0 MHz, are supported. The unique
feature of this architecture is its low spurious modulation
effect.
The use of a fractional synthesizer based on delta sigma
modulator allows for fast lock-up and system set-up times,
which reduces system power consumption. The loop filter is
included in the circuit to minimize the external noise coupling
and reduce the form factor applicable to the board level
application. Only one of the two RF VCOs is activated at a
given time, and each output is provided through its own
output pin.
RF_PLL SECTION
Frequency Selection
20067105
The divide ratio can be calculated using the following equations:
fVCO = {8 x RF_B + RF_A + (RF_FN / FD)} x (fOSC / R) where
(RF_A < RF_B) for PDC1500
fVCO = {4 x RF_B + RF_A + (RF_FN / FD)} x (fOSC / R) where
(RF_A < RF_B) for PDC800
fVCO: Output frequency of voltage controlled oscillator (VCO)
FIGURE 1. External Inductor Connection
In real implementation, the inductance of Lfixed and Lexternal
can vary from its nominal value. The LMX2505 utilizes a
built-in tracking algorithm to compensate for variations up to
± 15% and tunes the VCO to the required frequency. During
the frequency acquisition period, the loop bandwidth is extended to achieve the frequency lock. After the frequency
lock, the loop bandwidth of the PLL is set to the nominal
value and the phase lock is achieved. The transition between the two operating modes is very smooth and extremely fast to meet the stringent PDC requirements for lock
time and phase noise.
RF_B: Preset divide ratio of binary 4-bit programmable
counter (2 ≤ RF_B ≤ 15)
RF_A: Preset divide ratio of binary 3-bit swallow counter (0 ≤
RF_A ≤ 7 for PDC1500 and 0 ≤ RF_A ≤ 3 for PDC800)
RF_FN: Preset numerator of binary 10-bit modulus counter
(0 ≤ RF_FN < FD)
FD: Preset denominator for modulus counter (FD = fOSC/(R
X fCH) where fCH is the channel spacing)
fOSC: Reference oscillator frequency
R: Internal reference oscillator frequency divider (1 for 12.6
MHz and 14.4 MHz, 2 for 25.2 MHz and 26.0 MHz)
The denominator, FD, in the above equation is dependent on
the channel spacing and reference oscillator frequency. The
channel spacing will change based on the Rx/Tx and BS
bits. Table 6 in the R0 Register section summarizes the
values of FD.
POWER DOWN MODE
The LMX2505 includes the power down mode to reduce the
power consumption. The LMX2505 enters the power down
mode either by taking the CE pin LOW or by setting the
RF_PD bit in the R0 register. If the CE pin is set LOW, the
circuit is powered down regardless of the register values.
When the CE pin is HIGH, the RF_PD bit controls power to
the RF circuitry. Data can be written to the registers even
when the CE pin is set LOW. The following truth table
summarizes the power down logic.
VCO Frequency Tuning
The center frequency of the RF VCOs is determined by the
resonant frequency of the tank circuit, illustrated in Figure 1.
With an internal fixed bonding-wire inductor and an external
inductance, the center frequency of the VCO is given as
follows:
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TABLE 1. Power Down Modes
8
CE Pin
RF_PD Bit
Mode
HIGH
0
Active
HIGH
1
Not Active
LOW
0
Not Active
LOW
1
Not Active
on the LD pin. When the PLL is not locked, the LD pin
remains LOW. After obtaining phase lock, the LD pin will
have a logical HIGH level. The LD output is always LOW
when the LD register bit is 0 and in power down mode.
(Continued)
BAND SELECT MODE
The BS pin and BS bit can be used to select one of the two
RF VCO outputs. When using the BS pin, the BS bit must be
set to 0, and when using the BS bit, the BS pin must be tied
to ground. When using the BS pin, the state of the input must
exceed the minimum band select set up time prior to the LE
signal transition. The truth table summarizing the band select
logic is as follows:
TABLE 3. Lock Detect Modes
TABLE 2. Band Select Modes
LD Bit
Mode
0
Disable (GND)
1
Enable
TABLE 4. Lock Detect Logic
BS Pin
BS Bit
Mode
HIGH
0
PDC1500
LOW
0
PDC800
LOW
1
PDC1500
RF PLL Section
LD Output
Locked
HIGH
Not Locked
LOW
LOCK DETECT MODE
The LD output can be used to indicate the lock status of the
PLL. Bit 6 in Register R1 determines the signal that appears
20067108
FIGURE 2. Lock Detect Timing Diagram Waveform (Notes 14, 15, 16, 17, 18)
Note 14: LD output becomes LOW when the phase error is larger than tW2.
