1
LTC488/LTC489
Quad RS485 Line Receiver
S
FEATURE
s
Low Power: I
CC
= 7mA Typ
s
Designed for RS485 or RS422 Applications
s
Single 5V Supply
s
7V to 12V Bus Common Mode Range Permits
±
7V
Ground Difference Between Devices on the Bus
s
60mV Typical Input Hysteresis
s
Receiver Maintains High Impedance in Three-State or
with the Power Off
s
28ns Typical Receiver Propagation Delay
s
Pin Compatible with the SN75173 (LTC488)
s
Pin Compatible with the SN75175 (LTC489)
U
S
A
O
PPLICATI
s
Low Power RS485/RS422 Receivers
s
Level Translator
The LTC
®
488 and LTC489 are low power differential bus/
line receivers designed for multipoint data transmission
standard RS485 applications with extended common mode
range (12V to 7V). They also meet the requirements of
RS422.
The CMOS design offers significant power savings over its
bipolar counterpart without sacrificing ruggedness against
overload or ESD damage.
The receiver features three-state outputs, with the receiver
output maintaining high impedance over the entire com-
mon mode range.
The receiver has a fail-safe feature which guarantees a
high output state when the inputs are left open.
Both AC and DC specifications are guaranteed 4.75V to
5.25V supply voltage range.
D
U
ESCRIPTIO
U
A
O
PPLICATI
TYPICAL
120
4000 FT 24 GAUGE TWISTED PAIR
DI
RECEIVER
1/4 LTC488
120
DRIVER
1/4 LTC486
RO
EN
EN
1
2
4
12
3
EN
EN
120
4000 FT 24 GAUGE TWISTED PAIR
DI
RECEIVER
1/4 LTC489
120
DRIVER
1/4 LTC487
RO
EN12
1
2
4
3
EN12
LTC488/9 TA01
, LTC and LT are registered trademarks of Linear Technology Corporation.
2
LTC488/LTC489
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
(Note 1)
Supply Voltage (V
CC
) .............................................. 12V
Control Input Currents ........................ 25mA to 25mA
Control Input Voltages ................ 0.5V to (V
CC
+ 0.5V)
Receiver Input Voltages ........................................
±
14V
Receiver Output Voltages ........... 0.5V to (V
CC
+ 0.5V)
Operating Temperature Range
LTC488C/LTC489C ................................. 0
°
C to 70
°
C
LTC488I/LTC489I .............................. 40
°
C to 85
°
C
Storage Temperature Range ................ 65
°
C to 150
°
C
Lead Temperature (Soldering, 10 sec)................. 300
°
C
W
U
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
T
JMAX
= 150
°
C,
JA
= 70
°
C/W (N PKG)
T
JMAX
= 150
°
C,
JA
= 90
°
C/W (S PKG)
LTC488CN
LTC488CS
LTC488IN
LTC488IS
LTC489CN
LTC489CS
LTC489IN
LTC489IS
1
2
3
4
5
6
7
8
TOP VIEW
N PACKAGE
16-LEAD PLASTIC DIP
S PACKAGE
16-LEAD PLASTIC SOL
16
15
14
13
12
11
10
9
B1
A1
RO1
EN12
RO2
A2
B2
GND
V
CC
B4
A4
RO4
EN34
RO3
A3
B3
R
R
R
R
T
JMAX
= 150
°
C,
JA
= 70
°
C/W (N PKG)
T
JMAX
= 150
°
C,
JA
= 90
°
C/W (S PKG)
1
2
3
4
5
6
7
8
TOP VIEW
N PACKAGE
16-LEAD PLASTIC DIP
S PACKAGE
16-LEAD PLASTIC SOL
16
15
14
13
12
11
10
9
B1
A1
RO1
EN
RO2
A2
B2
GND
V
CC
B4
A4
RO4
EN
RO3
A3
B3
R
R
R
R
V
CC
= 5V (Notes 2, 3), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
INH
Input High Voltage
EN, EN, EN12, EN34
q
2.0
V
V
INL
Input Low Voltage
EN, EN, EN12, EN34
q
0.8
V
I
IN1
Input Current
EN, EN, EN12, EN34
q
±
2
µ
