LTC1686/LTC1687
52Mbps Precision Delay
RS485 Fail-Safe Transceivers
FEATURES
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DESCRIPTION
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.
A unique architecture provides very stable propagation
delays and low skew over a wide common mode and
ambient temperature range.
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.
The LTC1686/LTC1687 operate from a single 5V supply
and draw only 7mA of supply current.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Precision Propagation Delay Over Temperature:
Receiver/Driver: 18.5ns
±
3.5ns
High Data Rate:
52Mbps
Low t
PLH
/t
PHL
Skew:
Receiver/Driver: 500ps Typ
–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
APPLICATIONS
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High Speed RS485/RS422 Full Duplex Transceivers
Level Translator
Backplane Transceiver
STS-1/OC-1 Data Transceiver
Signal Repeaters
TYPICAL APPLICATION
LTC1686
5
D
3
DRIVER
100Ω
6
100Ω
RECEIVER
R
LTC1686
2V/DIV
CABLE DELAY
1V/DIV
8
R
2
RECEIVER
100Ω
7
100Ω
DRIVER
D
5V/DIV
400 FT OF CATEGORY 5 UTP
LTC1686/87 • TA01
U
U
U
10Mbps Data Pulse
400 Feet Category 5 UTP
DRIVER INPUT
RECEIVER
INPUT
RECEIVER
OUTPUT
100ns/DIV
1686/87 TA02
1
LTC1686/LTC1687
ABSOLUTE
(Note 1)
AXI U
RATI GS
Driver Short-Circuit Duration
(V
OUT
: – 7V to 10V)...................................... Indefinite
Receiver Short-Circuit Duration
(V
OUT
: 0V to V
DD
) ........................................ Indefinite
Operating Temperature Range .................... 0°C to 70°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Supply Voltage (V
DD
) .............................................. 10V
Control Input Currents .................... – 100mA to 100mA
Control Input Voltages .................. – 0.5V to V
DD
+ 0.5V
Driver Input Voltages .................... – 0.5V to V
DD
+ 0.5V
Driver Output Voltages ................................. + 12V/– 7V
Receiver Input Voltages ................................ + 12V/– 7V
Receiver Output Voltages ............. – 0.5V to V
DD
+ 0.5V
Receiver Input Differential ...................................... 10V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
DD
1
R 2
D 3
D
ORDER PART
NUMBER
8
A
B
Z
Y
7
6
5
R
LTC1686CS8
S8 PART MARKING
1686
GND 4
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
Consult factory for Industrial and Military grade parts.
DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
OD1
V
OD2
∆V
OD
PARAMETER
Differential Driver Output (Unloaded)
Differential Driver Output (With Load)
Change in Magnitude of Driver Differential
Output Voltage for Complementary
Output States
Driver Common Mode Output Voltage
Change in Magnitude of Driver Common
Mode Output Voltage for Complementary
Output States
Input High Voltage
Input Low Voltage
Input Current
Input Current (A, B)
Differential Input Threshold Voltage
for Receiver
Receiver Input Hysteresis
Receiver Output High Voltage
CONDITIONS
I
OUT
= 0
R = 50Ω (RS422)
R = 27Ω (RS485), Figure 1
R = 27Ω or 50Ω, Figure 1
V
OC
∆V
OC
R = 27Ω or 50Ω, V
DD
= 5V, Figure 1
R = 27Ω or 50Ω, Figure 1
V
IH
V
IL
I
IN1
I
IN2
V
TH
∆V
TH
V
OH
D, DE, RE
D, DE, RE
D, DE, RE
V
A
, V
B
= 12V, V
DD
= 0V or 5.25V
V
A
, V
B
= – 7V, V
DD
= 0V or 5.25V
– 7V
≤
V
CM
≤
12V
V
CM
= 0V
I
OUT
= – 4mA, V
ID
= 300mV
2
U
U
W
W W
U
W
TOP VIEW
NC
R
RE
DE
D
GND
GND
1
2
3
4
5
D
6
7
S PACKAGE
14-LEAD PLASTIC SO
9
8
Y
NC
R
14 V
DD
13 NC
12 A
11 B
10 Z
ORDER PART
NUMBER
LTC1687CS
T
JMAX
= 125°C,
θ
JA
= 90°C/ W
V
DD
= 5V
±
5% unless otherwise noted (Notes 2, 3).
