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SN65LVDS049
SLLS575A – AUGUST 2003 – REVISED JULY 2015
SN65LVDS049 Dual-LVDS Differential Drivers and Receivers
1 Features
3 Description
•
•
•
•
•
The SN65LVDS049 device is a dual flow-through
differential line driver-receiver pair that uses lowvoltage differential signaling (LVDS) to achieve
signaling rates as high as 400 Mbps. The driver and
receiver electrical interfaces are compliant to the
TIA/EIA-644-A standard.
1
•
•
•
•
•
•
•
•
•
DS90LV049 Compatible
Up to 400-Mbps Signaling Rates
Flow-Through Pinout
50-ps Driver Channel-to-Channel Skew (Typical)
50-ps Receiver Channel-to-Channel Skew
(Typical)
3.3-V Power Supply
High-Impedance Disable for All Outputs
Internal Fail-safe Biasing of Receiver Inputs
1.4-ns Driver Propagation Delay (Typical)
1.9-ns Receiver Propagation Delay (Typical)
High-Impedance Bus Pins on Power Down
ANSI TIA/EIA-644-A Compliant
Receiver Input and Driver Output ESD Exceeds
10 kV
16-Pin TSSOP Package
The intended application of this device and signaling
technique is for point-to-point baseband data
transmission over controlled impedance media of
approximately 100-Ω characteristic impedance. The
transmission media may be printed-circuit board
traces, backplanes, or cables. The ultimate rate and
distance of data transfer is dependent upon the
attenuation characteristics of the media, the noise
coupling to the environment, and other application
specific characteristics.
The SN65LVDS049 is characterized for operation
from –40°C to 85°C
Device Information(1)
2 Applications
•
•
PART NUMBER
SN65LVDS049
Full-Duplex LVDS Communications of Clock and
Data
Printers
PACKAGE
TSSOP (16)
BODY SIZE (NOM)
5.00 mm × 4.40 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Block Diagram
RIN1−
R1
ROUT1
R2
ROUT2
RIN1+
RIN2+
RIN2−
DOUT2−
D2
DIN2
D1
DIN1
DOUT2+
DOUT1+
DOUT1−
AND
EN
EN
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.
SN65LVDS049
SLLS575A – AUGUST 2003 – REVISED JULY 2015
www.ti.com
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
6.8
4
4
4
4
5
6
6
7
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Device Electrical Characteristics...............................
Switching Characteristics ..........................................
Dissipation Rating .....................................................
Typical Characteristics ..............................................
Parameter Measurement Information .................. 8
Detailed Description ............................................ 11
8.1 Overview ................................................................. 11
8.2 Functional Block Diagram ....................................... 11
8.3 Feature Description................................................. 11
8.4 Device Functional Modes........................................ 12
9
Application and Implementation ........................ 14
9.1 Application Information............................................ 14
9.2 Typical Applications ................................................ 14
10 Power Supply Recommendations ..................... 19
11 Layout................................................................... 20
11.1 Layout Guidelines ................................................. 20
11.2 Layout Example .................................................... 23
12 Device and Documentation Support ................. 25
12.1
12.2
12.3
12.4
12.5
12.6
Device Support......................................................
Documentation Support .......................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
25
25
25
25
25
25
13 Mechanical, Packaging, and Orderable
Information ........................................................... 25
4 Revision History
Changes from Original (August 2003) to Revision A
•
2
Page
Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1
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SLLS575A – AUGUST 2003 – REVISED JULY 2015
5 Pin Configuration and Functions
PW Package (Marked as LVDS049)
16-Pin TSSOP
(Top View)
RIN1 RIN1+
RIN2+
RIN2 DOUT2 DOUT2+
DOUT1+
DOUT1 -
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
EN
ROUT1
ROUT2
GND
VCC
DIN2
DIN1
EN
Pin Functions
PIN
NAME
NO.
GND
13
DIN1
10
DIN2
11
DOUT1+
7
DOUT2+
6
DOUT1–
8
DOUT2–
5
EN
EN
RIN1+
2
RIN2+
3
RIN1–
1
RIN2–
4
ROUT1
15
ROUT2
14
VCC
12
I/O
DESCRIPTION
–
Ground
I
LVTTL input signals
O
Differential (LVDS) noninverting output
O
Differential (LVDS) inverting output
16
I
Driver and receiver enable
9
I
Driver and receiver inverse-enable
I
Differential (LVDS) noninverting input
I
Differential (LVDS) inverting input
O
LVTTL output signals
–
Supply voltage
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
–0.3
4
V
DIN, ROUT, EN, or EN
–0.3
(VCC + 0.3 V)
RIN+ or RIN-
–0.3
4
DOUT+ or DOUT-
–0.3
3.9
Supply voltage (2), VCC
Voltage
LVDS output short circuit duration (DOUT+, DOUT-)
Continuous
Continuous power dissipation
See Dissipation Rating
Lead temperature 1.6 mm (1/16 inch) from case for 10 seconds
Storage temperature
(1)
(2)
V
–65
260
°C
150
°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.
