RS485 Quick Guide Datasheet by Linear Technology/Analog Devices

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Frammma. R5485 SPEBIHED/ LIMITS LTLJCUWW WWKNALOG DEVICES
What Distance Can Be Achieved?
The achievable distance is a function of the cable. The longer the cable, the greater
the attenuation. Because attenuation increases with frequency, cables also exhibit a
lowpass filter behavior so that achievable distance diminishes with data rate.
The distances recommended by the RS485 standard are shown in the graph to the
right. Many cables are capable of higher speed and distance. Consult the cable
manufacturer’s typical performance curve of 0 to 50% rise time vs cable length.
What is the Failsafe Receiver Output State with No Input Signal?
That depends on the failsafe type of the receiver. Type 1 devices (see over) output
a guaranteed 1 state when the receiver inputs are left open, but the output is
undetermined when the inputs are shorted. Type 2 devices output a guaranteed 1
state whether the receiver inputs are left open, shorted or terminated but not driven.
What is the Proper Way to Terminate the Cable?
The cable should be terminated at each end with a resistance equal to the cable’s
characteristic impedance.
RS485 Quick Guide
RS485 conveys data differentially over a terminated twisted pair, permitting up to 10Mbps data rates. The standard specifies electrical
characteristics of a driver and receiver, and does not specify any data protocol or connectors. RS485 is popular for inexpensive local
networks, multidrop communication links and long haul data transfer over distances of up to 4,000 feet. The use of a balanced line means
RS485 has excellent noise rejection and is ideal for industrial and commercial applications. You’ll find RS485 in applications as diverse as
monitoring oil wells and linking POS terminals, to alarm systems, motion control and HVAC controls. Extended capability transceivers offer
data rates up to 100Mbps and up to 256 nodes, as well as 6500VRMS isolation and fault protection up to ±60V.
Specification RS422 RS485
Mode of Operation Differential Differential
Number of Drivers and Receivers
Allowed on One Line
1 Driver,
10 Receivers
32 Drivers,
32 Receivers
Maximum Cable Length 4000 Feet 4000 Feet
Maximum Data Rate 10Mbps 10Mbps
Maximum Voltage Applied to Driver Output –0.25V to 6V –7V to 12V
Differential Driver Output Signal Minimum Loaded ±2V ±1.5V
Maximum Unloaded ±5V ±5V
Termination 100120
Receiver Input Voltage Range ±7V –7V to 12V
Receiver Input Sensitivity ±200mV ±200mV
Receiver Input Resistance 4k (Min) 12k (Min)
DATA RATE (bps)
CABLE LENGTH (FT)
10k 1M 10M100k 100M
PRACTICAL
LIMIT FOR
20Mbps
DEVICES
100
1k
10
10k
RS485
SPECIFIED
LIMITS
TIA/EIA-485-A Standard
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog Devices, Inc.
All other trademarks are the property of their respective owners.
WWKNALOG DEVICES L7LJCUWW
Part Number
Supply
(V)
Max Data
Rate (Bits/s) # Dr # Rec Duplex SHDN
ESD
(kV) Failsafe Comments
Temp
Grade Package
Galvanic Isolation
LTM2885 5 20M 1 1 Full Yes ±15 Type 2 6500VRMS Isolation,
No External Components,
Isolated 1W DC/DC
C, I, H 22 × 9 × 5.2 BGA
LTM
®
2881-3/
LTM2881-5
3.3/5 20M 1 1 Full Yes ±15 Type 2 2500VRMS Isolation,
No External Components,
Isolated 1W DC/DC
C, I, H, MP 15 × 11.25 × 2.8 LGA,
15 × 11.25 × 3.4 BGA
