LINER LTC1689 100mbps rs485 hot swapable quad driver Datasheet

LTC1688/LTC1689
100Mbps RS485
Hot Swapable Quad Drivers
U
DESCRIPTIO
FEATURES
■
■
■
■
■
■
■
■
■
■
■
Ultrahigh Speed: 100Mbps
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
U
APPLICATIO S
■
■
■
■
The driver outputs are Hot Swap capable, maintaining
backplane data integrity during board insertion and
removal. The drivers feature three-state outputs, maintaining 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.
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.
U
■
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.
TYPICAL APPLICATIO
20ns Pulse Across 100 Feet
of Category 5 UTP
50Mbps RS485 Data Connection
DRIVER
100Ω
100Ω
DRIVER INPUT
2V/DIV
DRIVER OUTPUTS
RECEIVER
CABLE DELAY
100 FT CATEGORY 5 UTP
1/4 LTC1688
2V/DIV
2V/DIV
RECEIVER INPUT
5V/DIV
RECEIVER OUTPUT
1/4 LTC1518
1688/89 TA01
20ns/DIV
1688/89 TA02
16889fa
1
LTC1688/LTC1689
U
U
RATI GS
W
W W
W
AXI U
U
ABSOLUTE
PACKAGE/ORDER 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
ORDER PART
NUMBER
TOP VIEW
DI1 1
16 VDD
DO1A 2
15 DI4
DO1B 3
14 DO4A
EN (EN12*) 4
13 DO4B
DO2B 5
12 ENB (EN34*)
DO2A 6
11 DO3B
DI2 7
10 DO3A
9
GND 8
LTC1688CS
LTC1689CS
LTC1688IS
LTC1689IS
DI3
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
MIN
TYP
MAX
UNITS
VDD
V
3.0
V
V
0.2
V
3
V
0.2
V
VDD = 5V, Per Driver, TA = 25°C, Unless Otherwise Noted (Note 2)
VOD1
Differential Driver Output (Unloaded)
IOUT = 0
●
VOD2
Differential Driver Output (With Load)
R = 50Ω (RS422)
R = 25Ω (RS485), Figure 1
●
●
Change in Magnitude of Driver Differential
Output Voltage for Complementary
Output States
R = 25Ω or 50Ω, Figure 1
●
VOC
Driver Common Mode Output Voltage
R = 25Ω or 50Ω, Figure 1
●
∆VOC
Change in Magnitude of Driver Common
Mode Output Voltage for Complementary
Output States
R = 25Ω or 50Ω, Figure 1
●
VIH
Input High Voltage
EN, ENB, EN12, EN34, DI
●
VIL
Input Low Voltage
EN, ENB, EN12, EN34, DI
●
0.8
V
IIN1
Input Current
EN, ENB, EN12, EN34, DI
●
±1
µA
IOZ
Three-State (High Impedance)
Output Current
VOUT = – 7V to 12V
●
±2
±200
µA
IDD
Supply Current of Entire Device
No Load, Digital Input Pins = 0V or VDD
●
9
18
mA
IOSD1
Driver Short-Circuit Current, VOUT = HIGH
VOUT = – 7V to 10V
●
± 20
mA
IOSD2
Driver Short-Circuit Current, VOUT = LOW
VOUT = – 7V to 10V
●
± 20
mA
∆VOD
2
1.5
2
2
V
VDD = 3V, Per Driver, TA = 25°C, Unless Otherwise Noted (Note 2)
VOD1
Differential Driver Output (Unloaded)
IOUT = 0
VOD2
Differential Driver Output (With Load)
R = 50Ω (RS422)
R = 25Ω (RS485), Figure 1
●
VDD
V
2.0
V
V
1.5
●
0.65
∆VOD
Change in Magnitude of Driver Differential
Output Voltage for Complementary
Output States
