LTC487
1
487fc
Typical applicaTion
DescripTion
Quad Low Power
RS485 Driver
The LTC
®
487 is a low power differential bus/line driver
designed for multipoint data transmission standard RS485
applications with extended common mode range (–7V to
12V). It also meets RS422 requirements.
The CMOS design offers significant power savings over
its bipolar counterpart without sacrificing ruggedness
against overload or ESD damage.
The driver features three-state outputs, with the driver
outputs maintaining high impedance over the entire com-
mon mode range. Excessive power dissipation caused
by bus contention or faults is prevented by a thermal
shutdown circuit which forces the driver outputs into a
high impedance state.
Both AC and DC specifications are guaranteed from 0°C to
70°C (Commercial), –40°C to 85°C (Industrial) and over
the 4.75V to 5.25V supply voltage range.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
FeaTures
applicaTions
n Very Low Power: ICC = 110µA Typ
n Designed for RS485 or RS422 Applications
n Single 5V Supply
n –7V to 12V Bus Common Mode Range Permits ±7V
GND Difference Between Devices on the Bus
n Thermal Shutdown Protection
n Power-Up/Down Glitch-Free Driver Outputs Permit
Live Insertion/Removal of Package
n Driver Maintains High Impedance in Three-State or
with the Power Off
n 28ns Typical Driver Propagation Delays with
5ns Skew
n Pin Compatible with the SN75174, DS96174,
µA96174, and DS96F174
n Low Power RS485/RS422 Drivers
n Level Translator
2
DRIVER
LTC487 TA01
RECEIVER
DI
EN 12
4
3
1
1/4 LTC487
120Ω 120Ω RO
3
EN 12
4
2
1 1/4 LTC489
4000 FT BELDEN 9841
DATA RATE (bps)
10k
10
CABLE LENGTH (FT)
100
1k
10k
100k 1M 10M
LTC487 TA09
2.5M
RS485 Cable Length Specification*
* APPLIES FOR 24 GAUGE, POLYETHYLENE
DIELECTRIC TWISTED PAIR
LTC487
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487fc
pin conFiguraTionabsoluTe MaxiMuM raTings
Supply Voltage (VCC) ................................................12V
Control Input Voltages .................... –0.5V to VCC + 0.5V
Driver Input Voltages ...................... –0.5V to VCC + 0.5V
Driver Output Voltages ............................................ ±14V
Control Input Currents .........................................±25mA
Driver Input Currents ...........................................±25mA
Operating Temperature Range
Commercial ............................................. 0°C to 70°C
Industrial .............................................–40°C to 85°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec.).................. 300°C
(Note 1)
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
DI1
DO1A
DO1B
EN12
DO2B
DO2A
DI2
GND DI3
DO3A
DO3B
EN34
DO4B
DO4A
DI4
V
N PACKAGE
16-LEAD PLASTIC DIP
TOP VIEW
CC
SW PACKAGE
16-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 70°C/W (N)
TJMAX = 150°C, θJA = 95°C/W (S)
Consult factory for Military grade parts.
