NSC DS90CR281 28-bit channel link Datasheet

DS90CR281/DS90CR282
28-Bit Channel Link
General Description
The DS90CR281 transmitter converts 28 bits of CMOS/TTL
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 DS90CR282 receiver converts the LVDS
data streams back into 28 bits of CMOS/TTL data. At a transmit clock frequency of 40 MHz, 28 bits of TTL data are transmitted at a rate of 280 Mbps per LVDS data channel. Using
a 40 MHz clock, the data throughput is 1.12 Gbit/s
(140 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 bus 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 CMOS/TTL inputs can support a variety of signal
combinations. For example, 7 4-bit nibbles or 3 9-bit (byte +
parity) and 1 control.
Features
n
n
n
n
n
n
n
n
Narrow bus reduces cable size and cost
± 1V common mode range (ground shifting)
290 mV swing LVDS data transmission
1.12 Gbit/s data throughput
Low swing differential current mode drivers reduce EMI
Rising edge data strobe
Power down mode
Offered in low profile 56-lead TSSOP package
Block Diagrams
DS90CR281
DS90CR282
DS012638-27
Order Number DS90CR281MTD
See NS Package Number MTD56
DS012638-1
Order Number DS90CR282MTD
See NS Package Number MTD56
TRI-STATE ® is a registered trademark of National Semiconductor Corporation.
© 1998 National Semiconductor Corporation
DS012638
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DS90CR281/DS90CR282 28-Bit Channel Link
July 1997
Connection Diagrams
DS90CR281
DS90CR282
DS012638-2
DS012638-3
Typical Application
DS012638-19
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2
Absolute Maximum Ratings (Note 1)
MTD56(TSSOP) Package:
DS90CR281
1.63W
DS90CR282
1.61W
Package Derating:
DS90CR281
12.5 mW/˚C above +25˚C
DS90CR282
12.4 mW/˚C above +25˚C
This device does not meet 2000V ESD rating (Note 4).
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 +6V
CMOS/TTL Input Voltage
−0.3V to (VCC + 0.3V)
CMOS/TTL Ouput 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)
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
Recommended Operating
Conditions
Supply Voltage (VCC)
Operating Free Air Temperature (TA)
Receiver Input Range
Supply Noise Voltage (VCC)
Min
4.5
−10
0
Max
5.5
+70
2.4
100
Units
V
˚C
V
mVP-P
Max
Units
Electrical Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified
Symbol
Parameter
Conditions
Min
Typ
CMOS/TTL 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
VOL
Low Level Output Voltage
0.1
0.3
V
VCL
Input Clamp Voltage
−0.79
−1.5
V
IIN
Input Current
± 5.1
± 10
µA
IOS
Output Short Circuit Current
−120
mA
450
mV
35
mV
IOH = −0.4 mA
IOL = 2 mA
3.8
ICL = −18 mA
VIN = VCC, GND, 2.5V or 0.4V
VOUT = 0V
4.9
V
LVDS DRIVER DC SPEClFlCATIONS
VOD
Differential Output Voltage
∆VOD
Change in VOD between
RL = 100Ω
250
290
Complementary Output States
VCM
Common Mode Voltage
∆VCM
Change in VCM between
1.1
1.25
1.375
V
35
mV
−2.9
−5
mA
±1
± 10
µA
+100
mV
Complementary Output States
IOS
Output Short Circuit Current
IOZ
Output TRI-STATE ® Current
