1
LTC491
s
Low Power: I
CC
= 300
µ
A Typical
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
Thermal Shutdown Protection
s
Power-Up/Down Glitch-Free Driver Outputs Permit
Live Insertion or Removal of Package
s
Driver Maintains High Impedance in Three-State or
with the Power Off
s
Combined Impedance of a Driver Output and
Receiver Allows up to 32 Transceivers on the Bus
s
70mV Typical Input Hysteresis
s
28ns Typical Driver Propagation Delays with 5ns
Skew
s
Pin Compatible with the SN75180
Differential Driver and
Receiver Pair
D
U
ESCRIPTIO
S
FEATURE
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.
s
Low Power RS485/RS422 Transceiver
s
Level Translator
U
S
A
O
PPLICATI
U
A
O
PPLICATI
TYPICAL
LTC491 · TA01
120
120
120
120
4000 FT 24 GAUGE TWISTED PAIR
4000 FT 24 GAUGE TWISTED PAIR
RECEIVER
LTC491
DRIVER
RECEIVER
LTC491
DRIVER
R
D
R
D
5
2
11
12
10
9
4
DE
3
REB
DE
REB
LTC491
2
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
W
U
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
LTC491CN
LTC491CS
LTC491IN
LTC491IS
(Note 1)
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
14
13
12
11
10
9
8
7
6
5
4
3
2
1
TOP VIEW
S PACKAGE
14-LEAD PLASTIC SOIC
NC
N PACKAGE
14-LEAD PLASTIC DIP
Y
NC
Z
B
NC
V
CC
D
GND
GND
R
REB
DE
LTC491 · POI01
A
R
D
Consult factory for Military grade parts.
ELECTRICAL C
C
HARA TERISTICS
C
D
V
CC
= 5V
±
5%
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OD1
Differential Driver Output Voltage (Unloaded)
I
O
= 0
q
5
V
V
OD2
Differential Driver Output Voltage (With load)
R = 50
; (RS422)
q
2
V
R = 27
; (RS485) (Figure 1)
q
1.5
5
V
V
OD
Change in Magnitude of Driver Differential Output
R = 27
or R = 50
(Figure 1)
q
0.2
V
Voltage for Complementary Output States
V
OC
Driver Common Mode Output Voltage
q
3
V
V
OC
Change in Magnitude of Driver Common Mode
q
0.2
V
Output Voltage for Complementary Output States
V
IH
Input High Voltage
D, DE, REB
q
2.0
V
V
IL
Input Low Voltage
q
0.8
V
l
IN1
Input Current
q
±
2
µ
A
l
IN2
Input Current (A, B)
V
CC
= 0V or 5.25V V
IN
= 12V
q
1.0
mA
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
q
70
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; D = GND, Outputs Enabled
q
300
500
µ
A
or V
CC
Outputs Disabled
q
300
500
µ
A
R
IN
Receiver Input Resistance
7V
V
CM
12V
q
12
k
I
OSD1
Driver Short Circuit Current, V
OUT
= High
V
O
=
7V
q
100
250
mA
I
OSD2
Driver Short Circuit Current, V
OUT
= Low
V
O
= 12V
q
100
250
mA
I
OSR
Receiver Short Circuit Current
0V
V
O
V
CC
q
7
85
mA
I
OZ
Driver Three-State Output Current
V
O
= 7V to 12V
q
±
2
±
200
µ
A
3
LTC491
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
t
PLH
Driver Input to Output
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
10
30
50
ns
t
PHL
Driver Input to Output
q
10
30
50
ns
t
SKEW
Driver Output to Output
q
5
ns
t
r
, t
f
Driver Rise or Fall Time
q
5
15
25
ns
t
ZH
Driver Enable to Output High
C
L
= 100pF (Figures 4, 6) S2 Closed
q
40
70
ns
t
ZL
Driver Enable to Output Low
C
L
= 100pF (Figures 4, 6) S1 Closed
q
40
70
ns
t
LZ
Driver Disable Time From Low
C
L
= 15pF (Figures 4, 6) S1 Closed
q
40
70
ns
t
HZ
Driver Disable Time From High
C
L
= 15pF (Figures 4, 6) S2 Closed
q
40
70
ns
t
PLH
Receiver Input to Output
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
40
70
150
ns
t
PHL
Receiver Input to Output
q
40
70
150
ns
t
SKD
t
PLH
t
PHL
Differential Receiver Skew
q
13
ns
t
ZL
Receiver Enable to Output Low
C
L
= 15pF (Figures 3, 8) S1 Closed
q
20
50
ns
t
ZH
Receiver Enable to Output High
C
L
= 15pF (Figures 3, 8) S2 Closed
q
20
50
ns
t
LZ
Receiver Disable From Low
C
L
= 15pF (Figures 3, 8) S1 Closed
q
20
50
ns
t
HZ
Receiver Disable From High
C
L
= 15pF (Figures 3, 8) S2 Closed
q
20
50
ns
S
U
G C
C
HARA TERISTICS
WITCHI
V
CC
= 5V
±
5%
(Figures 2, 5)
(Figures 2, 7)
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.