All voltage values, except differential I/O bus voltages, are with respect to network ground terminal.
6.2 ESD Ratings
VALUE
Electrostatic
discharge
V(ESD)
(1)
(2)
Human body model (HBM), per ANSI/ESDA/JEDEC RIN+, RIN–, DOUT+, and DOUT–
JS-001 (1)
All pins
UNIT
±10000
±2000
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
V
±500
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
MIN
NOM
MAX
3
3.3
3.6
Supply voltage, VCC
Receiver input voltage
GND
2.4
Common-mode input voltage, VIC
Operating free-air temperature, TA
VID
2
UNIT
V
V
2.4
VID
V
2
VCC - 0.8
V
85
°C
–40
6.4 Thermal Information
SN65LVDS049
THERMAL METRIC (1)
PW (TSSOP)
UNIT
16 PINS
RθJA
Junction-to-ambient thermal resistance
10.5
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
35.8
°C/W
RθJB
Junction-to-board thermal resistance
45.4
°C/W
ψJT
Junction-to-top characterization parameter
2.6
°C/W
ψJB
Junction-to-board characterization parameter
44.8
°C/W
(1)
4
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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6.5 Device Electrical Characteristics
over recommended operating conditions (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP (1)
MAX
UNIT
2
VCC
V
GND
0.8
V
3
10
µA
10
µA
INPUT DC SPECIFICATIONS (DIN, EN, EN)
VIH
Input high voltage
VIL
Input low voltage
IIH
Input high current
VIN = VCC
IIL
Input low current
VIN = GND
–10
1
VCL
Input clamp voltage
ICL = -18 mA
–1.5
–0.8
250
350
450
V
–35
1
35
mV
1.125
1.2
1.375
–25
1
25
mV
-4.5
-9
mA
–10
V
LVDS OUTPUT DC SPECIFICATIONS (DOUT+, DOUT–)
|VOD|
Differential output voltage
Δ|VOD|
Change in magnitude of VOD for
complementary output states
RL = 100 Ω, See Figure 3
VOS
Offset voltage
V
ΔVOS
Change in magnitude of VOS for
complementary output states
IOS
Output short-circuit current
Enabled
DIN = VCC and DOUT+ = 0 V, or
DIN = GND and DOUT- = 0 V
IOSD
Differential output short-circuit current (2)
Enabled, VOD = 0 V
–3.6
-9
mA
IOFF
Power-off leakage
VCC = 0 V or Open;
VO = 0 or 3.6 V
–20
0
20
µA
IOZ
Output high-impedance current
EN = 0 V and EN = VCC,
VO = 0 or VCC
–10
0
10
µA
100
mV
LVDS INPUT DC SPECIFICATIONS (RIN+, RIN–)
VIT+
Differential input high threshold
VCM = 1.2 V, 0.05 V, 2.35 V
VIT-
Differential input low threshold
VCM = 1.2 V, 0.05 V, 2.35 V
–100
VCMR
Common-mode voltage range
VID = ± 100 mV
0.05
2.35
IIN
Input current
VCC = 3.6 V, VIN = 0 V or 2.8 V
–20
20
VCC= 0 V, VIN = 0 V, 2.8 V, or 3.6 V
–20
20
2.7
mV
V
µA
OUTPUTS DC SPECIFICATIONS (ROUT)
VOH
Output high voltage
IOH = –0.4 mA, VID = 200 mV
VOL
Output low voltage
IOL = 2 mA, VID = –200 mV
IOZ
Output high-impedance current
Disabled, VOUT = 0 V or VCC
–10
3.3
V
0.05
0.25
V
0
10
µA
17
35
mA
1
25
mA
DEVICE DC SPECIFICATIONS
ICC
Power supply current
(LVDS loaded, enabled)
EN = 3.3 V, DIN = VCC or Gnd, 100-Ω
differential LVDS loads
ICCZ
High-impedance supply current (disabled)
No loads, EN = 0 V
(1)
(2)
All typical values are at 25°C and with a 3.3-V supply.
