NSC DS90CR482 48-bit lvds channel link ser/des − 65 - 112 mhz Datasheet

DS90CR481 / DS90CR482
48-Bit LVDS Channel Link SER/DES − 65 - 112 MHz
General Description
The DS90CR481 transmitter converts 48 bits of CMOS/TTL
data into eight LVDS (Low Voltage Differential Signaling)
data streams. A phase-locked transmit clock is transmitted in
parallel with the data streams over a ninth LVDS link. Every
cycle of the transmit clock 48 bits of input data are sampled
and transmitted. The DS90CR482 receiver converts the
LVDS data streams back into 48 bits of LVCMOS/TTL data.
At a transmit clock frequency of 112MHz, 48 bits of TTL data
are transmitted at a rate of 672Mbps per LVDS data channel.
Using a 112MHz clock, the data throughput is 5.38Gbit/s
(672Mbytes/s). At a transmit clock frequency of 112MHz, 48
bits of TTL data are transmitted at a rate of 672Mbps per
LVDS data channel. Using a 66MHz clock, the data throughput is 3.168Gbit/s (396Mbytes/s).
The multiplexing of 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 48-bit wide
data and one clock, up to 98 conductors are required. With
this Channel Link chipset as few as 19 conductors (8 data
pairs, 1 clock pair and a minimum of one ground) are
needed. This provides an 80% reduction in 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 48 CMOS/TTL inputs can support a variety of signal
combinations. For example, 6 8-bit words or 5 9-bit (byte +
parity) and 3 controls.
The DS90CR481/DS90CR482 chipset is improved over prior
generations of Channel Link devices and offers higher bandwidth support and longer cable drive with three areas of
enhancement. To increase bandwidth, the maximum clock
rate is increased to 112 MHz and 8 serialized LVDS outputs
are provided. Cable drive is enhanced with a user selectable
pre-emphasis feature that provides additional output current
during transitions to counteract cable loading effects. Optional DC balancing on a cycle-to-cycle basis, is also provided to reduce ISI (Inter-Symbol Interference). With preemphasis and DC balancing, a low distortion eye-pattern is
provided at the receiver end of the cable. A cable deskew
capability has been added to deskew long cables of pair-topair skew of up to +/−1 LVDS data bit time (up to 80 MHz
Clock Rate). These three enhancements allow cables 5+
meters in length to be driven.
The chipset is an ideal means to solve EMI and cable size
problems associated with wide, high speed TTL interfaces.
Features
n
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n
n
n
n
n
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n
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3.168 Gbits/sec bandwidth with 66 MHz Clock
5.376 Gbits/sec bandwidth with 112 MHz Clock
65 - 112 MHz input clock support
LVDS SER/DES reduces cable and connector size
Pre-emphasis reduces cable loading effects
Optional DC balance encoding reduces ISI distortion
Cable Deskew of +/−1 LVDS data bit time (up to 80
MHz Clock Rate)
5V Tolerant TxIN and control input pins
Flow through pinout for easy PCB design
+3.3V supply voltage
Transmitter rejects cycle-to-cycle jitter
Conforms to ANSI/TIA/EIA-644-1995 LVDS Standard
Generalized Block Diagrams (DS90CR481 and DS90CR482)
20009101
© 2005 National Semiconductor Corporation
DS200091
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DS90CR481/DS90CR482 48-Bit LVDS Channel Link SER/DES – 65 - 112 MHz
June 2005
DS90CR481/DS90CR482
Generalized Transmitter Block Diagram – DS90CR481
20009102
Generalized Receiver Block Diagram – DS90CR482
20009103
Ordering Information
Order Number
Function
DS90CR481VJD
Transmitter (Serializer)
VJD100A
DS90CR482VS
Receiver (Deserializer)
VJD100A
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Package
2
DS90CR482VS
Package Derating:
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 +4V
CMOS/TTL Input Voltage
−0.3V to (VCC + 0.3V)
LVDS Receiver Input
Voltage
−0.3V to +3.6V
DS90CR481VJD
18.1mW/˚C above +25˚C
DS90CR482VS
18.1mW/˚C above +25˚C
ESD Rating:
−0.3V to +5.5V
LVCMOS/TTL Output
Voltage
2.3W
DS90CR481
> 6 kV
> 300 V
(HBM, 1.5kΩ, 100pF)
(EIAJ, 0Ω, 200pF)
DS90CR482
LVDS Driver Output
Voltage
−0.3V to +3.6V
LVDS Output Short
Circuit Duration
Continuous
Junction Temperature
+150˚C
Storage Temperature
−65˚C to +150˚C
> 2 kV
> 200 V
(HBM, 1.5kΩ, 100pF)
(EIAJ, 0Ω, 200pF)
Recommended Operating
Conditions
Min Nom
Max
Units
Lead Temperature
Supply Voltage (VCC)
3.0
3.3
3.6
V
(Soldering, 4 sec.)
