LTC1686CS8#PBF [Linear]
LTC1686 - 52Mbps Precision Delay RS485 Fail-Safe Transceivers; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C;
| 型号： | LTC1686CS8#PBF |
| 厂家： | 
Linear |
| 描述： | LTC1686 - 52Mbps Precision Delay RS485 Fail-Safe Transceivers; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C 驱动 光电二极管 接口集成电路 驱动器 |
| 文件： | 总12页 (文件大小：181K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1686/LTC1687
52Mbps Precision Delay
RS485 Fail-Safe Transceivers
U
DESCRIPTION
FEATURES
The LTC®1686/LTC1687 are high speed, precision delay,
full-duplex RS485 transceivers that can operate at data
rates as high as 52Mbps. The devices also meet the
requirements of RS422.
■
Precision Propagation Delay Over Temperature:
Receiver/Driver: 18.5ns
High Data Rate: 52Mbps
Low tPLH/tPHL Skew:
±3.5ns
■
■
Receiver/Driver: 500ps Typ
A unique architecture provides very stable propagation
delays and low skew over a wide common mode and
ambient temperature range.
■
■
–7V to 12V RS485 Input Common Mode Range
Guaranteed Fail-Safe Operation Over the Entire
Common Mode Range
High Input Resistance: ≥22k, Even When Unpowered
Short-Circuit Protected
Thermal Shutdown Protected
Driver Maintains High Impedance in Three-State or
with Power Off
Single 5V Supply
Pin Compatible with LTC490/LTC491
45dB CMRR at 26MHz
■
■
■
■
The driver and receiver feature three-state outputs, with
disabled driver outputs maintaining high impedance over
the entire common mode range. A short-circuit feature
detects shorted outputs and substantially reduces driver
output current. A similar feature also protects the receiver
output from short circuits. Thermal shutdown circuitry
protects from excessive power dissipation.
■
■
■
The receiver has a fail-safe feature that guarantees a high
output state when the inputs are shorted or are left floating.
The LTC1686/LTC1687 RS485 transceivers guarantee
receiver fail-safe operation over the entire common mode
range (–7V to 12V). Receiver input resistance remains
≥22k when the device is unpowered or disabled.
U
APPLICATIONS
■
High Speed RS485/RS422 Full Duplex Transceivers
■
Level Translator
■
Backplane Transceiver
■
The LTC1686/LTC1687 operate from a single 5V supply
and draw only 7mA of supply current.
STS-1/OC-1 Data Transceiver
■
Signal Repeaters
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATION
10Mbps Data Pulse
400 Feet Category 5 UTP
LTC1686
LTC1686
DRIVER INPUT
2V/DIV
5
3
100Ω
100Ω
100Ω
D
DRIVER
RECEIVER
R
D
6
RECEIVER
INPUT
1V/DIV
5V/DIV
8
7
2
100Ω
R
DRIVER
RECEIVER
RECEIVER
OUTPUT
400 FT OF CATEGORY 5 UTP
100ns/DIV
1686/87 TA02
LTC1686/87 • TA01
1
LTC1686/LTC1687
W W W
U
ABSOLUTE AXI U RATI GS
(Note 1)
Driver Short-Circuit Duration
(VOUT: –7V to 10V) ..................................... Indefinite
Receiver Short-Circuit Duration
(VOUT: 0V to VDD) ........................................ Indefinite
Operating Temperature Range
LTC1686C/LTC1687C ............................. 0°C to 70°C
LTC1686I/LTC1687I .......................... –40°C to 85°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Supply Voltage (VDD).............................................. 10V
Control Input Currents .................... –100mA to 100mA
Control Input Voltages .................. –0.5V to VDD + 0.5V
Driver Input Voltages .................... –0.5V to VDD + 0.5V
Driver Output Voltages ................................. +12V/–7V
Receiver Input Voltages ................................ +12V/–7V
Receiver Output Voltages ............. –0.5V to VDD + 0.5V
Receiver Input Differential ...................................... 10V
W
U
/O
PACKAGE RDER I FOR ATIO
TOP VIEW
ORDER PART
ORDER PART
NC
R
1
2
3
4
5
6
7
14
V
DD
TOP VIEW
NUMBER
NUMBER
R
13 NC
V
1
2
3
4
8
7
6
5
A
B
Z
Y
DD
R
12
11
10
9
RE
A
B
LTC1686CS8
LTC1686IS8
R
LTC1687CS
LTC1687IS
DE
D
D
D
Z
GND
D
Y
GND
GND
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
8
NC
S PACKAGE
14-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 90°C/ W
TJMAX = 125°C, θJA = 150°C/ W
1686
1686I
Consult factory for Industrial and Military grade parts.