Output short-circuit current (IOS) is specified as magnitude only; the minus sign indicates direction only
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6.6 Switching Characteristics
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP (1)
MAX
UNIT
LVDS OUTPUTS (DOUT+, DOUT-)
tPLHD
Differential propagation delay low to high
1.3
2
ns
tPHLD
Differential propagation delay high to low
1.4
2
ns
tsk(p)
Differential pulse skew (|tPHL - tPLH|)
0
0.15
0.4
ns
0
0.05
0.5
ns
1
ns
RL = 100 Ω,
CL = 15 pF distributed,
See Figure 4
(2)
tsk(o)
Differential channel-to-channel skew
tsk(pp)
Differential part-to-part skew (3)
tr
Differential rise time
0.2
0.5
1
ns
tf
Differential fall time
0.2
0.5
1
ns
tPHZ
Disable time, high level to high impedance
2.7
4
ns
tPLZ
Disable time, low level to high impedance
2.7
4
ns
tPZH
Enable time, high impedance to high level
1
5
8
ns
tPZL
Enable time, high impedance to low level
1
5
8
fMAX
Maximum operating frequency (4)
0
RL = 100 Ω,
CL = 15 pF distributed,
See Figure 5
250
ns
MHz
LVCMOS OUTPUTS (ROUT)
tPLH
Propagation delay low to high
0.5
1.9
3.5
ns
tPHL
Propagation delay high to low
0.5
1.7
3.5
ns
tsk(p)
Pulse skew (|tPHL - tPLH|)
0
0.2
0.4
ns
0
0.05
0.5
ns
1
ns
VID= 200 mV,
CL = 15 pF distributed,
See Figure 6
(5)
tsk(o)
Channel-to-channel skew
tsk(pp)
Part-to-part skew (6)
tr
Rise time
0.3
0.5
1.4
ns
tf
Fall time
0.3
0.5
1.4
ns
tPHZ
Disable time, high level to high impedance
3
7.2
9
ns
tPLZ
Disable time, low level to high impedance
2.5
4
8
ns
tPZH
Enable time, high impedance to high level
2.5
4.2
7
ns
tPZL
Enable time, high impedance to low level
2
3.3
7
fMAX
Maximum operating frequency (7)
200
250
(1)
(2)
(3)
(4)
(5)
(6)
(7)
0
CL = 15 pF distributed,
See Figure 7
ns
MHz
All typical values are at 25°C and with a 3.3 V supply.
tsk(o) is the magnitude of the time difference between the tPLH or tPHL of all drivers of a single device with all of their inputs connected
together.
tsk(pp) is the magnitude of the difference in propagation delay times between any specified terminals of two devices when both devices
operate with the same supply voltages, at the same temperature, and have identical packages and test circuits.
f(MAX) generator input conditions: tr = tf < 1 ns (0% to 100%), 50% duty cycle, 0 V to 3 V. Output Criteria: duty cycle = 45% to 55%, VOD
> 250 mV, all channels switching.
tsk(lim) is the maximum delay time difference between drivers over temperature, VCC, and process.
tsk(pp) is the magnitude of the difference in propagation delay times between any specified terminals of two devices when both devices
operate wf(MAX) generaith the same supply voltages, at the same temperature, and have identical packages and test circuits
f(MAX) generator input conditions: tr = tf < 1 ns (0% to 100%), 50% duty cycle, VID = 200 mV, VCM = 1.2 V. Output criteria: duty cycle =
45% to 55%, VOH > 2.7 V, VOL < 0.25 V, all channels switching.
6.7 Dissipation Rating
(1)
(2)
6
PACKAGE
CIRCUIT BOARD
MODEL
TA ≤25°C
POWER RATING
DERATING FACTOR (1)
ABOVE TA = 25°C
TA = 85°C
POWER RATING
PW
Low-K (2)
774 mW
6.2 mW/°C
402 mW
This is the inverse of the junction-to-ambient thermal resistance when board-mounted and with no air flow.
In accordance with the Low-K thermal metric definitions of EIA/JESD51-3.
