NSC DS90CR286MTD 3.3v rising edge data strobe lvds 28-bit channel link-66 mhz Datasheet

DS90CR285/DS90CR286
+3.3V Rising Edge Data Strobe LVDS 28-Bit Channel
Link-66 MHz
General Description
The DS90CR285 transmitter converts 28 bits of LVCMOS/
LVTTL data into four LVDS (Low Voltage Differential Signaling) data streams. A phase-locked transmit clock is transmitted in parallel with the data streams over a fifth LVDS link.
Every cycle of the transmit clock 28 bits of input data are
sampled and transmitted. The DS90CR286 receiver converts the LVDS data streams back into 28 bits of LVCMOS/
LVTTL data. At a transmit clock frequency of 66 MHz, 28 bits
of TTL data are transmitted at a rate of 462 Mbps per LVDS
data channel. Using a 66 MHz clock, the data throughput is
1.848 Gbit/s (231 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 limited noise rejection capability). Thus, for a 28-bit wide
data and one clock, up to 58 conductors are required. With
the Channel Link chipset as few as 11 conductors (4 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 physical size and cost, and reduces shielding requirements due to the cables’ smaller form factor.
The 28 LVCMOS/LVTTL inputs can support a variety of
signal combinations. For example, seven 4-bit nibbles or
three 9-bit (byte + parity) and 1 control.
Features
n
n
n
n
n
n
n
n
n
n
n
n
n
n
Single +3.3V supply
Chipset (Tx + Rx) power consumption < 250 mW (typ)
Power-down mode ( < 0.5 mW total)
Up to 231 Megabytes/sec bandwidth
Up to 1.848 Gbps data throughput
Narrow bus reduces cable size
290 mV swing LVDS devices for low EMI
+1V common mode range (around +1.2V)
PLL requires no external components
Both devices are offered in a Low profile 56-lead
TSSOP package
Rising edge data strobe
Compatible with TIA/EIA-644 LVDS standard
ESD Rating > 7 kV
Operating Temperature: −40˚C to +85˚C
Block Diagrams
DS90CR285
DS90CR286
01291001
Order Number DS90CR285MTD
See NS Package Number MTD56
01291027
Order Number DS90CR286MTD
See NS Package Number MTD56
TRI-STATE ® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation
DS012910
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DS90CR285/DS90CR286 +3.3V Rising Edge Data Strobe LVDS 28-Bit Channel Link-66 MHz
July 2004
DS90CR285/DS90CR286
Pin Diagrams for TSSOP Packages
DS90CR285
DS90CR286
01291021
01291022
Typical Application
01291023
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2
Maximum Package Power Dissipation @ +25˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (VCC)
−0.3V to (VCC + 0.3V)
CMOS/TTL Output Voltage
−0.3V to (VCC + 0.3V)
LVDS Receiver Input
Voltage
−0.3V to (VCC + 0.3V)
LVDS Driver Output
Voltage
−0.3V to (VCC + 0.3V)
1.63 W
DS90CR286MTD
1.61 W
Package Derating:
−0.3V to +4V
CMOS/TTL Input Voltage
DS90CR285MTD
DS90CR285MTD
12.5 mW/˚C above +25˚C
DS90CR286MTD
12.4 mW/˚C above +25˚C
ESD Rating
> 7 kV
(HBM, 1.5 kΩ, 100 pF)
Recommended Operating
Conditions
LVDS Output Short Circuit
Duration
Continuous
Junction Temperature
+150˚C
Storage Temperature
−65˚C to +150˚C
Supply Voltage (VCC)
Nom
Max
Units
3.0
3.3
3.6
V
+25
+85
˚C
2.4
V
Operating Free Air
Lead Temperature
Temperature (TA)
(Soldering, 4 sec.)