Operating Free Air
Temperature (TA)
−10
+25
+70
˚C
100
mVp-p
112
MHz
100L TQFP
+260˚C
Maximum Package Power Dissipation Capacity @
25˚C
Supply Noise Voltage
Input Clock (TX)
65
100 TQFP Package:
DS90CR481VJD
2.3W
Electrical Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
CMOS/TTL DC SPECIFICATIONS
VIH
High Level Input
Voltage
2.0
VIL
Low Level Input
Voltage
GND
VOH
High Level Output
Voltage
V
0.8
V
IOH = −0.4 mA
2.7
2.9
V
IOH = −2mA
2.7
2.85
V
VOL
Low Level Output
Voltage
IOL = 2 mA
VCL
Input Clamp Voltage
IIN
Input Current
IOS
Output Short Circuit
Current
0.1
0.3
ICL = −18 mA
−0.79
−1.5
V
VIN = 0.4V, 2.5V or VCC
+1.8
+15
µA
−120
mA
450
mV
35
mV
VIN = GND
−15
0
VOUT = 0V
V
µA
LVDS DRIVER DC SPECIFICATIONS
|VOD|
Differential Output
Voltage
∆VOD
Change in VOD
between
Complimentary Output
States
VOS
Offset Voltage
∆VOS
Change in VOS
between
Complimentary Output
States
RL = 100Ω
250
1.125
3
345
1.25
1.375
V
35
mV
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DS90CR481/DS90CR482
Absolute Maximum Ratings (Note 1)
DS90CR481/DS90CR482
Electrical Characteristics
(Continued)
Over recommended operating supply and temperature ranges unless otherwise specified.
Symbol
Parameter
Conditions
IOS
Output Short Circuit
Current
VOUT = 0V, RL = 100Ω
IOZ
Output TRI-STATE
Current
PD = 0V, VOUT = 0V or VCC
Min
Typ
Max
Units
−3.5
−5
mA
±1
± 10
µA
+100
mV
LVDS RECEIVER DC SPECIFICATIONS
VTH
Differential Input High
Threshold
VTL
Differential Input Low
Threshold
IIN
Input Current
VCM = +1.2V
−100
mV
VIN = +2.4V, VCC = 3.6V
VIN = 0V, VCC = 3.6V
± 10
± 10
µA
µA
TRANSMITTER SUPPLY CURRENT
ICCTW
ICCTZ
Transmitter Supply
Current
Worst Case
RL = 100Ω, CL = 5 pF,
BAL = High,
Worst Case Pattern
(Figures 1, 2)
Transmitter Supply
Current
Power Down
PD = Low
f = 66MHz
106
160
mA
f = 112MHz
155
210
mA
5
50
µA
f = 66MHz
200
210
mA
f = 112MHz
250
280
mA
20
100
µA
Driver Outputs in TRI-STATE during power down
Mode
RECEIVER SUPPLY CURRENT
ICCRW
ICCRZ
Receiver Supply
Current
Worst Case
CL = 8 pF, BAL = High,
Worst Case Pattern
(Figures 1, 3)
Receiver Supply
Current
Power Down
PD = Low
Receiver Outputs stay low during power down
mode.
Recommended Transmitter Input Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified.
Min
Typ
Max
Units
TCIT
Symbol
TxCLK IN Transition Time (Figure 4)
Parameter
1.0
2.0
3.0
ns
TCIP
TxCLK IN Period (Figure 5)
8.93
15.38
ns
TCIH
TxCLK in High Time (Figure 5)
0.35T
0.5T
0.65T
ns
TCIL
TxCLK in Low Time (Figure 5)
0.35T
0.5T
0.65T
ns
TXIT
TxIN Transition Time
6.0
ns
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1.5
4
Over recommended operating supply and temperature ranges unless otherwise specified.