DC ELECTRICAL CHARACTERISTICS VDD = 5V ± 5% unless otherwise noted (Notes 2, 3).
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
Differential Driver Output (Unloaded)
Differential Driver Output (With Load)
I
= 0
●
V
V
OD1
OD2
OUT
DD
R = 50Ω (RS422)
R = 27Ω (RS485), Figure 1
2.0
1.5
V
V
●
●
V
DD
∆V
Change in Magnitude of Driver Differential
Output Voltage for Complementary
Output States
R = 27Ω or 50Ω, Figure 1
0.2
V
OD
V
Driver Common Mode Output Voltage
R = 27Ω or 50Ω, V = 5V, Figure 1
●
●
2
3
V
V
OC
DD
∆ V
Change in Magnitude of Driver Common
Mode Output Voltage for Complementary
Output States
R = 27Ω or 50Ω, Figure 1
0.2
OC
V
V
Input High Voltage
Input Low Voltage
Input Current
D, DE, RE
D, DE, RE
D, DE, RE
●
●
●
2
V
V
IH
IL
0.8
1
I
I
–1
µA
IN1
IN2
Input Current (A, B)
V , V = 12V, V = 0V or 5.25V
●
●
500
µA
µA
A
B
DD
V , V = –7V, V = 0V or 5.25V
–500
–0.3
A
B
DD
V
Differential Input Threshold Voltage
for Receiver
–7V ≤ V ≤ 12V
●
0.3
V
TH
CM
∆V
Receiver Input Hysteresis
V
= 0V
25
mV
V
TH
CM
V
Receiver Output High Voltage
I
= –4mA, V = 300mV
●
3.5
4.8
OH
OUT
ID
2
LTC1686/LTC1687
VDD = 5V ±5% unless otherwise noted (Notes 2, 3).
DC ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
0.4
1
UNITS
V
V
Receiver Output Low Voltage
I
= 4mA, V = –300mV
●
●
OL
OUT
ID
I
Three-State (High Impedance) Output
Current at Receiver
0.4V ≤ V
≤ 2.4V
–1
µA
OZR
OUT
I
Three-State (High Impedance) Output
Current at Driver
V
= –7V to 12V
OUT
●
–200
200
µA
OZD
C
Receiver and Driver Output Load Capacitance (Note 4)
●
●
●
●
●
●
500
12
20
20
20
pF
mA
mA
mA
mA
kΩ
pF
LOAD
I
I
I
I
Supply Current
No Load, Pins D, DE, RE = 0V or V
7
DD
DD
Driver Short-Circuit Current, V
Driver Short-Circuit Current, V
Receiver Short-Circuit Current
Input Resistance
= HIGH
= LOW
V
V
V
= –7V or 10V (Note 5)
= –7V or 10V (Note 5)
OSD1
OSD2
OSR
OUT
OUT
OUT
OUT
OUT
= 0V or V (Note 5)
DD
R
–7V ≤ V ≤ 12V
22
IN
IN
CM
C
Input Capacitance
A, B, D, DE, RE Inputs (Note 4)
3
3.3
2
Open-Circuit Input Voltage
V
= 5V (Note 4), Figure 5
●
3.2
3.4
V
DD
Fail-Safe
Time
Time to Detect Fail-Safe Condition
µs
CMRR
Receiver Input Common Mode
Rejection Ratio
V
= 2.5V, f = 26MHz
45
dB
CM
U
SWITCHING CHARACTERISTICS VDD = 5V, unless otherwise noted (Notes 2, 3).
