LTC1688IS [LINEAR_DIMENSIONS]
100Mbps RS485 Hot Swapable Quad Drivers; 100Mbps的RS485热可插拔Quad驱动程序
| 型号： | LTC1688IS |
| 厂家： | 
Linear Dimensions |
| 描述： | 100Mbps RS485 Hot Swapable Quad Drivers |
| 文件： | 总12页 (文件大小：229K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1688/LTC1689
100Mbps RS485
Hot Swapable Quad Drivers
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DESCRIPTIO
FEATURES
■
Ultrahigh Speed: 100Mbps
The LTC®1688/LTC1689 are ultrahigh speed, differential
bus/line drivers that can operate at data rates up to
100Mbps. Propagation delay is guaranteed at 8ns ±4ns
over the full operating temperature range. These devices
operate over the full RS485 common mode range (–7V
to 12V), and also meet RS422 requirements.
■
Guaranteed Propagation Delay: 8ns ±4ns
Over Temperature
■
Low Channel-to-Channel Skew: 500ps Typ
Hot SwapTM Capable
■
■
■
■
50Mbps Operation with VDD = 3V
Low tPLH/tPHL Skew: 500ps Typ
Driver Outputs Maintain High Impedance in
Three-State or with Power Off
Short-Circuit Protected: 3mA Typ Output Current
for an Indefinite Short
Thermal Shutdown Protected
Single 5V or 3V Supply
Pin Compatible with LTC486/LTC487
The driver outputs are Hot Swap capable, maintaining
backplane data integrity during board insertion and
removal. The drivers feature three-state outputs, maintain-
ing high impedance over the entire common mode range
(–7V to 12V). Outputs also remain high impedance during
power-up and with the power off. A short-circuit feature
detects bus contention and substantially reduces driver
output current. Thermal shutdown circuitry protects the
parts from excessive power dissipation.
■
■
■
■
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APPLICATIO S
■
The LTC1688 allows all four drivers to be enabled together,
while the LTC1689 allows two drivers at a time to be
enabled.
High Speed RS485 Twisted-Pair Drivers
High Speed Backplane Drivers
Complementary Clock Drivers
STS-1/OC-1 Data Drivers
SCSI Drivers
■
■
The LTC1688/LTC1689 operate from a single 5V or 3V
supply and draw only 9mA of supply current.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
■
■
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TYPICAL APPLICATIO
20ns Pulse Across 100 Feet
of Category 5 UTP
2V/DIV
2V/DIV
50Mbps RS485 Data Connection
CABLE DELAY
100Ω
100Ω
DRIVER
RECEIVER
100 FT CATEGORY 5 UTP
2V/DIV
5V/DIV
1/4 LTC1688
1/4 LTC1518
1688/89 TA01
20ns/DIV
1688/89 TA02
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LTC1688/LTC1689
W W W
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ABSOLUTE AXI U RATI GS
/O
PACKAGE RDER I FOR ATIO
(Note 1)
Supply Voltage (VDD)................................................ 7V
Enable Input Voltages ................. –0.5V to (VDD + 0.5V)
Enable Input Currents ..................... –100mA to 100mA
Driver Input Voltages .................. –0.5V to (VDD + 0.5V)
Driver Output Voltages ................. (–12V + VDD) to 12V
Driver Input Currents ...................... –100mA to 100mA
Short-Circuit Duration (VOUT: –7V to 10V) ...... Indefinite
Operating Temperature Range
LTC1688C/LTC1689C ............................. 0°C to 70°C
LTC1688I/LTC1689I .......................... –40°C to 85°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
ORDER PART
NUMBER
DI1
DO1A
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
DD
DI4
LTC1688CS
LTC1689CS
LTC1688IS
LTC1689IS
DO1B
DO4A
DO4B
ENB (EN34*)
DO3B
DO3A
DI3
EN (EN12*)
DO2B
DO2A
DI2
GND
S PACKAGE
16-LEAD PLASTIC SO
*LTC1689 ONLY
TJMAX = 150°C, θJA = 90°C/ W
Consult factory for parts specified with wider operating temperature ranges.
DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
SYMBOL PARAMETER
CONDITIONS
= 5V, Per Driver, T = 25°C, Unless Otherwise Noted (Note 2)
A
MIN
TYP
MAX
UNITS
V
V
V
DD
Differential Driver Output (Unloaded)
Differential Driver Output (With Load)
I
= 0
●
V
DD
V
OD1
OD2
OUT
R = 50Ω (RS422)
R = 25Ω (RS485), Figure 1
●
●
2
1.5
V
V
3.0
0.2
∆V
OD
Change in Magnitude of Driver Differential
Output Voltage for Complementary
Output States
R = 25Ω or 50Ω, Figure 1
●
V
V
Driver Common Mode Output Voltage
R = 25Ω or 50Ω, Figure 1
R = 25Ω or 50Ω, Figure 1
●
●
2
2
3
V
V
OC
∆ V
Change in Magnitude of Driver Common
Mode Output Voltage for Complementary
Output States
0.2
OC
V
V
Input High Voltage
Input Low Voltage
Input Current
EN, ENB, EN12, EN34, DI
EN, ENB, EN12, EN34, DI
EN, ENB, EN12, EN34, DI
●
●
●
●
V
V
IH
IL
0.8
±1
I
I
µA
µA
IN1
OZ
Three-State (High Impedance)
Output Current
V
= –7V to 12V
±2
±200
OUT
I
I
I
Supply Current of Entire Device
No Load, Digital Input Pins = 0V or V
●
●
●
9
18
mA
mA
mA
DD
DD
Driver Short-Circuit Current, V
Driver Short-Circuit Current, V
= HIGH
= LOW
V
V
= –7V to 10V
= –7V to 10V
±
±
20
20
OSD1
OSD2
OUT
OUT
OUT
OUT
V
V
V
= 3V, Per Driver, T = 25°C, Unless Otherwise Noted (Note 2)
A
DD
Differential Driver Output (Unloaded)
Differential Driver Output (With Load)
I
= 0
●
●
V
V
OD1
OD2
OUT
DD
R = 50Ω (RS422)
R = 25Ω (RS485), Figure 1
1.5
0.1
V
V
0.65
2.0
∆V
Change in Magnitude of Driver Differential
Output Voltage for Complementary
Output States
R = 25Ω or 50Ω, Figure 1
V
OD
V
Driver Common Mode Output Voltage
R = 25Ω or 50Ω, Figure 1
1.3
V
OC
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LTC1688/LTC1689
The ● denotes the specifications which apply over the full operating
DC ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
∆ V
Change in Magnitude of Driver Common
Mode Output Voltage for Complementary
Output States
R = 25Ω or 50Ω, Figure 1
0.1
V
OC
V
V
Input High Voltage
Input Low Voltage
Input Current
EN, ENB, EN12, EN34, DI
●
●
●
●
1.4
V
V
IH
IL
EN, ENB, EN12, EN34, DI
0.5
±1
I
I
EN, ENB, EN12, EN34, DI (Note 3)
µA
µA
IN1
OZ
Three-State (High Impedance)
Output Current
V
= –7V to 10V (Note 3)
±1
±200
OUT
I
I
I
Supply Current of Entire Device
No Load, Digital Input Pins = 0V or V
5
mA
mA
mA
DD
DD
Driver Short-Circuit Current, V
Driver Short-Circuit Current, V
= HIGH
= LOW
V
V
= –7V to 8V (Note 3)
= –7V to 8V (Note 3)
●
●
±20
±20
OSD1
OSD2
OUT
OUT
OUT
OUT
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The ● denotes the specifications which apply over the full operating
SWITCHING CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C.