Symbol
LLHT
LHLT
Typ
Max
Units
LVDS Low-to-High Transition Time, (Figure 2),
PRE = 0.75V (disabled)
Parameter
Min
0.14
0.7
ns
LVDS Low-to-High Transition Time, (Figure 2),
PRE = Vcc (max)
0.11
0.6
ns
LVDS High-to-Low Transition Time, (Figure 2),
PRE = 0.75V (disabled)
0.16
0.8
ns
LVDS High-to-Low Transition Time, (Figure 2),
PRE = Vcc (max)
0.11
0.7
ns
TBIT
Transmitter Bit Width
f = 66 MHz,
112MHz
1/7 TCIP
TPPOS
Transmitter Pulse Positions Normalized
f = 65 to 112
MHz
TJCC
Tranmitter Jitter - Cycle-to-Cycle
100
ps
TCCS
TxOUT Channel to Channel Skew
40
ps
− 200
TSTC
TxIN Setup to TxCLK IN, (Figure 5)
2.5
THTC
TxIN Hold to TxCLK IN, (Figure 5)
0
TPDL
Transmitter Propagation Delay - Latency, (Figure 7)
TPLLS
TPDD
1.5(TCIP)+3.72
0
ns
+200
ps
ns
ns
1.5(TCIP)+4.4
1.5(TCIP)+6.24
ns
Transmitter Phase Lock Loop Set, (Figure 9)
10
ms
Transmitter Powerdown Delay, (Figure 11)
100
ns
Receiver Switching Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified.
Symbol
CLHT
CHLT
Max
Units
CMOS/TTL Low-to-High Transition Time, Rx data out,
(Figure 3)
Parameter
Min
2.0
ns
CMOS/TTL Low-to-High Transition Time, Rx clock
out, (Figure 3)
1.0
ns
CMOS/TTL High-to-Low Transition Time, Rx data out,
(Figure 3)
2.0
ns
CMOS/TTL High-to-Low Transition Time, Rx clock
out, (Figure 3)
1.0
ns
15.38
ns
RCOP
RxCLK OUT Period, (Figure 6)
RCOH
RxCLK OUT High Time, (Figure 6),
(Note 4)
f = 112 MHz
3.5
ns
f = 66 MHz
6.0
ns
RCOL
RxCLK OUT Low Time, (Figure 6),
(Note 4)
f = 112 MHz
3.5
ns
f = 66 MHz
6.0
ns
RxOUT Setup to RxCLK
OUT,(Figure 6)
f = 112 MHz
2.4
ns
f = 66 MHz
3.6
ns
RHRC
RxOUT Hold to RxCLK OUT,
(Figure 6), (Note 4)
f = 112 MHz
3.4
ns
RPDL
Receiver Propagation Delay - Latency, (Figure 8)
RSRC
8.928
Typ
f = 66 MHz
T
6.0
3(TCIP)+4.0
ns
3(TCIP)+4.8
3(TCIP)+6.5
ns
RPLLS
Receiver Phase Lock Loop Set, (Figure 10)
10
ms
RPDD
Receiver Powerdown Delay, (Figure 12)
1
µs
5
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DS90CR481/DS90CR482
Transmitter Switching Characteristics
DS90CR481/DS90CR482
Chipset RSKM Characteristics
Over recommended operating supply and temperature ranges unless otherwise specified.(Notes 4, 7). See Applications Information section for more details on this parameter and how to apply it.
Symbol
RSKM
RSKM
Parameter
Receiver Skew Margin without
Deskew in non-DC Balance Mode,
(Figure 13), (Note 5)
Receiver Skew Margin without
Deskew in DC Balance Mode,
(Figure 13), (Note 5)
Min
Typ
Max
Units
f = 112 MHz
170
f = 100 MHz
170
240
ps
ps
f = 85MHz
300
350
ps
f = 66MHz
300
350
ps
f = 112 MHz
170
f = 100 MHz
170
200
ps
f = 85 MHz
250
300
ps
f = 66 MHz
250
300
ps
ps
RSKMD
Receiver Skew Margin with Deskew
in DC Balance, (Figure 14),
(Note 6)
f = 33 to 80
MHz
0.25TBIT
ps
RDR
Receiver Deskew Range
f = 80 MHz
±1
TBIT
RDSS
Receiver Deskew Step Size
f = 80 MHz
0.3 TBIT
ns
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 T A = +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 VTH, VTL, VOD and ∆VOD).
Note 4: The Minimum and Maximum Limits are based on statistical analysis of the device performance over voltage and temperature ranges. This parameter is
functionally tested on Automatic Test Equipment (ATE). ATE is limited to 85MHz. A sample of characterization parts have been bench tested to verify functional
performance.
Note 5: Receiver Skew Margin (RSKM) is defined as the valid data sampling region at the receiver inputs. This margin takes into account transmitter output pulse
positions (min and max) and the receiver input setup and hold time (internal data sampling window, RSPOS). This margin allows for LVDS interconnect skew,
inter-symbol interference (both dependent on type/length of cable) and clock jitter (TJCC).
RSKM ≥ cable skew (type, length) + source clock jitter (cycle to cycle,TJCC) + ISI (if any). See Applications Information section for more details.
