LMX2485QSQX/NOPB [TI]
500MHz 至 3GHz 汽车类 Δ-Σ 低功耗双路 PLL | RTW | 24 | -40 to 105;
| 型号： | LMX2485QSQX/NOPB |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 500MHz 至 3GHz 汽车类 Δ-Σ 低功耗双路 PLL | RTW | 24 | -40 to 105 |
| 文件： | 总52页 (文件大小：1570K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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LMX2485Q-Q1
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
LMX2485Q-Q1 具有 800MHz 整数 PLL 的 500MHz 至 3.1GHz 高性能 Δ-Σ
低功耗双路 PLLatinum™频率合成器
1 特性
3 说明
1
•
实现低分频系数分频的四模预分频器
LMX2485Q-Q1 是一款带有辅助性整数 N PLL 的低功
耗、高性能 Δ-Σ 分数 N PLL。该器件采用 TI 高级工艺
制造。
–
射频 (RF) 锁相环 (PLL)：8/9/12/13 或
16/17/20/21
–
中频 (IF) PLL：8/9 或 16/17
凭借 Δ-Σ 架构，低偏移频率下的分数杂波被推至回路
带宽之外的更高频率。将杂波和相位噪声能量推至更高
频率的能力是调制器阶数功能的直接体现。与模拟补偿
不同，LMX2485Q-Q1 采用的数字反馈技术对于温度
变化和晶圆制造工艺变化的抗扰度较高。LMX2485Q-
Q1 Δ-Σ 调制器经编程最高可达四阶，允许设计人员根
据需要选择最优调制器阶数，从而满足系统对于相位噪
声、杂波和锁定时间的要求。
•
•
高级 Δ-Σ 分频补偿
–
–
12 位或 22 位可选分频模量
最高可达四阶的可编程 Δ-Σ 调制器
提升了锁定时间和编程性能
–
–
执行单字写操作即可实现快速锁定/周跳减弱
集成超时计数器
•
•
宽工作频率范围：
LMX2485Q-Q1 RF PLL：500MHz 至 3.1GHz
有用的 特性
–
对 LMX2485Q-Q1 进行编程的串行数据通过三线制高
速 (20MHz) MICROWIRE 接口进行传输。
LMX2485Q-Q1 提供精确的频率分辨率、低杂波、快
速编程以及改变频率的单字写入功能。这使其成为直接
数字调制 应用的理想选择。此类应用的 N 计数器通过
信息直接调制。LMX2485Q-Q1 采用 4.0mm × 4.0mm
× 0.8mm 24 引脚超薄型四方扁平无引线 (WQFN) 封
装。
–
–
–
–
–
–
数字锁定检测输出
硬件和软件掉电控制
片上输入倍频器
RF 相位检测器频率最高可达 50 MHz
在 2.5V 至 3.6V 电压下运行（ICC = 5.0mA）
LMX2485Q-Q1 采用汽车级流程制造，符合
AEC-Q100 2 级标准
器件信息(1)
2 应用范围
器件型号
封装
WQFN (24)
封装尺寸（标称值）
•
•
•
•
移动电话和基站
直接数字调制 应用
卫星和有线电视调谐器
WLAN 标准
LMX2485Q-Q1
4.00mm x 4.00mm
(1) 要了解所有可用封装，请见数据表末尾的可订购产品附录。
功能方框图
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SD
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1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
English Data Sheet: SNOSCP7
LMX2485Q-Q1
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
www.ti.com.cn
目录
8.2 Functional Block Diagram ....................................... 19
8.3 Feature Description................................................. 19
8.4 Device Functional Modes........................................ 25
8.5 Programming........................................................... 26
8.6 Register Maps......................................................... 28
Application and Implementation ........................ 40
9.1 Application Information............................................ 40
9.2 Typical Application ................................................. 41
1
2
3
4
5
6
特性.......................................................................... 1
应用范围................................................................... 1
说明.......................................................................... 1
修订历史记录 ........................................................... 2
Pin Configuration and Functions......................... 3
Specifications......................................................... 4
6.1 Absolute Maximum Ratings ...................................... 4
6.2 ESD Ratings – Commercial ...................................... 4
6.3 ESD Ratings – Automotive ....................................... 4
6.4 Recommended Operating Conditions....................... 4
6.5 Thermal Information.................................................. 4
6.6 Electrical Characteristics........................................... 5
6.7 Timing Characteristics............................................... 7
6.8 Typical Characteristics.............................................. 8
Parameter Measurement Information ................ 14
7.1 Bench Test Set-Ups................................................ 14
Detailed Description ............................................ 19
8.1 Overview ................................................................. 19
9
10 Power Supply Recommendations ..................... 43
11 Layout................................................................... 43
11.1 Layout Guidelines ................................................. 43
11.2 Layout Example .................................................... 43
12 器件和文档支持 ..................................................... 44
12.1 社区资源................................................................ 44
12.2 商标....................................................................... 44
12.3 静电放电警告......................................................... 44
12.4 Glossary................................................................ 44
13 机械、封装和可订购信息....................................... 44
7
8
4 修订历史记录
注：之前版本的页码可能与当前版本有所不同。
Changes from Original (March 2013) to Revision A
Page
•
已添加引脚配置和功能部分，ESD 额定值表，特性 描述 部分，器件功能模式，应用和实施部分，电源相关建议部
分，布局部分，器件和文档支持部分以及机械、封装和可订购信息部分 ................................................................................ 1
2
Copyright © 2013–2016, Texas Instruments Incorporated
LMX2485Q-Q1
www.ti.com.cn
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
5 Pin Configuration and Functions
RTW Package
24-Pin WQFN
Top View
24 23 22 21 20 19
CPoutRF
1
18 OSCout
17 VddIF2
GND
2
VddRF1
3
CPoutIF
GND
16
15
Pin 0
(Ground Substrate)
FinRF
FinRF*
LE
4
5
6
14 VddIF1
FinIF
13
7
8
9
10 11 12
Pin Functions
PIN
I/O
DESCRIPTION
NAME
NO.
CE
10
I
I
Chip Enable control pin. Must be pulled high for normal operation.
MICROWIRE Clock. High-impedance CMOS Clock input. Data for the various counters is
clocked into the 24 bit shift register on the rising edge
CLK
8
CPoutIF
CPoutRF
DATA
16
1
O
O
I
IF PLL charge pump output
RF PLL charge pump output.
7
MICROWIRE Data. High-impedance binary serial data input.
Oscillator enable. When this is set to high, the OSCout pin is enabled regardless of the state
of other pins or register bits.
ENOSC
19
I
FinIF
13
4
I
IF PLL high-frequency input pin.
FinRF
FinRF*
FLoutRF
Ftest/LD
GND
I
RF PLL high-frequency input pin.
5
I
RF PLL complementary high-frequency input pin. Shunt to ground with a 100-pF capacitor.
RF PLL Fastlock Output. Also functions as Programmable TRI-STATE CMOS output.
Test frequency output / Lock Detect.
23
12
0
O
O
—
—
—
Ground Substrate. This is on the bottom of the package and must be grounded.
RF PLL analog ground.
GND
2
GND
15
IF PLL digital ground.
MICROWIRE Load Enable. High impedance CMOS input. Data stored in the shift registers is
loaded into the internal latches when LE goes HIGH
LE
6
I
NC
21
20
18
3
I
This pin must be left open.
OSCin
OSCout
VddRF1
VddRF2
VddRF3
VddRF4
VddIF1
VddIF2
I
Input for TCXO signal.
O
—
—
—
—
—
—
Buffered output of the OSCin signal.
RF PLL analog power supply.
Power supply for RF PLL digital circuitry.
Power supply for RF PLL digital circuitry.
RF PLL analog power supply.
IF PLL analog power supply.
IF PLL power supply.
9
22
24
14
17
Copyright © 2013–2016, Texas Instruments Incorporated
3
LMX2485Q-Q1
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
www.ti.com.cn
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)
MIN
–0.3
–0.3
MAX
4.25
UNIT
V
VCC
Vi
Power supply voltage
Voltage on any pin with GND = 0 V
Lead temperature (solder 4 sec.)
Storage temperature
VCC + 0.3
260
V
TL
°C
°C
Tstg
-65
150
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
6.2 ESD Ratings – Commercial
VALUE
±2000
±750
UNIT
Human-body model (HBM)
Charged-device model (CDM)
Machine model (MM)
V(ESD)
Electrostatic discharge(1)
V
±200
(1) This is a high performance RF device is ESD-sensitive. Handling and assembly of this device should be done at an ESD free
workstation.
6.3 ESD Ratings – Automotive
VALUE
UNIT
Human-body model (HBM), per AEC Q100-002(1)
Charged-device model (CDM), per AEC Q100-011
±2000
±750
±200
V(ESD)
Electrostatic discharge
V
(1) AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
6.4 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
2.5
NOM
3
MAX
3.6
UNIT
V
VCC
TA
Power supply voltage(1)
Operating temperature
–40
25
105
°C
(1) 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 ensure specific performance limits. For ensured specifications
and test conditions, see the Electrical Characteristics. The ensured specifications apply only for the test conditions listed. The voltage at
all the power supply pins of VddRF1, VddRF2, VddRF3, VddRF4, VddRF5, VddIF1 and VddIF2 must be the same. VCC will be used to
refer to the voltage at these pins and ICC will be used to refer to the sum of all currents through all these power pins.
6.5 Thermal Information
LMX2485Q-Q1
THERMAL METRIC(1)
RTW (WQFN)
UNIT
24 PINS
47.2
43
RθJA
Junction-to-ambient thermal resistance
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
RθJC(top)
RθJB
Junction-to-case (top) thermal resistance
Junction-to-board thermal resistance
24
ψJT
Junction-to-top characterization parameter
Junction-to-board characterization parameter
Junction-to-case (bottom) thermal resistance
0.8
ψJB
24
RθJC(bot)
7
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
4
Copyright © 2013–2016, Texas Instruments Incorporated
LMX2485Q-Q1
www.ti.com.cn
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
6.6 Electrical Characteristics
over operating free-air temperature range (unless otherwise noted). (VCC = 3V; -40°C ≤ TA ≤ +105°C unless otherwise
specified).
PARAMETER
Icc PARAMETERS
TEST CONDITIONS
MIN
TYP
MAX
UNIT
IF PLL OFF
RF PLL ON
Charge Pump TRI-STATE
Power supply current, RF
synthesizer
ICCRF
ICCIF
3.3
1.7
mA
mA
IF PLL ON
RF PLL OFF
Charge Pump TRI-STATE
Power supply current, IF
synthesizer
IF PLL ON
RF PLL ON
Charge Pump TRI-STATE
Power supply current, entire
synthesizer
ICCTOTAL
ICCPD
5
1
mA
µA
CE = ENOSC = 0V
CLK, DATA, LE = 0V
Power-down current
10
RF SYNTHESIZER PARAMETERS
RF_P = 8
500
500
-15
2000
3100
0
fFinRF
Operating frequency(1)
MHz
RF_P = 16
pFinRF
fPD
Input sensitivity
Phase detector frequency(2)
dBm
MHz
50
RF_CPG = 0
VCPoutRF = VCC/2
95
RF_CPG = 1
VCPoutRF = VCC/2
190
RF charge pump source
current(3)
ICPoutRFSRCE
µA
...
