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DS90LV027AH
SNLS206B – SEPTEMBER 2005 – REVISED JANUARY 2019
DS90LV027AH high temperature LVDS dual differential driver
1 Features
•
•
•
•
•
•
•
•
•
•
1
−40°C to +125°C Operating Temperature Range
>600-Mbps (300-MHz) Switching Rates
0.3-ns Typical Differential Skew
0.7-ns Maximum Differential Skew
3.3-V Power Supply Design
Low power dissipation (46 mW at 3.3-V Static)
Flow-Through Design Simplifies PCB Layout
Power Off Protection (Outputs in High Impedance)
Conforms to TIA/EIA-644 Standard
8-Pin SOIC Package Saves Space
2 Applications
•
•
•
•
•
•
•
•
•
•
Board-to-Board Communication
Test and Measurement
Motor Drives
LED Video Walls
Wireless Infrastructure
Telecom Infrastructure
Multi-Function Printers
NIC Cards
Rack Servers
Ultrasound Scanners
Functional Diagram of Channel 1
3 Description
The DS90LV027AH is a dual LVDS driver device
optimized for high data rate and low power
applications. The device is designed to support data
rates in excess of 600Mbps (300MHz) utilizing Low
Voltage Differential Signaling (LVDS) technology. The
DS90LV027AH is a current mode driver allowing
power dissipation to remain low even at high
frequency. In addition, the short circuit fault current is
also minimized.
The device is in a 8-lead SOIC package. The
DS90LV027AH has a flow-through design for easy
PCB layout. The differential driver outputs provides
low EMI with its typical low output swing of 360 mV. It
is perfect for high speed transfer of clock and data.
The DS90LV027AH can be paired with its companion
dual line receiver, the DS90LV028AH, or with any of
TI's LVDS receivers, to provide a high-speed point-topoint LVDS interface.
Device Information(1)
PART NUMBER
DS90LV027AH
PACKAGE
SOIC (8)
BODY SIZE (NOM)
4.90 mm × 3.91 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Functional Diagram of Channel 2
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.
DS90LV027AH
SNLS206B – SEPTEMBER 2005 – REVISED JANUARY 2019
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Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
5
6
Absolute Maximum Ratings .....................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Switching Characteristics ..........................................
Typical Characteristics ..............................................
Parameter Measurement Information .................. 9
Detailed Description ............................................ 10
8.1 Overview ................................................................. 10
8.2 Functional Block Diagrams ..................................... 10
8.3 Feature Description................................................. 10
8.4 Device Functional Modes........................................ 11
9
Application and Implementation ........................ 12
9.1 Application Information............................................ 12
9.2 Typical Application ................................................. 12
10 Power Supply Recommendations ..................... 16
11 Layout................................................................... 16
11.1 Layout Guidelines ................................................. 16
11.2 Layout Example ................................................... 20
12 Device and Documentation Support ................. 21
12.1
12.2
12.3
12.4
12.5
12.6
Related Documentation .......................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
21
21
21
21
21
21
13 Mechanical, Packaging, and Orderable
Information ........................................................... 21
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (April 2013) to Revision B
Page
•
Added Device Information table, Device Comparison table, ESD Ratings table, Feature Description section, Device
Functional Modes, Application and Implementation section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section. ................................................................................................. 1
•
Added navigation links and removed the NRND banner from the top of the datasheet page .............................................. 1
•
Moved the thermal resistance (θJA) parameter in the Absolute Maximum Ratings table to the Thermal Information
table ....................................................................................................................................................................................... 4
Changes from Original (April 2013) to Revision A
•
2
Page
Changed layout of National Data Sheet to TI format ............................................................................................................. 7
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5 Pin Configuration and Functions
D Package
8-Pin SOT-23
Top View
Pin Functions
PIN
I/O
DESCRIPTION
NAME
NO.