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
t
, t
Driver Input-to-Output Propagation Delay
Driver Output A-to-Output B Skew
Driver Rise/Fall Time
R
= 54Ω, Figures 3, 5
LTC1686C/LTC1687C
LTC1686I/LTC1687I
●
●
15
13
18.5
18.5
22
25
ns
ns
PLH PHL
DIFF
C
L1
= C = 100pF
L2
t
R
DIFF
= 54Ω, C = C = 100pF,
500
ps
SKEW
L1
L2
Figures 3, 5
R = 54Ω, C = C = 100pF,
DIFF
t , t
3.5
ns
r
f
L1
L2
Figures 3, 5
t
t
t
t
t
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable from Low
Driver Disable from High
C = 100pF, S2 Closed, Figures 4, 6
●
●
●
●
25
25
25
25
50
50
50
50
ns
ns
ns
ns
ZH
ZL
LZ
HZ
L
C = 100pF, S1 Closed, Figures 4, 6
L
C = 15pF, S1 Closed, Figures 4, 6
L
C = 15pF, S2 Closed, Figures 4, 6
L
, t
Receiver Input-to-Output Propagation Delay C = 15pF, Figures 3, 7
LTC1686C/LTC1687C
LTC1686I/LTC1687I
●
●
15
13
18.5
18.5
22
25
ns
ns
PLH PHL
L
t
t
t
t
t
Receiver Skew
t
– t
C = 15pF, Figures 3, 7
500
25
ps
ns
ns
ns
ns
ns
SQD
ZL
PLH
PHL
L
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Receiver Disable from High
C = 15pF, S1 Closed, Figures 2, 8
L
●
●
●
●
●
50
50
C = 15pF, S2 Closed, Figures 2, 8
L
25
ZH
LZ
C = 15pF, S1 Closed, Figures 2, 8
L
25
50
C = 15pF, S2 Closed, Figures 2, 8
L
25
50
HZ
Maximum Receiver Input
Rise/Fall Times
(Note 4)
2000
t
Package-to-Package Skew
C = 15pF, Same Temperature (Note 4)
L
1.5
ns
PKG-PKG
3
LTC1686/LTC1687
U
SWITCHING CHARACTERISTICS VDD = 5V, unless otherwise noted (Notes 2, 3).
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Minimum Input Pulse Width
V
DD
V
DD
V
DD
= 5V ±5% (Note 4)
= 5V ±5% (Note 4)
= 5V ±5% (Note 4)
LTC1686C/LTC1687C
LTC1686I/LTC1687I
●
●
17
20
19.2
25
ns
ns
Maximum Data Rate
LTC1686C/LTC1687C
LTC1686I/LTC1687I
●
●
52
40
60
50
Mbps
Mbps
Maximum Input Frequency
LTC1686C/LTC1687C
LTC1686I/LTC1687I
●
●
26
20
30
25
MHz
MHz
The
●
denotes specifications which apply over the full operating
Note 3: All typicals are given for V = 5V, T = 25°C.
DD A
Note 4: Guaranteed by design, but not tested.
temperature range.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: All currents into the device pins are positive; all currents out of the
device pins are negative.
Note 5: Short-circuit current does not represent output drive capability.
When the output detects a short-circuit condition, output drive current is
significantly reduced (from hundreds of mA to 20mA max) until the short
is removed.