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600
60
500
50
ICC - Supply Current - mA
|VOD | - Differential Output Voltage - mV
6.8 Typical Characteristics
400
300
200
100
40
All Switching
30
Single Receiver
20
Single Driver
10
0
40
60
VCC = 3.3 V
80
100
120
RL - Load Resistance - Ω
TA = 25°C
140
160
0
0.1
VCC = 3.3 V
VI = 3 V
Figure 1. VOD vs. Load Resistance
1
10
100
1000
f - Frequency - MHz
TA = 25°C
VID = 40 MVp-p
RL = 100 Ω
CL = 15-pF Distributed
Figure 2. Power Supply Current vs. Frequency
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7 Parameter Measurement Information
DOUT+
VCC
RL/2
DIN
VOD
GND
RL/2
VOS
Driver Enabled
DOUT-
Figure 3. Driver VOD and VOS Test Circuit
Oscilloscope
*
DOUT+
C1
50 Ω
*
Pulse
Generator
50 Ω
DIN
*
C2
DOUT* Matched 50-Ω Cables,
C = 15 pF Distributed
50 Ω
Blocking Capacitors
C1 = C2 = 50 nF
3V
DIN
1.5 V
1.5 V
0V
t PLHD
t PLLD
DOUT-
0 V*
*Differential
0 V*
VOL
DOUT+
VOD
VOH
0V
20 %
tr
80 %
80 %
VOD = DOUT+ - DOUTtf
t
0V
20 %
Figure 4. Driver Propagation Delay and Rise and Fall Time Test Circuit and Waveforms
8
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Parameter Measurement Information (continued)
2.4 V
1 kΩ
1 kΩ
DOUT+
VCC
Oscilloscope
*
DIN
100Ω 950Ω
50 Ω
GND
950Ω
DOUT-
EN or EN
Pulse
Generator
*
50 Ω
*
50 Ω
* Matched 50-Ω Cables,
C = 15 pF Distributed
3V
EN When EN = GND or Open
1.5 V
1.5 V
0V
3V
EN When EN = V CC
1.5 V
1.5 V
0V
t PHZ
t PZH
DOUT+ When D IN = VCC
VOH
50 %
50 %
DOUT- When D IN = GND
1.2 V
1.2 V
DOUT+ When D IN = GND
50 %
DOUT- When D IN = VCC
50 %
VOL
t PLZ
t PZL
Figure 5. Driver High-Impedance State Delay Test Circuit and Waveforms
Oscilloscope
*
RIN+
ROUT
*
Pulse
Generator
50 Ω
*
50 Ω
100 Ω
*
950 Ω
*
RIN-
50 Ω
* Matched 50-Ω Cables,
C = 15 pF Distributed
1.3 V
RIN0 V Differential
RIN+
VID = 200 mV
1.1 V
t PLH
ROUT
1.2 V
t PHL
1.5 V
20 %
tr
80 %
VOH
80 %
1.5 V
20 %
VOL
tf
Figure 6. Receiver Propagation Delay and Rise and Fall Test Circuit and Waveforms
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Parameter Measurement Information (continued)
VCC
RIN+
1.4 V
100 Ω
1V
950 Ω
RIN-
Pulse
Generator
Oscilloscope
1 kΩ
ROUT
*
50 Ω
EN or EN
*
50 Ω
* Matched 50-Ω Cables,
C = 15 pF Distributed
3V
EN When EN = GND or OPEN
1.5 V
1.5 V
0V
3V
EN When EN = V CC
1.5 V
1.5 V
0V
t PHZ
ROUT for R IN+ = 1.4 V
and R IN- = 1 V
ROUT for R IN+ = 1 V
and R IN- = 1.4 V
t PHZ
VOH
50 %
0.5 V
VCC/2
VCC/2
0.5 V
50 %
VOL
t PLZ
t PZL
Figure 7. Receiver High-Impedance State Delay Test Circuit and Waveforms
(VCC = 3.3 V)
10
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8 Detailed Description
8.1 Overview
The SN65LVDS049 device is a dual flow-through differential line driver-receiver pair that uses low-voltage
differential signaling (LVDS) to achieve signaling rates of up to 400 Mbps. The device operates from a single
supply that is nominally 3.3 V, but can be as low as 3.0 V and as high as 3.6 V. The TIA/EIA-644-A standard
compliant electrical interface provides a minimum differential output voltage magnitude of 250 mV into a 100-Ω
load and receipt of signals with up to 1 V of ground potential difference between a transmitter and receiver. The
LVDS receivers have internal fail-safe biasing that places the outputs into a known high state for unconnected
differential inputs.