DI
2, 3
I
TTL/CMOS driver input pins
DO+
6, 7
O
Non-inverting driver output pin
DO−
5, 8
O
Inverting driver output pin
GND
4
I
Ground pin
VCC
1
I
Positive power supply pin, +3.3 V ± 0.3 V
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6 Specifications
6.1 Absolute Maximum Ratings
(1)
MIN
MAX
UNIT
Supply Voltage (VCC)
−0.3V
4
V
Input Voltage (DI)
−0.3V
3.6
V
Output Voltage (DO±)
−0.3V
3.9
V
D Package
Maximum Package Power Dissipation at +25°C
mW
9.5
mW/°C
150
°C
−65
Storage Temperature, Tstg
(1)
1190
Derate D Package (above +25°C)
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
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (1.5 kΩ,
100 pF)
8000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
1000
EIAJ (0 Ω, 200 pF)
1000
IEC (direct 330 Ω, 150 pF)
4000
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. Pins listed as ±8000
V may actually have higher performance.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. Pins listed as ±1000
V may actually have higher performance.
6.3 Recommended Operating Conditions
Supply Voltage (VCC)
Ambient Temperature (TA)
MIN
TYP
MAX
3
3.3
3.6
V
−40
25
+125
°C
+130
°C
Junction Temperature (TJ)
UNIT
6.4 Thermal Information
DS90LV027AH
THERMAL METRIC
(1)
D (SOIC)
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
123.2
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
63.5
°C/W
RθJB
Junction-to-board thermal resistance
65.8
°C/W
ψJT
Junction-to-top characterization parameter
13.7
°C/W
ψJB
Junction-to-board characterization parameter
65.2
°C/W
(1)
4
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
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6.5 Electrical Characteristics
Over Supply Voltage and Operating Temperature ranges, unless otherwise specified.
PARAMETER
TEST CONDITIONS
(1) (2) (3)
PIN
MIN
TYP
MAX
UNIT
250
360
450
mV
1
35
mV
1.4
1.6
V
DIFFERENTIAL DRIVER CHARACTERISTICS
VOD
Output Differential Voltage
ΔVOD
VOD Magnitude Change
VOH
Output High Voltage
VOL
Output Low Voltage
VOS
Offset Voltage
ΔVOS
Offset Magnitude Change
IOXD
Power-off Leakage
IOSD
Output Short Circuit Current
VIH
Input High Voltage
VIL
Input Low Voltage
IIH
Input High Current
VIN = 3.3V or 2.4V
IIL
Input Low Current
VIN = GND or 0.5V
VCL
Input Clamp Voltage
ICL = −18 mA
ICC
Power Supply Current
(1)
(2)
(3)
RL = 100Ω
(Figure 15)
DO+,
DO−
0.9
1.1
1.125
1.2
1.375
0
3
25
±1
±10
μA
−5.7
−8
mA
VOUT = VCC or GND, VCC = 0V
2.0
VCC
GND
No Load
RL = 100Ω
DI
−1.5
VIN = VCC or GND
VCC
V
V
mV
V
0.8
V
±2
±10
μA
±1
±10
μA
−0.6
V
8
14
mA
14
20
mA
Current into device pins is defined as positive. Current out of device pins is defined as negative. All voltages are referenced to ground
except VOD.
All typicals are given for: VCC = +3.3 V and TA = +25°C.
The DS90LV027AH is a current mode device and only function with datasheet specification when a resistive load is applied to the
drivers outputs.
6.6 Switching Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified.
(1) (2) (3) (4)
PARAMETER
MIN
TYP
MAX
UNIT
2
ns
DIFFERENTIAL DRIVER CHARACTERISTICS
tPHLD
Differential Propagation Delay High to Low
0.3
0.8
tPLHD
Differential Propagation Delay Low to High
0.3
1.1
2
ns
tSKD1
Differential Pulse Skew |tPHLD − tPLHD|
0
0.3
0.7
ns
tSKD2
Channel to Channel Skew
0
0.4
0.8
ns
0
1
ns
0
1.2
ns
0.5
1
ns
0.5
1
(6)
tSKD3
Differential Part to Part Skew
(7)
tSKD4
Differential Part to Part Skew
(8)
tTLH
Transition Low to High Time
tTHL
Transition High to Low Time
fMAX
Maximum Operating Frequency
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(5)
RL = 100Ω, CL = 15 pF
(Figure 16 and Figure 17)
0.2
0.2
(9)
350
ns
MHz
All typicals are given for: VCC = +3.3 V and TA = +25°C.
These parameters are ensured by design. The limits are based on statistical analysis of the device over PVT (process, voltage,
temperature) ranges.
CL includes probe and fixture capacitance.