VOUT = OV, RL = 100Ω
Power Down = 0V, VOUT = 0V or VCC
LVDS RECEIVER DC SPECIFlCATIONS
VTH
Differential Input High
Threshold
VTL
Differential Input Low Threshold
IIN
Input Current
VCM = +1.2V
−100
VIN = +2.4V
VIN = 0V
VCC = 5.5V
Transmitter Supply Current,
RL = 100Ω, CL = 5 pF,
Worst Case
Worst Case Pattern (Figures 1, 2)
Power Down = Low
f = 32.5 MHz
f = 37.5 MHz
mV
< ±1
< ±1
± 10
± 10
µA
µA
TRANSMITTER SUPPLY CURRENT
ICCTW
ICCTZ
Transmitter Supply Current,
34
51
mA
36
53
mA
1
25
µA
Power Down
3
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Electrical Characteristics
(Continued)
Over recommended operating supply and temperature ranges unless otherwise specified
Symbol
Parameter
Conditions
Min
Typ
Max
Units
RECEIVER SUPPLY CURRENT
ICCRW
ICCRZ
Receiver Supply Current,
CL = 8 pF,
Worst Case
Worst Case Pattern (Figures 1, 3)
Power Down = Low
Receiver Supply Current,
f = 32.5 MHz
f = 37.5 MHz
55
75
mA
60
80
mA
1
10
µA
Power Down
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 = 5.0V 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: ESD Rating: HBM (1.5 kΩ, 100 pF)
PLL V CC ≥ 1000V
All other pins ≥ 2000V
EIAJ (0Ω, 200 pF) ≥ 150V
Transmitter Switching Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified
Typ
Max
Units
LLHT
Symbol
LVDS Low-to-High Transition Time (Figure 2)
Parameter
Min
0.75
1.5
ns
LHLT
LVDS High-to-Low Transition Time (Figure 2)
0.75
1.5
ns
TCIT
TxCLK IN Transition Time (Figure 4)
8
ns
TCCS
TxOUT Channel-to-Channel Skew (Note 5) (Figure 5)
TPPos0
Transmitter Output Pulse Position for Bit 0 (Figure 16)
TPPos1
Transmitter Output Pulse Position for Bit 1
6.3
7.2
7.5
ns
TPPos2
Transmitter Output Pulse Position for Bit 2
12.8
13.6
14.6
ns
TPPos3
Transmitter Output Pulse Position for Bit 3
20
20.8
21.5
ns
TPPos4
Transmitter Output Pulse Position for Bit 4
27.2
28
28.5
ns
TPPos5
Transmitter Output Pulse Position for Bit 5
34.5
35.2
35.6
ns
TPPos6
Transmitter Output Pulse Position for Bit 6
ns
TPPos0
Transmitter Output Pulse Position for Bit 0 (Figure 16)
TPPos1
f = 20 MHz
−200
150
350
ps
350
ps
42.2
42.6
42.9
−100
100
300
ps
Transmitter Output Pulse Position for Bit 1
2.9
3.3
3.9
ns
TPPos2
Transmitter Output Pulse Position for Bit 2
6.1
6.6
7.1
ns
TPPos3
Transmitter Output Pulse Position for Bit 3
9.7
10.2
10.7
ns
TPPos4
Transmitter Output Pulse Position for Bit 4
13
13.5
14.1
ns
TPPos5
Transmitter Output Pulse Position for Bit 5
17
17.4
17.8
ns
TPPos6
Transmitter Output Pulse Position for Bit 6
20.3
20.8
21.4
ns
TCIP
TxCLK IN Period (Figure 6)
25
T
50
ns
TCIH
TxCLK IN High Time (Figure 6)
0.35T
0.5T
0.65T
ns
0.35T
0.5T
0.65T
ns
TCIL
TxCLK IN Low Time (Figure 6)
TSTC
TxIN Setup to TxCLK IN (Figure 6)
THTC
TxIN Hold to TxCLK IN (Figure 6)
TCCD
TxCLK IN to TxCLK OUT Delay @ 25˚C,
VCC = 5.0V (Figure 8)
f = 40 MHz
f = 20 MHz
14
f = 40 MHz
8
2.5
5
ns
ns
2
ns
9.7
ns
TPLLS
Transmitter Phase Lock Loop Set (Figure 10)
10
ms
TPDD
Transmitter Powerdown Delay (Figure 14)
100
ns
Note 5: This limit based on bench characterization.