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Input CMRR
Supply Current vs Data Rate
Supply Current vs Temperature
46.5
46.0
45.5
45.0
44.5
44.0
43.5
43.0
42.5
70
60
58
57
56
55
BOTH DRIVER AND RECEIVER
ENABLED AND LOADED
A
T
= 25°C
50
40
30
20
10
0
54
53
52
51
50
BOTH DRIVER AND RECEIVER
ENABLED AND LOADED
25Mbps DATA RATE
T
A
= 25°C
42.0
10
20
DATA RATE (Mbps)
50
0
25
TEMPERATURE (°C)
75
1
30
40
–25
100
50
10
1k
100k
FREQUENCY (Hz)
1M
1686/87 G02
1686/87 G03
1686/87 G01
Receiver Propagation Delay
vs Load Capacitance
Receiver Propagation Delay
vs Common Mode
Receiver Propagation Delay
vs Input Overdrive
25
20
15
10
5
30
25
20
15
10
5
25
20
T
= 25°C
T = 25°C
A
T
= 25°C
A
A
15
10
5
0
0
0
5
25
35
55
105
205
0.3 0.5 0.7
1.0 1.25 1.5 2.0 2.5
15
–7 –4 –2
0
2
4
6
8
10 12
LOAD CAPACITANCE (pF)
RECEIVER INPUT OVERDRIVE (V)
RECEIVER COMMON MODE (V)
1686/87 G04
1686/87 G06
1686/87 G05
4
LTC1686/LTC1687
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Propagation Delay
vs Temperature
Receiver Maximum Data Rate
vs Input Overdrive
Driver Propagation Delay
vs Temperature
25
20
15
10
5
70
60
25
T
= 25°C
A
20
15
10
50
40
30
20
10
5
0
0
0
50
75 100 125
0.3 0.4
0.5 0.6
0.7
1.0
1.5
2.5
–50 –25
0
25
–20
20
40
60
80
100
0
TEMPERATURE (°C)
TEMPERATURE (°C)
RECEIVER INPUT DIFFERENTIAL (V)
1686/87 G09
1686/87 G10
1686/87 G07
Driver Propagation Delay
vs Driver Input Voltage
Driver Propagation Delay
vs Capacitive Load
19.0
18.5
18.0
17.5
17.0
16.5
16.0
25
20
15
10
5
V
= 5V
T
= 25°C
DD
A
INPUT THRESHOLD = 1.5V
T
= 25°C
A
t
HL
t
LH
0
5
25
50
75
100
150
2.5
3.0
3.5
4.0
4.5
5.0
15
LOAD CAPACITANCE (pF)
DRIVER INPUT VOLTAGE (V)
1686/87 G11
1686/87 G08
U
U
U
PIN FUNCTIONS
LTC1686
B (Pin 7): Inverting Receiver Input.
VDD (Pin 1): Positive Supply, 5V to ±5%. Bypass with
0.1µF ceramic capacitor.
A (Pin 8): Noninverting Receiver Input.
LTC1687
NC (Pins 1, 8, 13): No Connection.
R (Pin 2): Receiver Output. If A ≥ B by 300mV, then R will
be high. If A ≤ B by 300mV, then R will be low.
R (Pin 2): Receiver Output. If A ≥ B by 300mV, then R will
be high. If A ≤ B by 300mV, then R will be low.
D (Pin 3): Driver Input. Controls the states of the Y and Z
outputs. Do not float.
RE(Pin3):ReceiverEnable. RE=lowenablesthereceiver.
RE = high forces receiver output into high impedance
state. Do not float.
GND (Pin 4): Ground.
Y (Pin 5): Noninverting Driver Output.
Z (Pin 6): Inverting Driver Output.
5
LTC1686/LTC1687
U
U
U
PIN FUNCTIONS
DE (Pin 4): Driver Enable. DE = high enables the driver.
DE = low will force the driver output into a high impedance
state. Do not float.
Z (Pin 10): Inverting Driver Output.
B (Pin 11): Inverting Receiver Input.
A (Pin 12): Noninverting Receiver Input.
D (Pin 5): Driver Input. Controls the states of the Y and Z
outputs when DE = high. Do not float.
VDD (Pin 14): Positive Supply, 5V to ±5%. Bypass with
0.1µF ceramic capacitor.
GND (Pins 6, 7): Ground.
Y (Pin 9): Noninverting Driver Output.