A
I
IN2
Input Current (A, B)
V
CC
= 0V or 5.25V, V
IN
= 12V
q
1.0
mA
V
CC
= 0V or 5.25V, V
IN
= 7V
q
0.8
mA
V
TH
Differential Input Threshold Voltage for Receiver
7V
V
CM
12V
q
0.2
0.2
V
V
TH
Receiver Input Hysteresis
V
CM
= 0V
60
mV
V
OH
Receiver Output High Voltage
I
O
= 4mA, V
ID
= 0.2V
q
3.5
V
V
OL
Receiver Output Low Voltage
I
O
= 4mA, V
ID
= 0.2V
q
0.4
V
I
OZR
Three-State Output Current at Receiver
V
CC
= Max 0.4V
V
O
2.4V
q
±
1
µ
A
I
CC
Supply Current
No Load, Digital Pins = GND or V
CC
q
7
10
mA
R
IN
Receiver Input Resistance
7V
V
CM
12V, V
CC
= 0V
q
12
k
I
OSR
Receiver Short-Circuit Current
0V
V
O
V
CC
q
7
85
mA
t
PLH
Receiver Input to Output
C
L
= 15pF (Figures 1, 3)
q
12
28
55
ns
t
PHL
Receiver Input to Output
C
L
= 15pF (Figures 1, 3)
q
12
28
55
ns
t
SKD
| t
PLH
t
PHL
|
C
L
= 15pF (Figures 1, 3)
4
ns
Differential Receiver Skew
ELECTRICAL C
C
HARA TERISTICS
C
D
Consult factory for Military grade parts.
3
LTC488/LTC489
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
t
ZL
Receiver Enable to Output Low
C
L
= 15pF (Figures 2, 4) S1 Closed
q
30
60
ns
t
ZH
Receiver Enable to Output High
C
L
= 15pF (Figures 2, 4) S2 Closed
q
30
60
ns
t
LZ
Receiver Disable from Low
C
L
= 15pF (Figures 2, 4) S1 Closed
q
30
60
ns
t
HZ
Receiver Disable from High
C
L
= 15pF (Figures 2, 4) S2 Closed
q
30
60
ns
The
q
denotes specifications that apply over the operating temperature
range.
Note 1: Absolute Maximum Ratings are those beyond which the safety of
the device may be impaired.
Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
Note 3: All typicals are given for V
CC
= 5V and T
A
= 25
°
C.
V
CC
= 5V
±
5% (Notes 2, 3), unless otherwise noted.
ELECTRICAL C
C
HARA TERISTICS
C
D
OUTPUT VOLTAGE (V)
0
0
OUTPUT CURRENT (mA)
16
1.0
488 G04
8
0.5
1.5
24
32
2.0
4
12
20
28
36
Receiver Output Low Voltage vs
Output Current at T
A
= 25
°
C
OUTPUT VOLTAGE (V)
5
0
OUTPUT CURRENT (mA)
8
488 G03
4
4
3
12
16
2
2
6
10
14
18
Receiver Output High Voltage vs
Output Current at T
A
= 25
°
C
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Receiver Output Low Voltage vs
Temperature at I = 8mA
TEMPERATURE (°C)
50
0
OUTPUT VOLTAGE (V)
0.1
0.3
0.4
0.5
50
0.9
488 G01
0.2
25
125
0.6
0.7
0.8
0
25
75
100
TEMPERATURE (°C)
50
3.0
OUTPUT VOLTAGE (V)
3.8
50
488 G02
3.4
25
125
4.2
4.6
0
25
75
100
4.8
4.4
4.0
3.6
3.2
Receiver Output High Voltage vs
Temperature at I = 8mA
4
LTC488/LTC489
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
PI FU CTIO S
U
U
U
B3 (Pin 9) Receiver 3 Input.
A3 (Pin 10) Receiver 3 Input.
RO3 (Pin 11) Receiver 3 Output. Refer to RO1.
EN (Pin 12)(LTC488) Receiver Output Disabled. See
Function Table for details.
EN34 (Pin 12)(LTC489) Receiver 3, Receiver 4 output
enabled. See Function Table for details.
RO4 (Pin 13) Receiver 4 Output. Refer to RO1.
A4 (Pin 14) Receiver 4 Input.
B4 (Pin 15) Receiver 4 Input.
V
CC
(Pin 16) Positive Supply; 4.75V
V
CC
5.25V.
B 1 (Pin 1) Receiver 1 Input.
A1 (Pin 2) Receiver 1 Input.
RO1 (Pin 3) Receiver 1 Output. If the receiver output is
enabled, then if A > B by 200mV, RO1 will be high. If
A < B by 200mV, then RO1 will be low.