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Receiver Switching Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified
Symbol
Typ
Max
Units
CLHT
CMOS/TTL Low-to-High Transition Time (Figure 3)
3.5
6.5
ns
CHLT
CMOS/TTL High-to-Low Transition Time (Figure 3)
2.7
6.5
ns
RCOP
RxCLK OUT Period (Figure 7)
T
50
ns
RSKM
Receiver Skew Margin (Note 6)
VCC = 5V, TA = 25˚C (Figure 17)
RCOH
Parameter
Min
25
f = 20 MHz
f = 40 MHz
1.1
ns
700
ps
RxCLK OUT High Time (Figure 7)
f = 20 MHz
f = 40 MHz
RCOL
RHRC
RCCD
ns
6
ns
RxCLK OUT Low Time (Figure 7)
f = 20 MHz
f = 40 MHz
RSRC
19
21.5
ns
10.5
ns
RxOUT Setup to RxCLK OUT (Figure 7)
f = 20 MHz
f = 40 MHz
14
ns
4.5
ns
f = 20 MHz
f = 40 MHz
16
ns
6.5
RxOUT Hold to RxCLK OUT (Figure 7)
RxCLK IN to RxCLK OUT Delay @ 25˚C,
VCC = 5.0V (Figure 9)
7.6
ns
11.9
ns
RPLLS
Receiver Phase Lock Loop Set (Figure 11)
10
ms
RPDD
Receiver Powerdown Delay (Figure 15 )
1
µs
Note 6: Receiver Skew Margin is defined as the valid data sampling region at the receiver inputs. This margin takes into account for transmitter output skew (TCCS)
and the setup and hold time (internal data sampling window), allowing LVDS cable skew dependent on the type/length and source clock (TxCLK IN) jitter.
RSKM ≥ cable skew (type, length) + source clock jitter (cycle to cycle).
AC Timing Diagrams
DS012638-4
FIGURE 1. “WORST CASE” Test Pattern
DS012638-5
DS012638-6
FIGURE 2. DS90CR281 (Transmitter) LVDS Output Load and Transition Timing
5
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AC Timing Diagrams
(Continued)
DS012638-7
DS012638-8
FIGURE 3. DS90CR282 (Receiver) CMOS/TTL Output Load and Transition Timing
DS012638-9
FIGURE 4. DS90CR281 (Transmitter) Input Clock Transition Time
DS012638-10
Measurements at Vdiff = 0V
Measurements at Vdiff = 0V
TCCS measured between earliest and latest initial LVDS edges.Measurements at Vdiff = 0V
TxCLK OUT Differential Low→High Edge
FIGURE 5. DS90CR281 (Transmitter) Channel-to-Channel Skew and Pulse Width
DS012638-11
FIGURE 6. DS90CR281 (Transmitter) Setup/Hold and High/Low Times
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AC Timing Diagrams
(Continued)
DS012638-12
FIGURE 7. (Receiver) DS90CR282 Setup/Hold and High/Low Times
DS012638-13
FIGURE 8. DS90CR281 (Transmitter) Clock In to Clock Out Delay
DS012638-14
FIGURE 9. DS90CR282 (Receiver) Clock In to Clock Out Delay
DS012638-15
FIGURE 10. DS90CR281 (Transmitter) Phase Lock Loop Set Time
7
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AC Timing Diagrams
(Continued)
DS012638-16
FIGURE 11. DS90CR282 (Receiver) Phase Lock Loop Set Time
DS012638-17
FIGURE 12. Seven Bits of LVDS in One Clock Cycle
DS012638-18
FIGURE 13. 28 Parallel TTL Data Inputs Mapped to LVDS Outputs (DS90CR281)
DS012638-23
FIGURE 14. Transmitter Powerdown Delay
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AC Timing Diagrams
(Continued)
DS012638-24
FIGURE 15. Receiver Powerdown Delay
DS012638-25
FIGURE 16. Transmitter LVDS Output Pulse Position Measurement
DS012638-26
SW — Setup and Hold Time (Internal data sampling window)
TCCS — Transmitter Output Skew
RSKM ≥ Cable Skew (type, length) + Source Clock Jitter (cycle to cycle)
Cable Skew — Typically 10 ps–40 ps per foot
FIGURE 17. Receiver LVDS Input Skew Margin
9
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DS90CR281 Pin Description — Channel Link Transmitter (Tx)
I/O
No.