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC487CN#PBF LTC487CN#TRPBF LTC487CN 16-Lead Plastic DIP 0°C to 70°C
LTC487CSW#PBF LTC487CSW#TRPBF LTC487CSW 16-Lead Plastic SO 0°C to 70°C
LTC487IN#PBF LTC487IN#TRPBF LTC487IN 16-Lead Plastic DIP –40°C to 85°C
LTC487ISW#PBF LTC487IS#TRPBF LTC487ISW 16-Lead Plastic SO –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
LTC487
3
487fc
Dc elecTrical characTerisTics
VCC = 5V ±5%, 0°C ≤ TA ≤ 70°C (Commercial), –40°C ≤ TA ≤ 85°C
(Industrial) (Notes 2, 3)
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VOD1 Differential Driver Output Voltage (Unloaded) IO = 0 5 V
VOD2 Differential Driver Output Voltage (With Load) R = 50Ω; (RS422) 2 V
R = 27Ω; (RS485) (Figure 3) 1.5 5 V
VOD Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
R = 27Ω or R = 50Ω
(Figure 3)
0.2 V
VOC Driver Common Mode Output Voltage 3 V
VOCChange in Magnitude of Driver Common Mode
Output Voltage for Complementary Output States
0.2 V
VIH Input High Voltage DI, EN12, EN34 2.0 V
VIL Input Low Voltage 0.8 V
IIN1 Input Current ±2 µA
ICC Supply Current No Load Output Enabled 110 200 µA
Output Enabled 110 200 µA
IOSD1 Driver Short-Circuit Current, VOUT = High VO = – 7V 100 250 mA
IOSD2 Driver Short-Circuit Current, VOUT = Low VO = 12V 100 250 mA
IOZ High Impedance State Output Current VO = –7V to 12V ±10 ±200 µA
swiTching characTerisTics
VCC = 5V ±5%, 0°C ≤ TA ≤ 70°C (Notes 2, 3)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
tPLH Driver Input to Output RDIFF = 54Ω, CL1 = CL2 = 100pF 10 30 50 ns
tPHL Driver Input to Output (Figures 1, 4) 10 30 50 ns
tSKEW Driver Output to Output 5 15 ns
tr, tfDriver Rise or Fall Time 5 20 25 ns
tZH Driver Enable to Output High CL = 100pF (Figures 2, 5) S2 Closed 35 70 ns
tZL Driver Enable to Output Low CL = 100pF (Figures 2, 5) S1 Closed 35 70 ns
tLZ Driver Disable Time from Low CL = 15pF (Figures 2, 5) S1 Closed 35 70 ns
tHZ Driver Disable Time from High CL = 15pF (Figures 2, 5) S2 Closed 35 70 ns
Note 2: All currents into device pins are positive; all currents out of
device pins are negative. All voltages are referenced to device GND unless
otherwise specified.
Note 3: All typicals are given for VCC = 5V and Temperature = 25°C.
LTC487
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Typical perForMance characTerisTics
TTL Input Threshold
vs Temperature Driver Skew vs Temperature Supply Current vs Temperature
Driver Differential Output Voltage
vs Temperature
Driver Output High Voltage
vs Output Current
Driver Differential Output Voltage
vs Output Current
Driver Output Low Voltage
vs Output Current
OUTPUT VOLTAGE (V)
0
OUTPUT CURRENT (mA)
0
–24
– 48
–72
–96
1 2 3 4
487 G01
TA = 25°C
OUTPUT VOLTAGE (V)
0
OUTPUT CURRENT (mA)
0
16
32
48
64
1 2 3 4
487 G02
TA = 25°C
OUTPUT VOLTAGE (V)
0
OUTPUT CURRENT (mA)
0
20
40
60
80
1 2 3 4
487 G03
TA = 25°C
TEMPERATURE (°C )
–50
INPUT THRESHOLD VOLTAGE (V)
1.55
1.57
1.59
1.61
1.63
0 50 100
487 G04
TEMPERATURE (°C )
–50
TIME (ns)
1.0
2.0
3.0
4.0
5.0
0 50 100
487 G05
TEMPERATURE (°C )
–50
SUPPLY CURRENT (µA)
90
100
110
120
130
0 50 100
487 G06
TEMPERATURE (°C )
–50
DIFFERENTIAL VOLTAGE (V)
1.5
1.7
1.9
2.1
2.3
0 50 100
487 G07
RO= 54Ω
LTC487
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pin FuncTions
DI1 (Pin 1): Driver 1 Input. If Driver 1 is enabled, then a
low on DI1 forces the driver outputs DO1A low and DO1B
high. A high on DI1 with the driver outputs enabled will
force DO1A high and DO1B low.
DO1A (Pin 2): Driver 1 Output.
DO1B (Pin 3): Driver 1 Output.
EN12 (Pin 4): Driver 1 and 2 Outputs Enabled. See Func-
tion Table for details.
DO2B (Pin 5): Driver 2 Output.
DO2A (Pin 6): Driver 2 Output.
DI2 (Pin 7): Driver 2 Input. Refer to DI1.
GND (Pin 8): GND Connection.
DI3 (Pin 9): Driver 3 Input. Refer to DI1.
DO3A (Pin 10): Driver 3 Output.
DO3B (Pin 11): Driver 3 Output.
EN34 (Pin 12): Driver 3 and 4 Outputs Enabled. See Func-
tion Table for details.
DO4B (Pin 13): Driver 4 Output.