Generator waveform for all tests unless otherwise specified: f = 1 MHz, ZO = 50Ω, tr ≤ 1 ns, tf ≤ 1 ns (10%-90%).
tSKD1, |tPHLD − tPLHD|, is the magnitude difference in differential propagation delay time between the positive going edge and the negative
going edge of the same channel.
tSKD2 is the Differential Channel to Channel Skew of any event on the same device.
tSKD3, Differential Part to Part Skew, is defined as the difference between the minimum and maximum specified differential propagation
delays. This specification applies to devices at the same VCC and within 5°C of each other within the operating temperature range.
tSKD4, part to part skew, is the differential channel to channel skew of any event between devices. This specification applies to devices
over recommended operating temperature and voltage ranges, and across process distribution. tSKD4 is defined as |Max − Min|
differential propagation delay.
fMAX generator input conditions: tr = tf < 1 ns (0% to 100%), 50% duty cycle, 0V to 3V. Output criteria: duty cycle = 45%/55%, VOD >
250mV, all channels switching.
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6.7 Typical Characteristics
6
Figure 1. Output High Voltage vs
Power Supply Voltage
Figure 2. Output Low Voltage vs
Power Supply Voltage
Figure 3. Output Short Circuit Current vs
Power Supply Voltage
Figure 4. Differential Output Voltage
vs Power Supply Voltage
Figure 5. Differential Output Voltage
vs Load Resistor
Figure 6. Offset Voltage vs
Power Supply Voltage
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Typical Characteristics (continued)
Figure 7. Power Supply Current vs
Power Supply Voltage
Figure 8. Power Supply Current vs
Ambient Temperature
Figure 9. Differential Propagation Delay vs
Power Supply Voltage
Figure 10. Differential Propagation Delay vs
Ambient Temperature
Figure 11. Differential Skew vs
Power Supply Voltage
Figure 12. Differential Skew vs
Ambient Temperature
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Typical Characteristics (continued)
Figure 13. Transition Time vs
Power Supply Voltage
8
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Figure 14. Transition Time vs
Ambient Temperature
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7 Parameter Measurement Information
Figure 15. Differential Driver DC Test Circuit
Figure 16. Differential Driver Propagation Delay and Transition Time Test Circuit
Figure 17. Differential Driver Propagation Delay and Transition Time Waveforms
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8 Detailed Description
8.1 Overview
The DS90LV027AH is a dual-channel, low-voltage differential signaling (LVDS) line driver with a balanced
current source design. It operates from a single power supply that is nominally 3.3 V, but the supply can be as
low as 3.0 V and as high as 3.6 V. The input signal to the DS90LV027AH is an LVCMOS/LVTTL signal. The
output of the device is a differential signal complying with the LVDS standard (TIA/EIA-644). The differential
output signal operates with a signal level of 360 mV (nominally) at a common-mode voltage of 1.2 V. This low
differential output voltage results in low electromagnetic interference (EMI). The differential nature of the output
provides immunity to common-mode coupled signals that the driven signal may experience.
The DS90LV027AH is primarily used in point-to-point configurations, as seen in Figure 20. This configuration
provides a clean signaling environment for the fast edge rates of the DS90LV027AH and other LVDS drivers.
The DS90LV027AH is connected through a balanced media which may be a standard twisted-pair cable, a
parallel pair cable, or simply PCB traces to a LVDS receiver. Typically, the characteristic differential impedance
of the media is in the range of 100 Ω. The DS90LV027AH device is intended to drive a 100-Ω transmission line.
The 100-Ω termination resistor is selected to match the media and is placed as close to the LVDS receiver input
pins as possible.
8.2 Functional Block Diagrams
Figure 18. Functional Diagram of Channel 1
Figure 19. Functional Diagram of Channel 2
8.3 Feature Description
8.3.1 DS90LV027AH Driver Functionality
As can be seen in Table 1, the driver single-ended input to differential output relationship is defined. When the
driver input is left open, the differential output is undefined.
Table 1. DS90LV027AH Driver Functionality (1)
INPUT
OUT +
OUT -
H
H
L
L
L
H
Open
?
?
(1)
10
OUTPUTS
LVCMOS/LVTTL IN
This table is valid for both Channel 1 and Channel 2 of this device.