Min
+260˚C
−40
Receiver Input Range
Solder Reflow Temperature
0
Supply Noise Voltage (VCC)
100 mVPP
Electrical Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified
Symbol
Parameter
Conditions
Min
Typ
Max
Units
LVCMOS/LVTTL DC SPECIFICATIONS
VIH
High Level Input Voltage
2.0
VCC
V
VIL
Low Level Input Voltage
GND
0.8
V
VOH
High Level Output Voltage
IOH = −0.4 mA
VOL
Low Level Output Voltage
IOL = 2 mA
VCL
Input Clamp Voltage
ICL = −18 mA
IIN
Input Current
IOS
Output Short Circuit Current
2.7
3.3
V
0.06
0.3
V
−0.79
−1.5
V
VIN = VCC, GND, 2.5V or 0.4V
± 5.1
± 10
µA
VOUT = 0V
−60
−120
mA
290
450
mV
35
mV
LVDS DRIVER DC SPECIFICATIONS
VOD
Differential Output Voltage
∆VOD
Change in VOD between
Complimentary Output States
RL = 100Ω
250
VOS
Offset Voltage (Note 4)
∆VOS
Change in VOS between
Complimentary Output States
1.125
IOS
Output Short Circuit Current
VOUT = 0V, RL = 100Ω
IOZ
Output TRI-STATE ® Current
PWR DWN = 0V,
1.25
1.375
V
35
mV
−3.5
−5
mA
±1
± 10
µA
VOUT = 0V or VCC
LVDS RECEIVER DC SPECIFICATIONS
VTH
Differential Input High Threshold
VTL
Differential Input Low Threshold
IIN
Input Current
VCM = +1.2V
+100
−100
VIN = +2.4V, VCC = 3.6V
VIN = 0V, VCC = 3.6V
3
mV
mV
± 10
± 10
µA
µA
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DS90CR285/DS90CR286
Absolute Maximum Ratings (Note 1)
DS90CR285/DS90CR286
Electrical Characteristics
(Continued)
Over recommended operating supply and temperature ranges unless otherwise specified
Symbol
Parameter
Conditions
Min
Typ
Max
Units
TRANSMITTER SUPPLY CURRENT
ICCTW
Transmitter Supply Current Worst
Case (with Loads)
Transmitter Supply Current Power
Down
ICCTZ
RL = 100Ω,
CL = 5 pF,
Worst Case
Pattern
(Figures 1, 2)
, TA = −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
RL = 100Ω,
CL = 5 pF,
Worst Case
Pattern
(Figures 1, 2)
, TA = −40˚C to
+85˚C
f = 40 MHz
38
51
mA
f = 66 MHz
42
55
mA
10
55
µA
PWR DWN = Low
Driver Outputs in TRI-STATE
under Powerdown Mode
RECEIVER SUPPLY CURRENT
Receiver Supply Current Worst
Case
ICCRW
ICCRZ
Receiver Supply Current Power
Down
CL = 8 pF,
Worst Case
Pattern
(Figures 1, 3)
, TA = −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
CL = 8 pF,
Worst Case
Pattern
(Figures 1, 3)
, TA = −40˚C to
+85˚C
f = 40 MHz
55
82
mA
f = 66 MHz
78
105
mA
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 VCC = 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 are referenced to ground unless otherwise
specified (except VOD and ∆VOD).
Note 4: VOS 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)
5
ns
TCCS
TxOUT Channel-to-Channel Skew (Figure 5)
TPPos0
Transmitter Output Pulse Position for Bit0
(Note 7) (Figure 16)
TPPos1
TPPos2
250
−0.4
0
0.4
ns
Transmitter Output Pulse Position for Bit1
3.1
3.3
4.0
ns
Transmitter Output Pulse Position for Bit2
6.5
6.8
7.6
ns
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f = 40 MHz
ps
4
(Continued)
Over recommended operating supply and −40˚C to +85˚C ranges unless otherwise specified
Min
Typ
Max
Units
TPPos3
Symbol
Transmitter Output Pulse Position for Bit3
Parameter
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
TPPos0
Transmitter Output Pulse Position for Bit0
(Note 6) (Figure 16)
TPPos1
21.0
21.2
21.8
ns
−0.4
0
0.3
ns
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
3
f = 66 MHz
3.7
5.5
ns
8)
TPLLS
Transmitter Phase Lock Loop Set (Figure 10)
10
ms
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
2.2
5.0
ns
ns
CLHT
CMOS/TTL Low-to-High Transition Time (Figure 3)
CHLT
CMOS/TTL High-to-Low Transition Time (Figure 3)
RSPos0
Receiver Input Strobe Position for Bit 0 (Note 7)(Figure 17)
RSPos1
Receiver Input Strobe Position for Bit 1
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
RSPos0
Receiver Input Strobe Position for Bit 0 (Note 6)(Figure 17)