...
RF_CPG = 15
VCPoutRF = VCC/2
1520
–95
RF_CPG = 0
VCPoutRF = VCC/2
RF_CPG = 1
VCPoutRF = VCC/2
–190
...
ICPoutRFSINK
RF charge pump sink current(3)
µA
nA
...
RF_CPG = 15
VCPoutRF = VCC/2
–1520
RF charge pump TRI-STATE
current magnitude
ICPoutRFTRI
0.5 ≤ VCPoutRF ≤ VCC – 0.5
2
10
RF_CPG > 2
RF_CPG ≤ 2
3%
3%
10%
13%
Magnitude of RF CP sink vs
CP source mismatch
VCPoutRF = VCC/2
TA = 25°C
| ICPoutRF%MIS |
| ICPoutRF%T |
Magnitude of RF CP current vs
temperature
VCPoutRF = VCC/2
4%
IF SYNTHESIZER PARAMETERS
fFinIF
Operating Frequency
75
800
5
MHz
dBm
MHz
pFinIF
fCOMP
IF Input Sensitivity
-10
Phase Detector Frequency
10
IF Charge Pump Source
Current
ICPoutIFSRCE
ICPoutIFSINK
ICPoutIFTRI
VCPoutIF = VCC/2
VCPoutIF = VCC/2
3.5
–3.5
2
mA
mA
nA
IF Charge Pump Sink Current
IF Charge Pump TRI-STATE
Current Magnitude
0.5 ≤ VCPoutIF ≤ VCC RF -0.5
10
Magnitude of IF CP sink vs CP VCPoutIF = VCC/2
source mismatch TA = 25°C
| ICPoutIF%MIS |
1%
8%
(1) A slew rate of at least 100 V/uS is recommended for frequencies below 500 MHz for optimal performance.
(2) For Phase Detector Frequencies above 20 MHz, Cycle Slip Reduction (CSR) may be required. Legal divide ratios are also required.
(3) Refer to table in Table 25 for complete listing of charge pump currents.
Copyright © 2013–2016, Texas Instruments Incorporated
5
LMX2485Q-Q1
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
www.ti.com.cn
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted). (VCC = 3V; -40°C ≤ TA ≤ +105°C unless otherwise
specified).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Magnitude of IF CP Current vs. 0.5 ≤ VCPoutIF ≤ VCC -0.5
| ICPoutIF%V |
4%
10%
CP Voltage
TA = 25°C
Magnitude of IF CP current vs
temperature
| ICPoutIF%TEMP
VCPoutIF = VCC/2
4%
OSCILLATOR PARAMETERS
OSC2X = 0
OSC2X = 1
5
5
110
MHz
MHz
VP-P
µA
fOSCin
Oscillator operating frequency
20
vOSCin
IOSCin
Oscillator input sensitivity
Oscillator input current
0.5
VCC
100
–100
SPURS
(4)
Spurs in band
See
–55
dBc
PHASE NOISE
RF_CPG = 0
RF_CPG = 1
RF_CPG = 3
RF_CPG = 7
RF_CPG = 15
–202
–202
–206
–208
–210
RF synthesizer normalized
phase noise contribution(5)
LF1HzRF
dBc/Hz
dBc/Hz
IF synthesizer normalized
phase noise contribution
LF1HzIF
–209
DIGITAL INTERFACE (DATA, CLK, LE, ENOSC, CE, Ftest/LD, FLoutRF)
VIH
VIL
IIH
High-level input voltage
Low-level input voltage
High-level input current
Low-level input current
1.6
VCC
V
V
0.4
5
VIH = VCC
VIL = 0 V
–5
–5
µA
µA
IIL
5
VCC
0.4
–
VOH
VOL
High-level output voltage
Low-level output voltage
IOH = –500 µA
IOL = 500 µA
V
V
0.4
(4) In order to measure the in-band spur, the fractional word is chosen such that when reduced to lowest terms, the fractional numerator is
one. The spur offset frequency is chosen to be the comparison frequency divided by the reduced fractional denominator. The loop
bandwidth must be sufficiently wide to negate the impact of the loop filter. Measurement conditions are: Spur Offset Frequency = 10
kHz, Loop Bandwidth = 100 kHz, Fraction = 1/2000, Comparison Frequency = 20 MHz, RF_CPG = 7, DITH = 0, and a 4th Order
Modulator (FM = 0). These are relatively consistent over tuning range.
(5) Normalized Phase Noise Contribution is defined as: LN(f) = L(f) – 20log(N) – 10log(fCOMP) where L(f) is defined as the single side band
phase noise measured at an offset frequency, f, in a 1 Hz Bandwidth. The offset frequency, f, must be chosen sufficiently smaller than
the PLL loop bandwidth, yet large enough to avoid substantial phase noise contribution from the reference source. Measurement
conditions are: Offset Frequency = 11 kHz, Loop Bandwidth = 100 kHz for RF_CPG = 7, Fraction = 1/2000, Comparison Frequency =
20 MHz, FM = 0, DITH = 0.
6
Copyright © 2013–2016, Texas Instruments Incorporated
LMX2485Q-Q1
www.ti.com.cn
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
6.7 Timing Characteristics
over operating free-air temperature range (unless otherwise noted)
MIN
NOM
MAX
UNIT
MICROWIRE INTERFACE TIMING
tCS
Data to Clock Set Up Time
Data to Clock Hold Time
Clock Pulse Width High
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
See Figure 1
25
8
ns
ns
ns
ns
ns
ns
tCH
tCWH
tCWL
tES
25
25
25
25
Clock Pulse Width Low
Clock to Load Enable Set Up Time
Load Enable Pulse Width
tEW
MSB
LSB
C0
DATA
CLK
LE
D19
D18
D17
D16
D15
D0
C3
C2
C1
t
t
CWH
CS
t
ES
t
CH
t
CWL
t
EW
Figure 1. Microwire Input Timing Diagram
Copyright © 2013–2016, Texas Instruments Incorporated
7
LMX2485Q-Q1
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
www.ti.com.cn
6.8 Typical Characteristics
6.8.1 Sensitivity
Typical characteristics do not imply any sort of specification. Ensured specifications are in the Electrical Characteristics
section.
20
10
20
10
V
CC
= 2.5V, 3.0V and 3.6V
T
A
=
25oC, and 85oC
0
0
T
= -40oC
A
-10
-20
-30
-40
-50
-10
-20
-30
-40
-50
T
= 85oC
A
V
CC
= 3.6V
T
= -40oC
A
= 25oC
V
CC
= 2.5V
V
CC
= 3.0V
T
A
0
1000
2000
(MHz)
3000
4000
0
1000
2000
3000
4000
f
fFinRF (MHz)
FinRF
TA = 25°C, RF_P = 16
Figure 2. RF PLL Fin Sensitivity
VCC = 3 V, RF_P = 16
Figure 3. RF PLL Fin Sensitivity
20
20
10
10
= -40oC, 25oC, and 85oC
V
= 3.0V
V
CC
T
A
= 3.6V
CC
0
0
V
= 2.5V
CC
-10
-20
-30
-40
-50
-10
-20
-30
-40
-50
V
CC
= 3.6V
T
= -40oC
A
V
= 3.0V
CC
T
= 85oC
A
T
A
= 25oC
V
= 2.5V
CC
0
200
400
600
800
1000
400
0
200
600
800
1000
f
(MHz)
FinIF
f
(MHz)
FinIF
VCC = 3 V, IF_P = 16
TA = 25°C, IF_P = 16
Figure 4. IF PLL Fin Sensitivity
Figure 5. IF PLL Fin Sensitivity
20
10
20
10
= -40oC, 25oC, and 85oC
V
CC
= 2.5V, 3.0V, and 3.6V
T
A
0
0
-10
-20
-30
-40
-50
-10
-20
-30
-40
-50
V
= 3.6V
CC
T
= -40oC
V
= 3.0V
CC
A
V
= 2.5V
= 85oC
CC
T
A
T
= 25oC
A
0
30
60
120
150
ꢀ0
10
120
10
0
30
60
ꢀ0
150
f
(MHz)
OSCin
f
(MHz)
OSCin
TA = 25°C, OSC_2X = 0
Figure 6. OSCin Sensitivity
VCC = 3 V, OSC_2X = 0
Figure 7. OSCin Sensitivity
8
Copyright © 2013–2016, Texas Instruments Incorporated
LMX2485Q-Q1
www.ti.com.cn
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
Sensitivity (continued)
Typical characteristics do not imply any sort of specification. Ensured specifications are in the Electrical Characteristics
section.
20
20
10
10
V
= 2.5V, 3.0V, and 3.6V
T
= -40oC, 25oC, and 85oC
CC
A
0
0
V
CC
= 3.6V
-10
-20
-30
-40
-50
-10
-20
-30
-40
-50
T
= 85oC
A
V
CC
= 3.0V
= -40oC
V
CC
=2.5V
T
A
T
= 25oC
A
10
0
5
15
20
25
10
0
5
15
20
25
f
(MHz)
OSCin
f
(MHz)
OSCin
TA = 25°C, OSC_2X = 1
Figure 8. OSCin Sensitivity
VCC = 3 V, OSC_2X = 1
Figure 9. OSCin Sensitivity
6.8.2 FinRF Input Impedance
Marker 1:
50 MHz
Marker 2:
1.0 GHz
Marker 3:
2.0 GHz
1
2
Marker 4:
3.0 GHz
3
Start 1.0 GHz
Stop 3.5 GHz
4
Figure 10. FinRF Input Impedance
Table 1. RF PLL Input Impedance
FREQUENCY (MHz)
REAL (Ω)
670
IMAGINARY (Ω)
–276
50
100
200
300
400
500
600
700
800
900
1000
1100
1200
531
–247
452
–209
408
–212
373
–222
337
–231
302
–237
270
–239
241
–236
215
–231
192
–221
172
–218
154
–209
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FinRF Input Impedance (continued)
Table 1. RF PLL Input Impedance (continued)
FREQUENCY (MHz)
1300
REAL (Ω)
139
127
114
104
96
IMAGINARY (Ω)
–200
–192
–184
–175
–168
–160
–153
–147
–134
–123
–113
–103
–94
1400
1500
1600
1700
1800
88
1900
80
2000
74
2200
64
2400
56
2600
50
2800
45
3000
39
3200
37
–86
3400
33
–78
3600
30
–72
3800
28
–69
4000
26
–66
10
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6.8.3 FinIF Input Impedance
Typical characteristics do not imply any sort of specification. Ensured specifications are in the Electrical Characteristics
section.