Note 6: Receiver Skew Margin with Deskew (RSKMD) is defined as the valid data sampling region at the receiver inputs. The DESKEW function will constrain the
receiver’s sampling strobes to the middle half of the LVDS bit and removes (adjusts for) fixed interconnect skew. This margin (RSKMD) allows for inter-symbol
interference (dependent on type/length of cable), Transmitter Pulse Position (TPPOS) variance, and LVDS clock jitter (TJCC).
RSKMD ≥ ISI + TPPOS(variance) + source clock jitter (cycle to cycle, TJCC). See Applications Information section for more details.
Note 7: Typical values for RSKM and RSKMD are applicable for fixed VCC and T A of the Transmitter and Receiver (both are assumed to be at the same VCC and
T A points).
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6
DS90CR481/DS90CR482
AC Timing Diagrams
20009110
FIGURE 1. “Worst Case” Test Pattern
Note 8: The worst case test pattern produces a maximum toggling of digital circuits, LVDS I/O and CMOS/TTL I/O.
20009112
FIGURE 2. DS90CR481 (Transmitter) LVDS Output Load and Transition Times
20009130
FIGURE 3. DS90CR482 (Receiver) CMOS/TTL Output Load and Transition Times
20009114
FIGURE 4. DS90CR481 (Transmitter) Input Clock Transition Time
7
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DS90CR481/DS90CR482
AC Timing Diagrams
(Continued)
20009115
FIGURE 5. DS90CR481 (Transmitter) Setup/Hold and High/Low Times
20009131
FIGURE 6. DS90CR482 (Receiver) Setup/Hold and High/Low Times
20009127
FIGURE 7. DS90CR481 (Transmitter) Propagation Delay - Latency
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8
DS90CR481/DS90CR482
AC Timing Diagrams
(Continued)
20009132
FIGURE 8. DS90CR482 (Receiver) Propagation Delay - Latency
20009119
FIGURE 9. DS90CR481 (Transmitter) Phase Lock Loop Set Time
20009133
FIGURE 10. DS90CR482 (Receiver) Phase Lock Loop Set Time
9
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DS90CR481/DS90CR482
AC Timing Diagrams
(Continued)
20009121
FIGURE 11. DS90CR481 (Transmitter) Power Down Delay
20009134
FIGURE 12. DS90CR482 (Receiver) Power Down Delay
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10
DS90CR481/DS90CR482
AC Timing Diagrams
(Continued)
20009125
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) + LVDS Source Clock Jitter (cycle to cycle) + ISI (Inter-symbol interference)
j Cable Skew — typically 10 ps–40 ps per foot, media dependent
j Cycle-to-cycle LVDS Output jitter (TJCC) is less than 100 ps (worse case estimate).
j ISI is dependent on interconnect length; may be zero
See Applications Information section for more details.
FIGURE 13. Receiver Skew Margin (RSKM) for Chipset without DESKEW
20009137
C — Setup and Hold Time (Internal data sampling window) defined by Rspos (receiver input strobe position) min and max
RSKMD ≥ TPPOSvariance (d) + TJCC (output jitter)(f) + ISI (m)
j d= Tppos — Transmitter output pulse position (min and max)
j f= Cycle-to-cycle LVDS Output jitter (TJCC) is less than 100 ps (worse case estimate)
j m= extra margin - assigned to ISI in long cable applications
See Applications Informations section for more details.
FIGURE 14. Receiver Skew Margin (RSKMD) for Chipset with DESKEW
11
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DS90CR481/DS90CR482
LVDS Interface
20009104
Optional features supported: Pre-emphasis and DESKEW
FIGURE 15. 48 Parallel TTL Data Bits Mapped to LVDS Bits with DC Balance Enabled
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12
DS90CR481/DS90CR482
LVDS Interface
(Continued)
20009135
Optional feature supported: Pre-emphasis
FIGURE 16. 48 Parallel TTL Data Bits Mapped to LVDS Bits with DC Balance Disabled
13
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DS90CR481/DS90CR482
Applications Information
The DS90CR481/DS90CR482 chipset is improved over prior
generations of Channel Link devices and offers higher bandwidth support and longer cable drive with three areas of
enhancement. To increase bandwidth, the maximum clock
rate is increased to 112 MHz and 8 serialized LVDS outputs
are provided. Cable drive is enhanced with a user selectable
pre-emphasis feature that provides additional output current
during transitions to counteract cable loading effects. This
requires the use of one pull up resistor to Vcc; please refer to
Table 1 to set the level needed. Optional DC balancing on a
cycle-to-cycle basis, is also provided to reduce ISI (InterSymbol Interference). With pre-emphasis and DC balancing,
a low distortion eye-pattern is provided at the receiver end of
the cable. A cable deskew capability has been added to
deskew long cables of pair-to-pair skew of up to ± 1 LVDS
data bit time (up to 80 MHz clock rates). For details on
deskew, refer to “Deskew” section below. These three enhancements allow cables 5+ meters in length to be driven
depending upon media and clock rate.
