DS90CR215/DS90CR216
+3.3V Rising Edge Data Strobe LVDS 21-Bit Channel
Link - 66 MHz
General Description
The DS90CR215 transmitter converts 21 bits of CMOS/TTL
data into three LVDS (Low Voltage Differential Signaling)
data streams.Aphase-locked transmit clockis transmitted in
parallel with thedata streams over a fourth LVDS link.Every
cycle of the transmit clock 21 bits of input data are sampled
and transmitted. The DS90CR216 receiver converts the
LVDS data streams back into 21 bits of CMOS/TTL data. At
a transmitclock frequencyof 66 MHz,21 bitsof TTLdata are
transmitted at a rate of 462 Mbps per LVDS data channel.
Using a 66 MHz clock, the data throughput is 1.386 Gbit/s
(173 Mbytes/s).
The multiplexing of the data lines provides a substantial
cable reduction. Long distance parallel single-ended buses
typically require a ground wire per active signal (and have
very limitednoise rejectioncapability). Thus,for a21-bit wide
data and one clock, up to 44 conductors are required. With
the Channel Link chipset as few as 9 conductors (3 data
pairs, 1 clock pair and a minimum of one ground) are
needed. This provides a 80%reduction in required cable
width, which provides a system cost savings, reduces connector physicalsize and cost,and reduces shieldingrequirements due to the cables’ smaller form factor.
The 21 CMOS/TTL inputs can support a variety of signal
combinations. For example, five 4-bit nibbles plus 1 control,
or two 9-bit (byte + parity) and 3 control.
Features
n Single +3.3V supply
n Chipset (Tx + Rx) power consumption
<
250 mW (typ)
n Power-down mode (
<
0.5 mW total)
n Up to 173 Megabytes/sec bandwidth
n Up to 1.386 Gbps data throughput
n Narrow bus reduces cable size
n 290 mV swing LVDS devices for low EMI
n +1V common mode range (around +1.2V)
n PLL requires no external components
n Low profile 48-lead TSSOP package
n Rising edge data strobe
n Compatible with TIA/EIA-644 LVDS standard
n ESD Rating
>
7kV
n Operating Temperature: −40˚C to +85˚C
Block Diagrams
TRI-STATE®is a registered trademark of National Semiconductor Corporation.
DS90CR215
DS012909-1
Order Number DS90CR215MTD
See NS Package Number MTD48
DS90CR216
DS012909-27
Order Number DS90CR216MTD
See NS Package Number MTD48
March 1999
DS90CR215/DS90CR216 +3.3V Rising Edge Data Strobe LVDS 21-Bit Channel Link-66 MHz
© 1999 National Semiconductor Corporation DS012909 www.national.com
Pin Diagrams
Typical Application
DS012909-21
DS90CR215
DS012909-22
DS90CR216
DS012909-23
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contactthe National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V
CC
) −0.3V to +4V
CMOS/TTL Input Voltage −0.3V to (V
CC
+ 0.3V)
CMOS/TTL Output Voltage −0.3V to (V
CC
+ 0.3V)
LVDS Receiver Input Voltage −0.3V to (V
CC
+ 0.3V)
LVDS Driver Output Voltage −0.3V to (V
CC
+ 0.3V)
LVDS Output Short
Circuit Duration Continuous
Junction Temperature +150˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temperature
(Soldering, 4 sec.) +260˚C
Maximum Package Power Dissipation
@
+25˚C
MTD48 (TSSOP) Package:
DS90CR215 1.98 W