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8.3.2 Driver Output Voltage and Power-On Reset
The DS90LV027AH driver operates and meets all the specified performance requirements for supply voltages in
the range of 3.0 V to 3.6 V. When the supply voltage drops below 1.5 V, or the voltage has not yet reached 1.5 V
during turnon, the power-on reset circuitry will set the driver output to a high-impedance state.
8.3.3 Driver Offset
An LVDS-compliant driver is required to maintain the common-mode output voltage at 1.2 V (±75 mV). The
DS90LV027AH incorporates sense circuitry and a control loop to source common-mode current and keep the
output signal within specified values. Further, the device maintains the output common-mode voltage at this set
point over the full 3.0-V to 3.6-V supply range.
8.4 Device Functional Modes
The device has one mode of operation that applies when operated within the Recommended Operating
Conditions.
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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
The DS90LV027AH device is a dual-channel LVDS driver. The functionality of this device is simple yet extremely
flexible, leading to its use in designs ranging from wireless base stations to desktop computers. The
DS90LV027AH has a flow-through pinout that allows for easy PCB layout. The LVDS signals on one side of the
device allow easy matching of the electrical lengths for differential pair trace lines between the driver and the
receiver, as well as allow trace lines to be close together to couple noise as common-mode. Noise isolation is
achieved with the LVDS signals on one side of the device and the TTL signals on the other side.
9.2 Typical Application
Figure 20. Point-to-Point Application
9.2.1 Design Requirements
Table 2 lists the design parameters as an example.
Table 2. Design Parameters
12
DESIGN PARAMETERS
EXAMPLE VALUE
Driver Supply Voltage (VDD)
3 to 3.6 V
Driver Input Voltage
0 to VDD
Signaling Rate
0 to 600 Mbps
Interconnect Characteristic Impedance
100 Ω
Number of Receiver Nodes
2
Ground shift between driver and receiver
±1 V
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9.2.2 Detailed Design Procedure
9.2.2.1 Driver Supply Voltage
DS90LV027AH is a dual-channel LVDS driver that operates from a single supply. The device can support
operation with a supply as low as 3.0 V and as high as 3.6 V. The driver output voltage is dependent upon the
chosen supply voltage. The minimum output voltage stays within the specified LVDS limits (247 mV to 450 mV)
for a 3.3-V supply. If the supply range is between 3.0 V and 3.6 V, the minimum output voltage may be as low as
150 mV. If a communication link is designed to operate with a supply within this lower range, the channel noise
margin must be looked at carefully to ensure error-free operation.
9.2.2.2 Driver Bypass Capacitance
Bypass capacitors play a key role in power distribution circuitry. Specifically, they create low-impedance paths
between power and ground. At low frequencies, a good digital power supply offers very low-impedance paths
between its terminals. However, as higher frequency currents propagate through power traces, the source is
quite often incapable of maintaining a low-impedance path to ground. Bypass capacitors are used to address this
shortcoming. Usually, large bypass capacitors (10 μF to 1000 μF) at the board-level do a good job up into the
kHz range. Due to their size and length of their leads, they tend to have large inductance values at the switching
frequencies of modern digital circuitry. To solve this problem, one must resort to the use of smaller capacitors
(nF to μF range) installed locally next to the integrated circuit.
Multilayer ceramic chip or surface-mount capacitors (size 0603 or 0805) minimize lead inductances of bypass
capacitors in high-speed environments, because their lead inductance is about 1 nH. For comparison purposes,
a typical capacitor with leads has a lead inductance around 5 nH.
The value of the bypass capacitors used locally with LVDS chips can be determined by Equation 1 and
Equation 2, according to Johnson (1) equations 8.18 to 8.21. A conservative rise time of 200 ps and a worst-case
change in supply current of 1 A covers the whole range of LVDS devices offered by Texas Instruments. In this
example, the maximum power supply noise tolerated is 200 mV. However, this figure varies depending on the
noise budget available in the design. (1)
æ DIMaximum Step Change Supply Current ö
Cchip = ç
÷ ´ TRise Time
è DVMaximum Power Supply Noise ø
(1)
æ 1A ö
CLVDS = ç
÷ ´ 200 ps = 0.001 mF
è 0.2V ø
(2)
Figure 21 lowers lead inductance and covers intermediate frequencies between the board-level capacitor (>10
µF) and the value of capacitance found above (0.001 µF). TI recommends to place the smallest value of
capacitance as close to the chip as possible.