U
U
FU CTIO TABLES
(LTC1687)
Receiving
Transmitting
INPUTS
OUTPUT
R
INPUTS
DE
LINE
CONDITION
OUTPUTS
RE
0
DE
X
A – B
RE
X
D
1
0
X
X
Z
0
Y
1
≥ 300mV
1
0
1
1
1
1
0
1
No Fault
No Fault
X
0
X
≤ –300mV
Inputs Open
X
1
0
0
X
X
Hi- Z
Hi- Z
0
X
Inputs Shorted Together
A = B = –7V to 12V
X
Fault
±10mA Current
Source
1
X
X
Hi- Z
TEST CIRCUITS
Y
S1
S2
TEST POINT
1k
R
R
RECEIVER
OUTPUT
V
DD
V
OD
C
L
15pF
1k
V
OC
1686/87 F02
Z
1686/87 • F01
Figure 2. Driver DC Test Load
Figure 1. Driver DC Test Load
3V
DE
A
C
Y
Z
L1
S1
R
D
R
DIFF
V
DD
B
500Ω
C
OUTPUT
UNDER TEST
L2
RE
S2
15pF
C
L
1686/87 F04
1686/87 F03
Figure 3. Driver/Receiver Timing Test Circuit
Figure 4. Driver Timing Test Load #2
6
LTC1686/LTC1687
U W
W
SWITCHI G TI E WAVEFOR S
3V
f = 1MHz, t ≤ 3ns, t ≤ 3ns
D
1.5V
1.5V
r
f
0V
Z
1/2 V
O
t
t
PHL
PLH
V
O
Y
t
t
SKEW
1/2 V
SKEW
O
90%
10%
V
O
90%
V
DIFF
= V(Y) – V(Z)
0V
–V
10%
O
1686/87 F05
t
t
f
r
Figure 5. Driver Propagation Delays
3V
f = 1MHz, t ≤ 3ns, t ≤ 3ns
1.5V
1.5V
DE
r
f
0V
5V
t
t
LZ
ZL
Y, Z
Y, Z
2.5V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
0.5V
0.5V
V
OL
OH
0V
V
2.5V
t
1686/87 F06
t
HZ
ZH
Figure 6. Driver Enable and Disable Times
V
OH
2.5V
2.5V
R
OUTPUT
V
OL
f = 1MHz, t ≤ 3ns, t ≤ 3ns
t
t
PLH
r
f
PHL
V
A – B
–V
OD2
OD2
0V
INPUT
1686/87 F07
Figure 7. Receiver Propagation Delays
3V
0V
5V
1.5V
f = 1MHz, t ≤ 3ns, t ≤ 3ns
1.5V
RE
R
r
f
t
t
LZ
ZL
2.5V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
0.5V
0.5V
R
2.5V
0V
t
1686/87 F08
t
HZ
ZH
Figure 8. Receiver Enable and Disable Times
7
LTC1686/LTC1687
U U
EQUIVALE T I PUT NETWORKS
≥22k
≥22k
≥22k
A
A
B
3.3V
≥22k
B
3.3V
RE = 0 OR 1, V = 5V
DD
V
= 0V
DD
1686/87 F09
Figure 9. Input Thevenin Equivalent
U
W U U
APPLICATIONS INFORMATION
THEORY OF OPERATION
high frequency performance, it is necessary to slow down
the transient response of the fail-safe feature. When a line
fault is detected, the output will go HIGH typically in 2µs.
NotethattheLTC1686/LTC1687guaranteereceiverfail-
safe performance over the entire (–7V to 12V) common
mode range!
Unlike typical CMOS transceivers whose propagation
delay can vary by as much as 500% from package to
package and show significant temperature drift, the
LTC1686/LTC1687 employ a novel architecture that pro-
duces a tightly controlled and temperature compensated
propagation delay. The differential timing skew is also
minimized between rising and falling output edges of the
receiver output and the complementary driver outputs.
When the inputs are accidentally shorted (by cutting
through a cable, for example), the short circuit fail-safe
feature will guarantee a high output logic level. Note also
thatifthelinedriverisremovedandthegroundterminated
resistors are left in place, the receiver will see this as a
“short” and output a logic HIGH. Both of these fail-safe
features will keep the receiver from outputting false data
pulses under line fault conditions.
The precision timing features of the LTC1686/LTC1687
reduce overall system timing constraints by providing a
narrow ±3.5ns window during which valid data appears at
the receiver/driver output. The driver and receiver will
havepropagationdelaysthattypicallymatchtowithin1ns.
Thermal shutdown and short-circuit protection prevent
latchup damage to the LTC1686/LTC1687 during fault
conditions.
In clocked data systems, the low skew minimizes duty
cycledistortionoftheclocksignal.TheLTC1686/LTC1687
canbeusedatdataratesof52Mbpswithlessthan5%duty
cycledistortion(dependingoncablelength).Whenaclock
signalisusedtoretimeparalleldata,themaximumrecom-
mended data transmission rate is 26Mbps to avoid timing
errors due to clock distortion.