Note 17: tW1 is 5 ns for PDC1500 and 10 ns for PDC800. tW2 is 10 ns for
both bands.
Note 15: LD output becomes HIGH when the phase error is less than tW1 for
four or more consecutive cycles.
Note 18: The lock detect comparison occurs with every 64th cycle of fR and
fN.
Note 16: Phase Error is measured on leading edge. Only errors greater than
tW1 and tW2 are labeled.
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LMX2505
Functional Description
LMX2505
Functional Description
(Continued)
20067109
FIGURE 3. Lock Detect Flow Diagram
MICROWIRE INTERFACE
The programmable register set is accessed via the
MICROWIRE serial interface. The interface is comprised of
three signal pins: CLK, DATA, and LE (Latch Enable). Serial
data is clocked into the 24-bit shift register on the rising edge
of the clock. The last bits decode the internal control register
address. When the latch enable (LE) transitions from LOW
to HIGH, data stored in the shift registers is loaded into the
corresponding control register. The data is loaded MSB first.
HIGH SPEED LOCK-UP MODE
Two frequency-locking modes are provided: a Normal mode
and a High Speed mode for faster lock times. The HS bit in
register R0 controls the locking mode.
TABLE 5. Lock-up Modes
HS Bit
Mode
0
Normal mode
1
High Speed mode
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10
LMX2505
Programming Description
GENERAL PROGRAMMING INFORMATION
The serial interface has a 24-bit shift register to store the incoming data bits temporarily. The incoming data is first loaded into the
shift register from MSB to LSB. The data is shifted at the rising edge of the clock signal. When the latch enable signal transitions
from LOW to HIGH, the data stored in shift register is transferred to the proper register depending on the address bit setting. The
selection of the particular register is determined by the control bits indicated in boldface text.
At initial start-up, the MICROWIRE loading requires three default words (registers R2, loaded first, to R0, loaded last). After the
device has been initially programmed, the RF VCO frequency can be changed using a single register (R0).
The control register content map describes how the bits within each control register are allocated to the specific control functions.
Register
COMPLETE REGISTER MAP
MSB
SHIFT REGISTER BIT LOCATION
23
22
21
20
19
R0
(Default)
RX/
TX
RF_
PD
HS
0
BS
R1
(Default)
SPI_
DEF
0
0
1
0
0
1
0
1
0
0
0
0
0
0
1
0
LD
OB_
CRL
[1:0]
R2
(Default)
1
1
0
0
1
0
0
0
0
1
1
1
1
0
0
0
0
0
0
18
17
16
15
14
RF_B
[3:0]
13
12
11
10
9
LSB
8
RF_A
[2:0]
7
6
5
4
3
2
1
0
0
0
OSC_
FREQ
[1:0]
0
1
0
0
1
1
0
RF_FN
[9:0]
R3
1
0
0
0
0
1
1
0
1
0
0
0
0
0
0
0
0
0
0
1
1
0
1
1
R4
0
0
0
0
0
0
1
1
1
0
1
0
0
0
1
1
0
0
1
0
0
1
1
1
R5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
NOTE: R0 control register will be used when hot start frequency change.
NOTE: Boldface text represent address bits.
11
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(Continued)
R0 REGISTER
The R0 register address bits (R0 [1:0]) are “00”.
The Rx/Tx bit selects between receive and transmit modes and, in conjunction with the band select bit (BS), the channel spacing
to be synthesized.
The RF_PD bit selects the power down mode of the RF PLL and selected VCO.
The HS bit selects between normal and high speed locking mode.
The BS bit determines which of the two internal VCOs (PDC800 or PDC1500) is active.
The RF N counter consists of the 4-bit programmable counter (RF_B counter), the 3-bit swallow counter (RF_A counter) and the
10-bit delta sigma modulator (RF_FN counter). The equations for calculating the counter values are presented below.