8.2 Functional Block Diagram
RIN1−
R1
ROUT1
R2
ROUT2
RIN1+
RIN2+
RIN2−
DOUT2−
D2
DIN2
D1
DIN1
DOUT2+
DOUT1+
DOUT1−
AND
EN
EN
8.3 Feature Description
8.3.1 Driver Offset
An LVDS-compliant driver is required to maintain the common-mode output voltage at 1.2 V. The SN65LVDS049
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 V
to 3.6 V supply range.
8.3.2 Receiver Open Circuit Fail-Safe
One of the most common problems with differential signaling applications is how the system responds when no
differential voltage is present on the signal pair. The LVDS receiver is like most differential line receivers in that
its output logic state can be indeterminate when the differential input voltage is in the range from –100 mV to 100
mV and within its recommended input common-mode voltage range. However, the TI LVDS receiver is different
in how it handles the open-input circuit situation.
Open circuit means that there is little or no input current to the receiver from the data line itself. This could be
when the driver is in a high-impedance state or the cable is disconnected. When this occurs, the LVDS receiver
pulls each line of the signal to VCC through 300-kΩ resistors as shown in Figure 8. The fail-safe feature uses an
AND gate to detect this condition and force the output to a high level.
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Feature Description (continued)
VCC
300 kW
300 kW
A
Rt = 100 W(Typ)
Y
B
Vp≈2.3 V
Figure 8. Open-Circuit Fail-Safe of the LVDS Receiver
Only under these conditions is the output of the receiver valid with less than a 100-mV differential input voltage
magnitude. The presence of the termination resistor, Rt, does not affect the fail-safe function as long as it is
connected as shown in Figure 8. Other termination circuits may allow a DC to ground that could defeat the pullup
currents from the receiver and the fail-safe feature.
8.3.3 Receiver Common-Mode Range
For all supply voltages, the valid input signal is from ground to 0.9 V below the supply rail. Hence, if the device is
operating with a 3.3-V supply, and a minimum differential voltage of 100 mV, common-mode values in the range
of 0.05 V to 2.35 V are supported.
8.4 Device Functional Modes
Table 1. Driver Truth Table
INPUT
DIN
EN
L
EN
H
H
X
(1)
OUTPUTS (1)
ENABLES
L or OPEN
All other conditions
DOUT+
DOUT–
L
H
H
L
Z
Z
H = high level, L = low level, X = irrelevant, Z = high impedance (off)
Table 2. Receiver Truth Table
DIFFERENTIAL INPUT
RIN- - RIN+
OUTPUT (1)
ENABLES
EN
EN
ROUT
H
L or OPEN
VID ≥ 100 mV
VID ≤ - 100 mV
H
Open/short or terminated
X
(1)
12
L
H
All other conditions
Z
H = high level, L = low level, X = irrelevant, Z = high impedance (off)
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Table 3. Enable Function Table
ENABLES
OUTPUTS
EN
EN
LVDS Out
LVCMOS Out
L or Open
L or Open
Disabled
Disabled
H
L or Open
Enabled
Enabled
L or Open
H
Disabled
Disabled
H
H
Disabled
Disabled
VCC
300 kΩ
VCC
300 kΩ
50 Ω
EN,EN,DIN
RIN
RIN
7V
7V
7V
300 kΩ
Figure 9. Equivalent Input and Output Schematic Diagrams
VCC
VCC
50 Ω
ROUT
50 Ω
10 kΩ
DOut
7V
7V
Figure 10. Equivalent Input and Output Schematic Diagrams
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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 SN65LVDS049 is a dual LVDS driver-receiver pair. The functionality of these devices is simple, yet
extremely flexible, leading to their use in designs ranging from wireless base stations to desktop computers. The
varied class of potential applications share features and applications discussed in the paragraphs below.
9.2 Typical Applications
9.2.1 Point-to-Point Communications
The most basic application for LVDS buffers, as found in this data sheet, is for point-to-point communications of
digital data, as shown in Figure 11.
IN+
OUT+
Driver
Receiver
100
IN-
OUT-
Figure 11. Point-to-Point Topology
A point-to-point communications channel has a single transmitter (driver) and a single receiver. This
communications topology is often referred to as simplex. In Figure 11 the driver receives a single-ended input
signal and the receiver outputs a single-ended recovered signal. The LVDS driver converts the single-ended
input to a differential signal for transmission over a balanced interconnecting media of 100-Ω characteristic
impedance. The conversion from a single-ended signal to an LVDS signal retains the digital data payload while
translating to a signal whose features are more appropriate for communication over extended distances or in a
noisy environment.