MIN
q
q
q
TYP
MAX
V
DD
UNITS
V
V
V
V
2.0
1.5
V
DD
0.2
q
q
2
3
0.2
V
V
q
q
q
q
q
q
2
0.8
–1
– 500
– 0.3
25
0.3
1
500
V
V
µA
µA
µA
V
mV
V
q
3.5
4.8
LTC1686/LTC1687
DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
OL
I
OZR
I
OZD
C
LOAD
I
DD
I
OSD1
I
OSD2
I
OSR
R
IN
C
IN
Fail-Safe
Time
CMRR
PARAMETER
Receiver Output Low Voltage
Three-State (High Impedance) Output
Current at Receiver
Three-State (High Impedance) Output
Current at Driver
Supply Current
Driver Short-Circuit Current, V
OUT
= HIGH
Driver Short-Circuit Current, V
OUT
= LOW
Receiver Short-Circuit Current
Input Resistance
Input Capacitance
Open-Circuit Input Voltage
Time to Detect Fail-Safe Condition
Receiver Input Common Mode
Rejection Ratio
CONDITIONS
V
DD
= 5V
±5%
unless otherwise noted (Notes 2, 3).
MIN
q
q
q
q
q
q
q
q
q
TYP
MAX
0.4
1
200
500
UNITS
V
µA
µA
pF
mA
mA
mA
mA
kΩ
pF
I
OUT
= 4mA, V
ID
= – 300mV
0.4V
≤
V
OUT
≤
2.4V
V
OUT
= – 7V to 12V
–1
– 200
Receiver and Driver Output Load Capacitance (Note 4)
No Load, Pins D, DE, RE = 0V or V
DD
V
OUT
= – 7V or 10V (Note 5)
V
OUT
= – 7V or 10V (Note 5)
V
OUT
= 0V or V
DD
(Note 5)
– 7V
≤
V
CM
≤
12V
A, B, D, DE, RE Inputs (Note 4)
V
DD
= 5V (Note 4), Figure 5
7
12
20
20
20
22
3
3.2
3.3
2
3.4
q
V
µs
dB
V
CM
= 2.5V, f = 26MHz
45
SWITCHING CHARACTERISTICS
SYMBOL
t
PLH
, t
PHL
t
SKEW
t
r
, t
f
t
ZH
t
ZL
t
LZ
t
HZ
t
PLH
, t
PHL
t
SQD
t
ZL
t
ZH
t
LZ
t
HZ
PARAMETER
Driver Input-to-Output Propagation Delay
Driver Output A-to-Output B Skew
Driver Rise/Fall Time
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable from Low
Driver Disable from High
Receiver Input-to-Output Propagation Delay C
L
= 15pF, Figures 3, 7
Receiver Skew
t
PLH
– t
PHL
C
L
= 15pF, Figures 3, 7
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Receiver Disable from High
Maximum Receiver Input
Rise/Fall Times
C
L
= 15pF, S1 Closed, Figures 2, 8
C
L
= 15pF, S2 Closed, Figures 2, 8
C
L
= 15pF, S1 Closed, Figures 2, 8
C
L
= 15pF, S2 Closed, Figures 2, 8
(Note 4)
C
L
= 15pF, Same Temperature (Note 4)
V
DD
= 5V
±5%
(Note 4)
V
DD
= 5V
±5%
(Note 4)
V
DD
= 5V
±5%
(Note 4)
t
PKG-PKG
Package-to-Package Skew
Minimum Input Pulse Width
Maximum Data Rate
Maximum Input Frequency
U
V
DD
= 5V, unless otherwise noted (Notes 2, 3).
MIN
q
CONDITIONS
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
Figures 3, 5
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
Figures 3, 5
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
Figures 3, 5
C
L
= 100pF, S2 Closed, Figures 4, 6
C
L
= 100pF, S1 Closed, Figures 4, 6
C
L
= 15pF, S1 Closed, Figures 4, 6
C
L
= 15pF, S2 Closed, Figures 4, 6
q
q
q
q
q
TYP
18.5
500
3.5
25
25
25
25
MAX
22
UNITS
ns
ps
ns
15
50
50
50
50
22
50
50
50
50
2000
ns
ns
ns
ns
ns
ps
ns
ns
ns
ns
ns
ns
15
18.5
500
25
25
25
25
q
q
q
q
q
1.5
q
q
q
17
52
26
60
30
19.2
ns
Mbps
MHz
3
LTC1686/LTC1687
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating
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 3:
All typicals are given for V
DD
= 5V, T
A
= 25°C.