The DS90CR481/482 chipset may also be used in a non-DC
Balance mode. In this mode pre-emphasis is supported. In
this mode, the chipset is also compatible with 21 and 28-bit
Channel Link Receivers. See Figure 16 for the LVDS mapping.
NEW FEATURES DESCRIPTION
1. Pre-emphasis
Adds extra current during LVDS logic transition to reduce the
cable loading effects. Pre-emphasis strength is set via a DC
voltage level applied from min to max (0.75V to Vcc) at the
“PRE” pin. A higher input voltage on the ”PRE” pin increases
the magnitude of dynamic current during data transition. The
“PRE” pin requires one pull-up resistor (Rpre) to Vcc in order
to set the DC level. There is an internal resistor network,
which cause a voltage drop. Please refer to the tables below
to set the voltage level.
The waveshape at the Receiver input should not exhibit over
or undershoot with the proper amount of pre-emphasis set.
Too much pre-emphasis generates excess noise and increases power dissipation. Cables less than 2 meters in
length typically do not require pre-emphasis.
TABLE 1. Pre-emphasis DC voltage level with (Rpre)
Rpre
Resulting PRE Voltage
Effect
1MΩ or NC
0.75V
Standard LVDS
50kΩ
1.0V
9kΩ
1.5V
3kΩ
2.0V
1kΩ
2.6V
100Ω
Vcc
50% pre-emphasis
100% pre-emphasis
TABLE 2. Pre-emphasis needed per cable length
Frequency
PRE Voltage
Typical cable length
112MHz
1.0V
2 meters
112MHz
1.5V
5 meters
80MHz
1.0V
2 meters
80MHz
1.2V
5+ meters
66MHz
1.5V
7 meters
Note 9: This is based on testing with standard shield twisted pair cable. The amount of pre-emphasis will vary depending on the type of cable, length and operating
frequency.
2. DC Balance
In addition to data information an additional bit is transmitted
on every LVDS data signal line during each cycle as shown
in Figure 15. This bit is the DC balance bit (DCBAL). The
purpose of the DC Balance bit is to minimize the short- and
long-term DC bias on the signal lines. This is achieved by
selectively sending the data either unmodified or inverted.
The value of the DC balance bit is calculated from the
running word disparity and the data disparity of the current
word to be sent. The data disparity of the current word shall
be calculated by subtracting the number of bits of value 0
from the number of bits value 1 in the current word. Initially,
the running word disparity may be any value between +7 and
−6. The running word disparity shall be calculated as a
continuous sum of all the modified data disparity values,
where the unmodified data disparity value is the calculated
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data disparity minus 1 if the data is sent unmodified and 1
plus the inverse of the calculated data disparity if the data is
sent inverted. The value of the running word disparity shall
saturate at +7 and −6.
The value of the DC balance bit (DCBAL) shall be 0 when
the data is sent unmodified and 1 when the data is sent
inverted. To determine whether to send data unmodified or
inverted, the running word disparity and the current data
disparity are used. If the running word disparity is positive
and the current data disparity is positive, the data shall be
sent inverted. If the running word disparity is positive and the
current data disparity is zero or negative, the data shall be
sent unmodified. If the running word disparity is negative and
the current data disparity is positive, the data shall be sent
unmodified. If the running word disparity is negative and the
14
RSKM - RECEIVER SKEW MARGIN
(Continued)
RSKM is a chipset parameter and is explained in AN-1059 in
detail. It is the difference between the transmitter’s pulse
position and the receiver’s strobe window. RSKM must be
greater than the summation of: Interconnect skew, LVDS
Source Clock Jitter (TJCC), and ISI (if any). See Figure 13.
Interconnect skew includes PCB traces differences, connector skew and cable skew for a cable application. PCB trace
and connector skew can be compensated for in the design of
the system. Cable skew is media type and length dependant.
current data disparity is zero or negative, the data shall be
sent inverted. If the running word disparity is zero, the data
shall be sent inverted.
DC Balance mode is set when the BAL pin on the transmitter
is tied HIGH - see pin descriptions. DC Balancing is useful
on long cable applications which are typically greater than 5
meters in length.
3. Deskew
RSKMD - RECEIVER SKEW MARGIN WITH DESKEW
Deskew is supported in the DC Balance mode only (BAL =
high on DS90CR481). The “DESKEW” pin on the receiver
when set high will deskew a minimum of ± 1 LVDS data bit
time skew from the ideal strobe location between signals
arriving on independent differential pairs (pair-to-pair skew).