SYMBOL PARAMETER CONDITIONS
= 5V, T = 25 C, Unless Otherwise Noted (Note 2)
MIN
TYP
MAX
UNITS
V
°
DD
A
t
, t
Driver Input-to-Output Propagation Delay
Driver Output-to-Output Skew
Driver Rise/Fall Time
R
= 50Ω, C = C = 25pF,
●
4
8
500
2
12
ns
ps
ns
PLH PHL
DIFF
L1
L2
Figures 2, 4
t
R
DIFF
= 50Ω, C = C = 25pF,
SKEW
L1
L2
Figures 2, 4
t , t
R
DIFF
Figures 2, 4
= 50Ω, C = C = 25pF,
r
f
L1
L2
t
t
t
t
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable from Low
C = 25pF, S2 Closed, Figures 3, 5
●
●
●
●
●
●
●
10
10
25
25
35
35
ns
ns
ZH
ZL
LZ
HZ
L
C = 25pF, S1 Closed, Figures 3, 5
L
C = 15pF, S1 Closed, Figures 3, 5
L
65
ns
Driver Disable from High
C = 15pF, S2 Closed, Figures 3, 5
L
65
ns
C
Maximum Output Capacitive Load
Maximum Data Rate
(Note 3)
(Note 3)
(Note 3)
200
pF
L(MAX)
100
Mbps
ns
Maximum Driver Input Rise/Fall Time
500
V
= 3V, T = 25°C, Unless Otherwise Noted (Note 2)
A
DD
t
, t
Driver Input-to-Output Propagation Delay
Driver Output-to-Output Skew
Driver Rise/Fall Time
R
= 50Ω, C = C = 25pF,
11
1
ns
ns
ns
PLH PHL
DIFF
L1
L2
Figures 2, 4
t
R
DIFF
= 50Ω, C = C = 25pF,
SKEW
L1
L2
Figures 2, 4
t , t
R
DIFF
= 50Ω, C = C = 25pF,
4
r
f
L1
L2
Figures 2, 4
t
t
t
t
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable from Low
C = 25pF, S2 Closed, Figures 3, 5
25
25
50
50
ns
ns
ZH
ZL
LZ
HZ
L
C = 25pF, S1 Closed, Figures 3, 5
L
C = 15pF, S1 Closed, Figures 3, 5
L
ns
Driver Disable from High
C = 15pF, S2 Closed, Figures 3, 5
L
ns
C
Maximum Output Capacitive Load
Maximum Data Rate
(Note 3)
●
●
200
500
pF
L(MAX)
50
Mbps
ns
Maximum Driver Input Rise/Fall Time
(Note 3)
Note 2: All currents into the device pins are positive; all currents out of the
device pins are negative.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 3: Guaranteed by design or correlation, but not tested.
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LTC1688/LTC1689
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TYPICAL PERFORMANCE CHARACTERISTICS
Propagation Delay
vs Temperature
Propagation Delay
vs Load Capacitance
14
12
10
8
14
V
= 3V
= 5V
DD
DD
V
= 3V
= 5V
12
10
8
DD
V
DD
V
6
6
4
4
V
= 0V TO 3V
DIFF
= 25°C
V
= 0V TO 3V
DIFF
= 25pF
DI
DI
R
T
= 50Ω
R
C
= 50Ω
2
2
A
L
0
0
0
10
20
30
40
50
60
0
20
40
60
80
100
LOAD CAPACITANCE (pF)
TEMPERATURE (°C)
1688/89 G02
1688/89 G01
Three-State Output Current
Supply Current vs Data Rate
250
200
150
100
50
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
V
= 5V
DD
4 DRIVERS
SWITCHING
V
= –7V
OUT
V
= 5V
DIFF
= 25pF, PER DRIVER
= 25°C
DD
R
= 50Ω, PER DRIVER
C
T
L
A
1 DRIVER
SWITCHING
V
= 12V
OUT
0
0
20
40
60
80
100
120
0
20
40
60
80
100
DATA RATE (Mbps)
TEMPERATURE (°C)
1688/89 G03
1688/89 G04
VOD2 vs Temperature
IDD vs Temperature
2.5
2.0
1.5
1.0
0.5
0
180
160
140
120
100
80
4 DRIVERS LOADED
V
= 5V
= 3V
DD
1 DRIVER LOADED
V
DD
60
40
V
= 5V
DIFF
DD
R
= 50Ω, PER DRIVER
20
R
0
= 50Ω
0.1Mbps
DIFF
0
20
40
60
80
100
0
20
40
60
80
100
TEMPERATURE (°C)
TEMPERATURE (°C)
1688/89 G05
1688/89 G06
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LTC1688/LTC1689
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PIN FUNCTIONS
DI1 (Pin 1): Driver 1 Input. Do not float.