R = 25Ω or 50Ω, Figure 1
0.1
VOC
Driver Common Mode Output Voltage
R = 25Ω or 50Ω, Figure 1
1.3
V
V
16889fa
2
LTC1688/LTC1689
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
MIN
TYP
MAX
∆VOC
Change in Magnitude of Driver Common
Mode Output Voltage for Complementary
Output States
R = 25Ω or 50Ω, Figure 1
VIH
Input High Voltage
EN, ENB, EN12, EN34, DI
●
VIL
Input Low Voltage
EN, ENB, EN12, EN34, DI
●
IIN1
Input Current
EN, ENB, EN12, EN34, DI (Note 3)
●
IOZ
Three-State (High Impedance)
Output Current
VOUT = – 7V to 10V (Note 3)
●
IDD
Supply Current of Entire Device
No Load, Digital Input Pins = 0V or VDD
IOSD1
Driver Short-Circuit Current, VOUT = HIGH
VOUT = – 7V to 8V (Note 3)
●
±20
mA
IOSD2
Driver Short-Circuit Current, VOUT = LOW
VOUT = – 7V to 8V (Note 3)
●
±20
mA
0.1
UNITS
V
1.4
V
0.5
±1
V
±1
µA
±200
µA
5
mA
U
SWITCHING CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
4
8
12
UNITS
VDD = 5V, TA = 25°C, Unless Otherwise Noted (Note 2)
tPLH, tPHL
Driver Input-to-Output Propagation Delay
RDIFF = 50Ω, CL1 = CL2 = 25pF,
Figures 2, 4
tSKEW
Driver Output-to-Output Skew
RDIFF = 50Ω, CL1 = CL2 = 25pF,
Figures 2, 4
500
ps
tr, tf
Driver Rise/Fall Time
RDIFF = 50Ω, CL1 = CL2 = 25pF,
Figures 2, 4
2
ns
tZH
Driver Enable to Output High
CL = 25pF, S2 Closed, Figures 3, 5
●
10
35
ns
tZL
Driver Enable to Output Low
CL = 25pF, S1 Closed, Figures 3, 5
●
10
35
ns
tLZ
Driver Disable from Low
CL = 15pF, S1 Closed, Figures 3, 5
●
25
65
ns
t HZ
Driver Disable from High
CL = 15pF, S2 Closed, Figures 3, 5
●
25
CL(MAX)
Maximum Output Capacitive Load
(Note 3)
●
Maximum Data Rate
(Note 3)
●
Maximum Driver Input Rise/Fall Time
(Note 3)
●
●
ns
65
ns
200
pF
100
Mbps
500
ns
VDD = 3V, TA = 25°C, Unless Otherwise Noted (Note 2)
tPLH, tPHL
Driver Input-to-Output Propagation Delay
RDIFF = 50Ω, CL1 = CL2 = 25pF,
Figures 2, 4
11
ns
tSKEW
Driver Output-to-Output Skew
RDIFF = 50Ω, CL1 = CL2 = 25pF,
Figures 2, 4
1
ns
tr, tf
Driver Rise/Fall Time
RDIFF = 50Ω, CL1 = CL2 = 25pF,
Figures 2, 4
4
ns
tZH
Driver Enable to Output High
CL = 25pF, S2 Closed, Figures 3, 5
25
ns
tZL
Driver Enable to Output Low
CL = 25pF, S1 Closed, Figures 3, 5
25
ns
tLZ
Driver Disable from Low
CL = 15pF, S1 Closed, Figures 3, 5
50
ns
t HZ
Driver Disable from High
CL = 15pF, S2 Closed, Figures 3, 5
50
ns
CL(MAX)
Maximum Output Capacitive Load
(Note 3)
Maximum Driver Input Rise/Fall Time
200
●
Maximum Data Rate
50
(Note 3)
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
●
pF
Mbps
500
ns
Note 2: All currents into the device pins are positive; all currents out of the
device pins are negative.
Note 3: Guaranteed by design or correlation, but not tested.