It is required that the “DS_OPT” pin on the Transmitter must
be applied low for a minimum of four clock cycles to complete the deskew operation. It is also required that this must
be performed at least once at any time after the PLLs have
locked to the input clock frequency. If power is lost, or if the
cable has been switched, this procedure must be repeated
or else the receiver may not sample the incoming LVDS data
correctly. When the receiver is in the deskew mode, all
receiver outputs are set to a LOW state. Setting the
“DESKEW” pin to low will disable the deskew operation and
allow the receiver to operation on a fixed data sampling
strobe. In this case, the ”DS_OPT” pin on the transmitter
must then be set high.
The DS_OPT pin at the input of the transmitter
(DS90CR481) is used to initiate the deskew calibration pattern. It must be applied low for a minimum of four clock
cycles in order for the receiver to complete the deskew
operation. For this reason, the LVDS clock signal with
DS_OPT applied high (active data sampling) shall be
1111000 or 1110000 pattern. During the deskew operation
with DS_OPT applied low, the LVDS clock signal shall be
1111100 or 1100000 pattern. The transmitter will also output
a series of 1111000 or 1110000 onto the LVDS data lines
(TxOUT 0-7) during deskew so that the receiver can automatically calibrated the data sampling strobes at the receiver
inputs. Each data channel is deskewed independently and is
tuned with a step size of 1/3 of a bit time over a range of +/−1
TBIT from the ideal strobe location. The Deskew feature
operates up to clock rates of 80 MHz only. If the Receiver is
enabled in the deskew mode, then it must be trained before
data transfer.
RSKMD is a chipset parameter and is applicable when the
DESKEW feature of the DS90CR482 is employed. It is the
difference between the receiver’s strobe window and the
ideal pulse locations. The DESKEW feature adjusts for skew
between each data channel and the clock channel. This
feature is supported up to 80MHz clock rate. RSKMD must
be greater than the summation of: Transmitter’s Pulse Position variance, LVDS Source Clock Jitter (TJCC), and ISI (if
any). See Figure 14. With DESKEW, RSKMD will be a
minimum of 25% of TBIT. Deskew compensates for interconnect skew which includes PCB traces differences, connector
skew and cable skew (for a cable application). PCB trace
and connector skew can be compensated for in the design of
the system. Note, cable skew is media type and length
dependant. Cable length may be limited by the RSKMD
parameter prior to the interconnect skew reaching 1 TBIT in
length due to ISI effects.
POWER DOWN
Both transmitter and receiver provide a power down feature.
When asserted current draw through the supply pins is
minimized and the PLLs are shut down. The transmitter
outputs are in TRI-STATE when in power down mode. The
receiver outputs are forced to a active LOW state when in
the power down mode. (See Pin Description Tables). The PD
pin should be driven HIGH to enable the device once VCC is
stable.
CONFIGURATIONS
The transmitter is designed to be connected typically to a
single receiver load. This is known as a point-to-point configuration. It is also possible to drive multiple receiver loads if
certain restrictions are made. Only the final receiver at the
end of the interconnect should provide termination across
the pair. In this case, the driver still sees the intended DC
load of 100 Ohms. Receivers connected to the cable between the transmitter and the final receiver must not load
down the signal. To meet this system requirement, stub
lengths from the line to the receiver inputs must be kept very
short.
CLOCK JITTER
The transmitter is designed to reject cycle-to-cycle jitter
which may be seen at the transmitter input clock. Very low
cycle-to-cycle jitter is passed on to the transmitter outputs.
Cycle-to-cycle jitter has been measured over frequency to
be less than 100 ps with input step function jitter applied.
This should be subtracted from the RSKM/RSKMD budget
as shown and described in Figure 13 and Figure 14. This
rejection capability significantly reduces the impact of jitter at
the TXinput clock pin, and improves the accuracy of data
sampling in the receiver. Transmitter output jitter is effected
by PLLVCC noise and input clock jitter - minimize supply
noise and use a low jitter clock source to limit output jitter.
The falling edge of the input clock to the transmitter is the
critical edge and is used by the PLL circuit.
CABLE TERMINATION
A termination resistor is required for proper operation to be
obtained. The termination resistor should be equal to the
differential impedance of the media being driven. This should
be in the range of 90 to 132 Ohms. 100 Ohms is a typical
value common used with standard 100 Ohm twisted pair
cables. This resistor is required for control of reflections and
also to complete the current loop. It should be placed as
close to the receiver inputs to minimize the stub length from
the resistor to the receiver input pins.