DO4A (Pin 14): Driver 4 Output.
DI4 (Pin 15): Driver 4 Input. Refer to DI1.
VCC (Pin 16): Positive Supply; 4.75 < VCC < 5.25.
H: High Level
L: Low Level
X: Irrelevant
Z: High Impedance (Off)
INPUT ENABLES OUTPUTS
DI EN12 or EN34 OUT A OUT B
H
L
X
H
H
L
H
L
Z
L
H
Z
FuncTion Table
swiTching TiMe waveForMs
–V
O
LTC487 • TA05
B
A
DI
V
O
1/2 V
O
3V
0V
tSKEW
1.5V
tPLH
1.5V
tPHL
1/2 V
O
V = V(A) – V(B)
V
O80%
20%
tf
90%
DIFF
10%
tSKEW
tr
f = 1MHz : t 10ns : t 10ns
< <
r f
LTC487 • TA06
A, B
EN12
3V
0V
f = 1MHz : t 10ns : t 10ns
VOL
V
OH
1.5V 1.5V
5V
OUTPUT NORMALLY LOW
tZL
2.3V
tLZ
0.5V
≤ ≤
A, B
0V
tZH
2.3V OUTPUT NORMALLY HIGH
tHZ
0.5V
r f
Figure 2. Driver Enable and Disable Times
Figure 1. Driver Propagation Delays
LTC487
6
487fc
TesT circuiT
applicaTions inForMaTion
LTC487 TA02
A
B
R
R
OD
V
OC
V
LTC487 TA04
OUTPUT
UNDER TEST
CL
S1
500
CC
V
Ω
S2
Figure 5. Driver Timing Test Load #2Figure 4. Driver Timing Test CircuitFigure 3. Driver DC Test Load
Typical Application
A typical connection of the LTC487 is shown in Figure 6.
A twisted pair of wires connect up to 32 drivers and
receivers 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 im-
pedance, typically 120Ω. The optional shields around the
twisted pair help reduce unwanted noise, and are connected
to GND at one end.
Thermal Shutdown
The LTC487 has a thermal shutdown feature which protects
the part from excessive power dissipation. If the outputs
of the driver are accidently shorted to a power supply or
low impedance source, up to 250mA can flow through
the part. The thermal shutdown circuit disables the driver
outputs when the internal temperature reaches 150°C and
turns them back on when the temperature cools to 130°C.
If the outputs of two or more LTC487 drivers are shorted
directly, the driver outputs can not supply enough cur-
rent to activate the thermal shutdown. Thus, the thermal
shutdown circuit will not prevent contention faults when
two drivers are active on the bus at the same time.
Cable 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
120Ω cables designed for RS485 applications.
EN12
4
LTC487 • TA07
120Ω
DX
1
2
3SHIELD
120Ω RX RX
SHIELD
3
DX
EN12
42
EN12
4
1
2
3
RX RX
3
DX
EN12
41
DX
1/4 LTC4891/4 LTC487
1/4 LTC4891/4 LTC487
2
1
Figure 6. Typical Connection
LTC487
7
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applicaTions inForMaTion
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 cables 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 7).
FREQUENCY (MHz)
0.1
0.1
LOSS PER 100 FT (dB)
1.0
10
1.0 10 100
LTC487 TA08
Figure 7. Attenuation vs Frequency for Belden 9841
When using low loss cables, Figure 8 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
(> 100kbs) and greatly reduce the maximum cable length.
At low data rates however, they are acceptable and much
more economical.
DATA RATE (bps)
10k
10
CABLE LENGTH (FT)
100
1k
10k
100k 1M 10M
LTC487 TA09
2.5M
Figure 8. 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
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 termi-
nated properly, the waveform will look like a square wave
(Figure 9).
Rt
DRIVERDX RECEIVER RX
Rt = 120Ω
Rt = 47Ω
Rt = 470Ω
LTC487 TA10
PROBE HERE
Figure 9. Termination Effects
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 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 (470Ω), the signal reflects in
phase and increases the amplitude at the driver output.
An input frequency of 30kHz is adequate for tests out to
4000 feet of cable.