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)
RCOP
RxCLK OUT Period (Figure 7)
RCOH
RxCLK OUT High Time (Figure 7)
RCOL
RxCLK OUT Low Time (Figure 7)
5
f = 40 MHz
f = 66 MHz
2.2
5.0
1.0
1.4
2.15
ns
4.5
5.0
5.8
ns
f = 40 MHz
490
ps
f = 66 MHz
400
ps
15
T
f = 40 MHz
6.0
10.0
ns
f = 66 MHz
4.0
6.1
ns
f = 40 MHz
10.0
13.0
ns
f = 66 MHz
6.0
7.8
ns
50
ns
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DS90CR285/DS90CR286
Transmitter Switching Characteristics
DS90CR285/DS90CR286
Receiver Switching Characteristics
(Continued)
Over recommended operating supply and −40˚C to +85˚C ranges unless otherwise specified
Symbol
RSRC
Parameter
RxOUT Setup to RxCLK OUT (Figure 7)
RHRC
RxOUT Hold to RxCLK OUT (Figure 7)
RCCD
RxCLK IN to RxCLK OUT Delay (Figure 9)
Min
Typ
f = 40 MHz
6.5
14.0
Max
Units
f = 66 MHz
2.5
8.0
ns
f = 40 MHz
6.0
8.0
ns
f = 66 MHz
2.5
4.0
f = 40 MHz
4.0
6.7
8.0
ns
f = 66 MHz
5.0
6.6
9.0
ns
ns
ns
RPLLS
Receiver Phase Lock Loop Set (Figure 11)
10
ms
RPDD
Receiver Powerdown Delay (Figure 15)
1
µs
Note 5: Receiver Skew Margin is defined as the valid data sampling region at the receiver inputs. This margin takes into account the 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
01291002
FIGURE 1. “Worst Case” Test Pattern
01291003
01291004
FIGURE 2. DS90CR285 (Transmitter) LVDS Output Load and Transition Times
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DS90CR285/DS90CR286
AC Timing Diagrams
(Continued)
01291005
01291006
FIGURE 3. DS90CR286 (Receiver) CMOS/TTL Output Load and Transition Times
01291007
FIGURE 4. DS90CR285 (Transmitter) Input Clock Transition Time
01291008
Note 8: Measurements at VDIFF = 0V
Note 9: TCCS measured between earliest and latest LVDS edges.
Note 10: TxCLK Differential Low→High Edge
FIGURE 5. DS90CR285 (Transmitter) Channel-to-Channel Skew
7
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DS90CR285/DS90CR286
AC Timing Diagrams
(Continued)
01291009
FIGURE 6. DS90CR285 (Transmitter) Setup/Hold and High/Low Times
01291010
FIGURE 7. DS90CR286 (Receiver) Setup/Hold and High/Low Times
01291011
FIGURE 8. DS90CR285 (Transmitter) Clock In to Clock Out Delay
01291012
FIGURE 9. DS90CR286 (Receiver) Clock In to Clock Out Delay
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DS90CR285/DS90CR286
AC Timing Diagrams
(Continued)
01291013
FIGURE 10. DS90CR285 (Transmitter) Phase Lock Loop Set Time
01291014
FIGURE 11. DS90CR286 (Receiver) Phase Lock Loop Set Time
01291015
FIGURE 12. Seven Bits of LVDS in Once Clock Cycle
9
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DS90CR285/DS90CR286
AC Timing Diagrams
(Continued)
01291016
FIGURE 13. 28 ParalIeI TTL Data Inputs Mapped to LVDS Outputs
01291017
FIGURE 14. Transmitter Powerdown DeIay
01291018
FIGURE 15. Receiver Powerdown Delay
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DS90CR285/DS90CR286
AC Timing Diagrams
(Continued)
01291019
FIGURE 16. Transmitter LVDS Output Pulse Position Measurement
11
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DS90CR285/DS90CR286
AC Timing Diagrams
(Continued)
01291028
FIGURE 17. Receiver LVDS Input Strobe Position
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DS90CR285/DS90CR286
AC Timing Diagrams
(Continued)
01291020
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 — typically 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
Pin Descriptions
DS90CR285 MTD56 (TSSOP) Package Pin Description — Channel Link Transmitter
I/O
No.
TxIN
Pin Name
I
28
TTL level input.
Description
TxOUT+
O
4
Positive LVDS differential data output.
TxOUT−
O
4
Negative LVDS differential data output.
TxCLK IN
I
1
TTL IeveI 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.
VCC
I
4
Power supply pins for TTL inputs.