ꢀarker 1:
75 ꢀIz
ꢀarker 2:
800 ꢀIz
1
2
{tart 50 ꢀIz
{top 1000 ꢀIz
Figure 11. FinIF Input Impedance
Table 2. IF PLL Input Impedance
FinIF INPUT IMPEDANCE
FREQUENCY (MHz)
REAL (Ω)
583
IMAGINARY (Ω)
–286
50
75
530
–256
100
200
300
400
500
600
700
800
900
1000
499
–241
426
–209
384
–209
347
–219
310
–224
276
–228
244
–228
216
–223
192
–218
173
–208
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6.8.4 OSCin Input Impedance
Typical characteristics do not imply any sort of specification. Ensured specifications are in the Electrical Characteristics
section.
6000
5000
4000
3000
toꢀered
ꢁoꢀn
2000
1000
toꢀered
Üp
0
100
0
25
50
75
125
150
Cw9vÜ9b/ò (aIz)
Figure 12. OSCin Input Impedance Magnitude
Table 3. OSCin Input Impedance
POWERED-UP
POWERED-DOWN
IMAGINARY
–8137
–4487
–2215
–1495
–1144
–912
FREQUENCY
(MHz)
REAL
1730
846
466
351
316
278
261
252
239
234
230
225
219
214
208
207
IMAGINARY
–3779
–2236
–1196
–863
MAGNITUDE
4157
2391
1284
932
REAL
392
155
107
166
182
155
153
154
147
145
140
138
133
133
132
133
MAGNITUDE
8146
4490
2217
–1504
1158
925
5
10
20
30
40
–672
742
50
–566
631
60
–481
547
–758
774
70
–425
494
–652
669
80
–388
456
–576
595
90
–358
428
–518
538
100
110
120
130
140
150
–337
407
–471
492
–321
392
–436
458
–309
379
–402
123
–295
364
–374
397
–285
353
–349
373
–279
348
–329
355
12
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6.8.5 Currents
Typical characteristics do not imply any sort of specification. Ensured specifications are in the Electrical Characteristics
section.
6.0
0.5
0.4
T
A
= 85oC
5.0
4.0
= 25oC
T
= -40oC
A
T
A
0.3
0.2
3.0
2.0
1.0
0
T
A
= 85oC
T
= -40oC
A
T
= 25oC
A
0.1
0
2.5
3.3
3.6
2.75
3.0
2.5
2.75
3.6
3.0
3.3
V
CC
(V)
V
CC
(V)
CE = High
CE = LOW
Figure 13. Power Supply Current
Figure 14. Power Supply Current
2000
1500
1000
500
5.0
4.0
3.0
2.0
1.0
0
RF_CPG = 15
RF_CPG = 8
0
-1.0
-500
RF_CPG = 0
RF_CPG = 1
-2.0
-3.0
-4.0
-1000
-1500
-2000
0
-5.0
0
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
V
(V)
CPoutRF
V
(V)
CPoutIF
VCC = 3 V
VCC = 3 V
Figure 15. RF PLL Charge Pump Current
Figure 16. IF PLL Charge Pump Current
10
8
10
8
6
6
TA = 85o
C
4
4
TA = 85o
C
2
0
2
0
TA = -40o
C
-2
-4
-2
-4
TA = -40o
C
TA = 25o
C
TA = 25o
C
-6
-8
-6
-8
-10
0
-10
0
2.5
0.5
1.0
1.5
2.0
3.0
0.5
1.0
1.5
2.0
3.0
2.5
VCPoutIF (V)
V
(V)
CPoutRF
VCC = 3 V
VCC = 3 V
Figure 18. Charge Pump Leakage
IF PLL
Figure 17. Charge Pump Leakage
RF PLL
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7 Parameter Measurement Information
7.1 Bench Test Set-Ups
7.1.1 Charge Pump Current Measurement Procedure
5/
.locking
/apacitor
10 ꢁIz
{ꢁ! /able
Crequency
Lnput ꢀin
Signal Generator
5evice
Ünder
Çest
{emiconductor
{ꢁ! /able
ꢀarameter
!nalyzer
/ꢀout
ꢀin
h{/in
ꢀin
9valuation .oard
ꢀower {upply
Figure 19. Setup for Charge Pump Current Measurement
Figure 19 shows the test procedure for testing the RF and IF charge pumps. These tests include absolute current
level, mismatch, and leakage measurement. In order to measure the charge pump currents, a signal is applied to
the high-frequency input pins. The reason for this is to specify that the phase detector gets enough transitions in
order to be able to change states. If no signal is applied, it is possible that the charge pump current reading will
be low due to the fact that the duty cycle is not 100%. The OSCin Pin is tied to the supply. The charge pump
currents can be measured by simply programming the phase detector to the necessary polarity. For instance, in
order to measure the RF charge pump, a 10-MHz signal is applied to the FinRF pin. The source current can be
measured by setting the RF PLL phase detector to a positive polarity, and the sink current can be measured by
setting the phase detector to a negative polarity. The IF PLL currents can be measured in a similar way.
NOTE
The magnitude of the RF PLL charge pump current is controlled by the RF_CPG bit. Once
the charge pump currents are known, the mismatch can be calculated as well. In order to
measure leakage, the charge pump is set to a TRI-STATE mode by enabling the RF_CPT
and IF_CPT bits. The table below shows a summary of the various charge pump tests.
Table 4. Programmable Settings for Charge Pump Current Measurement
CURRENT TEST
RF Source
RF Sink
RF_CPG
RF_CPP
RF_CPT
IF_CPP
IF_CPT
0 to 15
0
1
0
0
X
X
X
0
X
X
X
0
0
1
0 to 15
RF TRI-STATE
IF Source
X
X
X
X
X
X
X
X
1
X
X
X
IF Sink
1
IF TRI-STATE
X
14
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7.1.2 Charge Pump Current Specification Definitions
Figure 20. Charge Pump Current Definitions
I1 = Charge Pump Sink Current at VCPout = Vcc - ΔV
I2 = Charge Pump Sink Current at VCPout = Vcc/2
I3 = Charge Pump Sink Current at VCPout = ΔV
I4 = Charge Pump Source Current at VCPout = Vcc - ΔV
I5 = Charge Pump Source Current at VCPout = Vcc/2
I6 = Charge Pump Source Current at VCPout = ΔV
ΔV = Voltage offset from the positive and negative supply rails. Defined to be 0.5 V for this part.
vCPout refers to either VCPoutRF or VCPoutIF
ICPout refers to either ICPoutRF or ICPoutIF
7.1.2.1 Charge Pump Output Current Variation vs Charge Pump Output Voltage
(1)
(2)
7.1.2.2 Charge Pump Sink Current vs Charge Pump Output Source Current Mismatch
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7.1.2.3 Charge Pump Output Current Variation vs Temperature
(3)
16
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7.1.3 Sensitivity Measurement Procedure
{a! /ꢀꢂle
aꢀtching
betwork
Crequency
Lnput ꢁin
Signal Generator
5/
.locking
/ꢀpꢀcitor
5evice
Ünder
Çest
{a! /ꢀꢂle
Ctestꢃ[5
ꢁin
Crequency /ounter
9vꢀluꢀtion .oꢀrd
ꢁower {upply
Figure 21. Setup for Sensitivity Measurement
Table 5. Programmable Settings for Sensitivity Measurement
DC-BLOCKING
CAPACITOR
CORRESPONDING
COUNTER
DEFAULT COUNTER
VALUE
FREQUENCY INPUT PIN
MUX VALUE
OSCin
FinRF
FinIF
1000 pF
100 pF// 1000 pF
100 pF
RF_R / 2
RF_N / 2
IF_N / 2
IF_R / 2
50
14
15
13
12
502 + 2097150 / 4194301
534
50
OSCin
1000 pF
Sensitivity is defined as the power level limits beyond which the output of the counter being tested is off by 1 Hz
or more of its expected value. It is typically measured over frequency, voltage, and temperature. In order to test
sensitivity, the MUX[3:0] word is programmed to the appropriate value. The counter value is then programmed to
a fixed value and a frequency counter is set to monitor the frequency of this pin. The expected frequency at the
Ftest/LD pin should be the signal generator frequency divided by twice the corresponding counter value. The
factor of two comes in because the LMX2485Q-Q1 has a flip-flop which divides this frequency by two to make
the duty cycle 50% in order to make it easier to read with the frequency counter. The frequency counter input
impedance should be set to high impedance. In order to perform the measurement, the temperature, frequency,
and voltage is set to a fixed value and the power level of the signal is varied.
NOTE
The power level at the part is assumed to be 4 dB less than the signal generator power
level. This accounts for 1 dB for cable losses and 3 dB for the pad.
The power level range where the frequency is correct at the Ftest/LD pin to within 1-Hz accuracy is recorded for
the sensitivity limits. The temperature, frequency, and voltage can be varied in order to produce a family of
sensitivity curves. Because this is an open-loop test, the charge pump is set to TRI-STATE and the unused side
of the PLL (RF or IF) is powered down when not being tested. For this part, there are actually four frequency
input pins, although there is only one frequency test pin (Ftest/LD). The conditions specific to each pin are shown
in above table.
NOTE
For the RF N counter, a fourth order fractional modulator is used in 22-bit mode with a
fraction of 2097150 / 4194301 is used. The reason for this long fraction is to test the RF N
counter and supporting fractional circuitry as completely as possible.
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7.1.4 Input Impedance Measurement Procedure
Crequency
Lnput ꢀin
betwork !nalyzer
5evice
Ünder
Çest
9valuation .oard
ꢀower {upply
Figure 22. Setup for Input Impedance Measurement
Figure 22 shows the test set-up used for measuring the input impedance for the LMX2485Q-Q1. The DC-
blocking capacitor used between the input SMA connector and the pin being measured must be changed to a 0-
Ω resistor. This procedure applies to the FinRF, FinIF, and OSCin pins. The basic test procedure is to calibrate
the network analyzer, ensure that the part is powered up, and then measure the input impedance. The network
analyzer can be calibrated by using either calibration standards or by soldering resistors directly to the evaluation
board. An open can be implemented by putting no resistor, a short can be implemented by soldering a 0-Ω
resistor as close as possible to the pin being measured, and a short can be implemented by soldering two 100-Ω
resistors in parallel as close as possible to the pin being measured. Calibration is done with the PLL removed
from the PCB. This requires the use of a clamp down fixture that may not always be generally available. If no
clamp down fixture is available, then this procedure can be done by calibrating up to the point where the DC-
blocking capacitor usually is, and then implementing port extensions with the network analyzer. The 0-Ω resistor
is added back for the actual measurement. Once the set-up is calibrated, it is necessary to ensure that the PLL is
powered up. This can be done by toggling the power down bits (RF_PD and IF_PD) and observing that the
current consumption indeed increases when the bit is disabled. Sometimes it may be necessary to apply a signal
to the OSCin pin in order to program the part. If this is necessary, disconnect the signal once it is established
that the part is powered up. It is useful to know the input impedance of the PLL for the purposes of debugging
RF problems and designing matching networks. Another use of knowing this parameter is make the trace width
on the PCB such that the input impedance of this trace matches the real part of the input impedance of the PLL
frequency of operation. In general, it is good practice to keep trace lengths short and make designs that are
relatively resistant to variations in the input impedance of the PLL.