16889fa
3
LTC1688/LTC1689
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Propagation Delay
vs Temperature
Propagation Delay
vs Load Capacitance
14
14
VDD = 3V
10
8
VDD = 5V
6
4
VDI = 0V TO 3V
RDIFF = 50Ω
CL = 25pF
2
VDD = 3V
12
PROPAGATION DELAY (ns)
PROPAGATION DELAY (ns)
12
10
VDD = 5V
8
6
4
VDI = 0V TO 3V
RDIFF = 50Ω
TA = 25°C
2
0
0
0
20
40
60
80
TEMPERATURE (°C)
0
100
10
20
30
40
50
LOAD CAPACITANCE (pF)
60
1688/89 G02
1688/89 G01
Three-State Output Current
Supply Current vs Data Rate
250
4.0
3.5
VDD = 5V
OUTPUT CURRENT (µA)
SUPPLY CURRENT (mA)
200
4 DRIVERS
SWITCHING
150
VDD = 5V
RDIFF = 50Ω, PER DRIVER
CL = 25pF, PER DRIVER
TA = 25°C
100
1 DRIVER
SWITCHING
50
3.0
VOUT = –7V
2.5
2.0
1.5
1.0
0.5
0
VOUT = 12V
0
0
20
40
60
80
DATA RATE (Mbps)
100
120
0
20
40
60
80
TEMPERATURE (°C)
1688/89 G03
100
1688/89 G04
IDD vs Temperature
VOD2 vs Temperature
2.5
180
4 DRIVERS LOADED
160
VDD = 5V
2.0
140
120
VOD2
IDD (mA)
1.5
VDD = 3V
1.0
100
1 DRIVER LOADED
80
60
40
0.5
20
RDIFF = 50Ω
0
VDD = 5V
RDIFF = 50Ω, PER DRIVER
0.1Mbps
0
0
20
40
60
80
TEMPERATURE (°C)
100
1688/89 G05
0
20
40
60
80
TEMPERATURE (°C)
100
1688/89 G06
16889fa
4
LTC1688/LTC1689
U
U
U
PIN FUNCTIONS
DI1 (Pin 1): Driver 1 Input. Do not float.
DI3 (Pin 9): Driver 3 Input. Do not float.
DO1A (Pin 2): Driver 1 Noninverting Output.
DO3A (Pin 10): Driver 3 Noninverting Output.
DO1B (Pin 3): Driver 1 Inverting 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.
DO4B (Pin 13): Driver 4 Inverting Output.
DO2A (Pin 6): Driver 2 Noninverting Output.
DO4A (Pin 14): Driver 4 Noninverting Output.
DI2 (Pin 7): Driver 2 Input. Do not float.
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.
U
U
FU CTIO TABLES
LTC1688
LTC1689
INPUTS
OUTPUTS
INPUTS
OUTPUTS
DI
EN
ENB
OUTA
OUTB
DI
EN12/EN34
OUTA
OUTB
H
H
X
H
L
H
H
H
L
L
H
X
L
H
L
H
L
H
H
X
L
H
L
X
L
HI-Z
HI-Z
L
X
L
L
H
X
L
H
HI-Z
HI-Z
TEST CIRCUITS
EN (EN12)
A
S1
CL1
R
VDD
A
VOD
R
VOC
DI
DRIVER
B
OUTPUT
UNDER TEST
RDIFF
CL
B
CL2
1688/89 TC01
S2
1688/89 TC02
ENB (EN34)
Figure 1. Driver DC Test Load
500Ω
Figure 2. Driver Timing Test Circuit
1688/89 TC03
Figure 3. Driver Timing Test Load
16889fa
5
LTC1688/LTC1689
U
W
W
SWITCHI G TI E WAVEFOR S
3V
DI
f = 1MHz; tr < 3ns; tf < 3ns
1.5V
1.5V
0V
tPLH
tPHL
B
VO
A
tSKEW
1/2 VO
VO
1/2 VO
90%
tSKEW
90%
10%
VDIFF = V(A) – V(B)
10%
– VO
1688/89 F04
tf
tr
Figure 4. Driver Propagation Delays
3V
EN
f = 1MHz; tr ≤ 3ns; tf ≤ 3ns
1.5V
1.5V
0V
tZL
5V
A, B
VOL
VOH
A, B
tLZ
1/2 VDD
OUTPUT NORMALLY LOW
1/2 VDD
OUTPUT NORMALLY HIGH
0.5V
0.5V
0V
tZH
1688/89 F05
tHZ
Figure 5. Driver Enable and Disable Times
U
W
U
U
APPLICATIONS INFORMATION
The LTC1688/LTC1689 family of RS485 quad differential
drivers employs a novel architecture and fabrication process that allows ultra high speed operation (100Mbps)
and Hot Swap capability while maintaining the ruggedness
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
500%, the propagation delay of the LTC1688/LTC1689
drivers will only vary by ±50% (a narrow ±4ns window).
This performance is achieved by designing the input stage
of each driver to have minimum propagation delay shift
over temperature and from part to part.
The LTC1688/LTC1689 have an ESD rating of 6kV human
body model.
50Mbps with 3V Operation
The LTC1688/LTC1689 are designed to operate with a 3V
power supply and still achieve 50Mbps operation (see
Electrical Characteristics table for 3V DC and AC specifications). Figure 6 shows waveforms of an LTC1689 driving
a receiver using 100 feet of Category 5 UTP. Both parts are
operating at 3V supply.