GND
I
5
Ground pins for TTL inputs.
PLL VCC
I
1
Power supply pin for PLL.
PLL GND
I
2
Ground pins for PLL.
LVDS VCC
I
1
Power supply pin for LVDS outputs.
LVDS GND
I
3
Ground pins for LVDS outputs.
DS90CR286 MTD56 (TSSOP) Package Pin Description — Channel Link Receiver
I/O
No.
RxIN+
Pin Name
I
4
Positive LVDS differential data inputs.
Description
RxIN−
I
4
Negative LVDS differential data inputs.
RxOUT
O
28
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.
PWR DWN
I
1
TTL level input.When asserted (low input) the receiver outputs are low.
VCC
I
4
Power supply pins for TTL outputs.
GND
I
5
Ground pins for TTL outputs.
PLL VCC
I
1
Power supply for PLL.
13
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DS90CR285/DS90CR286
DS90CR286 MTD56 (TSSOP) Package Pin Description — Channel Link Receiver (Continued)
I/O
No.
PLL GND
Pin Name
I
2
Ground pin for PLL.
Description
LVDS VCC
I
1
Power supply pin for LVDS inputs.
LVDS GND
I
3
Ground pins for LVDS inputs.
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 provide the 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 that the differential trace impedance
match the differential impedance of the selected physical
media (this impedance should also match the value of the
termination resistor that is connected across the differential
pair at 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.
Applications Information
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), the media electrical performance is less
critical. For higher speed/long distance applications the media’s performance becomes more critical. Certain cable constructions provide tighter skew (matched electrical length
between the conductors and pairs). Twin-coax for example,
has been demonstrated at distances as great as 5 meters
and with the maximum data transfer of 1.848 Gbit/s. Additional applications information can be found in the following
National Interface Application Notes:
AN = ####
Topic
AN-1041
Introduction to Channel Link
AN-1108
Channel Link PCB and Interconnect
Design-In Guidelines
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
21-bit 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 would have 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 a common mode return path for the two devices. Some
of the more commonly used cable types for point-to-point
applications 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 is good for short and long applications. When using
ribbon cable, it is recommended to place a ground line
between each differential pair to act as a barrier to noise
coupling between adjacent pairs. For Twin-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
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UNUSED INPUTS: All unused inputs at the TxIN inputs of
the transmitter must be tied to ground. All unused outputs at
the RxOUT outputs of the receiver must then be left floating.
INPUTS: The TxIN and control inputs are compatible with
LVCMOS and LVTTL levels. These pins are not 5V tolerant.
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 the receiver input. The actual value 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 accompanies 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 decoupling capacitors (Multi-Layered Ceramic type in surface mount form factor) between each VCC
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 board space is limiting the
14
the most filtering/bypassing. Next would be the LVDS VCC
pins and finally the logic VCC pins.
(Continued)
number of bypass capacitors, the PLL VCC should receive
01291024
FIGURE 19. LVDS Serialized Link Termination
for channel-to-channel skew and interconnect 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 therefore providing approximately 200 mV of differential noise margin. Common mode protection is of more
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 of the CNANNEL LINK transmitter remain in TRISTATE ® until the power supply reaches 2V. Clock and data
outputs will begin to toggle 10 ms after VCC has reached 3V
and the Powerdown pin is above 1.5V. Either device may be
placed into a powerdown mode at any time by asserting 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 (input and output) stop. The data outputs (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.
01291025
FIGURE 20. CHANNEL LINK
Decoupling Configuration
CLOCK JITTER: The CHANNEL LINK devices employ a
PLL to generate and recover the clock transmitted across the
LVDS interface. The width of each bit in the serialized LVDS
data stream is one-seventh the clock period. For example, a
66 MHz clock has a period of 15 ns which results in a data bit
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 noise signal. Individual bypassing of each VCC to ground
will minimize the noise passed on to the PLL, thus creating a
low jitter LVDS clock. These measures provide more margin
15
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DS90CR285/DS90CR286
Applications Information
DS90CR285/DS90CR286
Applications Information
(Continued)
01291026
FIGURE 21. Single-Ended and Differential Waveforms
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16
inches (millimeters)
Order Number DS90CR285MTD or DS90CR286MTD
NS Package Number MTD56
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DS90CR285/DS90CR286 +3.3V Rising Edge Data Strobe LVDS 28-Bit Channel Link-66 MHz
Physical Dimensions
unless otherwise noted