1
LTC485
Low Power RS485
Interface Transceiver
S
FEATURE
D
U
ESCRIPTIO
The LTC485 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 of 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.
The LTC485 is fully specified over the commercial and
extended industrial temperature range.
s
Low Power: I
CC
= 300
A Typ
s
Designed for RS485 Interface 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 Transceiver
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
30ns Typical Driver Propagation Delays
with 5ns Skew
s
Pin Compatible with the SN75176A, DS75176A
and
A96176
s
Low Power RS485/RS422 Transceiver
s
Level Translator
U
S
A
O
PPLICATI
U
A
O
PPLICATI
TYPICAL
V
CC1
GND1
R
RO1
RE1
DE1
DI1
D
V
CC2
GND2
R
RO2
RE2
DE2
DI2
D
Rt
Rt
LTC485 TA01
Driver Outputs
A
B
LTC485 TA02
2
LTC485
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
(Note 1)
Supply Voltage ....................................................... 12V
Control Input Voltages ................... 0.5V to V
CC
+ 0.5V
Driver Input Voltage ....................... 0.5V to V
CC
+ 0.5V
Driver Output Voltage ...........................................
14V
Receiver Input Voltage ..........................................
14V
Receiver Output Voltages .............. 0.5V to V
CC
+ 0.5V
Operating Temperature Range
LTC485I...................................... 40
C
T
A
85
C
LTC485C.......................................... 0
C
T
A
70
C
LTC485M .................................. 55
C
T
A
125
C
Lead Temperature (Soldering, 10 sec)................. 300
C
W
U
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
S8 PART MARKING
LTC485CJ8
LTC485CN8
LTC485CS8
LTC485IN8
LTC485IS8
LTC485MJ8
485
485I
1
2
3
4
8
7
6
5
TOP VIEW
V
CC
B
A
GND
N8 PACKAGE
8-LEAD PLASTIC DIP
J8 PACKAGE
8-LEAD CERAMIC DIP
S8 PACKAGE
8-LEAD PLASTIC SOIC
R
D
RO
RE
DE
DI
T
JMAX
= 155
C,
JA
= 100
C/ W (J)
T
JMAX
= 100
C,
JA
= 130
C/ W (N)
T
JMAX
= 100
C,
JA
= 170
C/ W (S)
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
R = 27
or R = 50
, Figure 1
q
0.2
V
DifferentialOutput Voltage for
Complementary States
V
OC
Driver Common-Mode Output Voltage
R = 27
or R = 50
, Figure 1
q
3
V
V
OC
Change in Magnitude of Driver
R = 27
or R = 50
, Figure 1
q
0.2
V
Common-Mode Output Voltage
for Complementary States
V
IH
Input High Voltage
DE, DI, RE
q
2
V
V
IL
Input Low Voltage
DE, DI, RE
q
0.8
V
I
IN1
Input Current
DE, DI, RE
q
2
A
I
IN2
Input Current (A, B)
DE = 0, V
CC
= 0V
V
IN
= 12V
q
1
mA
or 5.25V
V
IN
= 7V
q
0.8
mA
V
TH
Differential Input Threshold Voltage
7V
V
CM
12V
q
0.2
0.2
V
for Receiver
V
TH
Receiver Input Hysteresis
V
CM
= 0V
q
70
mV
V
OH
Receiver Output High Voltage
I
O
= 4mA, V
ID
= 200mV
q
3.5
V
V
OL
Receiver Outpu Low Voltage
I
O
= 4mA, V
ID
= 200mV
q
0.4
V
I
OZR
Three-State (High Impedance) Output
V
CC
= Max, 0.4V
V
O
2.4V
q
1
A
Current at Receiver
R
IN
Receiver Input Resistance
7V
V
CM
12V
q
12
k
I
CC
Supply Current
No Load, Pins 2,
Outputs Enabled
q
500
900
A
3, 4 = 0V or 5V
Outputs Disabled
q
300
500
A
I
OSD1
Driver Short-Circuit Current, V
OUT
= HIGH
V
O
= 7V
q
35
100
250
mA
I
OSD2
Driver Short-Circuit Current, V
OUT
= LOW
V
O
= 10V
q
35
100
250
mA
I
OSR
Receiver Short-Circuit Current
0V
V
O
V
CC
q
7
85
mA
V
CC
= 5V
5%, unless otherwise noted. (Notes 2 and 3)
ELECTRICAL C
C
HARA TERISTICS
3
LTC485
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
(Figures 3 and 5)
q
10
30
50
ns
t
SKEW
Driver Output to Output
q
5
10
ns
t
r
, t
f
Driver Rise or Fall Time
q
3
15
25
ns
t
ZH
Driver Enable to Output High
C
L
= 100pF (Figures 4 and 6) S2 Closed
q
40
70
ns
t
ZL
Driver Enable to Output Low
C
L
= 100pF (Figures 4 and 6) S1 Closed
q
40
70
ns
t
LZ
Driver Disable Time from Low
C
L
= 15pF (Figures 4 and 6) S1 Closed
q
40
70
ns
t
HZ
Driver Disable Time from High
C
L
= 15pF (Figures 4 and 6) S2 Closed
q
40
70
ns
t
PLH
Receiver Input to Output
R
DIFF
= 54
, C
L1
= C
L2
= 100pF,
q
30
90
200
ns
t
PHL
(Figures 3 and 7)
q
30
90
200
ns
t
SKD
t
PLH
t
PHL
Differential Receiver Skew
q
13
ns
t
ZL
Receiver Enable to Output Low
C
RL
= 15pF (Figures 2 and 8) S1 Closed
q
20
50
ns
t
ZH
Receiver Enable to Output High
C
RL
= 15pF (Figures 2 and 8) S2 Closed
q
20
50
ns
t
LZ
Receiver Disable from Low
C
RL
= 15pF (Figures 2 and 8) S1 Closed
q
20
50
ns
t
HZ
Receiver Disable from High
C
RL
= 15pF (Figures 2 and 8) S2 Closed
q
20
50
ns
SWITCHI G CHARACTERISTICS
U
V
CC
= 5V
5%, unless otherwise noted. (Notes 2 and 3)
3V
DE
A
B
DI
R
DIFF
C
L1
C
L2
RO
15pF
A
B
RE
LTC485 F03
OUTPUT
UNDER TEST
C
L
S1
S2
V
CC
500
LTC485 F02
Figure 3. Driver/Receiver Timing Test Circuit
Figure 4. Driver Timing Test Load #2
RECEIVER
OUTPUT
C
RL
15pF
1k
S1
S2
TEST POINT
V
CC
1k
LTC485 F02
V
OD
A
B
R
R
V
OC
LTC485 F01
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
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.
