LTC487
Quad Low Power
RS485 Driver
FEATURES
■
■
■
■
■
■
■
■
■
DESCRIPTIO
Very Low Power: I
CC
= 110µA Typ
Designed for RS485 or RS422 Applications
Single 5V Supply
– 7V to 12V Bus Common-Mode Range Permits
±
7V
GND Difference Between Devices on the Bus
Thermal Shutdown Protection
Power-Up/Down Glitch-Free Driver Outputs Permit
Live Insertion/Removal of Package
Driver Maintains High Impedance in Three-State or
with the Power Off
28ns Typical Driver Propagation Delays with
5ns Skew
Pin Compatible with the SN75174, DS96174,
µA96174,
and DS96F174
The LTC487
®
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 shut-
down 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.
APPLICATI
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■
S
Low Power RS485/RS422 Drivers
Level Translator
and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATI
10k
EN 12
4
2
DI
1
DRIVER
3
1/4 LTC487
LTC487 • TA01
EN 12
CABLE LENGTH (FT)
4
2
120Ω
4000 FT BELDEN 9841
120Ω
1
RECEIVER
3
RO
1/4 LTC489
100
U
RS485 Cable Length Specification*
1k
10
10k
100k
1M
2.5M
10M
DATA RATE (bps)
LTC487 • TA09
UO
UO
* APPLIES FOR 24 GAUGE, POLYETHYLENE
DIELECTRIC TWISTED PAIR
1
LTC487
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
DI1
DO1A
DO1B
EN12
Supply Voltage (V
CC
) ............................................... 12V
Control Input Voltages .................... – 0.5V to V
CC
+ 0.5V
Driver Input Voltages ...................... – 0.5V to V
CC
+ 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
1
2
3
4
5
6
7
8
16
V
CC
15
DI4
14
DO4A
13
DO4B
12
EN34
11
DO3B
10
DO3A
9
DI3
ORDER PART
NUMBER
LTC487CN
LTC487CSW
LTC487IN
LTC487ISW
DO2B
DO2A
DI2
GND
N PACKAGE
S PACKAGE
16-LEAD PLASTIC DIP
16-LEAD PLASTIC SOL
T
JMAX
= 125°C,
θ
JA
= 70°C/W (N)
T
JMAX
= 150°C,
θ
JA
= 95°C/W (S)
Consult factory for Military grade parts.
DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
OD1
V
OD2
V
OD
V
OC
⏐
V
OC
⏐
V
CC
= 5V
±
5%, 0°C
≤
T
A
≤
70°C (Commercial), – 40°C
≤
T
A
≤
85°C (Industrial) (Note 2, 3)
PARAMETER
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (With Load)
Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
Driver Common-Mode Output Voltage
Change in Magnitude of Driver Common-Mode
Output Voltage for Complementary Output States
Input High Voltage
Input Low Voltage
Input Current
Supply Current
Driver Short-Circuit Current, V
OUT
= High
Driver Short-Circuit Current, V
OUT
= Low
High Impedance State Output Current
No Load
V
O
= – 7V
V
O
= 12V
V
O
= – 7V to 12V
Output Enabled
Output Disabled
I
OSD1
I
OSD2
I
OZ
110
110
100
100
±10
DI, EN12, EN34
2.0
CONDITIONS
I
O
= 0
R = 50Ω; (RS422)
R = 27Ω; (RS485) (Figure 3)
R = 27Ω or R = 50Ω
(Figure 3)
2
1.5
5
0.2
3
0.2
V
0.8
±2
200
200
250
250
±
200
V
µA
µA
µA
mA
mA
µA
MIN
TYP
MAX
5
UNITS
V
V
V
V
V
V
V
IH
V
IL
I
IN1
I
CC
SWITCHI G CHARACTERISTICS
V
CC
= 5V
±
5%, 0°C
≤
T
A
≤
70°C (Note 2, 3)
SYMBOL
t
PLH
t
PHL
t
SKEW
t
r,
t
f
t
ZH
t
ZL
t
LZ
t
HZ
PARAMETER
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
C
L
= 100pF (Figures 2, 5) S2 Closed
C
L
= 100pF (Figures 2, 5) S1 Closed
C
L
= 15pF (Figures 2, 5) S1 Closed
C
L
= 15pF (Figures 2, 5) S2 Closed
5
CONDITIONS
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 1, 4)
MIN
10
10
TYP
30
30
5
20
35
35
35
35
MAX
50
50
15
25
70
70
70
70
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
Note 1:
Absolute maximum ratings are those beyond which the safety of
the device cannot be guaranteed.