OUTPUT SHORT-CIRCUIT PROTECTION
The LTC1686/LTC1687 employ voltage sensing short-
circuit protection at the output terminals of both the driver
and receiver. For a given input polarity, this circuitry
determines what the correct output level should be. If the
output level is different from the expected, it shuts off the
big output devices. For example, if the driver input is >2V,
it expects the “A” output to be >3.25V and the “B” output
to be <1.75V. If the “A” output is subsequently shorted to
a voltage below VDD/2, this circuitry shuts off the big
output devices and turns on a smaller device in its place
FAIL-SAFE FEATURES
The LTC1686/LTC1687 have a fail-safe feature that guar-
antees the receiver output to be in a logic HIGH state when
the inputs are either shorted or left open (note that when
inputs are left open, large external leakage currents might
override the fail-safe circuitry). In order to maintain good
8
LTC1686/LTC1687
U
W U U
APPLICATIONS INFORMATION
should be pulsed low for at least 200ns after the short has
been removed. Since the LTC1686 driver is always
enabled, the LTC1686 should only be used with single
resistor termination, as shown in Figure 10.
(theconverseappliesforthe“B”output). Theoutputsthen
appearas±10mAcurrentsources.Notethatundernormal
operation, the output drivers can sink/source >50mA. A
time-out period of about 50ns is used in order to maintain
normal high frequency operation, even under heavy ca-
pacitive loads.
HIGH SPEED TWISTED-PAIR TRANSMISSION
If the cable is shorted at a large distance from the device
outputs, it is possible for the short to go unnoticed at the
driver outputs due to parasitic cable resistance. Addition-
ally, when the cable is shorted, it no longer appears as a
simple transmission line impedance, and the parasitic L’s
and C’s might give rise to ringing and even oscillation. All
these conditions disappear once the device comes out of
short-circuit mode.
Data rates up to 52Mbps can be transmitted over 100 feet
of category 5 twisted pair. Figure 10 shows the LTC1687
receiving differential data from another LTC1687 trans-
ceiver. Figure 11a shows a 26MHz (52Mbps) square wave
propagated over 100 feet of category 5 UTP. Figure 11b
shows a more stringent case of propagating a 20ns pulse
over 100 feet of category 5 UTP. Figure 12 shows a 2MHz
(4Mbps) square wave propagated over 1000 feet of
category 5unshieldedtwistedpair.NotethattheLTC1686/
LTC1687 can still perform reliably at this distance and
speed. Very inexpensive unshielded telephone grade
twisted pair is shown in Figure 13. Despite the noticeable
loss at the receiver input, the LTC1686/LTC1687 can still
transfer at 30Mbps over 100 feet of telephone grade UTP.
Notethatunderalltheseconditions,theLTC1686/LTC1687
can pass through a single data pulse equal to the inverse
of the data rate (e.g., 20ns for 50Mbps data rate).
For cables with the typical RS485 termination (no DC bias
on the cable, such as Figure 10), the LTC1686/LTC1687
willautomaticallycomeoutofshort-circuitmodeoncethe
physical short has been removed.