18
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8 Detailed Description
8.1 Overview
The LMX2485Q-Q1 consists of integrated N counters, R counters, and charge pumps. The TCXO, VCO and loop
filter are supplied external to the chip.
8.2 Functional Block Diagram
ëddLC1
LC b ꢂivider
ëddLC2
. /ounꢀer
8ꢁ9
or
CinLC
ꢄbꢅ{/
ꢅ{/in
thase
/omp
/harge
tump
16ꢁ17
trescaler
/touꢀLC
! /ounꢀer
LC
[ꢂ
LC w
ꢂivider
ꢅ{/ouꢀ
ëddwC1
ëddwC2
ëddwC3
ëddwC4
ëddwC5
CinwC
Cꢀesꢀꢁ[ꢂ
ꢃÜó
Cꢀesꢀꢁ[ꢂ
wC w
ꢂivider
1X / 2X
wC [ꢂ
wC b ꢂivider
/ /ounꢀer
8ꢁ9ꢁ12ꢁ13
or
16ꢁ17ꢁ20ꢁ21
trescaler
/harge
tump
/touꢀwC
C[ouꢀwC
. /ounꢀer
! /ounꢀer
FinRF*
/ꢄ
wC Casꢀlock
/[Y
ꢃL/wꢅíLwꢄ
Lnꢀerface
ꢂ!Ç!
Dbꢂ
Dbꢂ
Dbꢂ
SD
Compensation
[ꢄ
8.3 Feature Description
8.3.1 Tcxo, Oscillator Buffer, and R Counter
The oscillator buffer must be driven single-ended by a signal source, such as a TCXO. The OSCout pin is
included to provide a buffered output of this input signal and is active when the OSC_OUT bit is set to one. The
ENOSC pin can be also pulled high to ensure that the OSCout pin is active, regardless of the status of the
registers in the LMX2485Q-Q1.
The R counter divides this TXCO frequency down to the comparison frequency.
8.3.2 Phase Detector
The maximum phase detector operating frequency for the IF PLL is straightforward, but it is a little more involved
for the RF PLL because it is fractional. The maximum phase detector frequency for the LMX2485Q-Q1 RF PLL is
50 MHz. However, this is not possible in all circumstances due to illegal divide ratios of the N counter. The
crystal reference frequency also limits the phase detector frequency, although the doubler helps with this
limitation. There are trade-offs in choosing the phase detector frequency. If this frequency is run higher, then
phase noise will be lower, but lock time may be increased due to cycle slipping and the capacitors in the loop
filter may become rather large.
8.3.3 Charge Pump
For the majority of the time, the charge pump output is high impedance, and the only current through this pin is
the TRI-STATE leakage. However, it does put out fast correction pulses that have a width that is proportional to
the phase error presented at the phase detector.
The charge pump converts the phase error presented at the phase detector into a correction current. The
magnitude of this current is theoretically constant, but the duty cycle is proportional to the phase error. For the IF
PLL, this current is not programmable, but for the RF PLL it is programmable in 16 steps. Also, the RF PLL
allows for a higher charge pump current to be used when the PLL is locking in order to reduce the lock time.
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Feature Description (continued)
8.3.4 Loop Filter
The loop filter design can be rather involved. In addition to the regular constraints and design parameters, delta-
sigma PLLs have the additional constraint that the order of the loop filter should be one greater than the order of
the delta sigma modulator. This rule of thumb comes from the requirement that the loop filter must roll off the
delta sigma noise at 20 dB/decade faster than it rises. However, because the noise can not have infinite power, it
must eventually roll off. If the loop bandwidth is narrow, this requirement may not be necessary. For the purposes
of discussion in this datasheet, the pole of the loop filter at 0 Hz is not counted. So a second order filter has 3
components, a 3rd order loop filter has 5 components, and the 4th order loop filter has 7 components. Although a
5th order loop filter is theoretically necessary for use with a 4th order modulator, typically a 4th order filter is used
in this case. The loop filter design, especially for higher orders can be rather involved, but there are many
simulation tools and references available, such as the one given at the end of the functional description block.
8.3.5 N Counters and High Frequency Input Pins
The N counter divides the VCO frequency down to the comparison frequency. Because prescalers are used,
there are limitations on how small the N value can be. The N counters are discussed in greater depth in the
Programming section. Because the input pins to these counters (FinRF and FinIF) are high frequency, layout
considerations are important.
8.3.5.1 High Frequency Input Pins, FinRF and FinIF
It is generally recommended that the VCO output go through a resistive pad and then through a DC-blocking
capacitor before it gets to these high frequency input pins. If the trace length is sufficiently short (< 1/10th of a
wavelength), then the pad may not be necessary, but a series resistor of about 39 Ω is still recommended to
isolate the PLL from the VCO. The DC-blocking capacitor should be chosen at least to be 27 pF, depending on
frequency. It may turn out that the frequency is above the self-resonant frequency of the capacitor, but because
the input impedance of the PLL tends to be capacitive, it actually is a benefit to exceed the tune frequency. The
pad and the DC-blocking capacitor should be placed as close to the PLL as possible
8.3.5.2 Complementary High Frequency Pin, FinRF*
These inputs may be used to drive the PLL differentially, but it is very common to drive the PLL in a single ended
fashion. A shunt capacitor should be placed at the FinRF* pin. The value of this capacitor should be chosen such
that the impedance, including the ESR of the capacitor, is as close to an AC short as possible at the operating
frequency of the PLL. 100 pF is a typical value, depending on frequency.
8.3.6 Digital Lock Detect Operation
The RF PLL digital lock detect circuitry compares the difference between the phase of the inputs of the phase
detector to a RC generated delay of ε. To indicate a locked state (Lock = HIGH) the phase error must be less
than the ε RC delay for 5 consecutive reference cycles. Once in lock (Lock = HIGH), the RC delay is changed to
approximately δ. To indicate an out of lock state (Lock = LOW), the phase error must become greater δ. The
values of ε and δ are dependent on which PLL is used and are shown in Table 6:
Table 6. Programmable Digital Lock Detect Settings
PLL
RF
IF
ε
δ
10 ns
15 ns
20 ns
30 ns
When the PLL is in the power-down mode and the Ftest/LD pin is programmed for the lock detect function, it is
forced LOW. The accuracy of this circuit degrades at higher comparison frequencies. To compensate for this, the
DIV4 word should be set to one if the comparison frequency exceeds 20 MHz. The function of this word is to
divide the comparison frequency presented to the lock detect circuit by 4.
NOTE
If the MUX[3:0] word is set such as to view lock detect for both PLLs, an unlocked (LOW)
condition is shown whenever either one of the PLLs is determined to be out of lock.
20
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LMX2485Q-Q1
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
{Ç!wÇ
[5 = [hí
(bot [ocked)
bh
bh
bh
bh
Phase Error < e
ò9{
Phase Error < e
ò9{
Phase Error < e
ò9{
Phase Error < e
ò9{
bh
Phase Error < e
ò9{
[5 = ILDI
([ocked)
bh
ò9{
Phase Error > d
Figure 23. Digital Lock Detect Flowchart
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8.3.7 Cycle Slip Reduction and Fastlock
The LMX2485Q-Q1 offers both cycle slip reduction (CSR) and Fastlock with timeout counter support. This means
that it requires no additional programming overhead to use them. It is generally recommended that the charge
pump current in the steady-state be 8X or less in order to use cycle slip reduction, and 4X or less in steady-state
in order to use Fastlock. The next step is to decide between using Fastlock or CSR. This determination can be
made based on the ratio of the comparison frequency (fCOMP) to loop bandwidth (BW).
Table 7. Cycle Slip/Fastlock Usage
COMPARISON FREQUENCY
(fCOMP
CYCLE SLIP REDUCTION
(CSR)
FASTLOCK
)
fCOMP ≤ 1.25 MHz
1.25 MHz < fCOMP ≤ 2 MHz
fCOMP > 2 MHz
Noticeable better than CSR
Marginally better than CSR
Same or worse than CSR
Likely to provide a benefit, provided that
fCOMP > 100 X BW
8.3.7.1 Cycle Slip Reduction (CSR)
Cycle slip reduction works by reducing the comparison frequency during frequency acquisition while keeping the
same loop bandwidth, thereby reducing the ratio of the comparison frequency to the loop bandwidth. In cases
where the ratio of the comparison frequency exceeds about 100 times the loop bandwidth, cycle slipping can
occur and significantly degrade lock times. The greater this ratio, the greater the benefit of CSR. This is typically
the case of high comparison frequencies. In circumstances where there is not a problem with cycle slipping, CSR
provides no benefit. There is a glitch when CSR is disengaged, but because CSR should be disengaged long
before the PLL is actually in lock, this glitch is not an issue. A good rule of thumb for CSR disengagement is to
do this at the peak time of the transient response. Because this time is typically much sooner than Fastlock
should be disengaged, it does not make sense to use CSR and Fastlock in combination.
8.3.7.2 Fastlock
Fastlock works by increasing the loop bandwidth only during frequency acquisition. In circumstances where the
comparison frequency is less than or equal to 2 MHz, Fastlock may provide a benefit beyond what CSR can
offer. Because Fastlock also reduces the ratio of the comparison frequency to the loop bandwidth, it may provide
a significant benefit in cases where the comparison frequency is above 2 MHz. However, CSR can usually
provide an equal or larger benefit in these cases, and can be implemented without using an additional resistor.
The reason for this restriction on frequency is that Fastlock has a glitch when it is disengaged. As the time of
engagement for Fastlock decreases and becomes on the order of the fast lock time, this glitch grows and limits
the benefits of Fastlock. This effect becomes worse at higher comparison frequencies. There is always the option
of reducing the comparison frequency at the expense of phase noise in order to satisfy this constraint on
comparison frequency. Despite this glitch, there is still a net improvement in lock time using Fastlock in these
circumstances. When using Fastlock, it is also recommended that the steady-state charge pump state be 4X or
less. Also, Fastlock was originally intended only for second order filters, so when implementing it with higher
order filters, the third and fourth poles can not be too close in, or it will not be possible to keep the loop filter well
optimized when the higher charge pump current and Fastlock resistor are engaged.