15
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DS90CR481/DS90CR482
Applications Information
DS90CR481/DS90CR482
Applications Information
Input Characteristics" table for specifications. In addition
undershoots in excess of the ABS MAX specifications are
not recommended. If the line between the host device and
the transmitter is long and acts as a transmission line, then
termination should be employed. If the transmitter is being
driven from a device with programmable drive strengths,
data inputs are recommended to be set to a weak setting to
prevent transmission line effects. The clock signal is typically
set higher to provide a clean edge that is also low jitter.
(Continued)
HOW TO CONFIGURE FOR BACKPLANE
APPLICATIONS
In a backplane application with differential line impedance of
100Ω the differential line pair-to-pair skew can controlled by
trace layout. The transmitter-DS90CR481 “DS_OPT” pin
may be set high. In a backplane application with short PCB
distance traces, pre-emphasis from the transmitter is typically not required. The “PRE” pin should be left open (do not
tie to ground). A resistor pad provision for a pull up resistor to
Vcc can be implemented in case pre-emphasis is needed to
counteract heavy capacitive loading effects.
UNUSED LVDS OUTPUTS
Unused LVDS output channels should be terminated with
100 Ohm at the transmitter’s output pin.
LVDS INTERCONNECT GUIDELINES
See AN-1108 and AN-905 for full details.
• Use 100Ω coupled differential pairs
HOW TO CONFIGURE FOR CABLE INTERCONNECT
APPLICATIONS
In applications that require the long cable drive capability.
The DS90CR481/DS90CR482 chipset is improved over prior
generations of Channel Link devices and offers higher bandwidth support and longer cable drive with the use of DC
balanced data transmission, pre-emphasis. Cable drive is
enhanced with a user selectable pre-emphasis feature that
provides additional output current during transitions to counteract cable loading effects. This requires the use of one pull
up resistor to Vcc; please refer to Table 1 to set the level
needed. Optional DC balancing on a cycle-to-cycle basis, is
also provided to reduce ISI (Inter-Symbol Interference) for
long cable applications. With pre-emphasis and DC balancing, a low distortion eye-pattern is provided at the receiver
end of the cable. These enhancements allow cables 5+
meters in length to be driven. Depending upon clock rate and
the media being driven, the cable Deskew feature may also
be employed - see discussion on DESKEW, RSKM and
RSKMD above.
•
•
•
•
•
•
•
— 3S = space to TTL signal
Minimize the number of VIA
Use differential connectors when operating above
500Mbps line speed
Maintain balance of the traces
Minimize skew within the pair
Minimize skew between pairs
Terminate as close to the RXinputs as possible
RECEIVER OUTPUT DRIVE STRENGTH
The DS90CR482 output specify a 8pF load, VOH and VOL
are tested at ± 2mA, which is intended for only 1 or maybe
2 loads. If high fan-out is required or long transmission line
driving capability, buffering the receiver output is recommended. Receiver outputs do not support / provide a TRISTATE function.
SUPPLY BYPASS RECOMMENDATIONS
Bypass capacitors must be used on the power supply pins.
Different pins supply different portions of the circuit, therefore capacitors should be nearby all power supply pins except as noted in the pin description table. Use high frequency ceramic (surface mount recommended) 0.1µF
capacitors close to each supply pin. If space allows, a
0.01µF capacitor should be used in parallel, with the smallest value closest to the device pin. Additional scattered
capacitors over the printed circuit board will improve decoupling. Multiple (large) via should be used to connect the
decoupling capacitors to the power plane. A 4.7 to 10 µF bulk
cap is recommended near the PLLVCC pins and also the
LVDSVCC (pin #40) on the Transmitter. Connections between the caps and the pin should use wide traces.
DS90CR483/484
The DS90CR481/2 chipset is electrically similar to the
DS90CR483/4. The DS90CR481/2 differ only in the control
circuit of the internal PLL and are specified for 65 to 112 MHz
operation. The devices will directly inter-operate within the
scope of the respective datasheets.
FOR MORE INFORMATION
Channel Link Applications Notes currently available:
• AN-1041 Introduction to Channel Link
• AN-1059 RSKM Calculations
• AN-1108 PCB and Interconnect Guidelines
• AN-905 Differential Impedance
• National’s LVDS Owner’s Manual
INPUT SIGNAL QUALITY REQUIREMENTS TRANSMITTER
The input signal quality must comply to the datasheet requirements, please refer to the "Recommended Transmitter
www.national.com
Use the S/2S/3S rule in spacings
— S = space between the pair
— 2S = space between pairs
16
DS90CR481/DS90CR482
DS90CR481 Pin Descriptions—Channel Link Transmitter
Pin Name
I/O
Description
TxIN
I
TTL level input. (Note 10).
TxOUTP
O
Positive LVDS differential data output.