3.3 V
0.1 µF
0.001 µF
Figure 21. Recommended LVDS Bypass Capacitor Layout
9.2.2.3 Driver Input Votlage
The DS90LV027AH single-ended input is designed to support a wide input voltage range. The input stage can
accept signals as high as 3.6 V when the supply voltage is 3.6 V.
(1)
Howard Johnson & Martin Graham.1993. High Speed Digital Design – A Handbook of Black Magic. Prentice Hall PRT. ISBN number
013395724.
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9.2.2.4 Driver Output Voltage
DS90LV027AH driver output has a 1.2-V common-mode voltage, with a nominal differential output signal of 360
mV. This 360 mV is the absolute value of the differential swing (VOD = |V+– V–|). The peak-to-peak differential
voltage is either twice this value or 700 mV. LVDS receiver thresholds are ±100 mV. With these receiver decision
thresholds, it is clear that the disadvantage of operating the driver with a lower supply will be noise margin. With
fully-compliant LVDS drivers and receivers, the user could expect a minimum of approximately 150 mV of noise
margin (247-mV minimum output voltage – 100-mV maximum input requirement). If the DS90LV027AH operates
under a supply range of 3.0 V to 3.6 V, the minimum noise margin will drop to 150 mV.
9.2.2.5 Interconnecting Media
The physical communication channel between the LVDS driver and LVDS receiver may be any balanced and
paired metal conductors meeting the requirements of the LVDS standard, the key points of which are included
here. This media may be a twisted-pair, twinax, flat ribbon cable, or PCB traces. The nominal characteristic
impedance of the interconnect media should be between 100 Ω and 120 Ω with a variation of no more than 10%
(90 Ω to 132 Ω).
9.2.2.6 PCB Transmission Lines
As per the LVDS Owner's Manual Design Guide, 4th Edition (SNLA187), Figure 22 depicts several transmission
line structures commonly used in printed-circuit boards (PCBs). Each structure consists of a signal line and
return path with a uniform cross section along its length. A microstrip is a signal trace on the top (or bottom)
layer, separated by a dielectric layer from its return path in a ground or power plane. A stripline is a signal trace
in the inner layer, with a dielectric layer in between a ground plane above and below the signal trace. The
dimensions of the structure along with the dielectric material properties determine the characteristic impedance of
the transmission line (also called controlled-impedance transmission line).
When two signal lines are placed close by, they form a pair of coupled transmission lines. Figure 22 shows
examples of edge-coupled microstrip lines, and edge-coupled or broad-side-coupled striplines. When excited by
differential signals, the coupled transmission line is referred to as a differential pair. The characteristic impedance
of each line is called odd-mode impedance. The sum of the odd-mode impedances of each line is the differential
impedance of the differential pair. In addition to the trace dimensions and dielectric material properties, the
spacing between the two traces determines the mutual coupling and impacts the differential impedance. When
the two lines are immediately adjacent (like if S is less than 2 W, for example), the differential pair is called a
tightly-coupled differential pair. To maintain constant differential impedance along the length, it is important to
keep the trace width and spacing uniform along the length, as well as maintain good symmetry between the two
lines.
14
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Single-Ended Microstrip
Single-Ended Stripline
W
W
T
H
T
H
§ 5.98 H ·
ln ¨
¸
1.41 © 0.8 W T ¹
87
Z0
Hr
H
Z0
Edge-Coupled
60
Hr
§ 1.9 > 2 H T @ ·
ln ¨
¨ >0.8 W T @ ¸¸
©
¹
Edge-Coupled
S
S
H
H
Differential Microstrip
Zdiff
§
2 u Z0 u ¨ 1 0.48 u e
¨
©
Differential Stripline
0.96 u
s
H
·
¸
¸
¹
Zdiff
Co-Planar Coupled
Microstrips
W
G
2.9 u
s
H
·
¸
¸
¹
Broad-Side Coupled
Striplines
W
S
§
2 u Z0 u ¨ 1 0.347e
¨
©
W
G
S
H
H
Figure 22. Controlled-Impedance Transmission Lines
9.2.3 Termination Resistor
As shown earlier, an LVDS communication channel employs a current source driving a transmission line that is
terminated with a resistive load. This load serves to convert the transmitted current into a voltage at the receiver
input. To ensure incident wave switching (which is necessary to operate the channel at the highest signaling
rate), the termination resistance should be matched to the characteristic impedance of the transmission line. The
designer should ensure that the termination resistance is within 10% of the nominal media characteristic
impedance. If the transmission line is targeted for 100-Ω impedance, the termination resistance should be
between 90 Ω and 110 Ω. The line termination resistance should be placed as close to the receiver as possible
to minimize the stub length from the resistor to the receiver.
