LMS1485 5V Low Power RS-485 Differential Bus Transceiver
July 2003
LMS1485
5V Low Power RS-485 Differential Bus Transceiver
General Description
The LMS1485 is a low power differential bus/line transceiver
designed for high speed bidirectional data communication on
multipoint bus transmission lines. It is designed for balanced
transmission lines. It meets ANSI Standards TIA/EIA
RS422-B, TIA/EIA RS485-A and ITU recommendation and
V.11 and X.27.
The LMS1485 combines a TRI-STATE
™
differential line
driver and differential input receiver, both of which operate
from a single 5.0V power supply. The driver and receiver
have an active high and active low, respectively, that can be
externally connected to function as a direction control. The
driver and receiver differential inputs are internally con-
nected to form differential input/output (I/O) bus ports that
are designed to offer minimum loading to bus whenever the
driver is disabled or when V
CC
= 0V. These ports feature
wide positive and negative common mode voltage ranges,
making the device suitable for multipoint applications in
noisy environments.
The LMS1485 is build with National’s advanced BiCMOS
process and is available in a 8-Pin SOIC package. It is a
drop-in socket replacement to ADI’s ADM1485 and LTC’s
LT1485.
Features
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Meet ANSI standard RS-485-A and RS-422-B
Data rate 30Mbps
Single supply voltage operation, 5V
Wide input and output voltage range
Thermal shutdown protection
Short circuit protection
Driver propagation delay 10ns
Receiver propagation delay 25ns
High impedance outputs with power off
Open circuit fail-safe for receiver
Extended operating temperature range −40˚C to 85˚C
ESD rating 8kV HBM
Drop-in replacement to ADM1485 and LT1485
Available in 8-pin SOIC
Low supply current, I
CC
= 1mA
Applications
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Low power RS-485 systems
Network hubs, bridges, and routers
Point of sales equipment (ATM, barcode scanners,…)
Local area networks (LAN)
Integrated service digital network (ISDN)
Industrial programmable logic controllers
High speed parallel and serial applications
Multipoint applications with noisy environment
Typical Application
20048801
A typical multipoint application is shown in the above figure. Terminating resistors, RT, are typically required but only located at the two ends of the cable.
Pull up and pull down resistors maybe required at the end of the bus to provide failsafe biasing. The biasing resistors provide a bias to the cable when all
drivers are in TRI-STATE, See National Application Note, AN-847 for further information.
will be high also if the inputs (A and B) are open (non-terminated)
Receiver Output Enable: RO is enabled when RE is low; RO is in TRI-STATE when RE is high
Driver Output Enable: The driver outputs (A and B) are enabled when DE is high; they are in
TRI-STATE when DE is low. Pins A and B also function as the receiver input pins (see below)
Driver Input: A low on DI forces A low and B high while a high on DI forces A high and B low
when the driver is enabled
Ground
Non-inverting Driver Output and Receiver Input pin. Driver Output levels conform to RS-485
signaling levels
Inverting Driver Output and Receiver Input pin. Driver Output levels conform to RS-485 signaling
levels
Power Supply: 4.75V
≤
V
CC
≤
5.25V
Truth Table
DRIVER SECTION
RE
X
X
X
RECEIVER SECTION
RE
L
L
H
L
Note:
*
= Non Terminated, Open Input only
X = Irrelevant
Z = TRI-STATE
H = High level
L = Low level
DE
H
H
L
DE
L
L
X
L
DI
H
L
X
A-B
≥
+0.2V
≤
−0.2V
X
OPEN
*
A
H
L
Z
B
L
H
Z
RO
H
L
Z
H
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2
LMS1485
Absolute Maximum Ratings
(Note 1)
ESD Rating (Note 4) (Note 9)
Soldering Information
Infrared or Convection (20 sec.)