Cable Termination
The recommended cable termination for the LTC1686/
LTC1687 is a single resistor across the two wires at each
end of the twisted-pair line (see Figure 10). The LTC1687
can also be used with cable terminations with a DC bias
(such as Fast-20 and Fast-40 differential SCSI termina-
tors). When using a biased termination with the LTC1687,
however, the DE pin must be held low for at least 200ns
after the part has been powered up. This ensures proper
start-up into the DC load of the biased termination. Fur-
thermore, whentheLTC1687outputisshorted, theDEpin
TRANSMISSION OVER LONG DISTANCES
1Mbps Over 4000 Feet Category 5 UTP
The LTC1685/LTC1686/LTC1687 family of high speed
transceivers is capable of 1Mbps transmission over 4000
feet of category 5 UTP. High quality cable provides lower
DE
4
DE
9
5
2
100Ω
100Ω
100Ω
D
R
DRIVER
RECEIVER
R
D
10
LTC1687
LTC1687
DRIVER
12
11
100Ω
RECEIVER
CATEGORY 5 UTP
3
RE
RE
LTC1686/87 • F10
Figure 10
9
LTC1686/LTC1687
U
W U U
APPLICATIONS INFORMATION
DRIVER INPUT
2V/DIV
DRIVER
INPUT
2V/DIV
DIFFERENTIAL
RECEIVER
INPUT
2V/DIV
2V/DIV
2V/DIV
RECEIVER
OUTPUT
RECEIVER
OUTPUT
10ns/DIV
20ns/DIV
1686/87 F13
1686/87 F11a
Figure 13. 100 Feet of Telephone Grade UTP: 30Mbps
Figure 11a. 100 Feet of Category 5 UTP: 50Mbps
DRIVER
INPUT
DRIVER
2V/DIV
2V/DIV
CABLE DELAY
INPUT
CABLE DELAY
RECEIVER
INPUT
RECEIVER
INPUT
2V/DIV
1V/DIV
RECEIVER
5V/DIV
RECEIVER
OUTPUT
5V/DIV
OUTPUT
20ns/DIV
1µs/DIV
1685 F11b
1685 F14a
Figure 14a. 4000 Feet of Category 5 UTP 1µs Pulse
Figure 11b. 100 Feet of Category 5 UTP: 20ns Pulse
DRIVER
INPUT
2V/DIV
2V/DIV
DRIVER
INPUT
2V/DIV
5V/DIV
RECEIVER
OUTPUT
RECEIVER
OUTPUT
1µs/DIV
100ns/DIV
1685 F14b
1686/87 F12
Figure 12. 1000 Feet of Category 5 UTP: 4Mbps
Figure 14b. 4000 Feet of Category 5 UTP 1Mbps Square Wave
DC and AC attenuation over long distances. Figure 14a
showsa1µspulsepropagateddown4000feetofcategory
5 UTP. Notice the significant attenuation at the receiver
input and the clean pulse at the receiver output. The DC
attenuation is due to the parasitic resistance of the cable.
Figure 14b shows a 1Mbps square wave over the same
4000 feet of cable.
1.6Mbps Over 8000 Feet (1.5 Miles)
Category 5 UTP Using Repeaters
TheLTC1686/LTC1687canbeusedasrepeaterstoextend
theeffectivelengthofahighspeedtwisted-pairline.Figure
15a shows a three repeater configuration using 2000 feet
segments of category 5 UTP. Figure 15b shows the
10
LTC1686/LTC1687
U
W U U
APPLICATIONS INFORMATION
LTC1687
LTC1687
2000 FT
2000 FT
2000 FT
LTC1687
R4
REPEATER
2000 FT
LTC1687
R2
REPEATER
LTC1687
R3
REPEATER
D1
R
D
D
D
R5
1686/87 F15a
Figure 15a. 1.6Mbps, 8000 Feet (1.5 Miles) Using Three Repeaters
DRIVER 1
INPUT
DRIVER 1
INPUT
2V/DIV
2V/DIV
RECEIVER 2
INPUT
RECEIVER 3
INPUT
RECEIVER 4
INPUT
1V/DIV
1V/DIV
RECEIVER 5
OUTPUT
5V/DIV
2V/DIV
1V/DIV
DRIVER 1
INPUT
RECEIVER 5
OUTPUT
5V/DIV
RECEIVER 5
OUTPUT
5V/DIV
2µs/DIV
2µs/DIV
1686/87 F15b
1686/87 F16
Figure 15b. 1.6Mbps Pulse and Square Wave Signals
Over 8000 Feet Category 5 UTP Using Three Repeaters
Figure 16. Intermediate Signals of a 1µs Pulse
propagation of a 600ns pulse through the network of
Figure 15A. The bottom two traces show a 1.6Mbps
square wave. Notice that the duty cycle does not notice-
ably degrade. For the case of the single pulse, however,
there is a slight degradation of the pulse width.
goes above or below the rails. It is advisable to terminate
the PC traces when approaching maximum speeds. Since
the LTC1686/LTC1687 are not intended to drive parallel
terminated cables with characteristic impedances much
less than that of twisted pair, both ends of the PC trace
must be series terminated with the characteristic imped-
ance of the trace. For best results, the signal should be
routed differentially. The true and complement outputs of
the LTC1686/LTC1687 should be routed on adjacent lay-
ers of the PC board. The two traces should be routed very
symmetrically, minimizing and equalizing parasitics to
nearby signal and power/ground layers. For single-ended
transmission, route the series terminated single-ended
trace over an adjacent ground plane. Then set the (by-
passed) negative input of the receiver to roughly 2.5V.