8.3.7.3 Using Cycle Slip Reduction (CSR) to Avoid Cycle Slipping
Once it is decided that CSR is to be used, the cycle slip reduction factor needs to be chosen. The available
factors are 1/2, 1/4, and 1/16. In order to preserve the same loop characteristics, TI recommends that Equation 4
be satisfied:
(Fastlock Charge Pump Current) / (Steady-State Charge Pump Current) = CSR
(4)
In order to satisfy this constraint, the maximum charge pump current in steady-state is 8X for a CSR of 1/2, 4X
for a CSR of 1/4, and 1X for a CSR of 1/16. Because the PLL phase noise is better for higher charge pump
currents, it makes sense to choose CSR only as large as necessary to prevent cycle slipping. Choosing it larger
than this will not improve lock time, and will result in worse phase noise.
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Consider an example where the desired loop bandwidth in steady-state is 100 kHz and the comparison
frequency is 20 MHz. This yields a ratio of 200. Cycle slipping may be present, but would not be too severe if it
was there. If a CSR factor of 1/2 is used, this would reduce the ratio to 100 during frequency acquisition, which is
probably sufficient. A charge pump current of 8X could be used in steady-state, and a factor of 16X could be
used during frequency acquisition. This yields a ratio of 1/2, which is equal to the CSR factor and this satisfies
the above constraint. In this circumstance, it could also be decided to just use 16X charge pump current all the
time, because it would probably have better phase noise, and the degradation in lock time would not be too
severe.
8.3.7.4 Using Fastlock to Improve Lock Times
Figure 24. Loop Filter with Fastlock Resistor
Once it is decided that Fastlock is to be used, the loop bandwidth multiplier, K, is needed in order to determine
the theoretical impact of Fastlock on the loop bandwidth and the resistor value, R2p, that is switched in parallel
during Fastlock. This ratio is calculated in Equation 5:
K = (Fastlock Charge Pump Current) / (Steady-State Charge Pump Current)
(5)
Table 8. Fastlock Usage
K
1
LOOP BANDWIDTH
1.00 X
R2P VALUE
Open
LOCK TIME
100 %
71 %
2
1.41 X
R2/0.41
R2/0.73
R2
3
1.73 X
58%
4
2.00 X
50%
8
2.83 X
R2/1.83
R2/2
35%
9
3.00 X
33%
16
4.00 X
R2/3
25%
The above table shows how to calculate the Fastlock resistor and theoretical lock time improvement, once the
ratio , K, is known. This all assumes a second order filter (not counting the pole at 0 Hz). However, it is generally
recommended that the loop filter order be one greater than the order of the delta sigma modulator, which means
that a second order filter is never recommended. In this case, the value for R2p is typically about 80% of what it
would be for a second order filter. Because the Fastlock disengagement glitch gets larger and it is harder to keep
the loop filter optimized as the K value becomes larger, designing for the largest possible value for K usually, but
not always yields the best improvement in lock time. To get a more accurate estimate requires more simulation
tools, or trial and error.
8.3.7.5 Capacitor Dielectric Considerations for Lock Time
The LMX2485Q-Q1 has a high fractional modulus and high charge pump gain for the lowest possible phase
noise. One consideration is that the reduced N value and higher charge pump may cause the capacitors in the
loop filter to become larger in value. For larger capacitor values, it is common to have a trade-off between
capacitor dielectric quality and physical size. Using film capacitors or NPO/COG capacitors yields the best
possible lock times, where as using X7R or Z5R capacitors can increase lock time by 0 – 500%. However, it is a
general tendency that designs that use a higher compare frequency tend to be less sensitive to the effects of
capacitor dielectrics. Although the use of lesser quality dielectric capacitors may be unavoidable in many
circumstances, allowing a larger footprint for the loop filter capacitors, using a lower charge pump current, and
reducing the fractional modulus are all ways to reduce capacitor values. Capacitor dielectrics have very little
impact on phase noise and spurs.
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8.3.8 Fractional Spur and Phase Noise Controls
Control of the fractional spurs is more of an art than an exact science. The first differentiation that needs to be
made is between primary fractional and sub-fractional spurs. The primary fractional spurs are those that occur at
increments of the channel spacing only. The sub-fractional spurs are those that occur at a smaller resolution than
the channel spacing, usually one-half or one-fourth. There are trade-offs between fractional spurs, sub-fractional
spurs, and phase noise. The rules of thumb presented in this section are just that. There will be exceptions. The
bits that impact the fractional spurs are FM and DITH, and these bits should be set in this order.
The first step to do is choose FM, for the delta sigma modulator order. TI recommends to start with FM = 3 for a
third order modulator and use strong dithering. In general, there is a trade-off between primary and sub-fractional
spurs. Choosing the highest order modulator (FM = 0 for 4th order) typically provides the best primary fractional
spurs, but the worst sub-fractional spurs. Choosing the lowest modulator order (FM = 2 for 2nd order), typically
gives the worst primary fractional spurs, but the best sub-fractional spurs. Choosing FM = 3, for a 3rd order
modulator is a compromise.
The second step is to choose DITH, for dithering. Dithering has a very small impact on primary fractional spurs,
but a much larger impact on sub-fractional spurs. The only problem is that it can add a few dB of phase noise, or
even more if the loop bandwidth is very wide. Disabling dithering (DITH = 0), provides the best phase noise, but
the sub-fractional spurs are worst (except when the fractional numerator is 0, and in this case, they are the best).
Choosing strong dithering (DITH = 2) significantly reduces sub-fractional spurs, if not eliminating them
completely, but adds the most phase noise. Weak dithering (DITH = 1) is a compromise.
The third step is to tinker with the fractional word. Although 1/10 and 400/4000 are mathematically the same,
expressing fractions with much larger fractional numerators often improve the fractional spurs. Increasing the
fractional denominator only improves spurs to a point. A good practical limit could be to keep the fractional
denominator as large as possible, but not to exceed 4095, so it is not necessary to use the extended fractional
numerator or denominator.
This steps can be done in different orders and it might take a few iterations to find the optimum performance.
Special considerations should be taken for lower frequencies that are below about 100 MHz. In addition squaring
up the wave, it is often helpful to use lowest terms fractions instead of highest terms fractions. Also, dithering
may turn out to not be so useful. All the things are to introduce a methodical way of thinking about optimizing
spurs, not an exact method. There will be exceptions to all these rules.
NOTE
For more information concerning delta-sigma PLLs, loop filter design, cycle slip reduction,
Fastlock, and many other topics, visit ti.com/wireless. Here there is the EasyPLL
simulation tool and an online reference called PLL Performance, Simulation, and Design.
24
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8.4 Device Functional Modes
8.4.1 Power Pins, Power Down, and Power Up Modes
TI recommends that all of the power pins be filtered with a series 18-Ω resistor and then placing two capacitors
shunt to ground, thus creating a low pass filter. Although it makes sense to use large capacitor values in theory,
the ESR (Equivalent Series Resistance) is greater for larger capacitors. For optimal filtering minimize the sum of
the ESR and theoretical impedance of the capacitor. It is therefore recommended to provide two capacitors of
very different sizes for the best filtering. 1 µF and 100 pF are typical values. The small capacitor should be
placed as close as possible to the pin.
The power down state of the LMX2485Q-Q1 is controlled by many factors. The one factor that overrides all other
factors is the CE pin. If this pin is low, the part will be powered down. Asserting a high logic level on this pin is
necessary to power up the chip, however, there are other bits in the programming registers that can override this
and put the PLL back in a power down state. Provided that the voltage on the CE pin is high, programming the
RF_PD and IF_PD bits to zero specifies that the part will be powered up. Programming either one of these bits to
one will power down the appropriate section of the synthesizer, provided that the ATPU bit does not override this.
Table 9. Powerdown Modes
ATPU
CE Pin
RF_PD
PLL STATE
BIT ENABLED + N Counter Write
Powered Down
(Asynchronous)
Low
X
X
High
High
X
0
Yes
No
Powered Up
Powered Up
Powered Down
(Asynchronous)
High
1
No
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8.5 Programming
The 24-bit data registers are loaded through a MICROWIRE Interface. These data registers are used to program
the R counter, the N counter, and the internal mode control latches. The data format of a typical 24-bit data
register is shown below. The control bits CTL [3:0] decode the register address. On the rising edge of LE, data
stored in the shift register is loaded into one of the appropriate latches (selected by address bits). Data is shifted
in MSB first.
NOTE
It is best to program the N counter last, because doing so initializes the digital lock
detector and Fastlock circuitry. Note that initialize means it resets the counters, but it does
NOT program values into these registers. The exception is when 22-bit is not being used.
In this case, it is not necessary to program the R7 register.
Table 10. Programming Format
MSB
LSB
DATA [21:0]
CTL [3:0]
23
4
3
2
1
0
8.5.1 Register Location Truth Table
The control bits CTL [3:0] decode the internal register address. The table below shows how the control bits are
mapped to the target control register.
Table 11. Programmable Registers
C3
x
C2
x
C1
x
C0
0
DATA Location
R0
R1
R2
R3
R4
R5
R6
R7
0
0
1
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
1
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8.5.2 Control Register Content Map
Because the LMX2485Q-Q1 registers are complicated, they are organized into two groups, basic and advanced.
The first four registers are basic registers that contain critical information necessary for the PLL to achieve lock.
The last 5 registers are for features that optimize spur, phase noise, and lock time performance. The next page
shows these registers.
Although it is highly recommended that the user eventually take advantage of all the modes of the LMX2485, the
quick start register map is shown in order for the user to get the part up and running quickly using only those bits
critical for basic functionality. The following default conditions for this programming state are a third order delta-
sigma modulator in 12-bit mode with no dithering and no Fastlock.
Table 12. Quick Start Register Map
REGISTER
23
22
21 20 19 18 17 16 15 14
DATA[19:0] (Except for the RF_N Register, which is [22:0])
RF_N[10:0]
RF_R[5:0]
13
12 11
10
9
8
7
6
5
4
3
2
1
0
C0
0
C3
C2
C1
R0
R1
RF_FN[11:0]
RF_
PD
RF_P
RF_FD[11:0]
0
0
1
1
R2
R3
R4
IF_PD
IF_N[18:0]
0
0
1
1
1
0
0
1
0
1
1
1
0001
0
RF_CPG[3:0]
IF_R[11:0]
0
1
0
0
0
0
0
1
1
0
0
0
1
1
1
0
0
0
0
The complete register map shows all the functionality of all registers, including the last five.