R0 REGISTER
MSB
Register
LMX2505
Programming Description
23
R0
(Default)
RX/
TX
SHIFT REGISTER BIT LOCATION
22
21
20
19
18
17
16
15
14
13
12
11
10
9
LSB
8
7
6
5
4
3
Data Field
RF_
PD
HS
0
BS
RF_B
[3:0]
RF_A
[2:0]
RF_FN
[9:0]
Functions
RX/TX
RX/TX Mode
0 = Rx
1 = Tx
RF_PD
Power Down of RF Synthesizer
0 = RF synthesizer on (Active mode)
1 = RF synthesizer powered down
HS
Locking Mode
0 = Normal Mode
1 = High Speed Mode
BS
Band Select
1 = RF1 VCO (PDC1500)
0 = RF2 VCO (PDC800)
RF_B [3:0]
RF_B Counter
4-bit programmable counter
0 ≤ RF_B ≤ 15 for both bands
RF_A [2:0]
RF_A Counter
3-bit swallow counter
0 ≤ RF_A ≤ 7 for PDC1500
0 ≤ RF_A ≤ 3 for PDC800
RF_FN [9:0]
RF_FN Counter
10-bit modulus counter
0 ≤ RF_FN < FD See Table 6 for FD values.
0
Symbol
Functions
RF N Divider
N = 8 x RF_B + RF_A + RF_FN/FD (PDC1500)
N = 4 x RF_B + RF_A + RF_FN/FD (PDC800)
Modulus Counter
RF_FN
Programmable Counter
RF_B
Swallow Counter
RF_A
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1
12
0
Address
Field
Name
Counter Name
2
0
LMX2505
Programming Description
(Continued)
PULSE SWALLOW FUNCTION
fVCO = {8 x RF_B + RF_A + (RF_FN / FD)} x fOSC / R where (RF_A < RF_B) for PDC1500
fVCO = {4 x RF_B + RF_A + (RF_FN / FD)} x fOSC / R where (RF_A < RF_B) for PDC800
fVCO: Output frequency of voltage controlled oscillator (VCO)
RF_B: Preset divide ratio of binary 4-bit programmable counter (2 ≤ RF_B ≤ 15)
RF_A: Preset divide ratio of binary 3-bit swallow counter (0 ≤ RF_A ≤ 7 for PDC1500 and 0 ≤ RF_A ≤ 3 for PDC800)
RF_FN: Preset numerator of binary 10-bit modulus counter (0 ≤ RF_FN < FD)
FD: Preset denominator for modulus counter (FD = fOSC/(R x fCH) where fCH is the channel spacing)
fOSC: Reference oscillator frequency
R: Internal reference oscillator frequency divider
OSC_FREQ [1:0]
Reference Oscillator Frequency (MHz)
R Divider
00
12.6
1
01
14.4
1
10
25.2
2
11
26.0
2
The value of the denominator (FD) is depended on the channel spacing and reference oscillator frequency. Table 6 summarizes
the denominator values based on the settings of the Rx/Tx, BS, and OSC_FREQ [1:0] bits.
TABLE 6. Demonimator Values
Rx/Tx
BS
OSC_FREQ [1:0]
Reference Oscillator Frequency (MHz)
R
fCH (kHz)
Denominator (FD)
0
0
00
12.6
1
25.0
504
0
0
01
14.4
1
25.0
576
0
0
10
25.2
2
25.0
504
0
0
11
26.0
2
25.0
520
0
1
00
12.6
1
25.0
504
0
1
01
14.4
1
25.0
576
0
1
10
25.2
2
25.0
504
0
1
11
26.0
2
25.0
520
1
0
00
12.6
1
20.0
630
1
0
01
14.4
1
20.0
720
1
0
10
25.2
2
20.0
630
1
0
11
26.0
2
20.0
650
1
1
00
12.6
1
22.22
567
1
1
01
14.4
1
22.22
648
1
1
10
25.2
2
22.22
567
1
1
11
26.0
2
22.22
585
13
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(Continued)
R1 REGISTER
The R1 register address bits (R1 [1:0]) are “01”.