LTC487
8
487fc
applicaTions inForMaTion
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 120Ω resistors, causing
33mA of DC current to flow in the cable when no data is
being sent. This DC current is about 220 times greater than
the supply current of the LTC487. One way to eliminate
the unwanted current is by AC coupling the termination
resistors as shown in Figure 10.
LTC487 TA11
C = LINE LENGTH (FT) s 16.3pF
120Ω
RECEIVER RX
C
Figure 10. AC-Coupled Termination
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 ca-
pacitor 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).
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 into three-state. All LTC RS485 receivers
have a fail-safe feature which guarantees the output to be
in a logic 1 state when the receiver inputs are left floating
(open-circuit). However, when the cable is terminated with
120Ω, the differential inputs to the receiver are shorted
together, not left floating. Because the receiver has about
70mV of hysteresis, the receiver output will maintain the
last data bit received.
If the receiver output must be forced to a known state, the
circuits of Figure 11 can be used.
LTC487 TA12
140Ω RECEIVER RX
5V
1.5k
RECEIVER RX
5V
110Ω
130Ω110Ω 130Ω
120Ω
RECEIVER RX
C
5V
100k
1.5k
Figure 11. Forcing ‘0’ When All Drivers Are Off
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 pull-up resis-
tor. 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, 1.5kΩ). However, some applications need more
protection. The best protection method is to connect a
bidirectional TransZorb from each line side pin to ground
(Figure 12).
LTC487
9
487fc
applicaTions inForMaTion
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 Semiconductor Industries 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.
LTC487 TA13
120Ω
DRIVER
Z
Y
Figure 11. Forcing ‘0’ When All Drivers Are Off
package DescripTion
N16 1002
.255 ± .015*
(6.477 ± 0.381)
.770*
(19.558)
MAX
16
12345678
910
11
12
13
14
15
.020
(0.508)
MIN
.120
(3.048)
MIN
.130 ± .005
(3.302 ± 0.127)
.065
(1.651)
TYP
.045 – .065
(1.143 – 1.651)
.018 ± .003
(0.457 ± 0.076)
.008 – .015
(0.203 – 0.381)
.300 – .325
(7.620 – 8.255)
.325 +.035
–.015
+0.889
–0.381
8.255
( )
NOTE:
1. DIMENSIONS ARE INCHES
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
.100
(2.54)
BSC
N Package
16-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
LTC487
10
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package DescripTion
S16 (WIDE) 0502
NOTE 3
.398 – .413
(10.109 – 10.490)
NOTE 4
16 15 14 13 12 11 10 9
1
N
2 3 4567 8
N/2
.394 – .419
(10.007 – 10.643)
.037 – .045
(0.940 – 1.143)
.004 – .012
(0.102 – 0.305)
.093 – .104
(2.362 – 2.642)
.050
(1.270)
BSC .014 – .019
(0.356 – 0.482)
TYP
0° – 8° TYP
NOTE 3
.009 – .013
(0.229 – 0.330)
.005
(0.127)
RAD MIN
.016 – .050
(0.406 – 1.270)
.291 – .299
(7.391 – 7.595)
NOTE 4
× 45°
.010 – .029
(0.254 – 0.737)
INCHES
(MILLIMETERS)
NOTE:
1. DIMENSIONS IN
2. DRAWING NOT TO SCALE
3. 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
4. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
.420
MIN
.325 ±.005
RECOMMENDED SOLDER PAD LAYOUT
.045 ±.005
N
1 2 3 N/2
.050 BSC
.030 ±.005
TYP
SW Package
16-Lead Plastic Small Outline (Wide .300 Inch)
(Reference LTC DWG # 05-08-1620)
LTC487
11
487fc
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
revision hisTory
REV DATE DESCRIPTION PAGE NUMBER
C 8/10 Reversed temperature ranges for LTC487CSW#PBF and LTC487IN#PBF. 2
(Revision history begins at Rev C)
LTC487
12
487fc
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
LINEAR TECHNOLOGY CORPORATION 1994
LT 0810 REV C • PRINTED IN USA
Typical applicaTion
LTC487 TA14
HYSTERESIS = 10kΩ • ≈
¦VY - VZ ¦
————
R
19k
————
R
120Ω
DRIVER
Y
Z
R = 220k
10k
RS232 IN
5.6k 1/4 LTC487
RS232 to RS485 Level Translator with Hysteresis