Table 13. Complete Register Map
REGISTER
23
22
21 20 19 18 17 16 15 14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
DATA[19:0] (Except for the RF_N Register, which is [22:0])
C3
C2
C1
C0
R0
R1
RF_N[10:0]
RF_R[5:0]
RF_FN[11:0]
0
1
RF_
PD
0
0
0
1
1
0
RF_P
RF_FD[11:0]
R2
IF_
PD
1
IF_N[18:0]
R3
R4
ACCESS[3:0]
RF_CPG[3:0]
IF_R[11:0]
IF_ RF_
0
1
1
0
1
0
1
1
ATP
U
DITH
[1:0]
FM
[1:0]
OSC
_2X
OSC
_OUT CPP CPP
MUX
[3:0]
0
1
0
0
0
0
IF_P
R5
R6
R7
RF_FD[21:12]
RF_CPF[3:0]
RF_FN[21:12]
RF_TOC[13:0]
1
1
1
0
1
1
1
0
1
1
1
1
CSR[1:0]
IF_
RST
RF_
IF_
RF_
0
0
0
0
0
0
0
0
0
0
DIV4
0
1
0
0
1
RST CPT CPT
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8.6 Register Maps
8.6.1 R0 Register
NOTE
This register has only one control bit, so the N counter value to be changed with a single
write statement to the PLL.
Figure 25. R0 Register
23
13
12
1
0
0
RF_N[10:0]
RF_FN[11:0]
Table 14. R0 Register Field Descriptions
DESCRIPTION
BIT
FIELD
23-13
RF_N[10:0]
RF N Counter Value
The RF N counter contains an 8/9/12/13 and a 16/17/20/21 prescaler. The N
counter value can be calculated as follows:
N = RF_P·RF_C + 4·RF_B + RF_A
RF_C ≥Max{RF_A, RF_B} , for N-2FM-1 ... N+2FM is a necessary condition.
This rule is slightly modified in the case where the RF_B counter has an
unused bit, where this extra bit is used by the delta-sigma modulator for the
purposes of modulation. Consult the tables below for valid operating ranges
for each prescaler.
12-1
RF_FN[11:0]
Fractional Numerator for RF PLL
Refer to Table 33 for a more detailed description of this control word.
Table 15. Operation with the 8/9/12/13 Prescaler (RF_P=0)
RF_N [10:0]
RF_N
RF_C [6:0]
RF_B [1:0]
RF_A [1:0]
<25
25-26
27-30
31
N values less than 25 are prohibited.
Possible only with a second order delta-sigma engine.
Possible only with a second or third order delta-sigma engine.
0
.
0
0
.
0
.
0
.
1
.
1
.
0
0
0
1
.
1
1
.
...
.
.
1023
>1023
1
1
1
1
1
1
1
1
1
1
N values above 1023 are prohibited.
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RF_N
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
Table 16. Operation with the 16/17/20/21 Prescaler (RF_P=1)
RF_N [10:0]
RF_C [6:0]
RF_B [1:0]
RF_A [1:0]
<49
49-50
51-54
55
N values less than 49 are prohibited.
Possible only with a second order delta-sigma engine.
Possible with a second or third order delta-sigma engine.
0
.
0
.
0
.
0
.
0
.
1
.
1
.
0
1
.
1
1
.
...
.
.
2039
1
1
1
1
1
1
1
0
1
1
1
2040-
2043
Possible with a second or third order delta-sigma engine.
Possible only with a second order delta-sigma engine.
N values greater than 2045 are prohibited.
2044-
2045
>2045
8.6.2 R1 Register
Figure 26. R1 Register
23
22
21
16 15
4
3
0
2
0
1
1
0
1
RF_P RF_
RF_R[5:0]
RF_FD[11:0]
D
P
Table 17. R1 Register Field Descriptions
DESCRIPTION
BIT
FIELD
23
RF_PD
RF Power Down Control Bit
When this bit is set to 0, the RF PLL operates normally. When it is set to one,
the RF PLL is powered down and the RF Charge pump is set to a TRI-
STATE mode. The CE pin and ATPU bit also control power down functions,
and will override the RF_PD bit. The order of precedence is as follows. First,
if the CE pin is LOW, then the PLL will be powered down. Provided this is not
the case, the PLL will be powered up if the ATPU bit says to do so,
regardless of the state of the RF_PD bit. After the CE pin and the ATPU bit
are considered, then the RF_PD bit then takes control of the power down
function for the RF PLL.
22
RF_P
RF Prescaler bit
The prescaler used is determined by this bit.
21-16
RF_R[5:0]
RF R Divider Value
The RF R Counter value is determined by this control word. Note that this
counter does allow values down to one.
The RF R Counter value is determined by this control word. Note that this
counter does allow values down to one.
15-4
RF_FD[11:0]
RF PLL Fractional Denominator
The function of these bits are described in Table 34.
Table 18. RF_R [5:0] -- RF R Divider Value
R Value
RF_R[5:0]
1
0
.
0
.
0
.
0
.
0
.
1
.
...
63
1
1
1
1
1
1
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Table 19. RF_P -- RF Prescaler Bit
RF_P
PRESCALER
8/9/12/13
MAXIMUM FREQUENCY
0
1
2000 MHz
3000 MHz
16/17/20/21
8.6.3 R2 Register
Figure 27. R2 Register
23
22
4
3
0
2
1
1
0
0
1
IF_PD
IF_N[18:0]
Table 20. R2 Register Field Descriptions
DESCRIPTION
BIT
FIELD
23
IF_PD
IF Power Down Bit
When this bit is set to 0, the IF PLL operates normally. When it is set to 1,
the IF PLL powers down and the output of the IF PLL charge pump is set to a
TRI-STATE mode. If the ATPU bit is set and register R0 is written to, the
IF_PD will be reset to 0 and the IF PLL will be powered up. If the CE pin is
held low, the IF PLL will be powered down, overriding the IF_PD bit.
22-4
IF_N[18:0]
IF N Divider Value
Table 21. IF_N Counter Programming With the 8/9 Prescaler (IF_P=0)
IF_N[18:0]
N
VALUE
IF_B
IF_A
≤23
N values less than or equal to 23 are prohibited because IF_B ≥ 3 is required.
24-55
Legal divide ratios in this range are:
24-27, 32-36, 40-45, 48-54
56
57
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
1
1
.
1
1
.
1
1
.
0
0
.
0
0
.
0
0
1
.
0
.
...
262143
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
1
1
1
Table 22. Operation With the 16/17 Prescaler (IF_P=1)
N
IF_B
IF_A
VALUE
≤47
N values less than or equal to 47 are prohibited because IF_B ≥ 3 is required.
48-239
Legal divide ratios in this range are:
48-51, 64-68, 80-85, 96-102, 112-119, 128-136, 144-153, 160-170, 176-187, 192-204, 208-221, 224-238
240
241
0
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
1
1
.
1
1
.
1
1
.
1
1
.
0
0
.
0
0
.
0
0
.
0
1
.
0
.
...
524287
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
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8.6.4 R3 Register
Figure 28. R3 Register
23
20
19
16
15
4
3
0
2
1
1
1
0
0
ACCESS[3:0]
RF_CPG[3:0]
IF_R[11:0]
Table 23. R3 Register Field Descriptions
DESCRIPTION
BIT
FIELD
23-20
ACCESS[3:0]
Register Access word
It is mandatory that the first 5 registers R0-R4 be programmed. The
programming of registers R5-R7 is optional. The ACCESS[3:0] bits determine
which additional registers need to be programmed. Any one of these
registers can be individually programmed. According to the table below, when
the state of a register is in default mode, all the bits in that register are forced
to a default state and it is not necessary to program this register. When the
register is programmable, it needs to be programmed through the
MICROWIRE. Using this register access technique, the programming
required is reduced up to 37%.
19-16
15-4
RF_CPG[3:0]
IF_R[11:0]
RF PLL Charge Pump Gain
This is used to control the magnitude of the RF PLL charge pump in steady-
state operation.
IF R Divider Value
For the IF R divider, the R value is determined by the IF_R[11:0] bits in the
R3 register. The minimum value for IF_R is 3.
Table 24. IF_R[11:0] -- IF R Divider Value
R
IF_R[11:0]
VALUE
3
0
0
.
0
.
0
.
0
.
0
0
.
0
.
0
.
0
.
1
.
1
.
...
.
.
4095
1
1
1
1
1
1
1
1
1
1
1
1
Table 25. RF_CPG -- RF PLL Charge Pump Gain
RF_CPG
CHARGE PUMP STATE
TYPICAL RF CHARGE PUMP CURRENT
AT 3 VOLTS (µA)
0
1
1X
2X
95
190
2
3X
285
3
4X
380
4
5X
475
5
6X
570
6
7X
665
7
8X
760
8
9X
855
9
10X
11X
12X
13X
14X
15X
16X
950
10
11
12
13
14
15
1045
1140
1235
1330
1425
1520
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Table 26. ACCESS -- Register Access word
ACCESS BIT
ACCESS[0]
ACCESS[1]
ACCESS[2]
ACCESS[3]
REGISTER LOCATION
REGISTER CONTROLLED
R3[20]
R3[21]
R3[22]
R3[23]
Must be set to 1
R5
R6
R7
The default conditions the registers is shown below:
Table 27. Default Register States
REGISTER 23 22 21 20 19 18 17 16 15 14
13
12
11 10
9
8
7
6
5
4
3
2
1
0
Data[19:0]
C3
C2
C1
C0
R4
R4 Must be programmed manually.
R5
R6
R7
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
1
1
1
0
1
1
1
1
This corresponds to the following bit settings.
Table 28. Default Programmable States
REGISTER
BIT LOCATION
R4[23]
BIT NAME
ATPU
BIT DESCRIPTION
Autopowerup
BIT VALUE
BIT STATE
Disabled
Strong
0
2
3
0
0
R4[17:16]
R4[15:14]
R4[12]
DITH
Dithering
FM
Modulation Order
Oscillator Doubler
OSCout Pin Enable
3rd Order
Disabled
Disabled
OSC_2X
OSC_OUT
R4[11]
R4
IF Charge Pump
Polarity
R4[10]
R4[9]
IF_CPP
1
1
Positive
Positive
RF Charge Pump
Polarity
RF_CPP
R4[8]
IF_P
MUX
IF PLL Prescaler
Ftest/LD Output
1
0
16/17
R4[7:4]
Disabled
Extended Fractional
Denominator
R5[23:14]
RF_FD[21:12]
0
Disabled
R5
R6
Extended Fractional
Numerator
R5[13:4]
R6[23:22]
R6[21:18]
R6[17:4]
R7[13]
RF_FN[21:12]
CSR
0
0
0
0
0
0
0
Disabled
Disabled
Disabled
Disabled
Cycle Slip Reduction
Fastlock Charge
Pump Current
RF_CPF
RF_TOC
DIV4
RF Timeout Counter
Lock Detect
Adjustment
Disabled (Fcomp ≤
20 MHz)
R7[7]
IF_RST
RF_RST
IF PLL Counter Reset
Disabled
R7
RF PLL Counter
Reset
R7[6]
Disabled
R7[5]
R7[4]
IF_CPT
IF PLL Tri-State
RF PLL Tri-State
0
0
Disabled
Disabled
RF_CPT
32
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LMX2485Q-Q1
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
8.6.5 R4 Register
This register controls the conditions for the RF PLL in Fastlock.