9.2.1.1 Design Requirements
For this design example, use the parameters listed in Table 4.
Table 4. Design Parameters
DESIGN PARAMETERS
14
EXAMPLE VALUE
Driver supply voltage (VCCD)
3 to 3.6 V
Driver input voltage
0.8 to VCCD V
Driver signaling rate
DC to 400 Mbps
Interconnect characteristic impedance
100 Ω
Termination resistance
100 Ω
Receiver supply voltage (VCCR)
3 to 3.6 V
Number of receiver nodes
1
Receiver input voltage
0 to VCCR – 0.8 V
Ground shift between driver and receiver
±1 V
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9.2.1.2 Detailed Design Procedure
9.2.1.2.1 Bypass Capacitance
Bypass capacitors play a key role in power distribution circuitry. At low frequencies, power supply offers very lowimpedance paths between the 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 into the kHz range. Due to their size and length of their leads, large capacitors tend to have large
inductance values at the switching frequencies. To solve this problem, smaller capacitors should be (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 of approximately 5 nH.
The value of the bypass capacitors used locally with LVDS chips can be determined by the following formula
according to Johnson, equations 8.18 to 8.21. A conservative rise time of 4 ns and a worst-case change in
supply current of 100 mA covers the whole range of LVDS devices offered by TI. In this example, the maximum
power supply noise tolerated is 100 mV; however, this figure varies depending on the noise budget available in
your design. (1)
æ DIMaximum Step Change Supply Current ö
Cchip = ç
÷ ´ TRise Time
è DVMaximum Power Supply Noise ø
(1)
æ 100 mA ö
CLVDS = ç
÷ ´ 4 ns = 0.004 mF
è 0.1 V ø
(2)
The following example, Figure 12, lowers lead inductance and covers intermediate frequencies between the
board-level capacitor (>10 µF) and the value of capacitance found in Equation 2 (0.004 µF). You should place
the smallest value of capacitance as close as possible to the chip.
3.3 V
0.1 µF
0.004 µF
Figure 12. Recommended LVDS Bypass Capacitor Layout
9.2.1.2.2 Driver Supply Voltage
The device can support operation with a supply as low as 3 V and as high as 3.6 V. As shown in Device
Electrical Characteristics, the differential output voltage is nominally 350 mV over the complete output range. The
minimum output voltage stays within the specified LVDS limits (247 mV to 454 mV) for a 3.3-V supply.
9.2.1.2.3 Driver Input Voltage
The driver will operate with a decision threshold of approximately 1.4 V for LVTTL input signals.
9.2.1.2.4 Driver Output Voltage
The SN65LVDS049 driver output is a 1.2-V common-mode voltage, with a nominal differential output signal of
350 mV. This 350 mV is the absolute value of the differential swing (VOD = |V+ – V–|). The peak-to-peak
differential voltage is twice this value, or 700 mV.
9.2.1.2.5 Interconnecting Media
The physical communication channel between the driver and the receiver may be any balanced paired metal
conductors meeting the requirements of the LVDS standard. This media may be a twisted-pair, twinax, flat ribbon
cable, or PCB traces.
(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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The nominal characteristic impedance of the interconnect should be from 100 Ω to 120 Ω with variation no more
than 10% (90 Ω to 132 Ω).
9.2.1.2.6 PCB Transmission Lines
As per SNLA187, Figure 13 depicts several transmission line structures commonly used in PCBs. Each structure
consists of a signal line and a return path with 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 near one another, they form a pair of coupled transmission lines. Figure 13
shows examples of edge-coupled microstrips, 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; for example, if S is less than 2×W, 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.
Single-Ended Microstrip
Single-Ended Stripline
W
W
T
H
T
H
§ 5.98 H ·
87
ln ¨
¸
Hr 1.41 © 0.8 W T ¹
Z0
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
¨
©
Differential Stripline
s
0.96 u
H
e
·
¸
¸
¹
Zdiff
Co-Planar Coupled
Microstrips
W
G
s
§
2.9 u ·
H¸
2 u Z0 u ¨ 1 0.347e
¨
¸
©
¹
Broad-Side Coupled
Striplines
W
S
W
G
S
H
H
Figure 13. Controlled-Impedance Transmission Lines
16
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9.2.1.2.7 Termination Resistor
As shown earlier in Figure 11, an LVDS communication channel employs a current source driving a transmission
line which is terminated with a resistive load. This load serves to convert the transmitted current into a voltage at
the receiver input. To ensure good signal integrity, 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 from 90 Ω to 110 Ω.
