LINER LTC489CS Quad rs485 line receiver Datasheet

LTC488/LTC489
Quad RS485 Line Receiver
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DESCRIPTIO
FEATURES
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■
■
■
■
■
■
■
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Low Power: ICC = 7mA Typ
Designed for RS485 or RS422 Applications
Single 5V Supply
– 7V to 12V Bus Common Mode Range Permits ±7V
Ground Difference Between Devices on the Bus
60mV Typical Input Hysteresis
Receiver Maintains High Impedance in Three-State or
with the Power Off
28ns Typical Receiver Propagation Delay
Pin Compatible with the SN75173 (LTC488)
Pin Compatible with the SN75175 (LTC489)
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APPLICATI
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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 common mode range.
The receiver has a fail-safe feature which guarantees a
high output state when the inputs are left open.
S
Low Power RS485/RS422 Receivers
Level Translator
Both AC and DC specifications are guaranteed 4.75V to
5.25V supply voltage range.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATI
EN EN
EN
2
DI
DRIVER
1/4 LTC486
120Ω
120Ω
1
EN
4
12
RECEIVER
1/4 LTC488
3
RO
4000 FT 24 GAUGE TWISTED PAIR
EN12
EN12
2
DI
DRIVER
1/4 LTC487
120Ω
120Ω
1
4000 FT 24 GAUGE TWISTED PAIR
4
RECEIVER
1/4 LTC489
3
RO
LTC488/9 TA01
1
LTC488/LTC489
W W
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AXI U
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ABSOLUTE
RATI GS
(Note 1)
Supply Voltage (VCC) .............................................. 12V
Control Input Currents ........................ – 25mA to 25mA
Control Input Voltages ................ – 0.5V to (VCC + 0.5V)
Receiver Input Voltages ........................................ ±14V
Receiver Output Voltages ........... – 0.5V to (VCC + 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
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PACKAGE/ORDER I FOR ATIO
TOP VIEW
16 VCC
B1
1
A1
2
RO1
3
EN
4
13 RO4
RO2
5
12 EN
A2
6
11 RO3
B2
7
GND
8
9
N PACKAGE
16-LEAD PLASTIC DIP
S PACKAGE
16-LEAD PLASTIC SOL
R
R
R
R
TOP VIEW
ORDER PART
NUMBER
1
15 B4
A1
2
14 A4
RO1
3
EN12
4
13 RO4
RO2
5
12 EN34
A2
6
B2
7
GND
8
9
N PACKAGE
16-LEAD PLASTIC DIP
S PACKAGE
16-LEAD PLASTIC SOL
10 A3
LTC488CN
LTC488CS
LTC488IN
LTC488IS
B3
ORDER PART
NUMBER
16 VCC
B1
R
15 B4
R
14 A4
LTC489CN
LTC489CS
LTC489IN
LTC489IS
11 RO3
R
10 A3
R
B3
TJMAX = 150°C, θJA = 70°C/W (N PKG)
TJMAX = 150°C, θJA = 90°C/W (S PKG)
TJMAX = 150°C, θJA = 70°C/W (N PKG)
TJMAX = 150°C, θJA = 90°C/W (S PKG)
Consult factory for Military grade parts.
DC ELECTRICAL CHARACTERISTICS VCC = 5V (Notes 2, 3), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VINH
Input High Voltage
EN, EN, EN12, EN34
●
VINL
Input Low Voltage
EN, EN, EN12, EN34
●
0.8
V
IIN1
Input Current
EN, EN, EN12, EN34
●
±2
µA
IIN2
Input Current (A, B)
VCC = 0V or 5.25V, VIN = 12V
VCC = 0V or 5.25V, VIN = – 7V
●
●
1.0
– 0.8
mA
mA
VTH
Differential Input Threshold Voltage for Receiver
– 7V ≤ VCM ≤ 12V
●
– 0.2
∆VTH
Receiver Input Hysteresis
VCM = 0V
VOH
Receiver Output High Voltage
IO = – 4mA, VID = 0.2V
●
3.5
VOL
Receiver Output Low Voltage
IO = 4mA, VID = – 0.2V
●
IOZR
Three-State Output Current at Receiver
VCC = Max 0.4V ≤ VO ≤ 2.4V
●
ICC
Supply Current
No Load, Digital Pins = GND or VCC
●
RIN
Receiver Input Resistance
– 7V ≤ VCM ≤ 12V, VCC = 0V
●
IOSR
Receiver Short-Circuit Current
0V ≤ VO ≤ VCC
●
7
85
mA
t PLH
Receiver Input to Output
CL = 15pF (Figures 1, 3)
●
12
28
55
ns
t PHL
Receiver Input to Output
CL = 15pF (Figures 1, 3)
●
12
28
55
ns
t SKD
| t PLH – t PHL |
Differential Receiver Skew
CL = 15pF (Figures 1, 3)
2
MIN
TYP
MAX
2.0
UNITS
V
0.2
60
V
mV
V
0.4
7
V
±1
µA
10
mA
12
kΩ
4
ns
LTC488/LTC489
DC ELECTRICAL CHARACTERISTICS VCC = 5V ± 5% (Notes 2, 3), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
TYP
MAX
t ZL
Receiver Enable to Output Low
CL = 15pF (Figures 2, 4) S1 Closed
●
30
60
ns
t ZH
Receiver Enable to Output High
CL = 15pF (Figures 2, 4) S2 Closed
●
30
60
ns
t LZ
Receiver Disable from Low
CL = 15pF (Figures 2, 4) S1 Closed
●
30
60
ns
t HZ
Receiver Disable from High
CL = 15pF (Figures 2, 4) S2 Closed
●
30
60
ns
The ● 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.