Figure 29. R4 Register
23
ATPU
11
22
0
21
1
20
0
19
0
18
0
17
16
15
14
13
0
12
OSC_2X
0
DITH[1:0]
FM[1:0]
10
9
8
7
4
3
1
2
0
1
OSC_OU
T
IF_CPP
RF_CPP
IF_P
MUX[3:0]
0
1
Table 29. R4 Register Field Descriptions
DESCRIPTION
BIT
FIELD
23
ATPU
PLL Automatic Power Up
When this bit is set to 1, both the RF and IF PLL power up when the R0
register is written to. When the R0 register is written to, the PD_RF and
PD_IF bits are changed to 0 in the PLL registers. The exception to this case
is when the CE pin is low. In this case, the ATPU function is disabled.
17-16
DITH[1:0]
Dithering Control
Dithering is a technique used to spread out the spur energy. Enabling
dithering can reduce the main fractional spurs, but can also give rise to a
family of smaller spurs. Whether dithering helps or hurts is application
specific. Enabling the dithering may also increase the phase noise. In most
cases where the fractional numerator is zero, dithering usually degrades
performance.
Dithering tends to be most beneficial in applications where there is
insufficient filtering of the spurs. This often occurs when the loop bandwidth is
very wide or a higher order delta-sigma modulator is used. Dithering tends
not to impact the main fractional spurs much, but has a much larger impact
on the sub-fractional spurs. If it is decided that dithering will be used, best
results will be obtained when the fractional denominator is at least 1000.
0 = Disabled
1 = Weak Dithering
2 = Strong Dithering
3 = Reserved
15-14
FM[1:0]
Fractional Mode
Determines the order of the delta-sigma modulator. Higher order delta-sigma
modulators reduce the spur levels closer to the carrier by pushing this noise
to higher frequency offsets from the carrier. In general, the order of the loop
filter should be at least one greater than the order of the delta-sigma
modulator in order to allow for sufficient roll-off.
0 = Fractional PLL mode with a 4th order delta-sigma modulator
1 = Disable the delta-sigma modulator. Recommended for test use only.
2 = Fractional PLL mode with a 2nd order delta-sigma modulator
3 = Fractional PLL mode with a 3rd order delta-sigma modulator
12
OSC_2X
Oscillator Doubler Enable
When this bit is set to 0, the oscillator doubler is disabled and the TCXO
frequency presented to the IF R and RF R counters is equal to that of the
input frequency of the OSCin pin. When this bit is set to 1, the TCXO
frequency presented to the RF R counter is doubled. Phase noise added by
the doubler is negligible.
11
10
OSC_OUT
IF_CPP
Oscillator Output Buffer Enable
0 = Disabled (High Impedance)
1 = Buffered output of OSCin pin
IF PLL Charge Pump Polarity
For a positive phase detector polarity, which is normally the case, set this bit
to 1. Otherwise set this bit for a negative phase detector polarity.
0 = Negative
1 = Positive
Copyright © 2013–2016, Texas Instruments Incorporated
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LMX2485Q-Q1
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www.ti.com.cn
Table 29. R4 Register Field Descriptions (continued)
BIT
FIELD
DESCRIPTION
9
RF_CPP
RF PLL Charge Pump Polarity
0 = Negative
1 = Positive (Default)
8
IF_P
IF Prescaler
When this bit is set to 0, the 8/9 prescaler is used. Otherwise the 16/17
prescaler is used.
7-4
MUX[3:0]
Frequency Out & Lock Detect MUX
These bits determine the output state of the Ftest/LD pin.
Table 30. MUX[3:0] Frequency Out & Lock Detect MUX
MUX[3:0]
OUTPUT TYPE
OUTPUT DESCRIPTION
0
0
0
0
High
Disabled
Impedance
Push-Pull
Push-Pull
Push-Pull
Push-Pull
Push-Pull
Open Drain
Open Drain
Open Drain
Push-Pull
Push-Pull
Push-Pull
Push-Pull
Push-Pull
Push-Pull
Push-Pull
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
General-purpose output, Logical “High” State
General-purpose output, Logical “Low” State
RF & IF Digital Lock Detect
RF Digital Lock Detect
IF Digital Lock Detect
RF & IF Analog Lock Detect
RF Analog Lock Detect
IF Analog Lock Detect
RF & IF Analog Lock Detect
RF Analog Lock Detect
IF Analog Lock Detect
IF R Divider divided by 2
IF N Divider divided by 2
RF R Divider divided by 2
RF N Divider divided by 2
Table 31. IF_P -- IF Prescaler
IF_P
IF PRESCALER
MAXIMUM FREQUENCY
800 MHz
0
1
8/9
16/17
800 MHz
Table 32. OSC2X -- Oscillator Doubler Enable
OSC2X
FREQUENCY PRESENTED TO RF R
COUNTER
FREQUENCY PRESENTED TO IF R
COUNTER
0
1
fOSCin
fOSCin
2 x fOSCin
34
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LMX2485Q-Q1
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
8.6.6 R5 Register
Figure 30. R5 Register
23
14
13
4
3
1
2
0
1
1
0
1
RF_FD[21:12]
RF_FN[21:12]
In the case that the ACCESS[1] bit is 0, then the part operates in 12-bit fractional mode, and the RF_FN2[21:12]
bits become do not care bits. When the ACCESS[1] bit is set to 1, the part operates in 22-bit mode and the
fractional numerator is expanded from 12 to 22-bits.
Table 33. Fractional Numerator Determination { RF_FN[21:12], RF_FN[11:0], ACCESS[1] }
FRACTIONAL
RF_FN[21:12]
RF_FN[11:0]
NUMERATOR
(These bits only apply in 22-bit mode)
0
1
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
1
.
In 12-bit mode, these are do not care.
In 22-bit mode, for N <4096,
...
these bits should be all set to 0.
4095
4096
...
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
0
.
0
.
0
.
0
.
0
.
0
.
0
.
0
.
0
.
1
.
4194303
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
In the case that the ACCESS[1] bit is 0, then the part is operates in the 12-bit fractional mode, and the
RF_FD[21:12] bits become do not care bits. When the ACCESS[1] is set to 1, the part operates in 22-bit mode
and the fractional denominator is expanded from 12 to 22-bits.
Table 34. Fractional Denominator Determination { RF_FD[21:12], RF_FD[11:0], ACCESS[1]}
FRACTIONAL
RF_FD[21:12]
RF_FD[11:0]
DENOMINAT
OR
(These bits only apply in 22-bit mode)
0
1
In 12-bit mode, these are do not care.
In 22-bit mode, for N <4096,
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
0
.
0
1
.
these bits should be all set to 0.
...
4095
4096
...
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
1
0
.
0
.
0
.
0
.
0
.
0
.
0
.
0
.
0
.
0
.
1
.
4194303
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Copyright © 2013–2016, Texas Instruments Incorporated
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8.6.7 R6 Register
Figure 31. R6 Register
23
22
21
18
17
4
3
1
2
1
1
0
0
1
CSR[1:0]
RF_CPF[3:0]
RF_TOC[13:0]
Table 35. R6 Register Field Descriptions
DESCRIPTION
BIT
FIELD
23-22
CSR[1:0]
RF Cycle Slip Reduction
CSR controls the operation of the Cycle Slip Reduction Circuit. This circuit
can be used to reduce the occurrence of phase detector cycle slips. Note that
the Fastlock charge pump current, steady-state current, and CSR control are
all interrelated. Refer to Cycle Slip Reduction and Fastlock for information on
how to use this.
21-18
17-4
RF_CPF[3:0]
RF PLL Fastlock Charge Pump Current
Specify the charge pump current for the Fastlock operation mode for the RF
PLL. Note that the Fastlock charge pump current, steady-state current, and
CSR control are all interrelated.
RF_TOC[13:0]
RF Time Out Counter and Control for FLoutRF Pin
The RF_TOC[13:0] word controls the operation of the RF Fastlock circuitry
as well as the function of the FLoutRF output pin. When this word is set to a
value between 0 and 3, the RF Fastlock circuitry is disabled and the FLoutRF
pin operates as a general-purpose CMOS TRI-STATE I/O. When RF_TOC is
set to a value between 4 and 16383, the RF Fastlock mode is enabled and
the FLoutRF pin is utilized as the RF Fastlock output pin. The value
programmed into the RF_TOC[13:0] word represents two times the number
of phase detector comparison cycles the RF synthesizer will spend in the
Fastlock state.
Table 36. RF_TOC -- RF Time Out Counter and Control for FLoutRF Pin
RF_TOC
FASTLOCK MODE
Disabled
Fastlock Period [CP events]
FLoutRF PIN FUNCTIONALITY
0
1
N/A
N/A
High Impedance
Manual
Logic 0 State.
Forces all Fastlock conditions
2
Disabled
Disabled
Enabled
Enabled
Enabled
Enabled
N/A
N/A
Logic 0 State
Logic 1 State
Fastlock
3
4
4X2 = 8
5X2 = 10
…
5
Fastlock
…
Fastlock
16383
16383X2 = 32766
Fastlock
36
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LMX2485Q-Q1
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
Table 37. RF_CPF -- RF PLL Fastlock Charge Pump Current
RF_CPF
RF CHARGE PUMP STATE
TYPICAL RF CHARGE PUMP
CURRENT AT 3 VOLTS (µA)
0
1
1X
2X
95
190
2
3X
285
3
4X
380
4
5X
475
5
6X
570
6
7X
665
7
8X
760
8
9X
855
9
10X
11X
12X
13X
14X
15X
16X
950
10
11
12
13
14
15
1045
1140
1235
1330
1425
1520
Table 38. CSR[1:0] -- RF Cycle Slip Reduction
CSR
CSR STATE
SAMPLE RATE REDUCTION
FACTOR
0
1
2
3
Disabled
Enabled
Enabled
Enabled
1
1/2
1/4
1/16
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8.6.8 R7 Register
Figure 32. R7 Register
23
22
21
0
20
19
0
18
0
17
0
16
0
0
0
0
15
14
13
12
11
1
10
0
9
8
0
7
0
6
DIV4
5
0
4
0
1
3
2
1
0
IF_RST
RF_RST
IF_CPT
RF_CPT
1
1
1
1
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 39. R7 Register Field Descriptions
DESCRIPTION
BIT
FIELD
13
DIV4
RF Digital Lock Detect Divide By 4
Because the digital lock detect function is based on a phase error, it
becomes more difficult to detect a locked condition for larger comparison
frequencies. When this bit is enabled, it subdivides the RF PLL comparison
frequency (it does not apply to the IF comparison frequency) presented to the
digital lock detect circuitry by 4. This enables this circuitry to work at higher
comparison frequencies. TI recommends that this bit be enabled whenever
the comparison frequency exceeds 20 MHz and RF digital lock detect is
being used.