DS90CR216 1.89 W
Package Derating
DS90CR215 16 mW/˚C above +25˚C
DS90CR216 15 mW/˚C above +25˚C
ESD Rating
(HBM, 1.5 kΩ, 100 pF)
>
7kV
Recommended Operating
Conditions
Min Nom Max Units
Supply Voltage (V
CC
) 3.0 3.3 3.6 V
Operating Free Air
Temperature (T
A
) −40 +25 +85 ˚C
Receiver Input Range 0 2.4 V
Supply Noise Voltage (V
CC
) 100 mV
PP
Electrical Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified
Symbol Parameter Conditions Min Typ Max Units
CMOS/TTL DC SPECIFICATIONS
V
IH
High Level Input Voltage 2.0 V
CC
V
V
IL
Low Level Input Voltage GND 0.8 V
V
OH
High Level Output Voltage IOH= −0.4 mA 2.7 3.3 V
V
OL
Low Level Output Voltage IOL= 2 mA 0.06 0.3 V
V
CL
Input Clamp Voltage ICL= −18 mA −0.79 −1.5 V
I
IN
Input Current VIN=VCC, GND,
±
5.1
±
10 µA
2.5V or 0.4V
I
OS
Output Short Circuit Current V
OUT
= 0V -60 −120 mA
LVDS DRIVER DC SPECIFICATIONS
V
OD
Differential Output Voltage RL= 100Ω 250 290 450 mV
∆V
OD
Change in VODbetween
Complimentary Output States
35 mV
V
OS
Offset Voltage (Note 4) 1.125 1.25 1.375 V
∆V
OS
Change in VOSbetween
Complimentary Output States
35 mV
I
OS
Output Short Circuit Current V
OUT
= 0V, −3.5 −5 mA
R
L
= 100Ω
I
OZ
Output TRI-STATE®Current PWR DWN = 0V,
±
1
±
10 µA
V
OUT
=0VorV
CC
LVDS RECEIVER DC SPECIFICATIONS
V
TH
Differential Input High Threshold VCM= +1.2V +100 mV
V
TL
Differential Input Low Threshold −100 mV
I
IN
Input Current VIN= +2.4V, VCC= 3.6V
±
10 µA
V
IN
= 0V, VCC= 3.6V
±
10 µA
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Electrical Characteristics (Continued)
Over recommended operating supply and temperature ranges unless otherwise specified
Symbol Parameter Conditions Min Typ Max Units
TRANSMITTER SUPPLY CURRENT
I
CCTW
Transmitter Supply Current
Worst Case (with Loads)
RL= 100Ω,
C
L
= 5 pF,
Worst Case
Pattern
(
Figures 1, 2
),
T
A
= −10˚C to
+70˚C
f = 32.5 MHz 31 45 mA
f = 37.5 MHz 32 50 mA
f = 66 MHz 37 55 mA
R
L
= 100Ω,
C
L
= 5 pF,
Worst Case
Pattern
(
Figures 1, 2
),
T
A
= −40˚C to
+85˚C
f = 40 MHz 38 51 mA
f = 66 MHz 42 55 mA
I
CCTZ
Transmitter Supply Current
Power Down
PWR DWN = Low
Driver Outputs in TRI-STATE
under Powerdown Mode
10 55 µA
RECEIVER SUPPLY CURRENT
I
CCRW
Receiver Supply Current Worst
Case
CL= 8 pF,
Worst Case
Pattern
(
Figures 1, 3
),
T
A
= −10˚C to
+70˚C
f = 32.5 MHz 49 65 mA
f = 37.5 MHz 53 70 mA
f = 66 MHz 78 105 mA
C
L
= 8 pF,
Worst Case
Pattern
(
Figures 1, 3
),
T
A
= −40˚C to
+85˚C
f = 40 MHz 55 82 mA
f = 66 MHz 78 105 mA
I
CCRZ
Receiver Supply Current Power
Down
PWR DWN = Low
Receiver Outputs Stay Low during
Powerdown Mode
10 55 µA
Note 1: “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the device
should be operated at these limits. The tables of “Electrical Characteristics” specify conditions for device operation.
Note 2: Typical values are given for V
CC
= 3.3V and TA= +25˚C.
Note 3: Current into device pins is defined as positive. Current out of device pins is defined as negative. Voltages arereferenced toground unlessotherwise specified (except V
OD
and ∆VOD).
Note 4: V
OS
previously referred as VCM.