MIN
UNITS
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 VCC = 5V and TA = 25°C.
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TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Output High Voltage vs
Temperature at I = 8mA
Receiver Output Low Voltage vs
Temperature at I = 8mA
4.8
0.8
4.6
0.7
4.4
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
0.9
0.6
0.5
0.4
0.3
4.2
4.0
3.8
3.6
0.2
3.4
0.1
3.2
0
–50
–25
0
75
50
25
TEMPERATURE (°C)
100
3.0
–50
125
–25
0
75
50
25
TEMPERATURE (°C)
125
488 G02
488 G01
Receiver Output Low Voltage vs
Output Current at TA = 25°C
Receiver Output High Voltage vs
Output Current at TA = 25°C
–18
36
–16
32
–14
28
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
100
–12
–10
–8
–6
–4
24
20
16
12
8
4
–2
0
0
5
4
3
OUTPUT VOLTAGE (V)
2
488 G03
0
0.5
1.5
1.0
OUTPUT VOLTAGE (V)
2.0
488 G04
3
LTC488/LTC489
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TYPICAL PERFOR A CE CHARACTERISTICS
Receiver | tPLH – tPHL | vs
Temperature
5
1.61
4
1.59
1.57
1.55
–50
Supply Current vs Temperature
7.0
SUPPLY CURRENT (mA)
1.63
TIME (ns)
INPUT THRESHOLD VOLTAGE (V)
TTL Input Threshold vs
Temperature
3
2
–25
0
75
25
50
TEMPERATURE (°C)
100
125
1
–50
–25
0
75
25
50
TEMPERATURE (°C)
488 G05
100
125
488 G06
6.6
6.2
5.8
5.4
–50
–25
0
75
25
50
TEMPERATURE (°C)
100
488 G07
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PI FU CTIO S
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.
4
125
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.
VCC (Pin 16) Positive Supply; 4.75V ≤ VCC ≤ 5.25V.
LTC488/LTC489
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FU CTIO TABLES
LTC489
LTC488
DIFFERENTIAL
ENABLES
DIFFERENTIAL
OUTPUT
ENABLES
OUTPUT
A–B
EN
EN
RO
A–B
EN12 or EN34
RO
VID ≥ 0.2V
H
X
X
L
H
H
VID ≥ 0.2V
H
H
–0.2V < VID < 0.2V
H
?
–0.2V < VID < 0.2V
H
X
X
L
?
?
VID ≤ 0.2V
H
L
VID ≤ 0.2V
H
X
X
L
L
L
X
L
Z
X
L
H
Z
H: High Level
L: Low Level
X: Irrelevant
?: Indeterminate
Z: High Impedance (Off)
TEST CIRCUITS
100pF
A
D
DRIVER
RO
RECEIVER
54Ω
CL
B
100pF
488/9 F01
Figure 1. Receiver Timing Test Circuit
Note: The input pulse is supplied by a generator having the following characteristics:
f = 1MHz, Duty Cycle = 50%, tr < 10ns, tf ≤ 10ns, ZOUT = 50Ω
S1
RECEIVER
OUTPUT
1k
VCC
CL
1k
S2
488/9 F02
Figure 2. Receiver Enable and Disable Timing Test Circuit
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LTC488/LTC489
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SWITCHI G TI E WAVEFOR S
INPUT
VOD2
INPUT
A, B
f = 1MHz; tr ≤ 10ns; t f ≤ 10ns
0V
0V
–VOD2
tPHL
tPLH
VOH
RO
1.5V
1.5V
VOL
488/9 F03
Figure 3. Receiver Propagation Delays
3V
EN OR
EN12
f = 1MHz; tr ≤ 10ns; t f ≤ 10ns
1.5V
1.5V
0V
tZL
tLZ
5V
RO
1.5V
VOL
OUTPUT NORMALLY LOW
tZH
0.5V
tHZ
VOH
OUTPUT NORMALLY HIGH
RO
0.5V
1.5V
0V
488/9 F04
Figure 4. Receiver Enable and Disable Times
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APPLICATI
S I FOR ATIO
Typical Application
Cables and Data Rate
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 120Ω. 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.