7
6
IF_RST
IF PLL Counter Reset
When this bit is enabled, the IF PLL N and R counters are reset, and the
charge pump is put in a Tri-State condition. This feature should be disabled
for normal operation. Note that a counter reset is applied whenever the chip
is powered up through software or CE pin.
RF_RST
RF PLL Counter Reset
When this bit is enabled, the RF PLL N and R counters are reset and the
charge pump is put in a Tri-State condition. This feature should be disabled
for normal operation. This feature should be disabled for normal operation.
Note that a counter reset is applied whenever the chip is powered up through
software or CE pin.
5
4
IF_CPT
IF Charge Pump Tri-State
When this bit is enabled, the IF PLL charge pump is put in a Tri-State
condition, but the counters are not reset. This feature is typically disabled for
normal operation.
RF_CPT
RF Charge Pump Tri-State
When this bit is enabled, the RF PLL charge pump is put in a Tri-State
condition, but the counters are not reset. This feature is typically disabled for
normal operation.
Table 40. RF_RST - IF PLL Counter Reset
IF_RST
IF PLL N AND R COUNTERS
IF PLL CHARGE PUMP
Normal Operation
Tri-State
0 (Default)
1
Normal Operation
Counter Reset
Table 41. RF_RST -- RF PLL Counter Reset
RF_RST
0 (Default)
1
RF PLL N AND R COUNTERS
Normal Operation
RF PLL CHARGE PUMP
Normal Operation
Counter Reset
Tri-State
38
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LMX2485Q-Q1
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
Table 42. RF_TRI -- RF Charge Pump Tri-State
RF_TRI
0 (Default)
1
RF PLL N AND R COUNTERS
Normal Operation
RF PLL CHARGE PUMP
Normal Operation
Tri-State
Normal Operation
Table 43. IF_TRI -- IF Charge Pump Tri-State
IF_TRI
0 (Default)
1
IF PLL N AND R COUNTERS
Normal Operation
IF PLL CHARGE PUMP
Normal Operation
Tri-State
Normal Operation
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LMX2485Q-Q1
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
www.ti.com.cn
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
This device ideal for use in a broad class of applications, especially those requiring low current consumption and
low fractional spurs. For applications that only need a single PLL, the unused PLL can be powered down and will
not draw any extra current or generate any spurs or crosstalk. The automotive qualification on this device makes
it ideal for automotive applications.
40
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LMX2485Q-Q1
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
9.2 Typical Application
3.3 V
+3.3 V
R5
10
C7 R6
10 uF10
R4
10
R3
10
R2
10
R1
10
VddRF5
VddRF4
VddRF3
VddRF2
VddRF1
C6
C3p
C5
1µF
C4p
100 pF 1µF
C4
C3
1µF
C2
1µF
C2p
100 pF 1µF
C1
C1p
100 pF
C5p
100 pF
1µF
100 pF
U1
FINIF
13
16
18
12
1
CPOUTIF
OSCOUT
19
20
C8
ENOSC
OSCIN
C9
OSCin
FTEST/LD
CPOUTRF
FLOUTRF
Ftest/LD
R7
470
0.1µF
4
5
1
12
FINRF
FINRF
GND
GND
R3_LF
R4_LF
C3_LF
2
3
4
11
10
9
C11
Vtune
GND
GND
GND
RFout
GND
R8
18
R9
18
0.1µF
RFout
C1_LF
C2_LF
C4_LF
C10
100pF
10
8
7
23
CE
CLK
DATA
LE
CE
100pF
CLK
DATA
LE
6
R2_LF
R10
18
+3.3 V
14
17
VDDIF1
VDDIF2
21
U2
NC
3
9
22
24
11
VddRF1
VddRF2
VddRF3
VddRF4
VddRF5
VDDRF1
VDDRF2
VDDRF3
VDDRF4
VDDRF5
2
15
GND
GND
25
GND
LMX248x
Figure 33. Typical Application With Only One Side Used
Copyright © 2013–2016, Texas Instruments Incorporated
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
www.ti.com.cn
9.2.1 Design Requirements
Table 44 lists the design parameters of the LMX2485Q-Q1.
Table 44. Design Parameters
PARAMETER
Phase Margin
VALUE
48.3 degrees
11.3 KHz
40.20%
36.30%
400 µA
PM
BW
Loop Bandwidth
T3/T1
T4/T3
KPD
Pole Ratio
Charge Pump Gain
Phase Detector Frequncy
VCO Frequency
fPD
10 MHz
2400 – 2480 MHz
3 V
fVCO
Vcc
Supply Voltage
KVCO
CVCO
C1_LF
C2_LF
C3_LF
C4_LF
R2_LF
R3_LF
R4_LF
VCO Gain
55 MHz/V
22 pF
VCO Input Capacitance
2.7 nF
47 nF
270 pF
Loop Filter Components
180 pF
820 Ω
3.9 kΩ
5.6 kΩ
9.2.2 Detailed Design Procedure
The design of the loop filter involves balancing requirements of lock time, spurs, and phase noise. This design is
fairly involved, but the TI website has references, design tools, and simulation tools cover the loop filter design
and simulation in depth.
9.2.3 Application Curves
Figure 34. Phase Noise
Figure 35. Fractional Spur for 200-kHz Channel Spacing
42
Copyright © 2013–2016, Texas Instruments Incorporated
LMX2485Q-Q1
www.ti.com.cn
ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
10 Power Supply Recommendations
Low noise regulators are generally recommended for the supply pins. It is OK to have one regulator supply the
part, although it is best to put individual bypassing as shown in the Layout Guidelines for the best spur
performance. If only using one PLL and not both DO NOT DISCONNECT OR GROUND power pins! For
instance, the IF PLL supply pins also supply other blocks than just the IF PLL and they need to be connected.
However, if the IF PLL is disabled, then one can eliminate all bypass capacitors from these pins.
11 Layout
11.1 Layout Guidelines
The critical pin is the high-frequency input pin that should have a short trace. In general, try to keep the ground
and power planes 20 mils or more farther away from vias to supply pins to ensure that no spur energy can
couple to them.
11.2 Layout Example
High
Frequency
Input Pin
Figure 36. Layout Example
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ZHCSEI5A –MARCH 2013–REVISED JANUARY 2016
www.ti.com.cn
12 器件和文档支持
12.1 社区资源
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.2 商标
PLLatinum, E2E are trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
12.3 静电放电警告
这些装置包含有限的内置 ESD 保护。 存储或装卸时，应将导线一起截短或将装置放置于导电泡棉中，以防止 MOS 门极遭受静电损
伤。
12.4 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 机械、封装和可订购信息
以下页中包括机械、封装和可订购信息。这些信息是针对指定器件可提供的最新数据。这些数据会在无通知且不对
本文档进行修订的情况下发生改变。欲获得该数据表的浏览器版本，请查阅左侧的导航栏。
44
版权 © 2013–2016, Texas Instruments Incorporated
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status Package Type Package Pins Package
Eco Plan
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
(6)
LMX2485QSQ/NOPB
LMX2485QSQX/NOPB
ACTIVE
ACTIVE
WQFN
WQFN
RTW
RTW
24
24
1000 RoHS & Green
4500 RoHS & Green
SN
Level-3-260C-168 HR
Level-3-260C-168 HR
-40 to 105
-40 to 105
X2485Q
X2485Q
SN
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
9-Aug-2022
TAPE AND REEL INFORMATION
REEL DIMENSIONS
TAPE DIMENSIONS
K0
P1
W
B0
Reel
Diameter
Cavity
A0
A0 Dimension designed to accommodate the component width
B0 Dimension designed to accommodate the component length
K0 Dimension designed to accommodate the component thickness
Overall width of the carrier tape
W
P1 Pitch between successive cavity centers
Reel Width (W1)
QUADRANT ASSIGNMENTS FOR PIN 1 ORIENTATION IN TAPE
Sprocket Holes
Q1 Q2
Q3 Q4
Q1 Q2
Q3 Q4
User Direction of Feed
Pocket Quadrants
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LMX2485QSQ/NOPB
LMX2485QSQX/NOPB
WQFN
WQFN
RTW
RTW
24
24
1000
4500
178.0
330.0
12.4
12.4
4.3
4.3
4.3
4.3
1.3
1.3
8.0
8.0
12.0
12.0
Q1
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
9-Aug-2022
TAPE AND REEL BOX DIMENSIONS
Width (mm)
H
W
L
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LMX2485QSQ/NOPB
LMX2485QSQX/NOPB
WQFN
WQFN
RTW
RTW
24
24
1000
4500
208.0
356.0
191.0
356.0
35.0
35.0
Pack Materials-Page 2
PACKAGE OUTLINE
RTW0024A
WQFN - 0.8 mm max height
S
C
A
L
E
3
.
0
0
0
PLASTIC QUAD FLATPACK - NO LEAD
4.1
3.9
B
A
PIN 1 INDEX AREA
4.1
3.9
C
0.8 MAX
SEATING PLANE
0.08 C
0.05
0.00
2X 2.5
(0.1) TYP
EXPOSED
THERMAL PAD
7
12
20X 0.5
6
13
2X
25
2.5
2.6 0.1
1
18
0.3
24X
0.2
24
19
PIN 1 ID
(OPTIONAL)
0.1
C A B
C
0.05
0.5
0.3
24X
4222815/A 03/2016
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance.
www.ti.com
EXAMPLE BOARD LAYOUT
RTW0024A
WQFN - 0.8 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
(
2.6)
SYMM
24
19
24X (0.6)
1
18
24X (0.25)
(1.05)
SYMM
25
(3.8)
20X (0.5)
(R0.05)
TYP
6
13
(
0.2) TYP
VIA
7
12
(1.05)
(3.8)
LAND PATTERN EXAMPLE
SCALE:15X
0.07 MIN
ALL AROUND
0.07 MAX
ALL AROUND
SOLDER MASK
OPENING
METAL
SOLDER MASK
OPENING
METAL UNDER
SOLDER MASK
NON SOLDER MASK
DEFINED
SOLDER MASK
DEFINED
(PREFERRED)
SOLDER MASK DETAILS
4222815/A 03/2016
NOTES: (continued)
4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature
number SLUA271 (www.ti.com/lit/slua271).
www.ti.com
EXAMPLE STENCIL DESIGN
RTW0024A
WQFN - 0.8 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
4X ( 1.15)
(0.675) TYP
19
(R0.05) TYP
24
24X (0.6)
1
18
24X (0.25)
(0.675)
TYP
SYMM
20X (0.5)
25
(3.8)
6
13
METAL
TYP
7
12
SYMM
(3.8)
SOLDER PASTE EXAMPLE
BASED ON 0.125 mm THICK STENCIL
EXPOSED PAD 25:
78% PRINTED SOLDER COVERAGE BY AREA UNDER PACKAGE
SCALE:20X
4222815/A 03/2016
NOTES: (continued)
5. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
www.ti.com
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Copyright © 2022，德州仪器 (TI) 公司
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