The SPI_DEF bit allows for the programming of words R3 to R5. Under most circumstances, the SPI_DEF bit should be set to
1.
The LD bit sets the function of the lock detect pin. Enabling the lock detect function provides a digital lock detect output of the
active RF synthesizer at the LD pin.
The OB_CRL [1:0] bits determine the power level of the RF output buffer. The power level can be adjusted to best meet the
system requirement.
The reference frequency selection bits, OSC_FREQ [1:0], are used to set the reference clock and R divider for use with one of
the following reference frequencies: 12.6 MHz, 14.4 MHz, 25.2 MHz or 26.0 MHz. The LMX2505 uses the OSC_FREQ bits along
with the BS and RX/TX bits to determine the correct divide ratios needed to meet the required channel spacing for the mode of
operation selected. Refer to Table 6 for a summary of denominator values.
R1 REGISTER
MSB
Register
LMX2505
Programming Description
23
R1
(Default)
SPI_
DEF
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SHIFT REGISTER BIT LOCATION
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
LSB
7
6
5
4
3
2
Data Field
0
0
1
0
0
1
0
1
0
0
0
0
Address
Field
0
0
0
1
0
LD
OB_
CRL
[1:0]
OSC_
FREQ
[1:0]
Name
Functions
SPI_DEF
Default Register Selection
0 = OFF (Use values set in R0 to R5)
1 = ON (Use default values set in R0 to R2)
LD
Lock Detect
0 = Disable (GND)
1 = Enable
OB_CRL [1:0]
Output Buffer Control
PDC1500, PDC800
00 = -10 dBm, -12 dBm
01 = -7 dBm, -8 dBm
10 = -4 dBm, -6 dBm
11 = -2 dBm, -3 dBm
OSC_FREQ [1:0]
Reference Frequency Selection
00 = 12.6 MHz
01 = 14.4 MHz
10 = 25.2 MHz
11 = 26.0 MHz
14
1
0
1
LMX2505
Programming Description
(Continued)
R2 REGISTER
The R2 register address bits (R2 [1:0]) are “10”.
R2 REGISTER
Register
MSB
23
R2
(Default)
1
SHIFT REGISTER BIT LOCATION
22
21
20
19
18
17
16
15
14
13
12
11
10
9
LSB
8
7
6
5
4
3
2
Data Field
1
0
0
1
0
0
0
0
1
1
1
0
Address
Field
1
1
0
0
0
0
0
0
0
0
1
1
0
R3 REGISTER
The R3 register address bits (R3 [2:0]) are “011”. This register is only written to if the SPI_DEF bit is set to 0.
R3 REGISTER
Register
MSB
23
R3
1
SHIFT REGISTER BIT LOCATION
22
21
20
19
18
17
16
15
14
13
12
11
10
9
LSB
8
7
6
5
4
3
Data Field
0
0
0
0
1
1
0
1
0
0
2
1
0
Address
Field
0
0
0
0
0
0
0
0
1
1
0
1
2
1
1
R4 REGISTER
The R4 register address bits (R4 [3:0]) are “0111”. This register is only written to if the SPI_DEF bit is set to 0.
R4 REGISTER
Register
MSB
23
R4
0
SHIFT REGISTER BIT LOCATION
22
21
20
19
18
17
16
15
14
13
12
11
10
9
LSB
8
7
6
5
4
Data Field
0
0
0
0
0
1
1
1
0
3
0
Address
Field
1
0
0
0
1
1
0
0
1
0
0
1
1
1
R5 REGISTER
The R5 register address bits (R5 [4:0]) are “01111”. This register is only written to if the SPI_DEF bit is set to 0.
Register
R5 REGISTER
MSB
R5
0
23
SHIFT REGISTER BIT LOCATION
22
21
20
19
18
17
16
15
14
13
12
11
10
9
LSB
8
7
6
5
Data Field
0
0
0
0
0
0
0
0
0
4
3
2
1
0
Address Field
0
15
0
0
0
0
0
0
0
0
0
1
1
1
1
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LMX2505 PLLatinum Dual Frequency Synthesizer System with Integrated VCOs
Physical Dimensions
inches (millimeters) unless otherwise noted
28-Pin Leadless Leadframe Package (LLP)
NSC Package Number LQA28A
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