Transmitter Switching Characteristics
Over recommended operating supply and −40˚C to +85˚C ranges unless otherwise specified
Symbol Parameter Min Typ Max Units
LLHT LVDS Low-to-High Transition Time (
Figure 2
) 0.5 1.5 ns
LHLT LVDS High-to-Low Transition Time (
Figure 2
) 0.5 1.5 ns
TCIT TxCLK IN Transition Time (
Figure 4
)5ns
TCCS TxOUT Channel-to-Channel Skew (
Figure 5
) 250 ps
TPPos0 Transmitter Output Pulse Position for
Bit0 (Note 7) (
Figure 16
)
f = 40 MHz −0.4 0 0.4 ns
TPPos1 Transmitter Output Pulse Position for
Bit1
3.1 3.3 4.0 ns
TPPos2 Transmitter Output Pulse Position for
Bit2
6.5 6.8 7.6 ns
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Transmitter Switching Characteristics (Continued)
Over recommended operating supply and −40˚C to +85˚C ranges unless otherwise specified
Symbol Parameter Min Typ Max Units
TPPos3 Transmitter Output Pulse Position for
Bit3
10.2 10.4 11.0 ns
TPPos4 Transmitter Output Pulse Position for
Bit4
13.7 13.9 14.6 ns
TPPos5 Transmitter Output Pulse Position for
Bit5
17.3 17.6 18.2 ns
TPPos6 Transmitter Output Pulse Position for
Bit6
21.0 21.2 21.8 ns
TPPos0 Transmitter Output Pulse Position for
Bit0 (Note 6) (
Figure 16
)
f = 66 MHz −0.4 0 0.3 ns
TPPos1 Transmitter Output Pulse Position for
Bit1
1.8 2.2 2.5 ns
TPPos2 Transmitter Output Pulse Position for
Bit2
4.0 4.4 4.7 ns
TPPos3 Transmitter Output Pulse Position for
Bit3
6.2 6.6 6.9 ns
TPPos4 Transmitter Output Pulse Position for
Bit4
8.4 8.8 9.1 ns
TPPos5 Transmitter Output Pulse Position for
Bit5
10.6 11.0 11.3 ns
TPPos6 Transmitter Output Pulse Position for
Bit6
12.8 13.2 13.5 ns
TCIP TxCLK IN Period (
Figure 6
) 15 T 50 ns
TCIH TxCLK IN High Time (
Figure 6
) 0.35T 0.5T 0.65T ns
TCIL TxCLK IN Low Time (
Figure 6
) 0.35T 0.5T 0.65T ns
TSTC TxIN Setup to TxCLK IN (
Figure 6
) 2.5 ns
THTC TxIN Hold to TxCLK IN (
Figure 6
)0 ns
TCCD TxCLK IN to TxCLK OUT Delay
@
25˚C,VCC=3.3V
(
Figure 8
)
3 3.7 5.5 ns
TPLLS Transmitter Phase Lock Loop Set (
Figure 10
)10ms
TPDD Transmitter Powerdown Delay (
Figure 14
) 100 ns
Receiver Switching Characteristics
Over recommended operating supply and −40˚C to +85˚C ranges unless otherwise specified
Symbol Parameter Min Typ Max Units
CLHT CMOS/TTL Low-to-High Transition Time (
Figure 3
) 2.2 5.0 ns
CHLT CMOS/TTL High-to-Low Transition Time (
Figure 3
) 2.2 5.0 ns
RSPos0 Receiver Input Strobe Position for Bit 0 (Note 7)(
Figure 17
) f = 40 MHz 1.0 1.4 2.15 ns
RSPos1 Receiver Input Strobe Position for Bit 1 4.5 5.0 5.8 ns
RSPos2 Receiver Input Strobe Position for Bit 2 8.1 8.5 9.15 ns
RSPos3 Receiver Input Strobe Position for Bit 3 11.6 11.9 12.6 ns
RSPos4 Receiver Input Strobe Position for Bit 4 15.1 15.6 16.3 ns
RSPos5 Receiver Input Strobe Position for Bit 5 18.8 19.2 19.9 ns
RSPos6 Receiver Input Strobe Position for Bit 6 22.5 22.9 23.6 ns
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Receiver Switching Characteristics (Continued)
Over recommended operating supply and −40˚C to +85˚C ranges unless otherwise specified
Symbol Parameter Min Typ Max Units
RSPos0 Receiver Input Strobe Position for Bit 0 (Note 6)(
Figure 17
) f = 66 MHz 0.7 1.1 1.4 ns
RSPos1 Receiver Input Strobe Position for Bit 1 2.9 3.3 3.6 ns
RSPos2 Receiver Input Strobe Position for Bit 2 5.1 5.5 5.8 ns
RSPos3 Receiver Input Strobe Position for Bit 3 7.3 7.7 8.0 ns
RSPos4 Receiver Input Strobe Position for Bit 4 9.5 9.9 10.2 ns
RSPos5 Receiver Input Strobe Position for Bit 5 11.7 12.1 12.4 ns
RSPos6 Receiver Input Strobe Position for Bit 6 13.9 14.3 14.6 ns