DO1A (Pin 2): Driver 1 Noninverting Output.
DO1B (Pin 3): Driver 1 Inverting Output.
DI3 (Pin 9): Driver 3 Input. Do not float.
DO3A (Pin 10): Driver 3 Noninverting Output.
DO3B (Pin 11): Driver 3 Inverting Output.
EN (Pin 4, LTC1688): High True Enable Pin, enables all
four drivers. A low on Pin 4 and a high on Pin 12 will put
all driver outputs into a high impedance state. See
Function Tables for details. Do not float.
ENB (Pin 12, LTC1688):Low True Enable Pin, enables all
four drivers. A low on Pin 4 and a high on Pin 12 will put
all driver outputs into a high impedance state. See
Function Tables for details. Do not float.
EN12 (Pin 4, LTC1689): Enables Drivers 1 and 2. A low on
Pin 4 will put the outputs of drivers 1 and 2 into a high
impedance state. See Function Tables for details. Do not
float.
EN34 (Pin 12, LTC1689): Enables Drivers 3 and 4. A low
on Pin 12 will put the outputs of drivers 3 and 4 into a high
impedance state. See Function Tables for details. Do not
float.
DO2B (Pin 5): Driver 2 Inverting Output.
DO2A (Pin 6): Driver 2 Noninverting Output.
DI2 (Pin 7): Driver 2 Input. Do not float.
DO4B (Pin 13): Driver 4 Inverting Output.
DO4A (Pin 14): Driver 4 Noninverting Output.
DI4 (Pin 15): Driver 4 Input. Do not float.
GND (Pin 8): Ground Connection. A good ground plane is
recommended for all applications.
VDD (Pin 16): Power Supply Input. This pin should be
bypassed with a 0.1µF ceramic capacitor as close to the
pin as possible. Recommended: VDD = 3V to 5.25V.
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FU CTIO TABLES
LTC1688
LTC1689
INPUTS
OUTPUTS
INPUTS
OUTPUTS
DI
H
L
EN
H
H
X
ENB
X
OUTA
OUTB
DI
H
L
EN12/EN34
OUTA
H
OUTB
L
H
L
L
H
H
H
L
X
L
H
H
L
L
H
L
X
HI-Z
HI-Z
X
L
L
H
X
L
H
HI-Z
HI-Z
TEST CIRCUITS
EN (EN12)
DRIVER
A
S1
S2
C
L1
R
V
DD
A
B
V
OD
500Ω
OUTPUT
UNDER TEST
DI
R
R
DIFF
V
OC
B
C
L
C
L2
1688/89 TC01
1688/89 TC02
1688/89 TC03
ENB (EN34)
Figure 1. Driver DC Test Load
Figure 2. Driver Timing Test Circuit
Figure 3. Driver Timing Test Load
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LTC1688/LTC1689
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SWITCHI G TI E WAVEFOR S
3V
f = 1MHz; t < 3ns; t < 3ns
DI
1.5V
1.5V
PHL
r
f
0V
B
t
t
PLH
V
O
A
t
1/2 V
t
SKEW
1/2 V
SKEW
O
O
V
O
O
90%
90%
V
= V(A) – V(B)
DIFF
10%
10%
–V
1688/89 F04
t
t
f
r
Figure 4. Driver Propagation Delays
3V
f = 1MHz; t ≤ 3ns; t ≤ 3ns
EN
r
f
1.5V
1.5V
LZ
0V
5V
t
ZL
t
A, B
V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
1/2 V
DD
DD
0.5V
0.5V
OL
V
OH
A, B
1/2 V
0V
1688/89 F05
t
t
HZ
ZH
Figure 5. Driver Enable and Disable Times
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APPLICATIONS INFORMATION
The LTC1688/LTC1689 family of RS485 quad differential ElectricalCharacteristicstablefor3VDCandACspecifica-
drivers employs a novel architecture and fabrication pro- tions). Figure 6 shows waveforms of an LTC1689 driving
cess that allows ultra high speed operation (100Mbps) a receiver using 100 feet of Category 5 UTP. Both parts are
andHotSwapcapabilitywhilemaintainingtheruggedness operating at 3V supply.
of RS485 operation (three-state outputs can float from
–7V to 12V with a single 5V supply). Unlike typical CMOS
drivers whose propagation delay can vary as much as
LTC1689 OUTPUT
500%, the propagation delay of the LTC1688/LTC1689
2V/DIV
drivers will only vary by ±50% (a narrow ±4ns window).