Note 4:
Guaranteed by design, but not tested.
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Input CMRR
46.5
COMMON MODE REJECTION RATIO (dB)
46.0
SUPPLY CURRENT (mA)
45.0
44.5
44.0
43.5
43.0
42.5
T
A
= 25°C
42.0
10
1k
100k
FREQUENCY (Hz)
1M
1686/87 G01
50
40
30
20
10
0
1
10
30
DATA RATE (Mbps)
20
40
50
SUPPLY CURRENT (mA)
45.5
Receiver Propagation Delay
vs Load Capacitance
30
T
A
= 25°C
25
25
RECEIVER PROPAGATION DELAY (ns)
PROPAGATION DELAY (ns)
20
15
10
5
0
PROPAGATION DELAY (ns)
5
15
25
35
55
105
LOAD CAPACITANCE (pF)
4
U W
1686/87 G04
Supply Current vs Data Rate
70
BOTH DRIVER AND RECEIVER
ENABLED AND LOADED
60 T = 25°C
A
Supply Current vs Temperature
58
57
56
55
54
53
52
51
BOTH DRIVER AND RECEIVER
ENABLED AND LOADED
25Mbps DATA RATE
0
50
TEMPERATURE (°C)
25
75
100
1686/87 G03
50
– 25
1686/87 G02
Receiver Propagation Delay
vs Common Mode
25
Receiver Propagation Delay
vs Input Overdrive
T
A
= 25°C
20
T
A
= 25°C
20
15
15
10
10
5
5
205
0
8 10
4
–7 –4 –2 0
6
2
RECEIVER COMMON MODE (V)
12
0
0.3
0.5 0.7 1.0 1.25 1.5 2.0
RECEIVER INPUT OVERDRIVE (V)
2.5
1686/87 G05
1686/87 G06
LTC1686/LTC1687
TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Propagation Delay
vs Temperature
25
PROPAGATION DELAY (ns)
15
DATA RATE (Mbps)
50
40
30
20
10
PROPAGATION DELAY (ns)
1.5
0.4
0.5 0.6 0.7 1.0
RECEIVER INPUT DIFFERENTIAL (V)
2.5
20
10
5
0
–50 –25
50
75
0
25
TEMPERATURE (°C)
Driver Propagation Delay
vs Driver Input Voltage
25
V
DD
= 5V
INPUT THRESHOLD = 1.5V
T
A
= 25°C
t
HL
t
LH
15
19.0
PROPAGATION DELAY (ns)
PROPAGATION DELAY (ns)
20
10
5
0
2.5
3.0
4.0
4.5
3.5
DRIVER INPUT VOLTAGE (V)
PIN FUNCTIONS
LTC1686
V
DD
(Pin 1):
Positive Supply, 5V to
±5%.
Bypass with
0.1µF ceramic capacitor.
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.
GND (Pin 4):
Ground.
Y (Pin 5):
Noninverting Driver Output.
Z (Pin 6):
Inverting Driver Output.
B (Pin 7):
Inverting Receiver Input.
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.
RE (Pin 3):
Receiver Enable. RE = low enables the receiver.
RE = high forces receiver output into high impedance
state. Do not float.
U W
100
1686/87 G09
Receiver Maximum Data Rate
vs Input Overdrive
70
T
A
= 25°C
60
20
25
Driver Propagation Delay
vs Temperature
15
10
5
125
0
0.3
0
– 20
0
20
40
60
TEMPERATURE (°C)
80
100
1686/87 G10
1686/87 G07
Driver Propagation Delay
vs Capacitive Load
T
A
= 25°C
18.5
18.0
17.5
17.0
16.5
16.0
5.0
1686/87 G08
5
15
25
50
75
100
LOAD CAPACITANCE (pF)
150
1686/87 G11
U
U
U
5
RF/无线
