LTC491
Differential Driver and
Receiver Pair
FEATURES
s
s
s
s
DESCRIPTIO
s
s
s
s
s
s
s
Low Power: I
CC
= 300µA Typical
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
Thermal Shutdown Protection
Power-Up/Down Glitch-Free Driver Outputs Permit
Live Insertion or Removal of Package
Driver Maintains High Impedance in Three-State or
with the Power Off
Combined Impedance of a Driver Output and
Receiver Allows up to 32 Transceivers on the Bus
70mV Typical Input Hysteresis
28ns Typical Driver Propagation Delays with 5ns
Skew
Pin Compatible with the SN75180
The LTC491 is a low power differential bus/line transceiver
designed for multipoint data transmission standard RS485
applications with extended common mode range (+12V to
–7V). It also meets the requirements of RS422.
The CMOS design offers significant power savings over its
bipolar counterpart without sacrificing ruggedness against
overload or ESD damage.
The driver and receiver feature three-state outputs, with
the driver outputs maintaining high impedance over the
entire common 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.
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 from 0°C to
70°C and 4.75V to 5.25V supply voltage range.
APPLICATI
s
s
S
Low Power RS485/RS422 Transceiver
Level Translator
TYPICAL APPLICATI
DE
4
9
D
5
DRIVER
120Ω
10
4000 FT 24 GAUGE TWISTED PAIR
LTC491
12
R
2
RECEIVER
120Ω
11
4000 FT 24 GAUGE TWISTED PAIR
3
REB
120Ω
DRIVER
D
LTC491
120Ω
RECEIVER
R
U
DE
REB
LTC491 • TA01
UO
UO
1
LTC491
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
NC
R
REB
DE
D
GND
GND
1
2
3
4
5
D
6
7
9
8
Y
NC
R
14 V
CC
13 NC
12 A
11 B
10 Z
Supply Voltage (V
CC
) ............................................... 12V
Control Input Voltages ..................... –0.5V to V
CC
+0.5V
Control Input Currents .......................... –50mA to 50mA
Driver Input Voltages ....................... –0.5V to V
CC
+0.5V
Driver Input Currents ............................ –25mA to 25mA
Driver Output Voltages ..........................................
±14V
Receiver Input Voltages .........................................
±14V
Receiver Output Voltages ................ –0.5V to V
CC
+0.5V
Operating Temperature Range
LTC491C.................................................. 0°C to 70°C
LTC491I.............................................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................. 300°C
ORDER PART
NUMBER
LTC491CN
LTC491CS
LTC491IN
LTC491IS
S PACKAGE
N PACKAGE
14-LEAD PLASTIC DIP 14-LEAD PLASTIC SOIC
LTC491 • POI01
Consult factory for Military grade parts.
V
CC
= 5V
±5%
SYMBOL
V
OD1
V
OD2
∆V
OD
V
OC
∆
V
OC
V
IH
V
IL
l
IN1
l
IN2
V
TH
∆V
TH
V
OH
V
OL
I
OZR
I
CC
R
IN
I
OSD1
I
OSD2
I
OSR
I
OZ
DC ELECTRICAL CHARACTERISTICS
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
Input Current (A, B)
Differential Input Threshold Voltage for Receiver
Receiver Input Hysteresis
Receiver Output High Voltage
Receiver Output Low Voltage
Three-State Output Current at Receiver
Supply Current
Receiver Input Resistance
Driver Short Circuit Current, V
OUT
= High
Driver Short Circuit Current, V
OUT
= Low
Receiver Short Circuit Current
Driver Three-State Output Current
V
CC
= 0V or 5.25V
– 7V
≤
V
CM
≤
12V
V
CM
= 0V
I
O
= –4mA, V
ID
= 0.2V
I
O
= 4mA, V
ID
= –0.2V
V
CC
= Max 0.4V
≤
V
O
≤
2.4V
No Load; D = GND,
or V
CC
– 7V
≤
V
CM
≤
12V
V
O
= – 7V
V
O
= 12V
0V
≤
V
O
≤
V
CC
V
O
= – 7V to 12V
Outputs Enabled
Outputs Disabled
V
IN
= 12V
V
IN
= –7V
D, DE, REB
CONDITIONS
I
O
= 0
R = 50Ω; (RS422)
R = 27Ω; (RS485) (Figure 1)
R = 27Ω or R = 50Ω (Figure 1)
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
MIN
2
1.5
TYP
MAX
5
5
0.2
3
0.2
UNITS
V
V
V
V
V
V
V
2.0
0.8
±2
1.0
– 0.8
– 0.2
70
3.5
0.4
±1
300
300
12
100
100
7
±2
250
250
85
±200
500
500
0.2
2
U
V
µA
mA
mA
V
mV
V
V
µA
µA
µA
kΩ
mA
mA
mA
µA
W
U
U
W W
W
LTC491
V
CC
= 5V
±5%
SYMBOL
t
PLH
t
PHL
t
SKEW
t
r
, t
f
t
ZH
t
ZL
t
LZ
t
HZ
t
PLH
t
PHL
t
SKD
t
ZL
t
ZH
t
LZ
t
HZ
SWITCHI G CHARACTERISTICS
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
Receiver Input to Output
Receiver Input to Output
t
PLH
– t
PHL
Differential Receiver Skew
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable From Low
Receiver Disable From High
C
L
= 100pF (Figures 4, 6) S2 Closed
C
L
= 100pF (Figures 4, 6) S1 Closed
C
L
= 15pF (Figures 4, 6) S1 Closed
C
L
= 15pF (Figures 4, 6) S2 Closed
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 2, 7)
C
L
= 15pF (Figures 3, 8) S1 Closed
C
L
= 15pF (Figures 3, 8) S2 Closed
C
L
= 15pF (Figures 3, 8) S1 Closed
C
L
= 15pF (Figures 3, 8) S2 Closed
CONDITIONS
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 2, 5)
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
“Absolute Maximum Ratings” are those beyond which the safety
of the device cannot be guaranteed.