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.
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.
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.
PI
U
FU
U
C
U
S
O
TI
LTC491
4
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
TTL Input Threshold vs Temperature
Driver Skew vs Temperature
Supply Current vs Temperature
Driver Output High Voltage vs
Driver Differential Output Voltage vs
Driver Output Low Voltage vs
Output Current T
A
= 25
°
C
Output Current T
A
= 25
°
C
Output Current T
A
= 25
°
C
OUTPUT VOLTAGE (V)
0
OUTPUT CURRENT (mA)
0
24
48
72
96
1
2
3
4
LTC491 · TPC01
OUTPUT VOLTAGE (V)
0
OUTPUT CURRENT (mA)
0
20
40
60
80
1
2
3
4
LTC491 · TPC03
TEMPERATURE (
°
C )
50
INPUT THRESHOLD VOLTAGE (V)
1.55
1.57
1.59
1.61
1.63
0
50
100
LTC491 · TPC04
TEMPERATURE (
°
C )
50
DIFFERENTIAL VOLTAGE (V)
1.5
1.7
1.9
2.1
2.3
0
50
100
LTC491 · TPC07
Driver Differential Output Voltage vs
Receiver
t
PLH
t
PHL
vs
Receiver Output Low Voltage vs
Temperature R
O
= 54
Temperature
Temperature at I = 8mA
TEMPERATURE (
°
C )
50
OUTPUT VOLTAGE (V)
0
0.2
0.4
0.6
0.8
0
50
100
LTC491 · TPC09
TEMPERATURE (
°
C )
50
TIME (ns)
3.0
4.0
5.0
6.0
7.0
0
50
100
LTC491 · TPC08
TEMPERATURE (
°
C )
50
TIME (ns)
1.0
2.0
3.0
4.0
5.0
0
50
100
LTC491 · TPC05
TEMPERATURE (
°
C )
50
SUPPLY CURRENT (
µ
A)
310
320
330
340
350
0
50
100
LTC491 · TPC06
OUTPUT VOLTAGE (V)
0
OUTPUT CURRENT (mA)
0
16
32
48
64
1
2
3
4
LTC491 · TPC02
5
LTC491
TEST CIRCUITS
Figure 2. Driver/Receiver Timing Test Circuit
Figure 1. Driver DC Test Load
Figure 3. Receiver Timing Test Load
Figure 4. Driver Timing Test Load
LTC491 · TA04
RECEIVER
OUTPUT
C
L
S1
1k
CC
V
S2
1k
LTC491 · TA05
OUTPUT
UNDER TEST
C
L
S1
500
CC
V
S2
LTC491 · TA02
Y
Z
R
R
V
OD2
V
OC
LTC491 · TA03
DRIVER
D
Y
Z
RECEIVER
R
DIFF
A
B
15pF
C
L1
C
L2
R
PDF 
ZIP