EN (Pin 4) (LTC488) Receiver Output Enabled. See
Function Table for details.
EN12 (Pin 4) (LTC489) Receiver 1, Receiver 2 Output
Enabled. See Function Table for details.
RO2 (Pin 5) Receiver 2 Output. Refer to RO1.
A2 (Pin 6) Receiver 2 Input.
B2 (Pin 7) Receiver 2 Input.
GND (Pin 8) Ground Connection.
TEMPERATURE (°C)
50
5.4
SUPPLY CURRENT (mA)
6.2
50
488 G07
5.8
25
125
6.6
7.0
0
25
75
100
Supply Current vs Temperature
TEMPERATURE (°C)
50
1
TIME (ns)
3
50
488 G06
2
25
125
4
5
0
25
75
100
TEMPERATURE (°C)
50
1.55
INPUT THRESHOLD VOLTAGE (V)
1.59
50
488 G05
1.57
25
125
1.61
1.63
0
25
75
100
TTL Input Threshold vs
Temperature
Receiver
|
t
PLH
t
PHL
|
vs
Temperature
5
LTC488/LTC489
LTC488
LTC489
DIFFERENTIAL
ENABLES
OUTPUT
A B
EN12 or EN34
RO
V
ID
0.2V
H
H
0.2V < V
ID
< 0.2V
H
?
V
ID
0.2V
H
L
X
L
Z
H: High Level
L: Low Level
X: Irrelevant
?: Indeterminate
Z: High Impedance (Off)
FU CTIO TABLES
U
U
DIFFERENTIAL
ENABLES
OUTPUT
A B
EN
EN
RO
V
ID
0.2V
H
X
H
X
L
H
0.2V < V
ID
< 0.2V
H
X
?
X
L
?
V
ID
0.2V
H
X
L
X
L
L
X
L
H
Z
TEST CIRCUITS
Figure 1. Receiver Timing Test Circuit
Note:
The input pulse is supplied by a generator having the following characteristics:
f = 1MHz, Duty Cycle = 50%, t
r
< 10ns, t
f
10ns, Z
OUT
= 50
D
488/9 F01
DRIVER
RECEIVER
C
L
RO
A
B
54
100pF
100pF
Figure 2. Receiver Enable and Disable Timing Test Circuit
1k
488/9 F02
C
L
S1
S2
1k
V
CC
RECEIVER
OUTPUT
6
LTC488/LTC489
TI
W
E WAVEFOR
S
U
G
WITCHI
W
S
Figure 3. Receiver Propagation Delays
0V
V
OD2
t
PHL
f = 1MHz; t
r
10ns; t
f
10ns
0V
t
PLH
V
OD2
INPUT
A, B
V
OH
1.5V
1.5V
V
OL
RO
INPUT
488/9 F03
f = 1MHz; t
r
10ns; t
f
10ns
1.5V
RO
488/9 F04
0V
3V
1.5V
t
ZL
V
OL
V
OH
1.5V
t
LZ
0.5V
0.5V
t
HZ
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
0V
5V
1.5V
t
ZH
RO
EN OR
EN12
Figure 4. Receiver Enable and Disable Times
U
S
A
O
PPLICATI
W
U
U
I FOR ATIO
Typical Application
A typical connection of the LTC488/LTC489 is shown in
Figure 5. Two twisted-pair wires connect up to 32 driver/
receiver pairs for half-duplex data transmission. There are
no restrictions on where the chips are connected to the
wires, and it isn't necessary to have the chips connected
at the ends. However, the wires must be terminated only
at the ends with a resistor equal to their characteristic
impedance, typically 120
. The input impedance of a
receiver is typically 20k to GND, or 0.5 unit RS485 load, so
in practice 50 to 60 transceivers can be connected to the
same wires. The optional shields around the twisted-pair
help reduce unwanted noise, and are connected to GND at
one end.
Cables and Data Rate
The transmission line of choice for RS485 applications is
a twisted-pair. There are coaxial cables (twinaxial) made
for this purpose that contain straight-pairs, but these are
less flexible, more bulky, and more costly than twisted-
pairs. Many cable manufacturers offer a broad range of
120
cables designed for RS485 applications.
Losses in a transmission line are a complex combination
of DC conductor loss, AC losses (skin effect), leakage, and
AC losses in the dielectric. In good polyethylene cable
such as the Belden 9841, the conductor losses and dielec-
tric losses are of the same order of magnitude, leading to
relatively low overall loss (Figure 6).