RSKM RxIN Skew Margin (Note 5) (
Figure 18
) f = 40 MHz 490 ps
f = 66 MHz 400 ps
RCOP RxCLK OUT Period (
Figure 7
) 15 T 50 ns
RCOH RxCLK OUT High Time (
Figure 7
) f = 40 MHz 6.0 10.0 ns
f = 66 MHz 4.0 6.1 ns
RCOL RxCLK OUT Low Time (
Figure 7
) f = 40 MHz 10.0 13.0 ns
f = 66 MHz 6.0 7.8 ns
RSRC RxOUT Setup to RxCLK OUT (
Figure 7
) f = 40 MHz 6.5 14.0 ns
f = 66 MHz 2.5 8.0 ns
RHRC RxOUT Hold to RxCLK OUT (
Figure 7
) f = 40 MHz 6.0 8.0 ns
f = 66 MHz 2.5 4.0 ns
RCCD RxCLK IN to RxCLK OUT Delay (
Figure 9
) f = 40 MHz 4.0 6.7 8.0 ns
f = 66 MHz 5.0 6.6 9.0 ns
RPLLS Receiver Phase Lock Loop Set (
Figure 11
)10ms
RPDD Receiver Powerdown Delay (
Figure 15
)1µs
Note 5: Receiver Skew Margin is definedas thevalid data sampling region atthe receiver inputs. This margintakes intoaccount for transmitter pulse positions(min
and max) and the receiver input setup and hold time (internal data sampling window). This margin allows LVDS interconnect skew, inter-symbol interference (both
dependent on type/length of cable), and clock jitter less than 250 ps.
Note 6: The min. and max. limits are based on the worst bit by applying a −400ps/+300ps shift from ideal position.
Note 7: The min. and max. are based on the actual bit position of each of the 7 bits within the LVDS data stream across PVT.
AC Timing Diagrams
DS012909-2
FIGURE 1. “Worst Case” Test Pattern
DS012909-3
DS012909-4
FIGURE 2. DS90CR215 (Transmitter) LVDS Output Load and Transition Times
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AC Timing Diagrams (Continued)
DS012909-5
DS012909-6
FIGURE 3. DS90CR216 (Receiver) CMOS/TTL Output Load and Transition Times
DS012909-7
FIGURE 4. D590CR215 (Transmitter) Input Clock Transition Time
DS012909-8
Note 8: Measurements at V
DIFF
=0V
Note 9: TCCS measured between earliest and latest LVDS edges
Note 10: TxCLK Differential Low→High Edge
FIGURE 5. D590CR215 (Transmitter) Channel-to-Channel Skew
DS012909-9
FIGURE 6. D590CR215 (Transmitter) Setup/Hold and High/Low Times
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AC Timing Diagrams (Continued)
DS012909-10
FIGURE 7. D590CR216 (Receiver) Setup/Hold and High/Low Times
DS012909-11
FIGURE 8. DS90CR215 (Transmitter) Clock In to Clock Out Delay
DS012909-12
FIGURE 9. D590CR216 (Receiver) Clock In to Clock Out Delay
DS012909-13
FIGURE 10. DS90CR215 (Transmitter) Phase Lock Loop Set Time
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AC Timing Diagrams (Continued)
DS012909-14
FIGURE 11. DS9OCR216 (Receiver) Phase Lock Loop Set Time
DS012909-15
FIGURE 12. Seven Bits of LVDS in Once Clock Cycle
DS012909-16
FIGURE 13. 21 Parallel TTL Data Inputs Mapped to LVDS Outputs (DS90CR215)
DS012909-17
FIGURE 14. Transmitter Powerdown Delay
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AC Timing Diagrams (Continued)
DS012909-18
FIGURE 15. Receiver Powerdown Delay
DS012909-19
FIGURE 16. Transmitter LVDS Output Pulse Position Measurement
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AC Timing Diagrams (Continued)
DS012909-28
FIGURE 17. Receiver LVDS Input Strobe Position
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AC Timing Diagrams (Continued)
Applications Information
The DS90CR215and DS90CR216are backwardcompatible
with the existing 5V Channel Link transmitter/receiver pair
(DS90CR213, DS90CR214).Toupgrade froma 5V toa 3.3V
system the following must be addressed:
1. Change 5V power supply to 3.3V. Provide this supply to
the V
CC
, LVDS VCCand PLL VCC.