9.2.4 Application Curve
Figure 23. Power Supply Current vs Frequency
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10 Power Supply Recommendations
The DS90LV027AH driver is designed to operate from a single power supply with supply voltage in the range of
3.0 V to 3.6 V. In a typical application, a driver and a receiver may be on separate boards, or even separate
equipment. In these cases, separate supplies would be used at each location. The expected ground potential
difference between the driver power supply and the driver power supply would be less than |±1 V|. Board level
and local device level bypass capacitance should be used.
11 Layout
11.1 Layout Guidelines
11.1.1 Microstrip vs. Stripline Topologies
As per the LVDS Application and Data Handbook (SLLD009), printed-circuit boards usually offer designers two
transmission line options: Microstrip and stripline. Microstrips are traces on the outer layer of a PCB, as shown in
Figure 24.
Figure 24. Microstrip Topology
On the other hand, striplines are traces between two ground planes. Striplines are less prone to emissions and
susceptibility problems because the reference planes effectively shield the embedded traces. However, from the
standpoint of high-speed transmission, juxtaposing two planes creates additional capacitance. TI recommends
routing LVDS signals on microstrip transmission lines when possible. The PCB traces allow designers to specify
the necessary tolerances for ZO based on the overall noise budget and reflection allowances. Footnotes 1 (2), 2 (3),
and 3 (4) provide formulas for ZO and tPD for differential and single-ended traces. (2) (3) (4)
Figure 25. Stripline Topology
(2)
(3)
(4)
16
Howard Johnson & Martin Graham.1993. High Speed Digital Design – A Handbook of Black Magic. Prentice Hall PRT. ISBN number
013395724.
Mark I. Montrose. 1996. Printed Circuit Board Design Techniques for EMC Compliance. IEEE Press. ISBN number 0780311310.
Clyde F. Coombs, Jr. Ed, Printed Circuits Handbook, McGraw Hill, ISBN number 0070127549.
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Layout Guidelines (continued)
11.1.2 Dielectric Type and Board Construction
The speeds at which signals travel across the board dictates the choice of dielectric. FR-4, or an equivalent,
usually provides adequate performance for use with LVDS signals. If rise or fall times of LVCMOS/LVTTL signals
are less than 500 ps, empirical results indicate that a material with a dielectric constant near 3.4, such as
Rogers™ 4350 or Nelco N4000-13, may be desired. Once the designer chooses the dielectric, there are several
parameters pertaining to the board construction that can affect performance. The following set of guidelines were
developed experimentally through several designs involving LVDS devices:
• Copper weight: 15 g or 1/2 oz start, plated to 30 g or 1 oz
• All exposed circuitry should be solder-plated (60/40) to 7.62 μm or 0.0003 in (minimum).
• Copper plating should be 25.4 μm or 0.001 in (minimum) in plated-through-holes.
• Solder mask over bare copper with solder hot-air leveling
11.1.3 Recommended Stack Layout
Following the choice of dielectrics and design specifications, the designer must decide how many levels to use in
the stack. To reduce the LVCMOS/LVTTL to LVDS crosstalk, it is good practice to have at least two separate
signal planes as shown in Figure 26.
Layer 1: Routed Plane (LVDS Signals)
Layer 2: Ground Plane
Layer 3: Power Plane
Layer 4: Routed Plane (TTL/CMOS Signals)
Figure 26. Four-Layer PCB
NOTE
The separation between layers 2 and 3 should be 127 μm (0.005 in). By keeping the
power and ground planes tightly coupled, the increased capacitance acts as a bypass for
transients.