TxOUTM
O
Negative LVDS differential data output.
TxCLKIN
I
TTL level clock input. The rising edge acts as data strobe.
TxCLKP
O
Positive LVDS differential clock output.
TxCLKM
O
Negative LVDS differential clock output.
PD
I
TTL level input. Assertion (low input) tri-states the outputs, ensuring low
current at power down. (Note 10).
PLLSEL
I
PLL range select. This pin must be tied to VCC. NC or tied to Ground is
reserved for future use. (Note 10)
PRE
I
Pre-emphasis “level” select. Pre-emphasis is active when input is tied to VCC
through external pull-up resistor. Resistor value determines Pre-emphasis
level (See Applications Information Section). For normal LVDS drive level
(No Pre-emphasis) leave this pin open (do not tie to ground).
DS_OPT
I
Cable Deskew performed when TTL level input is low. No TxIN data is
sampled during Deskew. To perform Deskew function, input must be held
low for a minimum of 4 clock cycles. The Deskew operation is normally
conducted after the TX and RX PLLs have locked. It should also be
conducted after a system reset, or a reconfiguration event. It must be
peformed at least once when "DESKEW" is enabled. (Note 10)
BAL
I
TTL level input. This pin was previously labeled as VCC, which enabled the
DC Balance function. But when tied low or left open, the DC Balance
function is disabled. Please refer to (Figures 15, 16) for LVDS data bit
mapping respectively. (Note 10), (Note 12)
VCC
I
Power supply pins for TTL inputs and digital circuitry. Bypass not required
on Pins 20 and 21.
GND
I
Ground pins for TTL inputs and digital circuitry.
PLLVCC
I
Power supply pin for PLL circuitry.
PLLGND
I
Ground pins for PLL circuitry.
LVDSVCC
I
Power supply pin for LVDS outputs.
LVDSGND
I
Ground pins for LVDS outputs.
NC
No Connect. Make NO Connection to these pins - leave open.
Note 10: Inputs default to “low” when left open due to internal pull-down resistor.
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DS90CR481/DS90CR482
DS90CR482 Pin Descriptions—Channel Link Receiver
Pin Name
RxINP
I/O
Description
I
Positive LVDS differential data inputs.
RxINM
I
Negative LVDS differential data inputs.
RxOUT
O
TTL level data outputs. In PowerDown (PD = Low) mode, receiver outputs are
forced to a Low state.
RxCLKP
I
Positive LVDS differential clock input.
RxCLKM
I
Negative LVDS differential clock input.
RxCLKOUT
O
TTL level clock output. The rising edge acts as data strobe.
PLLSEL
I
PLL range select. This pin must be tied to VCC. NC or tied to Ground is reserved for
future use. (Note 10)
DESKEW
I
Deskew / Oversampling “on/off” select. When using the Deskew / Oversample
feature this pin must be tied to VCC. Tieing this pin to ground disables this feature.
(Note 10) Deskew is only supported in the DC Balance mode.
PD
I
TTL level input. When asserted (low input) the receiver outputs are Low. (Note 10)
VCC
I
Power supply pins for TTL outputs and digital circuitry. Bypass not required on Pins
6 and 77.
GND
I
Ground pins for TTL outputs and digital circuitry.
PLLVCC
I
Power supply for PLL circuitry.
PLLGND
I
Ground pin for PLL circuitry.
LVDSVCC
I
Power supply pin for LVDS inputs.
LVDSGND
I
Ground pins for LVDS inputs.
NC
No Connect. Make NO Connection to these pins - leave open.
Note 11: These receivers have input fail-safe bias circuitry to guarantee a stable receiver output for floating or terminated receiver inputs. Under test conditions
receiver inputs will be in a HIGH state. If the cable interconnect (media) are disconnected which results in floating/terminated inputs, the outputs will remain in the
last valid state.
Note 12: The DS90CR482 is design to automatically detect the DC Balance or non-DC Balance transmitted data from the DS90CR481 and deserialize the LVDS
data according to the define bit mapping.
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18
DS90CR481/DS90CR482
DS90DR481 — Connection Diagram
Transmitter - DS90CR481 - TQFP - Top View
20009106
19
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DS90CR481/DS90CR482
DS90CR482 – Connection Diagram
Receiver - DS90CR482 - TQFP - Top View
20009107
www.national.com
20
inches (millimeters) unless otherwise noted
Dimensions show in millimeters only
Order Number DS90CR481VJD or DS90CR482VS
NS Package Number VJD100A
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.
For the most current product information visit us at www.national.com.
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DS90CR481/DS90CR482 48-Bit LVDS Channel Link SER/DES – 65 - 112 MHz
Physical Dimensions