LTC1535 5 250k 1 1 Full No ±8 Type 2
2500VRMS Isolation
C, I SO(W)-28
±60V Fault Protection
LTC2862-1/-2 3 to 5.5 20M/250k 1 1 Half Yes ±15 Type 2 Pin-Compatible with LT1785A C, I, H, MP SO-8, 3 × 3 DFN-8
LTC2863-1/-2 3 to 5.5 20M/250k 1 1 Full No ±15 Type 2 C, I, H, MP SO-8, 3 × 3 DFN-8
LTC2864-1/-2 3 to 5.5 20M/250k 1 1 Full Yes ±15 Type 2 Pin-Compatible with LT1791A C, I, H, MP SO-14, 3 × 3 DFN-10
LTC2865 3 to 5.5 20M/250k 1 1 Full Yes ±15 Type 2 Logic Supply Pin, SLO Pin C, I, H MSOP-12, 4 × 3 DFN-12
LT1785A 5 250k 1 1 Half Yes ±15 Type 2 Pin-Compatible with LTC485 C, I, H SO-8, DIP-8
LT1791A 5 250k 1 1 Full Yes ±15 Type 2 Pin-Compatible with LTC491 C, I, H SO-14, DIP-14
Integrated Switchable 120 Termination
LTC2854 3.3 20M 1 1 Half Yes ± 25 Type 2 Low Power C, I, H 3 × 3 DFN-10
LTC2859 5 20M/250k 1 1 Half Yes ±15 Type 2 Slew Rate Control, Low Power C, I, H 3 × 3 DFN-10
LTC2855 3.3 20M 1 1 Full Yes ±15 Type 2 Low Power C, I, H 4 × 3 DFN-12, SSOP-16
LTC2861 5 20M/250k 1 1 Full Yes ±15 Type 2 Slew Rate Control, Low Power C, I 4 × 3 DFN-12, SSOP-16
3.3V Supply Operation
LTC2850 3.3 20M 1 1 Half Yes ±15 Type 2 Low Power C, I, H SO-8, MSOP-8, 3 × 3 DFN-8
LTC2851 3.3 20M 1 1 Full No ±15 Type 2 Low Power C, I, H SO-8, MSOP-8, 3 × 3 DFN-8
LTC2852 3.3 20M 1 1 Full Yes ±15 Type 2 DE and RE Pins, Low Power C, I, H SO-14, MSOP-10,
3 × 3 DFN-10
LTC1480 3.3 2.5M 1 1 Half Yes ± 3.5 Type 1 Low Power C, I SO-8, DIP- 8
Low Power
LTC2856-1/-2 5 20M/250k 1 1 Half Yes ±15 Type 2 Hot Swap Capable C, I, H MSOP-8, 3 × 3 DFN-8
LTC2857-1/-2 5 20M/250k 1 1 Full No ±15 Type 2 Hot Swap Capable C, I, H MSOP-8, 3 × 3 DFN-8
LTC2858-1/-2 5 20M/250k 1 1 Full Yes ±15 Type 2 Hot Swap Capable C, I, H MSOP-10, 3 × 3 DFN-10
LTC1690 5 5M 1 1 Full No ±15 Type 2 C, I MSOP-8, SO-8, DIP-8
LTC1481 5 2.5M 1 1 Half Yes ±10 Type 1 C, I SO-8, DIP-8
LTC1482 5 4M 1 1 Half Yes ±15 Type 2 Carrier Detect C, I MSOP-8, SO-8, DIP-8
LTC1483 5 150k 1 1 Half Yes ±10 Type 1 Low EMI C, I SO-8, DIP-8
LTC1484 5 4M 1 1 Half Yes ±15 Type 2 C, I MSOP-8, SO-8, DIP-8
LTC1485 5 10M 1 1 Half No ±10 Type 1 C, I SO-8, DIP-8
LTC1487 5 250k 1 1 Half Yes ±10 Type 1 Low EMI C SO-8, DIP-8
LTC485 5 2.5M 1 1 Half No ±4 Type 1 C, I, M SO-8, DIP-8, CERDIP-8
LTC490 5 2.5M 1 1 Full No ±2 Type 1 C, I SO-8, DIP-8
LTC491 5 2.5M 1 1 Full No ±2 Type 1 DE and RE Pins C, I SO-14, DIP-14
High Speed
LTC1685 5 52M 1 1 Half No ±4 Type 2 C, I SO-8
LTC1686 5 52M 1 1 Full No ±4 Type 1 C, I SO-8
LTC1687 5 52M 1 1 Full No ±4 Type 1 DE and RE Pins C, I SO-14
Quad Drivers and Receivers
LTC1688/89 5 100M 4 0 No ±4 Hot Swap Capable,
1/2 DE Pins
C, I SO-16
LTC486/87 5 10M 4 0 No ±2 Type 1 Low Power, 1/2 DE Pins C, I SO(W)-16, DIP-16
LTC1518/19 5 52M 0 4 No ±4 Type 2 C, I SO-16
LTC488/89 5 10M 0 4 No ±10 Type 1 1/2 DE Pins C, I SO(W)-16, DIP-16
LTC1520 5 50M 0 4 No ±4 High Speed, LVDS-Compatible C SO-16
RS232/RS485 Multiprotocol
LTC2870 3 to 5.5 20M/500k 1 1 Both Yes ± 26 Type 2 Two RS232 Transceivers C, I 4 × 5 QFN-28, TSSOP-28
LTC2871 3 to 5.5 20M/500k 1 1 Both Yes ±16 Type 2 Two RS232 Transceivers C, I 5 × 7 QFN-38, TSSOP-38
LTC2872 3 to 5.5 20M/500k 2 2 Both Yes ±16 Type 2 Four RS232 Transceivers C, I 5 × 7 QFN-38
Type 1 = Open; Type 2 = Idle, Open, Short
Linear Technology RS485/RS422 Transceivers
1116E
www.linear.com/RS485 n 1-800-4-LINEAR

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