Note 2: All currents into device pins are positive; all currents out ot 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 T
A
= 25
C.
Note 4: The LTC485 is guaranteed by design to be functional over a supply
voltage range of 5V
10%. Data sheet parameters are guaranteed over the
tested supply voltage range of 5V
5%.
TEST CIRCUITS
4
LTC485
SWITCHI G TI E WAVEFOR S
U
W
W
DI
3V
1.5V
t
PLH
t
r
t
SKEW
1/2 V
O
V
O
80%
10%
0V
B
A
V
O
V
O
0V
90%
1.5V
t
PLH
t
SKEW
1/2 V
O
f = 1MHz, t
r
10ns, t
f
10ns
20%
t
f
V
DIFF
= V(A) V(B)
LTC485 F05
Figure 5. Driver Propagation Delays
1.5V
t
ZL
2.3V
2.3V
t
ZH
1.5V
t
LZ
0.5V
0.5V
t
HZ
f = 1MHz, t
r
10ns, t
f
10ns
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V
0V
DI
5V
V
OL
V
OH
0V
A, B
A, B
LTC485 F06
Figure 6. Driver Enable and Disable Times
1.5V
t
PHL
f = 1MHz, t
r
10ns, t
f
10ns
R
V
OD2
A, B
0V
1.5V
t
PLH
OUTPUT
INPUT
V
OD2
V
OL
V
OH
LTC485 F07
Figure 7. Receiver Propagation Delays
Figure 8. Receiver Enable and Disable Times
1.5V
t
ZL
1.5V
1.5V
t
ZH
1.5V
t
LZ
0.5V
0.5V
t
HZ
f = 1MHz, t
r
10ns, t
f
10ns
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V
0V
RE
5V
0V
R
R
LTC485 F08
5
LTC485
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
LTC485 Transmitting
INPUTS
OUTPUTS
RE
DE
DI
B
A
X
1
1
No Fault
0
1
X
1
0
No Fault
1
0
X
0
X
X
Z
Z
X
1
X
Fault
Z
Z
LINE
CONDITION
LTC485 Receiving
INPUTS
OUTPUTS
RE
DE
A B
R
0
0
0.2V
1
0
0
0.2V
0
0
0
Inputs Open
1
1
0
X
Z
PIN #
NAME
DESCRIPTION
1
RO
Receiver Output. If the receiver output is enabled
(RE low), then if A > B by 200mV, RO will be
high. If A < B by 200mV, then RO will be low.
2
RE
Receiver Output Enable. A low enables the
receiver output, RO. A high input forces the
receiver output into a high impedance state.
3
DE
Driver Outputs Enable. A high on DE enables the
driver output. A and B, and the chip will function
as a line driver. A low input will force the driver
outputs into a high impedance state and the chip
will function as a line receiver.
4
DI
Driver Input. If the driver outputs are enabled
(DE high), then a low on DI forces the outputs A
low and B high. A high on DI with the driver
outputs enabled will force A high and B low.
5
GND
Ground Connection.
6
A
Driver Output/Receiver Input.
7
B
Driver Output/Receiver Input.
8
V
CC
Positive Supply; 4.75 < V
CC
< 5.25
PI FU CTIO S
U
U
U
FU CTIO TABLES
U
U
Receiver Output High Voltage
vs Output Current
Receiver Output Low Voltage
vs Output Current
OUTPUT VOLTAGE (V)
0
0
OUTPUT CURRENT (mA)
4
12
16
20
1.0
36
LTC485 TPC01
8
0.5
2.0
24
28
32
1.5
T
A
= 25C
OUTPUT VOLTAGE (V)
5
0
OUTPUT CURRENT (mA)
2
6
8
10
3
18
LTC485 TPC02
4
4
12
14
16
2
T
A
= 25C
TEMPERATURE (C)
50
3.0
OUTPUT VOLTAGE (V)
3.2
3.6
3.8
4.0
75
4.8
LTC485 TPC03
3.4
0
125
4.2
4.4
4.6
25
25
50
100
I = 8mA
Receiver Output High Voltage
vs Temperature
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