Note that single-ended operation might not reach maxi-
mum speeds.
By slowing down the data rate slightly to 1Mbps, one can
obtain minimal pulse width degradation as the signal
traverses through the repeater network. Figure 16 shows
that the output pulse (bottom trace) is nearly the same
width to the input pulse (top trace). The middle three
tracesofFigure16showthesignalattheendofeachofthe
first three 2000 feet sections of category 5 UTP. Notice
how the LTC1687 repeaters are able to regenerate the
signal with little loss. This implies that we can cascade
more repeater networks and potentially achieve 1Mbps
operation at total distances of over 10,000 feet!A higher
dataratecanbeachievediftherepeatersarespacedcloser
together.
LAYOUT CONSIDERATIONS
HIGH SPEED BACKPLANE TRANSMISSION
A ground plane is recommended when using high fre-
quency devices like the LTC1686/LTC1687. A 0.1µF ce-
ramic bypass capacitor less than 0.25 inch away from the
VDD pin is also recommended.
The LTC1686/LTC1687 can also be used in backplane
point-to-point transceiver applications, where the user
wants to assure operation even when the common mode
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
LTC1686/LTC1687
U
W U U
APPLICATIONS INFORMATION
Long traces bounded by a VDD and/or GND planes can add
substantial parasitic capacitance. Parasitic capacitances
on the receiver/driver outputs can also unduly slow down
both the propagation delay and the rise/fall times.
The receiver inputs are high bandwidth and high imped-
ance. If they are left floating, any capacitive coupling from
any other signal can cause a glitch at the receiver output.
Thus, if the receiver is not being used, it is advisable to
always ground at least one of the two receiver input pins.
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
(0.254 – 0.508)
7
5
8
6
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
SO8 0996
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1
2
3
4
S Package
14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.337 – 0.344*
(8.560 – 8.738)
0.010 – 0.020
(0.254 – 0.508)
14
13
12
11
10
9
8
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0° – 8° TYP
0.228 – 0.244
(5.791 – 6.197)
0.150 – 0.157**
(3.810 – 3.988)
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
0.016 – 0.050
0.406 – 1.270
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
S14 0695
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1
2
3
4
5
6
7
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC490
Low Power RS485 Full-Duplex Transceiver
Low Power RS485 Full-Duplex Transceiver
High Speed Quad RS485 Receiver
High Speed Quad RS485 Receiver
High Speed Quad Differential Receiver
High Speed RS485 Transceiver
I
I
= 300µA (Typ), SO-8 Package
CC
CC
LTC491
= 300µA (Typ), 14-Lead SO Package
LTC1518
LTC1519
LTC1520
LTC1685
52Mbps, Pin Compatible with LTC488
52Mbps, Pin Compatible with LTC489
52Mbps, ±100mV Threshold, Rail-to-Rail Common Mode
52Mbps, Pin Compatible with LTC485
16867fs, sn16867 LT/TP 1197 4K • PRINTED IN THE USA
LINEAR TECHNOLOGY CORPORATION 1997
Linear Technology Corporation
●
1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900
12
●
●
FAX: (408) 434-0507 TELEX: 499-3977 www.linear-tech.com
相关型号：
SI9130DB
5- and 3.3-V Step-Down Synchronous ConvertersWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135LG-T1
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135LG-T1-E3
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135_11
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9136_11
Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130CG-T1-E3
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130LG-T1-E3
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130_11
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137DB
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137LG
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9122E
500-kHz Half-Bridge DC/DC Controller with Integrated Secondary Synchronous Rectification DriversWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
©2020 ICPDF网 联系我们和版权申明