2. Transmitter input and control inputs except 3.3V TTL/
CMOS levels. They are not 5V tolerant.
3. The receiver powerdown feature when enabled wilI lock
receiver output to a logic low. However, the 5V/66 MHz
receiver maintain theoutputs in the previous statewhen
powerdown occurred.
DS90CR215 Pin Description—Channel Link Transmitter
Pin Name I/O No. Description
TxIN I 21 TTL level input.
TxOUT+ O 3 Positive LVDS differential data output.
TxOUT− O 3 Negative LVDS differential data output.
TxCLK IN I 1 TTL level clock input. The rising edge acts as data strobe. Pin name TxCLK IN.
TxCLK OUT+ O 1 Positive LVDS differential clock output.
TxCLK OUT− O 1 Negative LVDS differential clock output.
PWR DWN
I 1 TTL level input. Assertion (low input) TRI-STATEs the outputs, ensuring low current at
power down.
V
CC
I 4 Power supply pins for TTL inputs.
GND I 5 Ground pins for TTL inputs.
PLL V
CC
I 1 Power supply pins for PLL.
PLL GND I 2 Ground pins for PLL.
LVDS V
CC
I 1 Power supply pin for LVDS outputs.
LVDS GND I 3 Ground pins for LVDS outputs.
DS90CR216 Pin Description—Channel Link Receiver
Pin Name I/O No. Description
RxIN+ I 3 Positive LVDS differential data inputs.
RxIN− I 3 Negative LVDS differential data inputs.
RxOUT O 21 TTL level data outputs.
RxCLK IN+ I 1 Positive LVDS differential clock input.
RxCLK IN− I 1 Negative LVDS differential clock input.
RxCLK OUT O 1 TTL level clock output. The rising edge acts as data strobe. Pin name RxCLK OUT.
DS012909-20
C— Setup and Hold Time (Internal data sampling window) defined by Rspos (receiver input strobe position) min and max
Tppos— Transmitter output pulse position (min and max)
RSKM ≥ Cable Skew (type, length) + Source Clock Jitter (cycle to cycle) (Note 11) + ISI (Inter-symbol interference) (Note 12)
Cable Skew—typicaIIy 10 ps–40 ps per foot, media dependent
Note 11: Cycle-to-cycle jitter is less than 250 ps
Note 12: ISI is dependent on interconnect length; may be zero
FIGURE 18. Receiver LVDS Input Skew Margin
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Applications Information (Continued)
DS90CR216 Pin Description—Channel Link Receiver (Continued)
Pin Name I/O No. Description
PWR DWN
I 1 TTL level input. When asserted (low input) the receiver outputs are low.
V
CC
I 4 Power supply pins for TTL outputs.
GND I 5 Ground pins for TTL outputs.
PLL V
CC
I 1 Power supply for PLL.
PLL GND 1 2 Ground pin for PLL.
LVDS V
CC
I 1 Power supply pin for LVDS inputs.
LVDS GND I 3 Ground pins for LVDS inputs.