2kV
235˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage, V
CC
(Note 2)
Input Voltage, V
IN
(DI, DE, or RE)
Voltage Range at Any Bus Terminal
(AB)
Receiver Outputs
Package Thermal Impedance,
θ
JA
SOIC (Note 3)
Junction Temperature (Note 3)
Operating Free-Air Temperature
Range, T
A
Commercial
Industrial
Storage Temperature Range
ESD Rating (Note 4) (Note 8)
0˚C to 70˚C
−40˚C to 85˚C
−65˚C to 150˚C
8kV
125˚C/W
150˚C
7V
−0.3V to V
CC
+ 0.3V
−7V to 12V
−0.3V to V
CC
+ 0.3V
Operating Ratings
Min Nom Max
Supply Voltage, V
CC
Voltage at any Bus Terminal
(Separately or Common Mode)
V
IN
or V
IC
High-Level Input Voltage, V
IH
(Note 5)
Low-Level Input Voltage, V
IL
(Note 5)
Differential Input Voltage, V
ID
(Note 6)
2
0.8
V
V
V
4.75
−7
5.0 5.25
12
V
V
±
12
Electrical Characteristics
Over recommended ranges of supply voltage and operating free-air temperature (unless otherwise noted)
Symbol
Driver Section
V
OD
V
OD1
V
OD2
V
OD3
∆V
OD
V
OC
∆V
OC
Differential Output Voltage
Differential Output Voltage
Differential Output Voltage
Differential Output Voltage
Change in Magnitude of
Differential Output Voltage
Common-Mode Output
Voltage
Change in Magnitude of
Common-Mode Output
Voltage
Short-Circuit Output Current
CMOS Input Logic Threshold
Low
CMOS Input Logic Threshold
High
Logic Input Current
Differential Input Threshold
Voltage
Input Hysteresis Voltage
(V
TH+
− V
TH−
)
Input Resistance
Input Current (A, B)
Logic Enable Input Current
CMOS Low-Level Output
Voltage
R =
∞
(Figure
1)
R = 50Ω (Figure
1),
RS-422
R = 27Ω (Figure
1),
RS-485
V
TEST
= −7V to + 12V (Figure
2)
R = 27Ω or 50Ω (Figure
1
), (Note 7)
R = 27Ω or 50Ω (Figure
1),
(Note 7)
R = 27Ω or 50Ω (Figure
1),
(Note 7)
−0.2
2
1.5
1.5
−0.2
5
5
5
5
0.2
3
0.2
V
V
V
V
V
V
V
Parameter
Conditions
Min
Typ
Max
Units
I
OSD
V
INL
V
INH
I
IN
V
TH
∆V
TH
R
IN
I
IN
I
RE
V
OL
V
O
= High, −7V≤V
CM
≤+12V
V
O
= Low, −7V
≤V
CM
≤+12V
DE, DI, RE
DE, DI, RE
DE, DI
−7V
≤
V
CM
≤
+ 12V
V
CM
= 0
−7V
≤
V
CM
≤
+ 12V
V
IN
= 12V
V
IN
= −7V
RE
I
OL
= 4mA
−250
−250
250
250
0.8
mA
V
V
2
−1
−0.2
70
12
1
−0.8
−1
1
0.4
1
+0.2
µA
V
mV
kΩ
mA
µA
V
Receiver Section
3
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LMS1485
Electrical Characteristics
Symbol
V
OH
I
OSR
I
OZ
Parameter
CMOS High-Level Output
Voltage
Short-Circuit Output Current
Tristate Output Leakage
Current
Supply Current
(Continued)
Over recommended ranges of supply voltage and operating free-air temperature (unless otherwise noted)
Conditions
I
OH
= −4mA
V
O
= GND or V
CC
0.4V
≤V
O
≤+2.4V
Min
4
7
−1
85
1
Typ
Max
Units
V
mA
µA
Power Supply Current
I
CC
Driver Enabled, Output = No Load,
Digital Inputs = GND or V
CC
Driver Disabled, Output = No Load,
Digital Inputs = GND or V
CC
Switching Characteristics
Driver
T
PLH
,
T
PHL
T
SKEW
T
R
,
T
F
T
ENABLE
T
DISABLE
Receiver
T
PLH
,
T
PHL
T
SKEW
T
ENABLE
T
DISABLE
Propagation Delay Input to
Output
Receiver Output Skew
Receiver Enable Time
Receiver Disable Time
C
L
= 15pF
(Figure
5, Figure 7)
(Figure
5, Figure 7)
(Figure
6, Figure 10)
(Figure
6, Figure 10)
18
33
2
6
15
25
25
55
ns
ns
ns
ns
Propagation Delay Input to
Output
Driver Output Skew
Driver Rise and Fall Time
Driver Enable to Ouput Valid
Time
Output Disable Time
R
L
= 54Ω, C
L
= 100pF
(Figure
3, Figure 7)
R
L
= 54Ω, C
L
= 100pF
(Figure
3, Figure 7)
R
L
= 100Ω, C
L
= 100pF
(Figure
3, Figure 7)
(Figure
4, Figure 8)
(Figure
4, Figure 8)
11
1
5
18
20
10
32
40
20
ns
ns
ns
ns
ns
1.1
1
2.2
2.2
mA
mA
Note 1:
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics
Note 2:
All voltage values, except differential I/O bus voltage, are with respect to network ground terminal.
Note 3:
The maximum power dissipation is a function of T
J(MAX)
,
θ
JA
, and T
A
. The maximum allowable power dissipation at any ambient temperature is P
D
=
(T
J(MAX)
- T
A
)/θ
JA
. All numbers apply for packages soldered directly into a PC board.
Note 4:
ESD rating based upon human body model, 100pF discharged through 1.5kΩ.
Note 5:
Voltage limits apply to DI, DE, RE pins.
Note 6:
Differential input/output bus voltage is measured at the non-inverting terminal A with respect to the inverting terminal B.
Note 7:
|∆V
OD
| and |∆V
OC
| are changes in magnitude of V
OD
and V
OC
, respectively when the input changes from high to low levels.
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