LTC1689 OUTPUT
2V/DIV
FAR END OF CABLE
2V/DIV
RECEIVER OUTPUT
5V/DIV
20ns/DIV
1688/89 F06
Figure 6. 3V High Speed Data Transmission
16889fa
6
LTC1688/LTC1689
U
U
W
U
APPLICATIONS INFORMATION
Hot Swap Capability
With the LTC1688/LTC1689 outputs disabled but connected to the transmission line, the user can turn on/off the
power to the LTC1688/LTC1689 without inducing a differential signal on the transmission line. Due to capacitive
coupling, however, there can be a small amount of common mode charge injected into both disabled outputs,
which is not seen as a differential signal (see Figure 7). The
disabled outputs can be hooked/unhooked to a transmission line without disturbing the existing data.
Output Short-Circuit Protection
In addition to 100Mbps operation and Hot Swap capability,
the LTC1688/LTC1689 employ voltage sensing shortcircuit 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, if the driver input is > 2V, it expects the “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
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.
A time-out period of about 50ns is required before a shortcircuit 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
much resistance (user inserted or cable parasitic) between
the physical short and the actual driver output.
For cables with the recommended RS485 termination (no
DC bias on the cable, see Figure 8), the LTC1688/LTC1689
will automatically come out of short-circuit mode once the
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
16889fa
7
LTC1688/LTC1689
U
U
W
U
APPLICATIONS INFORMATION
Cable Termination
Enable Pins
The recommended cable termination for use with the
LTC1688/LTC1689 is a single resistor across the two ends
of a transmission cable (see Figure 8). When PC traces are
used as the transmission line, its characteristic impedance should be chosen close to 100Ω in order to better
match the specified timing characteristics of the LTC1688/
LTC1689. Category 5 unshielded twisted pair can be used
over short distances at the maximum data rates (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 outputs 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
single resistor termination (Figures 8 and 9), the LTC1688/
LTC1689 will come out of a short-circuit fault condition
automatically without having to disable the outputs.
1/4 LTC1519
1/4 LTC1688
100Ω
100Ω
1/4 LTC1518
100Ω
1/4 LTC1689
1/4 LTC1518
1688/89 F08
1688/89 F09
Figure 8. Multipoint Transmission
DE
DI
Figure 9. Point-to-Point Transmission
TERM POWER
TERM POWER
330Ω
330Ω
150Ω
150Ω
1/4 LTC1688
330Ω
1/4 LTC1518
1/4 LTC1518
330Ω
1688/89 F10
Figure 10. DC-Biased Termination
(Recommended for SCSI Applications Only)
16889fa
8
LTC1688/LTC1689
U
W
U
U
APPLICATIONS INFORMATION
High Speed Twisted-Pair Transmission
High Speed Backplane Transmission
Data rates up to 100Mbps can be transmitted over short
distances using Category 5 UTP (unshielded twisted pair).
The cable distance will determine the maximum data rate.
Figures 11 and 12 show an 8ns pulse propagating over 25
feet of Category 5 UTP. Notice how the cable attenuates the
signal. Lucent Technologies’ BRF2A and BRS2A receivers
are recommended for these ultrahigh speed applications.
The LTC1688/LTC1689 can be used in backplane point-topoint 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
specification calls for characteristic impedances near 100Ω;
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
2V/DIV
2V/DIV
5V/DIV
DRIVER INPUT
DRIVER OUTPUT
UltraFast is a trademark of Linear Technology Corporation.
RECEIVER INPUT
RECEIVER OUTPUT
DRIVER
100Ω
100Ω
+
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
1/2 LT1720
BACKPLANE
DRIVER
TRANSMISSION LINE
100Ω
RECEIVER
1688/89 F13
Figure 13. 100Mbps Backplane Transmission
16889fa
9
LTC1688/LTC1689
U
W
U
U
APPLICATIONS INFORMATION
Layout Considerations
A ground plane is recommended when using high frequency 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
in order to obtain the same parasitic capacitances and thus
maintain good propagation delay skew.
Parasitic capacitance from each input to its corresponding
outputs should also be minimized. Any excess capacitance could result in slower operation or even instability.
Channel output pairs should be kept away from other
output pairs to avoid parasitic coupling.
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 and receiver bandwidth affects the maximum data
rate only over distances of less than 100', even for the best
cables. The LTC1688/LTC1689 RS485 drivers and
LTC1518/LTC1519 52Mbps RS485 receivers are the fastest 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.