One of the most common stack configurations is the six-layer board, as shown in Figure 27.
Layer 1: Routed Plane (LVDS Signals)
Layer 2: Ground Plane
Layer 3: Power Plane
Layer 4: Ground Plane
Layer 5: Ground Plane
Layer 4: Routed Plane (TTL Signals)
Figure 27. Six-Layer PCB
In this particular configuration, it is possible to isolate each signal layer from the power plane by at least one
ground plane. The result is improved signal integrity, but fabrication is more expensive. Using the 6-layer board is
preferable, because it offers the layout designer more flexibility in varying the distance between signal layers and
referenced planes in addition to ensuring reference to a ground plane for signal layers 1 and 6.
11.1.4 Separation Between Traces
The separation between traces depends on several factors, but the amount of coupling that can be tolerated
usually dictates the actual separation. Low-noise coupling requires close coupling between the differential pair of
an LVDS link to benefit from the electromagnetic field cancellation. The traces should be 100-Ω differential and
thus coupled in the manner that best fits this requirement. In addition, differential pairs should have the same
electrical length to ensure that they are balanced, thus minimizing problems with skew and signal reflection.
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Layout Guidelines (continued)
In the case of two adjacent single-ended traces, one should use the 3-W rule, which stipulates that the distance
between two traces must be greater than two times the width of a single trace, or three times its width measured
from trace center to trace center. This increased separation effectively reduces the potential for crosstalk. The
same rule should be applied to the separation between adjacent LVDS differential pairs, whether the traces are
edge-coupled or broad-side-coupled.
W
Differential Traces
LVDS
Pair
S=
Minimum spacing as
defined by PCB vendor
W
t2W
Single-Ended Traces
TTL/CMOS
Trace
W
Figure 28. 3-W Rule for Single-Ended and Differential Traces (Top View)
Exercise caution when using autorouters, because they do not always account for all factors affecting crosstalk
and signal reflection. For instance, it is best to avoid sharp 90° turns to prevent discontinuities in the signal path.
Using successive 45° turns tends to minimize reflections.
11.1.5 Crosstalk and Ground Bounce Minimization
To reduce crosstalk, it is important to provide a return path to high-frequency currents that is as close to its
originating trace as possible. A ground plane usually achieves this. Because the returning currents always
choose the path of lowest inductance, they are most likely to return directly under the original trace, thus
minimizing crosstalk. Lowering the area of the current loop lowers the potential for crosstalk. Traces kept as short
as possible with an uninterrupted ground plane running beneath them emit the minimum amount of
electromagnetic field strength. Discontinuities in the ground plane increase the return path inductance and should
be avoided.
11.1.6 Decoupling
Each power or ground lead of a high-speed device should be connected to the PCB through a low inductance
path. For best results, one or more vias are used to connect a power or ground pin to the nearby plane. TI
recommends that the user place a via immediately adjacent to the pin to avoid adding trace inductance. Placing
a power plane closer to the top of the board reduces the effective via length and its associated inductance.
VCC
Via
GND
Via
4 mil
6 mil
TOP signal layer + GND fill
VDD 1 plane
Buried capacitor
GND plane
Signal layer
>
Board thickness
approximately 100 mil
2 mil
GND plane
Signal layers
VCC plane
4 mil
6 mil
Signal layer
GND plane
Buried capacitor
VDD 2 plane
BOTTOM signal layer + GND fill
>
Typical 12-Layer PCB
Figure 29. Low Inductance, High-Capacitance Power Connection
18
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Layout Guidelines (continued)
Bypass capacitors should be placed close to VDD pins. They can be placed conveniently near the
underneath the package to minimize the loop area. This extends the useful frequency range of
capacitance. Small-physical-size capacitors, such as 0402 or even 0201, or X7R surface-mount
should be used to minimize body inductance of capacitors. Each bypass capacitor is connected to the
ground plane through vias tangent to the pads of the capacitor as shown in Figure 30(a).
corners or
the added
capacitors
power and
An X7R surface-mount capacitor of size 0402 has about 0.5 nH of body inductance. At frequencies above 30
MHz or so, X7R capacitors behave as low-impedance inductors. To extend the operating frequency range to a
few hundred MHz, an array of different capacitor values like 100 pF, 1 nF, 0.03 μF, and 0.1 μF are commonly
used in parallel. The most effective bypass capacitor can be built using sandwiched layers of power and ground
at a separation of 2 to 3 mils. With a 2-mil FR4 dielectric, there is approximately 500 pF per square inch of PCB.