7
LTC488/LTC489
U
S
A
O
PPLICATI
W
U
U
I FOR ATIO
Figure 5. Typical Connection
120
120
3
RX
2
1
488/9 F05
DX
1
3
SHIELD
RX
EN
DX
1/4 LTC486
12
SHIELD
4
12
3
2
DX
DX
1/4 LTC486
1
EN
1/4 LTC488 OR
1/4 LTC489
RX
3
1
2
4
RX
1/4 LTC488 OR
1/4 LTC489
EN
EN
FREQUENCY (MHz)
0.1
0.1
LOSS PER 100 FT (dB)
1
10
1
10
100
488/9 F06
Figure 7. Cable Length vs Data Rate
DATA RATE (bps)
10k
10
CABLE LENGTH (FT)
100
1k
10k
100k
1M
10M
488/9 F07
2.5M
Figure 6. Attenuation vs Frequency for Belden 9841
When using low loss cables, Figure 7 can be used as a
guideline for choosing the maximum line length for a given
data rate. With lower quality PVC cables, the dielectric loss
factor can be 1000 times worse. PVC twisted-pairs have
terrible losses at high data rates (> 100kbps), and greatly
reduce the maximum cable length. At low data rates
however, they are acceptable and much more economical.
Cable Termination
The proper termination of the cable is very important. If the
cable is not terminated with its characteristic impedance,
distorted waveforms will result. In severe cases, distorted
(false) data and nulls will occur. A quick look at the output
of the driver will tell how well the cable is terminated. It is
8
LTC488/LTC489
U
S
A
O
PPLICATI
W
U
U
I FOR ATIO
best to look at a driver connected to the end of the cable,
since this eliminates the possibility of getting reflections
from two directions. Simply look at the driver output while
transmitting square wave data. If the cable is terminated
properly, the waveform will look like a square wave
(Figure 8).
If the cable is loaded excessively (47
), the signal initially
sees the surge impedance of the cable and jumps to an
initial amplitude. The signal travels down the cable and is
reflected back out of phase because of the mistermination.
When the reflected signal returns to the driver, the ampli-
tude will be lowered. The width of the pedestal is equal to
twice the electrical length of the cable (about 1.5ns/foot).
If the cable is lightly loaded (470
), the signal reflects in
phase and increases the amplitude at the drive output. An
input frequency of 30kHz is adequate for tests out to 4000
ft. of cable.
488/9 F08
DX
PROBE HERE
Rt = 120
Rt = 47
Rt = 470
Rt
RX
RECEIVER
DRIVER
Figure 8. Termination Effects
AC Cable Termination
Cable termination resistors are necessary to prevent un-
wanted reflections, but they consume power. The typical
differential output voltage of the driver is 2V when the
cable is terminated with two 120
resistors, causing
33mA of DC current to flow in the cable when no data is
being sent. This DC current is about 60 times greater than
the supply current of the LTC488/LTC489. One way to
eliminate the unwanted current is by AC coupling the
termination resistors as shown in Figure 9.
The coupling capacitor must allow high frequency energy
to flow to the termination, but block DC and low frequen-
cies. The dividing line between high and low frequency
depends on the length of the cable. The coupling capacitor
must pass frequencies above the point where the line
represents an electrical one-tenth wavelength. The value
of the coupling capacitor should therefore be set at 16.3pF
per foot of cable length for 120
cables. With the coupling
capacitors in place, power is consumed only on the signal
edges, and not when the driver output is idling at a 1 or 0
state. A 100nF capacitor is adequate for lines up to 4000
feet in length. Be aware that the power savings start to
decrease once the data rate surpasses 1/(120
)(
C).
488/9 F09
C = LINE LENGTH (FT)(16.3pF)
120
C
RX
RECEIVER
Figure 9. AC Coupled Termination
9
LTC488/LTC489
Receiver Open-Circuit Fail-Safe
Some data encoding schemes require that the output of
the receiver maintains a known state (usually a logic 1)
when the data is finished transmitting and all drivers on the
line are forced in three-state. The receiver of the LTC488/
LTC489 has a fail-safe feature which guarantees the out-
put to be in a logic 1 state when the receiver inputs are left
floating (open-circuit). When the input is terminated with
120
and the receiver output must be forced to a known
state, the circuits of Figure 10 can be used.