The Channel Link devices are intended to be used in a wide
variety of data transmission applications. Depending upon
the application the interconnecting media may vary. For example, for lower data rate (clock rate) and shorter cable
lengths (
<
2m), themedia electricalperformance is lesscritical. For higher speed/longdistance applications the media’s
performance becomes more critical. Certain cable constructions provide tighter skew (matched electrical length between theconductors andpairs). Twin-coax forexample, has
been demonstrated at distances as great as 5 meters and
with themaximum data transferof 1.38 Gbit/s.Additional applications information can be found in the following National
Interface Application Notes:
AN = #### Topic
AN-1041 Introduction to Channel Link
AN-1035 PCB Design Guidelines for LVDS and
Link Devices
AN-806 Transmission Line Theory
AN-905 Transmission Line Calculations and
Differential Impedance
AN-916 Cable Information
CABLES: A cable interface between the transmitter and receiver needs to support the differential LVDS pairs. The 21bit CHANNEL LINK chipset (DS90CR215/216) requires four
pairs of signal wires and the 28-bit CHANNEL LINK chipset
(DS90CR285/286) requires five pairs of signal wires. The
ideal cable/connector interface wouldhave a constant 100Ω
differential impedance throughout the path. It is also recommended that cable skew remain below 150 ps ( 66 MHz
clock rate) to maintain a sufficient data sampling window at
the receiver.
In addition to the four or five cable pairs that carry data and
clock, it is recommended to provide at least one additional
conductor (or pair) which connects ground between the
transmitter and receiver. This low impedance ground provides acommon modereturn path forthe twodevices. Some
of themore commonlyused cabletypes for point-to-pointapplications include flat ribbon, flex, twisted pair and TwinCoax. All are available in a variety of configurations and options. Flat ribbon cable, flex and twisted pair generally
perform well in short point-to-point applications while TwinCoax isgood forshort andlong applications. When using ribbon cable,it isrecommended to placea groundline between
each differential pair to act as a barrierto noise coupling between adjacent pairs. ForTwin-Coax cable applications, it is
recommended to utilize a shield on each cable pair. All extended point-to-point applications should also employ an
overall shield surrounding all cable pairs regardless of the
cable type. This overall shield results in improved transmission parameters such as faster attainable speeds, longer
distances between transmitter and receiver and reduced
problems associated with EMS or EMI.
The high-speed transport of LVDS signals has been demonstrated on several types of cables with excellent results.
However, the best overall performance has been seen when
using Twin-Coax cable. Twin-Coax has very low cable skew
and EMI due to its construction and double shielding. All of
the design considerations discussed here and listed in the
supplemental application notes providethe subsystem communications designer with many useful guidelines. It is recommended that the designer assess the tradeoffs of each
application thoroughly to arrive at a reliable and economical
cable solution.
BOARD LAYOUT: To obtain the maximum benefit from the
noise and EMI reductions of LVDS, attention should be paid
to the layout of differential lines. Lines of a differential pair
should always be adjacent to eliminate noise interference
from other signals and take full advantage of the noise canceling of the differential signals. The board designer should
also try to maintain equal length on signal traces for a given
differential pair. As with any high speed design, the impedance discontinuities should be limited (reduce the numbers
of vias and no 90 degree angles on traces).Any discontinuities which do occur on one signal line should be mirrored in
the other line of the differential pair. Care should be taken to
ensure thatthe differential trace impedance match the differential impedanceof the selected physical media (this impedance should also match the value of the termination resistor
that is connectedacross the differential pairat the receiver’s
input). Finally, the location of the CHANNEL LINK TxOUT/
RxIN pins should be as close as possible to the board edge
so as to eliminate excessive pcb runs. All of these considerations will limit reflections and crosstalk which adversely effect high frequency performance and EMI.
UNUSED INPUTS: All unused inputs at the TxIN inputs of
the transmitter must betied to ground. All unusedoutputs at
the RxOUT outputs of the receiver mustthen be left floating.