Detailed information on data rate vs cable length is provided 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.
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.
DRIVER INPUT
CABLE DELAY
RECEIVER INPUT
2V/DIV
DRIVER
100Ω
100Ω
RECEIVER OUTPUT
RECEIVER
CATEGORY 5 CABLE
UNDER TEST
1/4 LTC1688
1/4 LTC1689
2µs/DIV
1688/89 F14
1688/89 F15
Figure 14. Test Circuit for Cable Speed Evaluation
Figure 15. 4000 Feet, 0.5Mbps, LTC1518 Receiver
DRIVER INPUT
DRIVER INPUT
CABLE DELAY
CABLE DELAY
RECEIVER INPUT
RECEIVER INPUT
2V/DIV
2V/DIV
RECEIVER OUTPUT
RECEIVER OUTPUT
2µs/DIV
Figure 16. 4000 Feet, 1Mbps, LTC1518 Receiver
1688/89 F16
500ns/DIV
1688/89 F17
Figure 17. 1000 Feet, 2Mbps, LTC1518 Receiver
16889fa
10
LTC1688/LTC1689
U
W
U
U
APPLICATIONS INFORMATION
DRIVER INPUT
DRIVER INPUT
CABLE DELAY
CABLE DELAY
RECEIVER INPUT
2V/DIV
RECEIVER INPUT
2V/DIV
RECEIVER OUTPUT
500ns/DIV
RECEIVER OUTPUT
1µs/DIV
1688/89 F18
Figure 18. 1000 Feet, 5Mbps, LTC1518 Receiver
1688/89 F19
Figure 19. 1000 Feet, 1Mbps, LTC1518 Receiver
DRIVER INPUT
DRIVER INPUT
CABLE DELAY
CABLE DELAY
RECEIVER INPUT
RECEIVER INPUT
2V/DIV
2V/DIV
RECEIVER OUTPUT
100ns/DIV
RECEIVER
OUTPUT
50ns/DIV
1688/89 F20
Figure 20. 200 Feet, 20Mbps, LTC1518 Receiver
1688/89 F21
Figure 21. 200 Feet, 33Mbps, LTC1518 Receiver
DRIVER INPUT
DRIVER INPUT
CABLE DELAY
CABLE DELAY
RECEIVER INPUT
RECEIVER INPUT
2V/DIV
2V/DIV
RECEIVER OUTPUT
50ns/DIV
Figure 22. 100 Feet, 50Mbps, LTC1518 Receiver
1688/89 F22
RECEIVER
OUTPUT
10ns/DIV
1688/89 F23
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LTC1688/LTC1689
U
PACKAGE DESCRIPTION
S Package
16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
.386 – .394
(9.804 – 10.008)
NOTE 3
.045 ±.005
.050 BSC
16
N
15
14
13
12
11
10
9
N
.245
MIN
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
1
.030 ±.005
TYP
2
3
N/2
N/2
RECOMMENDED SOLDER PAD LAYOUT
2
1
.010 – .020
× 45°
(0.254 – 0.508)
.008 – .010
(0.203 – 0.254)
3
4
5
7
6
8
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
0° – 8° TYP
.014 – .019
(0.355 – 0.483)
TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
.050
(1.270)
BSC
S16 0502
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
DESCRIPTION
COMMENTS
LTC486/LTC487
Low Power Quad RS485 Drivers
110µA Typ Supply Current, 10Mbps, – 7V to 12V Common Mode Range
LT 1394
7ns UltraFast Single Supply Comparator
6mA Typ Supply Current, Ground Sensing on Single Supply
LTC1518/LTC1519
High Speed, Precision Quad RS485 Receivers
52Mbps, Pin Compatible with LTC488/LTC489
LTC1520
High Speed, Precision Quad Differential Line Receiver
Single Supply, 18ns Propagation Delay, 100mV Threshold
®
LTC1685
High Speed, Precision RS485 Transceiver
52Mbps, Pin Compatible with LTC485
LTC1686/LTC1687
High Speed, Precision RS485 Full-Duplex Transceivers
52Mbps, Pin Compatible with LTC490/LTC491
LT1720
Dual 4.5ns UltraFast Single Supply Comparator
4mA per Comparator, Optimized for 3V or 5V Operation
16889fa
12
Linear Technology Corporation
LT/TP 1003 1K REV A • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 1999