FAR END OF CABLE
This performance is achieved by designing the input stage
2V/DIV
of each driver to have minimum propagation delay shift
over temperature and from part to part.
RECEIVER OUTPUT
The LTC1688/LTC1689 have an ESD rating of 6kV human
body model.
5V/DIV
50Mbps with 3V Operation
20ns/DIV
1688/89 F06
The LTC1688/LTC1689 are designed to operate with a 3V
power supply and still achieve 50Mbps operation (see
Figure 6. 3V High Speed Data Transmission
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LTC1688/LTC1689
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APPLICATIONS INFORMATION
Hot Swap Capability
VDD/2, this circuitry shuts off the big outputs and turns on
3mA current sources instead (the converse applies to the
“B” output). Note that these 3mA current sources are
active only during a short-circuit fault. During normal
operation, the regular output drivers can sink/source
>50mA.
With the LTC1688/LTC1689 outputs disabled but con-
nectedtothetransmissionline,theusercanturnon/offthe
power to the LTC1688/LTC1689 without inducing a differ-
ential signal on the transmission line. Due to capacitive
coupling, however, there can be a small amount of com-
mon mode charge injected into both disabled outputs,
whichisnotseenasadifferentialsignal(seeFigure7). The
disabled outputs can be hooked/unhooked to a transmis-
sion line without disturbing the existing data.
A time-out period of about 50ns is required before a short-
circuit fault is detected. This circuitry might falsely detect
a short under excess output capacitive load (>200pF).
Additionally, a short might go undetected if there is too
muchresistance(userinsertedorcableparasitic)between
the physical short and the actual driver output.
Output Short-Circuit Protection
Inadditionto100MbpsoperationandHotSwapcapability,
the LTC1688/LTC1689 employ voltage sensing short-
circuit protection that reduces short-circuit current by
over an order of magnitude. For a given input polarity, this
circuitry determines what the correct output level should
be. If the output level is different from the expected, the
circuitry shuts off the big output devices. Much smaller
devices are instead turned on, thus producing a much
smaller short-circuit output current (3mA typical). For
example,ifthedriverinputis>2V,itexpectsthe“A”output
to be >3.25V and the “B” output to be less than 1.75V. If
the “A” output is subsequently shorted to a voltage below
For cables with the recommended RS485 termination (no
DCbiasonthecable, seeFigure8), theLTC1688/LTC1689
willautomaticallycomeoutofshort-circuitmodeoncethe
physical short has been removed.
To prevent permanent damage to the part, the maximum
allowable short is 10V (not 12V). Note that during a short,
the voltage right at the pin should not ring to a voltage
higher than 12V. Instability could surface if the short is
made with long leads (parasitic inductance). Once the
short is removed, the instability will disappear.
A OUTPUT
B OUTPUT
Figure 7. Common Mode Charge Injection During Hot Swapping
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LTC1688/LTC1689
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APPLICATIONS INFORMATION
Cable Termination
Enable Pins
The recommended cable termination for use with the
LTC1688/LTC1689isasingleresistoracrossthetwoends
of a transmission cable (see Figure 8). When PC traces are
used as the transmission line, its characteristic imped-
ance should be chosen close to 100Ω in order to better
matchthespecifiedtimingcharacteristicsoftheLTC1688/
LTC1689. Category 5 unshielded twisted pair can be used
overshortdistancesatthemaximumdatarates(100Mbps).
For point-to-point configurations (see Figure 9), a single
resistor across the cable at the receiver end is sufficient.
A single resistor termination lowers power consumption
and increases the differential output signal. See Enable
Pins section for cable terminations with a DC bias.
For cable terminations with a DC bias (such as High
Voltage Differential SCSI, see Figure 10), the driver out-
puts must be disabled for at least 200ns after power-up.