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 twistedpairs. Many cable manufacturers offer a broad range of
120Ω cables designed for RS485 applications.
6
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 dielectric losses are of the same order of magnitude, leading to
relatively low overall loss (Figure 6).
LTC488/LTC489
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APPLICATI
S I FOR ATIO
EN
SHIELD
SHIELD
4
DX
1
DX
1/4 LTC486
2
3
RX
1/4 LTC488 OR
1/4 LTC489
120Ω
120Ω
3
RX
1
12
1
EN
2
EN
12
DX
4
1/4 LTC486
1
DX
2
1/4 LTC488 OR
1/4 LTC489
RX
3
488/9 F05
EN
3
RX
Figure 5. Typical Connection
10k
CABLE LENGTH (FT)
LOSS PER 100 FT (dB)
10
1
0.1
0.1
1
10
FREQUENCY (MHz)
100
1k
100
10
10k
488/9 F06
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.
100k
1M
DATA RATE (bps)
2.5M
10M
488/9 F07
Figure 7. Cable Length vs Data Rate
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
7
LTC488/LTC489
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APPLICATI
S 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 (47Ω), 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 amplitude 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 (470Ω), 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.
PROBE HERE
DX
DRIVER
Rt
RECEIVER
RX
AC Cable Termination
Cable termination resistors are necessary to prevent unwanted reflections, but they consume power. The typical
differential output voltage of the driver is 2V when the
cable is terminated with two 120Ω 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 frequencies. 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 120Ω 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/(120Ω )(C).
Rt = 120Ω
120Ω
Rt = 47Ω
RECEIVER
RX
C
C = LINE LENGTH (FT)(16.3pF)
Rt = 470Ω
488/9 F08
Figure 8. Termination Effects
8
Figure 9. AC Coupled Termination
488/9 F09
LTC488/LTC489
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APPLICATI
S I FOR ATIO
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 output to be in a logic 1 state when the receiver inputs are left
floating (open-circuit). When the input is terminated with
120Ω and the receiver output must be forced to a known
state, the circuits of Figure 10 can be used.
5V
110Ω
130Ω
130Ω
110Ω
RECEIVER
RX
RECEIVER
RX
5V
1.5k
120Ω
1.5k
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 breakdown 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.
Y
5V
120Ω
DRIVER
100k
Z
C
120Ω
RECEIVER
RX
488/9 F11
488/9 F10
Figure 11. ESD Protection with TransZorbs®
Figure 10. Forcing “0” When All Drivers Are Off
TransZorb is a registered trademark of General Instruments, GSI
9
LTC488/LTC489
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PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
N Package
16-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.770*
(19.558)
MAX
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
0.255 ± 0.015*
(6.477 ± 0.381)
0.130 ± 0.005
(3.302 ± 0.127)
0.300 – 0.325
(7.620 – 8.255)
0.009 – 0.015
(0.229 – 0.381)
(
+0.035
0.325 –0.015
8.255
+0.889
–0.381
)
0.045 – 0.065
(1.143 – 1.651)
0.020
(0.508)
MIN
0.065
(1.651)
TYP
0.125
(3.175)
MIN
0.100 ± 0.010
(2.540 ± 0.254)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
10
0.018 ± 0.003
(0.457 ± 0.076)
N16 1197
LTC488/LTC489
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PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
SW Package
16-Lead Plastic Small Outline (Wide 0.300)
(LTC DWG # 05-08-1620)
0.398 – 0.413*
(10.109 – 10.490)
16
15
14
13
12
11 10
9
0.394 – 0.419
(10.007 – 10.643)
NOTE 1
1
0.291 – 0.299**
(7.391 – 7.595)
2
3
4
5
6
7
0.093 – 0.104
(2.362 – 2.642)
0.010 – 0.029 × 45°
(0.254 – 0.737)
8
0.037 – 0.045
(0.940 – 1.143)
0° – 8° TYP
0.009 – 0.013
(0.229 – 0.330)
NOTE 1
0.016 – 0.050
(0.406 – 1.270)
0.050
(1.270)
TYP
0.004 – 0.012
(0.102 – 0.305)
0.014 – 0.019
(0.356 – 0.482)
TYP
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
S16 (WIDE) 0396
*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
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
LTC488/LTC489
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TYPICAL APPLICATION
RS232 Receiver
RS232
IN
5.6k
RECEIVER
1/4 LTC488 OR
1/4 LTC489
RX
LTC488/9 TA02
RELATED PARTS
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
1µA 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
12
Linear Technology Corporation
52Mbps, Pin Compatible LTC490/LTC491
4889fa LT/TP 0898 REV A 2K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1992