The line termination resistance should be located as close as possible to the receiver, thereby minimizing the
stub length from the resistor to the receiver.
When a multidrop topology is used, line termination resistors are typically placed at the end (or ends) of the
transmission line.
9.2.1.2.8 Receiver Supply Voltage
The receiver can support operation with a supply as low as 3 V and as high as 3.6 V.
9.2.1.2.9 Receiver Input Common-Mode Range
Receiver supports common-mode values in the range of 0.05 V to 2.35 V. This is assuming 100 mV differential
signal and a 3.3 V supply.
The driver has an output common-mode range of 1.2 V. Using the receiver discussed here, we see that valid
operation of the communication link will occur when the ground difference between transmitter and receiver is
within approximately ±1 V. The use of differential signaling in LVDS allows operation in an environment where
the combination of ground difference and common-mode noise result in a common-mode difference between
transmitter and receiver of 1 V. This 1-V potential difference hints at the intended application of LVDS circuits.
Standards such as RS-485 support potential differences of almost 10 V, allowing for communication over
distances of greater than 1 km. The intended application of LVDS devices is more moderate distances, such as
those from chip to chip on a board, board to board in a rack, or from rack to nearby rack. When the 1 V potential
difference is not adequate, yet the high-speed and low-voltage features of LVDS are still needed, the designer
can choose from either M-LVDS devices available from TI, or from LVDS devices with extended common-mode
ranges, such as the SN65LVDS33.
9.2.1.2.10 Receiver Input Signal
The LVDS receivers herein comply with the LVDS standard and correctly determine the bus state when the
differential input voltage is greater than 100 mV (HI output) or less than –100 mV (LO output).
9.2.1.2.11 Receiver Output Signal
Receiver outputs comply with LVTTL output voltage standards when the supply voltage is within the range of 3 V
to 3.6 V.
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9.2.1.3 Application Curve
Figure 14. Typical Driver Output Eye Pattern in Point-to-Point System
9.2.2 Multidrop Communications
Minimize
Stub
Lengths
Minimize
Stub
Lengths
+
±
Receiver
+
Receiver
±
Driver
|100
A second common application of LVDS buffers is a multidrop topology. In a multidrop configuration, a single
driver and a shared bus are present, along with two or more receivers (with a maximum permissible number of
32 receivers). Figure 15 below shows an example of a multidrop system.
+
Receiver
±
Figure 15. Multidrop Topology
18
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9.2.2.1 Design Requirements
For this design example, use the parameters listed in Table 5.
Table 5. Design Parameters
DESIGN PARAMETERS
EXAMPLE VALUE
Driver Supply Voltage (VCCD)
3 to 3.6 V
Driver Input Voltage
0.8 to VCCD V
Driver Signaling Rate
DC to 400 Mbps
Interconnect Characteristic Impedance
100 Ω
Termination Resistance
100 Ω
Number of Receiver Nodes
2 to 32
Receiver Supply Voltage (VCCR)
3 to 3.6 V
Receiver Input Voltage
0 to VCCR – 0.8 V
Receiver Signaling Rate
DC to 400 Mbps
Ground shift between driver and receiver
±1 V
9.2.2.2 Detailed Design Procedure
9.2.2.2.1 Interconnecting Media
The interconnect in a multidrop system differs considerably from a point-to-point system. While point-to-point
interconnects are straightforward, and well understood, the bus type architecture encountered with multidrop
systems requires more careful attention. We will use Figure 15 to explore these details.
The most basic multidrop system would include a single driver, located at a bus origin, with multiple receiver
nodes branching off the main line, and a final receiver at the end of the transmission line, co-located with a bus
termination resistor. While this would be the most basic multidrop system, it has several considerations not yet
explored.
The location of the transmitter at one bus end allows the design concerns to be simplified, but this comes at the
cost of flexibility. With a transmitter located at the origin, a single bus termination at the far-end is required. The
far-end termination absorbs the incident traveling wave. The flexibility lost with this arrangement is thus: if the
single transmitter needed to be relocated on the bus, at any location other than the origin, we would be faced
with a bus with one open-circuited end, and one properly terminated end. Locating the transmitter say in the
middle of the bus may be desired to reduce (by ½) the maximum flight time from the transmitter to receiver.
Another new feature in Figure 15 is clear in that every node branching off the main line results in stubs. The
stubs should be minimized in any case, but have the unintended effect of locally changing the loaded impedance
of the bus.