This ensures that the driver outputs do not disturb the
cable upon power-up. It also ensures the correct output
start-up conditions. When there is an output short fault
condition and the cable has a DC biased termination, such
as Figure 10, the driver outputs must be disabled for at
least 200ns after the short has been removed. Recall that
for transmission lines that have the recommended RS485
singleresistortermination(Figures8and9),theLTC1688/
LTC1689 will come out of a short-circuit fault condition
automatically without having to disable the outputs.
1/4 LTC1519
100Ω
100Ω
100Ω
1/4 LTC1688
1/4 LTC1518
1/4 LTC1689
1/4 LTC1518
1688/89 F08
1688/89 F09
Figure 8. Multipoint Transmission
Figure 9. Point-to-Point Transmission
TERM POWER
TERM POWER
DE
DI
330Ω
150Ω
330Ω
150Ω
1/4 LTC1688
1/4 LTC1518
330Ω
330Ω
1/4 LTC1518
1688/89 F10
Figure 10. DC-Biased Termination
(Recommended for SCSI Applications Only)
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LTC1688/LTC1689
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APPLICATIONS INFORMATION
High Speed Twisted-Pair Transmission
High Speed Backplane Transmission
Data rates up to 100Mbps can be transmitted over short
distancesusingCategory5UTP(unshieldedtwistedpair).
The cable distance will determine the maximum data rate.
Figures 11 and 12 show an 8ns pulse propagating over 25
feetofCategory5UTP.Noticehowthecableattenuatesthe
signal. Lucent Technologies’ BRF2A and BRS2A receivers
are recommended for these ultrahigh speed applications.
TheLTC1688/LTC1689canbeusedinbackplanepoint-to-
point and multipoint applications. At high data rates,
signals should be routed differentially and PC traces
should be terminated (see Figure 13). Note that the RS485
specificationcallsforcharacteristicimpedancesnear100Ω;
therefore, PC trace transmission lines should be designed
with an impedance close to 100Ω. If trace impedance is
much less than 100Ω, and the trace is double terminated,
the part will experience excess heating. The propagation
delay could then fall outside the specified window. The
LT1720 dual UltraFastTM comparator is a good choice for
high data rate backplane applications.
2V/DIV
DRIVER INPUT
2V/DIV
2V/DIV
DRIVER OUTPUT
UltraFast is a trademark of Linear Technology Corporation.
RECEIVER INPUT
+
5V/DIV
100Ω
100Ω
RECEIVER OUTPUT
DRIVER
RECEIVER
–
25 FT CATEGORY 5 UTP
10ns/DIV
1/4 LTC1688
1688/89 F11
1688/89 F12
Figure 12. 100Mbps Differential Data Connection
Figure 11. 8ns Pulse Over 25 Feet Category 5 UTP
1/4 LTC1688
DRIVER
1/2 LT1720
BACKPLANE
100Ω
RECEIVER
TRANSMISSION LINE
1688/89 F13
Figure 13. 100Mbps Backplane Transmission
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9
LTC1688/LTC1689
U
W U U
APPLICATIONS INFORMATION
Layout Considerations
Driver and receiver bandwidth affects the maximum data
rateonlyoverdistancesoflessthan100', evenforthebest
cables. The LTC1688/LTC1689 RS485 drivers and
LTC1518/LTC1519 52Mbps RS485 receivers are the fast-
est in the industry. The LTC1688/LTC1689 drivers can
reach speeds over 100Mbps, with a rise and fall time of
just 2ns. At speeds in excess of 52Mbps, the non-RS485
Lucent Technologies’ BRF2A receiver is recommended.
A ground plane is recommended when using high fre-
quency devices like the LTC1688/LTC1689. A 0.1µF
ceramic bypass capacitor less than 0.25 inch away from
the VDD pin is also recommended. Special care should be
taken to route the differential outputs very symmetrically
inordertoobtainthesameparasiticcapacitancesandthus
maintain good propagation delay skew.
Detailed information on data rate vs cable length is pro-
vided by the cable manufacturer. They characterize their
cables for bit rate and 0% to 50% rise time vs cable length,
allowing a rapid comparison of various cable types.