U
S
A
O
PPLICATI
W
U
U
I FOR ATIO
The termination resistors are used to generate a DC bias
which forces the receiver output to a known state, in this
case a logic 0. The first method consumes about 208mW
and the second about 8mW. The lowest power solution is
to use an AC termination with a pullup resistor. Simply
swap the receiver inputs for data protocols ending in
logic 1.
Fault Protection
All of LTC's RS485 products are protected against ESD
transients up to 2kV using the human body model (100pF,
1.5k). However, some applications need more protection.
The best protection method is to connect a bidirectional
TransZorb
®
from each line side pin to ground (Figure 11).
A TransZorb is a silicon transient voltage suppressor that
has exceptional surge handling capabilities, fast response
time, and low series resistance. They are available from
General instruments, GSI, and come in a variety of break-
down voltages and prices. Be sure to pick a breakdown
voltage higher than the common mode voltage required
for your application (typically 12V). Also, don't forget to
check how much the added parasitic capacitance will load
down the bus.
TransZorb is a registered trademark of General Instruments, GSI
488/9 F11
120
DRIVER
Y
Z
Figure 11. ESD Protection with TransZorbs
®
488/9 F10
110
RX
130
130
110
5V
RX
RECEIVER
1.5k
120
5V
1.5k
RX
120
5V
C
100k
RECEIVER
RECEIVER
Figure 10. Forcing "0" When All Drivers Are Off
10
LTC488/LTC489
PACKAGE DESCRIPTIO
U
Dimensions in inches (millimeters) unless otherwise noted.
N Package
16-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
N16 1197
0.255
±
0.015*
(6.477
±
0.381)
0.770*
(19.558)
MAX
16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0.020
(0.508)
MIN
0.125
(3.175)
MIN
0.130
±
0.005
(3.302
±
0.127)
0.065
(1.651)
TYP
0.045 0.065
(1.143 1.651)
0.018
±
0.003
(0.457
±
0.076)
0.100
±
0.010
(2.540
±
0.254)
0.009 0.015
(0.229 0.381)
0.300 0.325
(7.620 8.255)
0.325
+0.035
0.015
+0.889
0.381
8.255
(
)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
11
LTC488/LTC489
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.
PACKAGE DESCRIPTIO
U
Dimensions in inches (millimeters) unless otherwise noted.
SW Package
16-Lead Plastic Small Outline (Wide 0.300)
(LTC DWG # 05-08-1620)
S16 (WIDE) 0396
NOTE 1
0.398 0.413*
(10.109 10.490)
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
0.394 0.419
(10.007 10.643)
0.037 0.045
(0.940 1.143)
0.004 0.012
(0.102 0.305)
0.093 0.104
(2.362 2.642)
0.050
(1.270)
TYP
0.014 0.019
(0.356 0.482)
TYP
0
°
8
°
TYP
NOTE 1
0.009 0.013
(0.229 0.330)
0.016 0.050
(0.406 1.270)
0.291 0.299**
(7.391 7.595)
×
45
°
0.010 0.029
(0.254 0.737)
NOTE:
1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
12
LTC488/LTC489
TYPICAL APPLICATIO
N
U
LTC488/9 TA02
RS232
IN
5.6k
RX
RECEIVER
1/4 LTC488 OR
1/4 LTC489
RS232 Receiver
RELATED PARTS
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507
q
www.linear-tech.com
4889fa LT/TP 0898 REV A 2K · PRINTED IN USA
©
LINEAR TECHNOLOGY CORPORATION 1992
PART NUMBER
DESCRIPTION
COMMENTS
LTC485
Low Power RS485 Transceiver
Low Power, Half-Duplex
LTC490
Low Power RS485 Full-Duplex Transceiver
Full-Duplex in SO-8
LTC1480
3V, Ultralow Power RS485 Transceiver
1
µ
A Shutdown Mode
LTC1481
3V, Ultralow Power RS485 Transceiver
Lowest Power on 5V Supply
LTC1483
Ultralow Power RS485 Low EMI Transceiver
Low EMI/Low Power with Shutdown
LTC1485
Fast RS485 Transceiver
10Mbps Operation
LTC1487
Ultralow Power RS485 with Low EMI and High Input Impedance
Up to 256 Nodes on a Bus
LTC1685
High Speed RS485 Transceiver
52Mbps, Pin Compatible with LTC485
LTC1686/LTC1687 High Speed RS485 Full-Duplex Transceiver
52Mbps, Pin Compatible LTC490/LTC491
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