To a good approximation, the characteristic transmission line impedance of an unloaded multipoint or multidrop
bus is defined by √L/C, where L is the inductance per unit length and C is the capacitance per unit length. As
capacitance is added to the bus in the form of devices and interconnections, the bus characteristic impedance is
lowered. This may result in signal reflections from the impedance mismatch between the unloaded and loaded
segments of the bus.
If the number of loads is constant and can be distributed evenly along the line, reflections can be reduced by
changing the bus termination resistors to match the loaded characteristic impedance. Normally, the number of
loads are not constant or distributed evenly and the reflections resulting from any mismatching must be
accounted for in the noise budget.
10 Power Supply Recommendations
The SN65LVDS049 is designed to operate from a single power supply in the range of 3 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 receiver power supply would be less than ±1 V. Board level and local device level bypass
capacitance should be used and are covered in Bypass Capacitance.
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11 Layout
11.1 Layout Guidelines
11.1.1 Microstrip vs. Stripline Topologies
As per SLLD009, PCBs usually offer designers two transmission line options: Microstrip and stripline. Microstrips
are traces on the outer layer of a PCB, as shown in Figure 16.
Figure 16. 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 if 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, and 3
provide formulas for ZO and tPD for differential and single-ended traces. (1) (2) (3)
Figure 17. Stripline Topology
(1)
(2)
(3)
20
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 equivalent, usually
provides adequate performance for use with LVDS signals. If rise or fall times of TTL/CMOS 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 is better suited. 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, you must decide how many levels to use in the
stack. To reduce the TTL/CMOS to LVDS crosstalk, it is a good practice to have at least two separate signal
planes as shown in Figure 18.
Layer 1: Routed Plane (LVDS Signals)
Layer 2: Ground Plane
Layer 3: Power Plane
Layer 4: Routed Plane (TTL/CMOS Signals)
Figure 18. Four-Layer PCB Board
NOTE
The separation between layers 2 and 3 should be 127 μm (0.005 inch). 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 6-layer board, as shown in Figure 19.
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 19. Six-Layer PCB Board
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; however, 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; however, 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
LVDS
Pair
Differential Traces
S=
Minimum spacing as
defined by PCB vendor
W
t2 W
Single-Ended Traces
TTL/CMOS
Trace
W
Figure 20. 3-W Rule for Single-Ended and Differential Traces (Top View)
You should 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 as possible
to its originating trace. 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. Ideally,
via placement is 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 21. Low Inductance, High-Capacitance Power Connection
22
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Layout Guidelines (continued)
Bypass capacitors should be placed close to VDD pins. They can be placed conveniently near the corners or
underneath the package to minimize the loop area. This extends the useful frequency range of the added
capacitance. Small-physical-size capacitors, such as 0402, 0201 or X7R surface-mount capacitors should be
used to minimize body inductance of capacitors. Each bypass capacitor is connected to the power and ground
plane through vias tangent to the pads of the capacitor as shown in Figure 22(a).
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.
Many high-speed devices provide a low-inductance GND connection on the backside of the package. This center
pad 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 pad 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 13) 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 pad that is so important for heat dissipation makes the optimal
decoupling layout impossible to achieve due to insufficient pad-to-pad spacing as shown in Figure 22(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 22. Typical Decoupling Capacitor Layouts
11.2 Layout Example
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 23.
Layer 1
Layer 6
Figure 23. 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 24. 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 Example (continued)
Signal Via
Signal Trace
Uninterrupted Ground Plane
Signal Trace
Uninterrupted Ground Plane
Ground Via
Figure 24. 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.
24
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12 Device and Documentation Support
12.1 Device Support
12.1.1 Development Support
For the IBIS model, see the SN65LVDS049 product folder, www.ti.com/product/SN65LVDS049.
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation see the following:
• Control-Impedance Transmission Lines (SNLA187)
• Microstrip vs Stripline Topologies (SLLD009)
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
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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
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Copyright © 2003–2015, Texas Instruments Incorporated
Product Folder Links: SN65LVDS049
25
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
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)
Samples
(4/5)
(6)
SN65LVDS049PW
ACTIVE
TSSOP
PW
16
90
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
LVDS049
Samples
SN65LVDS049PWR
ACTIVE
TSSOP
PW
16
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
LVDS049
Samples
SN65LVDS049PWRG4
ACTIVE
TSSOP
PW
16
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
LVDS049
Samples
(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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