TERMINATION: Use of current mode drivers requires a terminating resistor across the receiver inputs. The CHANNEL
LINK chipset will normally require a single 100Ω resistor between the true and complement lines on each differential
pair of thereceiver input. The actualvalue of the termination
resistor should be selected to match the differential mode
characteristic impedance (90Ω to 120Ω typical) of the cable.
Figure 19
shows an example. No additional pull-up or pulldown resistors are necessary as with some other differential
technologies such as PECL. Surface mount resistors are
recommended to avoid the additional inductance that ac-
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Applications Information (Continued)
companies leaded resistors. These resistors should be
placed as close as possible to the receiver input pins to reduce stubs and effectively terminate the differential lines.
DECOUPLING CAPACITORS: Bypassing capacitors are
needed to reduce the impact of switching noise which could
limit performance. For a conservative approach three
parallel-connected decouplingcapacitors (Multi-Layered Ceramic type in surface mount form factor) between each V
CC
and the ground plane(s) are recommended. The three capacitor values are 0.1 µF, 0.01µF and 0.001 µF.An example
is shown in
Figure 20
. The designer should employ wide
traces for power and ground and ensure each capacitor has
its own via to the ground plane. If boardspace is limiting the
number of bypass capacitors, the PLL V
CC
should receive
the most filtering/bypassing. Next would be the LVDS V
CC
pins and finally the logic VCCpins.
CLOCK JITTER: The CHANNEL LINK devices employ a
PLLto generate and recover theclock transmittedacross the
LVDS interface. The width of each bit in the serialized LVDS
data stream isone-seventh the clock period. Forexample, a
66 MHzclock hasa period of 15 nswhich resultsin a databit
width of 2.16 ns. Differential skew (∆t within one differential
pair), interconnect skew (∆t of one differential pair to another) and clock jitter will all reduce the available window for
sampling the LVDS serial data streams. Care must be taken
to ensure that the clock input to the transmitter be a clean
low noisesignal. Individual bypassing of each V
CC
to ground
will minimizethe noise passed on to the PLL, thus creating a
low jitter LVDS clock. These measures provide more margin
for channel-to-channelskew andinterconnect skew as a part
of the overall jitter/skew budget.
COMMON MODE vs. DIFFERENTIAL MODE NOISE MARGIN: The typical signal swing for LVDS is 300 mV centered
at +1.2V. The CHANNEL LINK receiver supports a 100 mV
threshold thereforeproviding approximately200 mVof differential noisemargin. Common modeprotection is ofmore importance to the system’s operation due to the differential
data transmission. LVDS supports an input voltage range of
Ground to +2.4V. This allows for a
±
1.0V shifting of the center point due to ground potential differences and common
mode noise.
POWER SEQUENCING AND POWERDOWN MODE: Outputs ofthe CNANNELLINK transmitterremain in TRI-STATE
until the power supply reaches 2V. Clock and data outputs
will begin to toggle 10 ms after V
CC
has reached 3V and the
Powerdown pin is above 1.5V. Either device may be placed
into a powerdownmode at any time byasserting the Powerdown pin (active low). Total power dissipation for each device will decrease to 5 µW (typical).
The CHANNEL LINK chipset is designed to protect itself
from accidental loss of power to either the transmitter or receiver. If power to the transmit board is lost, the receiver
clocks (inputand output) stop. The dataoutputs (RxOUT)retain the states they were in when the clocks stopped. When
the receiver board loses power, the receiver inputs are
shorted to V
CC
through an internal diode. Current is limited
(5 mA per input) by the fixed current mode drivers, thus
avoiding the potential for latchup when powering the device.
DS012909-24
FIGURE 19. LVDS Serialized Link Termination
DS012909-25
FIGURE 20. CHANNEL LINK
Decoupling Configuration
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Applications Information (Continued)
DS012909-26
FIGURE 21. Single-Ended and Differential Waveforms
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Physical Dimensions inches (millimeters) unless otherwise noted
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1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
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www.national.com
Order Number DS90CR215MTD or DS90CR216MTD
NS Package Number MTD48
DS90CR215/DS90CR216 +3.3V Rising Edge Data Strobe LVDS 21-Bit Channel Link-66 MHz
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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