PI FU CTI
NC (Pin 1):
Not Connected.
R (Pin 2):
Receiver output. If the receiver output is enabled
(REB low), then if A > B by 200mV, R will be high. If A < B
by 200mV, then R will be low.
REB (Pin 3):
Receiver output enable. A low enables the
receiver output, R. A high input forces the receiver output
into a high impedance state.
DE (Pin 4):
Driver output enable. A high on DE enables the
driver outputs, A and B. A low input forces the driver
outputs into a high impedance state.
D (Pin 5):
Driver input. If the driver outputs are enabled
(DE high), then A low on D forces the driver outputs A low
and B high. A high on D will force A high and B low.
UO
U
MIN
10
10
5
TYP
30
30
5
15
40
40
40
40
MAX
50
50
25
70
70
70
70
150
150
50
50
50
50
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
40
40
70
70
13
20
20
20
20
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 Temperature = 25°C.
U
U
S
GND (Pin 6):
Ground Connection.
GND (Pin 7):
Ground Connection.
NC (Pin 8):
Not Connected.
Y (Pin 9):
Driver output.
Z (Pin 10):
Driver output.
B (Pin 11):
Receiver input.
A (Pin 12):
Receiver input.
NC (Pin 13):
Not Connected.
V
CC
(Pin 14):
Positive supply; 4.75V
≤
V
CC
≤
5.25V.
3
LTC491
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output High Voltage vs
Output Current T
A
= 25°C
–96
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
–72
– 48
–24
0
0
1
2
3
4
LTC491 • TPC01
OUTPUT VOLTAGE (V)
TTL Input Threshold vs Temperature
1.63
INPUT THRESHOLD VOLTAGE (V)
1.61
TIME (ns)
4.0
SUPPLY CURRENT (µA)
1.59
1.57
1.55
–50
0
50
TEMPERATURE (°C )
LTC491 • TPC04
Driver Differential Output Voltage vs
Temperature R
O
= 54Ω
2.3
DIFFERENTIAL VOLTAGE (V)
7.0
2.1
OUTPUT VOLTAGE (V)
1.9
TIME (ns)
1.7
1.5
–50
0
50
TEMPERATURE (°C )
LTC491 • TPC07
4
U W
100
100
Driver Differential Output Voltage vs
Output Current T
A
= 25°C
64
80
Driver Output Low Voltage vs
Output Current T
A
= 25°C
48
60
32
40
16
20
0
0
1
2
3
4
LTC491 • TPC02
0
0
1
2
3
4
LTC491 • TPC03
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
Driver Skew vs Temperature
5.0
350
Supply Current vs Temperature
340
3.0
330
2.0
320
1.0
–50
0
50
100
LTC491 • TPC05
310
–50
0
50
100
LTC491 • TPC06
TEMPERATURE (°C )
TEMPERATURE (°C )
Receiver
t
PLH
t
PHL
vs
Temperature
0.8
Receiver Output Low Voltage vs
Temperature at I = 8mA
6.0
0.6
5.0
0.4
4.0
0.2
3.0
–50
0
50
100
LTC491 • TPC08
0
–50
0
50
100
LTC491 • TPC09
TEMPERATURE (°C )
TEMPERATURE (°C )
LTC491
TEST CIRCUITS
Y
R
V
OD2
R
Z
V
OC
LTC491 • TA02
Figure 1. Driver DC Test Load
Y
D
DRIVER
Z
R
DIFF
C
L1
A
RECEIVER
R
15pF
C
L2
B
LTC491 • TA03
Figure 2. Driver/Receiver Timing Test Circuit
RECEIVER
OUTPUT
C
L
1kΩ
S1
1kΩ
V
CC
OUTPUT
UNDER TEST
500
Ω
S1
V
CC
S2
C
L
S2
LTC491 • TA04
LTC491 • TA05
Figure 3. Receiver Timing Test Load
Figure 4. Driver Timing Test Load
5
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