Parasiticcapacitancefromeachinputtoitscorresponding
outputs should also be minimized. Any excess capaci-
tance could result in slower operation or even instability.
Channel output pairs should be kept away from other
output pairs to avoid parasitic coupling.
The following oscilloscope waveforms illustrate how a
cable attenuates the signal and slows its rise time at
different lengths. Also shown are the driver input and
receiver output.
Data Rate vs Cable Length
Cable length and quality limit the maximum data rate in a
twisted pair system. Category 5 unshielded twisted pair is
a good choice for high speed data transmission, as it
exhibits superior bandwidth over other cables of similar
cost.
DRIVER INPUT
CABLE DELAY
RECEIVER INPUT
2V/DIV
RECEIVER OUTPUT
100Ω
100Ω
DRIVER
RECEIVER
CATEGORY 5 CABLE
UNDER TEST
1/4 LTC1688
1/4 LTC1689
2µs/DIV
1688/89 F15
1688/89 F14
Figure 14. Test Circuit for Cable Speed Evaluation
Figure 15. 4000 Feet, 0.5Mbps, LTC1518 Receiver
DRIVER INPUT
CABLE DELAY
RECEIVER INPUT
2V/DIV
2V/DIV
RECEIVER OUTPUT
2µs/DIV
1688/89 F16
500ns/DIV
1688/89 F17
Figure 16. 4000 Feet, 1Mbps, LTC1518 Receiver
Figure 17. 1000 Feet, 2Mbps, LTC1518 Receiver
16889fa
10
LTC1688/LTC1689
U
W U U
APPLICATIONS INFORMATION
2V/DIV
2V/DIV
2V/DIV
2V/DIV
500ns/DIV
1688/89 F18
1µs/DIV
1688/89 F19
Figure 18. 1000 Feet, 5Mbps, LTC1518 Receiver
Figure 19. 1000 Feet, 1Mbps, LTC1518 Receiver
RECEIVER INPUT
2V/DIV
100ns/DIV
1688/89 F20
50ns/DIV
1688/89 F21
Figure 20. 200 Feet, 20Mbps, LTC1518 Receiver
Figure 21. 200 Feet, 33Mbps, LTC1518 Receiver
RECEIVER INPUT
2V/DIV
50ns/DIV
1688/89 F22
10ns/DIV
1688/89 F23
Figure 22. 100 Feet, 50Mbps, LTC1518 Receiver
Figure 23. 25 Feet, 100Mbps, BRF2A Receiver
16889fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LTC1688/LTC1689
PACKAGE DESCRIPTION
U
S Package
16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
.386 – .394
(9.804 – 10.008)
.045 ±.005
NOTE 3
.050 BSC
16
N
15
14
13
12
11
10
9
N
1
.245
MIN
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
2
3
N/2
N/2
8
.030 ±.005
TYP
RECOMMENDED SOLDER PAD LAYOUT
2
3
5
6
7
1
4
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0° – 8° TYP
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
.016 – .050
(0.406 – 1.270)
S16 0502
NOTE:
1. DIMENSIONS IN
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
RELATED PARTS
PART NUMBER
LTC486/LTC487
LT®1394
DESCRIPTION
COMMENTS
Low Power Quad RS485 Drivers
110µA Typ Supply Current, 10Mbps, –7V to 12V Common Mode Range
6mA Typ Supply Current, Ground Sensing on Single Supply
52Mbps, Pin Compatible with LTC488/LTC489
7ns UltraFast Single Supply Comparator
High Speed, Precision Quad RS485 Receivers
High Speed, Precision Quad Differential Line Receiver
High Speed, Precision RS485 Transceiver
LTC1518/LTC1519
LTC1520
Single Supply, 18ns Propagation Delay, 100mV Threshold
52Mbps, Pin Compatible with LTC485
LTC1685
LTC1686/LTC1687
LT1720
High Speed, Precision RS485 Full-Duplex Transceivers 52Mbps, Pin Compatible with LTC490/LTC491
Dual 4.5ns UltraFast Single Supply Comparator 4mA per Comparator, Optimized for 3V or 5V Operation
16889fa
LT/TP 1003 1K REV A • PRINTED IN THE USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 1999
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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