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 V
CC
= 5V and Temperature = 25°C.
2
U
W
U
U
W W
W
U
LTC487
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output High Voltage
vs Output Current
–96
T
A
= 25°C
64
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
–72
48
OUTPUT CURRENT (mA)
– 48
–24
0
0
1
2
3
4
LTC487 • TPC01
OUTPUT VOLTAGE (V)
TTL Input Threshold vs Temperature
1.63
INPUT THRESHOLD VOLTAGE (V)
5.0
1.61
TIME (ns)
4.0
SUPPLY CURRENT (µA)
1.59
1.57
1.55
–50
0
50
TEMPERATURE (°C )
DIFFERENTIAL VOLTAGE (V)
U W
100
Driver Differential Output Voltage
vs Output Current
T
A
= 25°C
80
Driver Output Low Voltage
vs Output Current
T
A
= 25°C
60
32
40
16
20
0
0
1
2
3
4
LTC487• TPC02
0
0
1
2
3
4
LTC487 • TPC03
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
Driver Skew vs Temperature
130
Supply Current vs Temperature
120
3.0
110
2.0
100
1.0
–50
0
50
100
LTC487 • TPC05
90
–50
0
50
100
LTC487 • TPC06
LTC487 • TPC04
TEMPERATURE (°C )
TEMPERATURE (°C )
Driver Differential Output
Voltage vs Temperature
2.3
R
O
= 54Ω
2.1
1.9
1.7
1.5
–50
0
50
100
LTC487 • TPC07
TEMPERATURE (°C )
3
LTC487
PI FU CTI
UO
H
H
L
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.
FU CTI
INPUT
DI
H
L
X
SWITCHI G TI E WAVEFOR S
3V
DI
0V
t
PLH
B
V
O
A
V
O
–V
O
1/2 V
O
80%
10%
t
r
t
SKEW
V
DIFF
= V(A) – V(B)
1/2 V
O
90%
20%
t
f
LTC487 • TA05
1.5V
Figure 1. Driver Propagation Delays
1.5V
f = 1MHz : t
r
≤
10ns : t
f
≤
10ns
3V
EN12
0V
t
ZL
5V
A, B
V
OL
V
OH
A, B
0V
t
ZH
2.3V
2.3V
Figure 2. Driver Enable and Disable Times
4
W
W
UO
U
U
U
U
S
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
Function Table for details.
DO4B (Pin 13):
Driver 4 output.
DO4A (Pin 14):
Driver 4 output.
DI4 (Pin 15):
Driver 4 input. Refer to DI1.
V
CC
(Pin 16):
Positive supply; 4.75 < V
CC
< 5.25.
TABLE
ENABLES
OUTPUTS
OUT A
H
L
Z
OUT B
L
H
Z
H: High Level
L: Low Level
X: Irrelevant
Z: High Impedance (Off)
EN12 or EN34
f = 1MHz : t
r
<
10ns : t
f
<
10ns
1.5V
t
PHL
t
SKEW
1.5V
t
LZ
OUTPUT NORMALLY LOW
0.5V
OUTPUT NORMALLY HIGH
t
HZ
0.5V
LTC487 • TA06
LTC487
TEST CIRCUITS
A
R
V
OD
R
B
B
DI
DRIVER 1
EN12
C
L1
A
R
DIFF
500
Ω
S1
V
CC
OUTPUT
UNDER TEST
V
OC
C
L2
LTC487 • TA03
C
L
S2
LTC487 • TA02
LTC487 • TA04
Figure 3. Driver DC Test Load
Figure 4. Driver Timing Test Circuit
Figure 5. Driver Timing Test Load #2
APPLICATI
S I FOR ATIO
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
impedance, 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 pro-
tects 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
EN12
4
DX
1
DX
2
1/4 LTC487
SHIELD
3
120Ω
EN12
4
DX
1
DX
2
1/4 LTC487
2
3
1
Figure 6. Typical Connection
U
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 current to activate the thermal shutdown.
Thus, the thermal shutdown circuit will not prevent con-
tention 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
SHIELD
2
120Ω
1
1/4 LTC489
RX
4
3
RX
EN12
4
RX
3
RX
1/4 LTC489
LTC487 • TA07
W
U
UO
5
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