TxIN
Pin Name
I
28
Description
TxOUT+
O
4
Positive LVDS differential data output
TxOUT−
O
4
Negative LVDS differential data output
TxCLK IN
I
1
TTL level clock input. The rising edge acts as data strobe
TxCLK OUT+
O
1
Positive LVDS differential clock output
TxCLK OUT−
O
1
Negative LVDS differential clock output
PWR DOWN
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
TTL Level inputs
DS90CR282 Pin Description — Channel Link Receiver (Rx)
Pin Name
RxIN+
I/O
No.
I
4
Description
Positive LVDS differential data inputs
RxIN−
I
4
RxOUT
O
28
Negative LVDS differential data inputs
RxCLK IN+
I
1
RxCLK IN−
I
1
Negative LVDS differential clock input
RxCLK OUT
O
1
TTL level clock output. The rising edge acts as data strobe
TTL level outputs
Positive LVDS differential clock input
PWR DOWN
I
1
TTL level input. Assertion (low input) maintains the receiver outputs in the previous state
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
PLL GND
I
2
Ground pin for PLL
LVDS VCC
I
1
Power supply pin for LVDS inputs
LVDS GND
I
3
Ground pins for LVDS inputs
Applications Information
AN-####
AN-916
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 10 meters and
with the maximum data transfer of 1.12 Gbit/s. Additional applications information can be found in the following National
Interface Application Notes:
AN-####
PCB Design Guidelines for LVDS and Link
Devices
AN-806
Transmission Line Theory
AN-905
Transmission Line Calculations and
Differential Impedance
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CABLES: A cable interface between the transmitter and receiver needs to support the differential LVDS pairs. The
21-bit CHANNEL LINK chipset (DS90CR211/212) requires
four pairs of signal wires and the 28-bit CHANNEL LINK
chipset (DS90CR281/282) 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 350 ps ( @ 40
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
Twin-Coax. 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 Twin-Coax
Topic
AN-1035
Topic
Cable Information
10
Applications Information
ance 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.
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.
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 18 shows an example. No additional pull-up or
pull-down 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 19. 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
number of bypass capacitors, the PLL VCC should receive
the most filtering/bypassing. Next would be the LVDS VCC
pins and finally the logic VCC pins.
(Continued)
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
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 imped-
DS012638-20
FIGURE 18. LVDS Serialized Link Termination
11
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Applications Information
low jitter LVDS clock. These measures provide more margin
for channel-to-channel skew and interconnect skew as a part
of the overall jitter/skew budget.
(Continued)
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 CHANNEL LINK transmitter remain in
TRI-STATE ® until the power supply reaches 3V. Clock and
data outputs will begin to toggle 10 ms after VCChas reached
4.5V and the Powerdown pin is above 2V. 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.
DS012638-21
FIGURE 19. 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
40 MHz clock has a period of 25 ns which results in a data bit
width of 3.57 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
DS012638-22
FIGURE 20. Single-Ended and Differential Waveforms
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12
13
DS90CR281/DS90CR282 28-Bit Channel Link
Physical Dimensions
inches (millimeters) unless otherwise noted
56-Lead Molded Thin Shrink Small Outline Package, JEDEC
Order Number DS90CR281MTD or DS90CR282MTD
NS Package Number MTD56
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