Refer back to Figure 22 for some examples. Many high-speed devices provide a low-inductance GND connection
on the backside of the package. This center dap must be connected to a ground plane through an array of vias.
The via array reduces the effective inductance to ground and enhances the thermal performance of the small
Surface Mount Technology (SMT) package. Placing vias around the perimeter of the dap connection ensures
proper heat spreading and the lowest possible die temperature. Placing high-performance devices on opposing
sides of the PCB using two GND planes (as shown in Figure 22) creates multiple paths for heat transfer. Often
thermal PCB issues are the result of one device adding heat to another, resulting in a very high local
temperature. Multiple paths for heat transfer minimize this possibility. In many cases the GND dap that is so
important for heat dissipation makes the optimal decoupling layout impossible to achieve due to insufficient padto-dap spacing as shown in Figure 30(b). When this occurs, placing the decoupling capacitor on the backside of
the board keeps the extra inductance to a minimum. It is important to place the VDD via as close to the device pin
as possible while still allowing for sufficient solder mask coverage. If the via is left open, solder may flow from the
pad and into the via barrel. This will result in a poor solder connection.
VDD
IN±
0402
IN+
0402
(a)
(b)
Figure 30. Typical Decoupling Capacitor Layouts
At least two or three times the width of an individual trace should separate single-ended traces and differential
pairs to minimize the potential for crosstalk. Single-ended traces that run in parallel for less than the wavelength
of the rise or fall times usually have negligible crosstalk. Increase the spacing between signal paths for long
parallel runs to reduce crosstalk. Boards with limited real estate can benefit from the staggered trace layout, as
shown in Figure 31.
Layer 1
Layer 6
Figure 31. Staggered Trace Layout
This configuration lays out alternating signal traces on different layers. Thus, the horizontal separation between
traces can be less than 2 or 3 times the width of individual traces. To ensure continuity in the ground signal path,
TI recommends having an adjacent ground via for every signal via, as shown in Figure 32. Note that vias create
additional capacitance. For example, a typical via has a lumped capacitance effect of 1/2 pF to 1 pF in FR4.
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Layout Guidelines (continued)
Signal Via
Signal Trace
Uninterrupted Ground Plane
Signal Trace
Uninterrupted Ground Plane
Ground Via
Figure 32. Ground Via Location (Side View)
Short and low-impedance connection of the device ground pins to the PCB ground plane reduces ground
bounce. Holes and cutouts in the ground planes can adversely affect current return paths if they create
discontinuities that increase returning current loop areas.
To minimize EMI problems, TI recommends avoiding discontinuities below a trace (for example, holes, slits, and
so on) and keeping traces as short as possible. Zoning the board wisely by placing all similar functions in the
same area, as opposed to mixing them together, helps reduce susceptibility issues.
11.2 Layout Example
Figure 33. Example DS90LV027AH Layout
20
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12 Device and Documentation Support
12.1 Related Documentation
For related documentation, see the following:
• LVDS Owner's Manual (SNLA187)
• AN-808 Long Transmission Lines and Data Signal Quality (SNLA028)
• AN-977 LVDS Signal Quality: Jitter Measurements Using Eye Patterns Test Report #1 (SNLA166)
• AN-971 An Overview of LVDS Technology (SNLA165)
• AN-916 A Practical Guide to Cable Selection (SNLA219)
• AN-805 Calculating Power Dissipation for Differential Line Drivers (SNOA233)
• AN-903 A Comparison of Differential Termination Techniques (SNLA034)
• AN-1194 Failsafe Biasing of LVDS Interfaces (SNLA051)
12.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.3 Community Resources
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.
12.4 Trademarks
E2E is a trademark of Texas Instruments.
Rogers is a trademark of Rogers Corporation.
All other trademarks are the property of their respective owners.
12.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
DS90LV027AHM/NOPB
ACTIVE
SOIC
D
8
95
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LV27A
HM
DS90LV027AHMX/NOPB
ACTIVE
SOIC
D
8
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LV27A
HM
(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
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