LTC485
Low Power RS485
Interface Transceiver
FEATURES
s
s
s
s
DESCRIPTIO
s
s
s
s
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s
Low Power: I
CC
= 300µA Typ
Designed for RS485 Interface 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 Transceiver
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
30ns Typical Driver Propagation Delays
with 5ns Skew
Pin Compatible with the SN75176A, DS75176A
and
µA96176
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.
APPLICATI
s
s
S
Low Power RS485/RS422 Transceiver
Level Translator
TYPICAL APPLICATI
RO1
RE1
DE1
DI1
D
R
V
CC1
Rt
GND1
A
Rt
RO2
RE2
DE2
DI2
D
GND2
LTC485 • TA01
R
V
CC2
B
U
Driver Outputs
LTC485 • TA02
UO
UO
1
LTC485
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RO 1
RE 2
DE 3
DI 4
D
R
8
7
6
5
V
CC
B
A
GND
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
ORDER PART
NUMBER
LTC485CJ8
LTC485CN8
LTC485CS8
LTC485IN8
LTC485IS8
LTC485MJ8
S8 PART MARKING
485
485I
J8 PACKAGE
8-LEAD CERAMIC DIP
N8 PACKAGE
8-LEAD PLASTIC DIP
S8 PACKAGE
8-LEAD PLASTIC SOIC
T
JMAX
= 155°C,
θ
JA
= 100°C/ W (J)
T
JMAX
= 100°C,
θ
JA
= 130°C/ W (N)
T
JMAX
= 100°C,
θ
JA
= 170°C/ W (S)
ELECTRICAL CHARACTERISTICS
SYMBOL
V
OD1
V
OD2
∆V
OD
PARAMETER
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (with Load)
Change in Magnitude of Driver
DifferentialOutput Voltage for
Complementary States
Driver Common-Mode Output Voltage
Change in Magnitude of Driver
Common-Mode Output Voltage
for Complementary 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 Outpu Low Voltage
Three-State (High Impedance) Output
Current at Receiver
Receiver Input Resistance
Supply Current
Driver Short-Circuit Current, V
OUT
= HIGH
Driver Short-Circuit Current, V
OUT
= LOW
Receiver Short-Circuit Current
V
CC
= 5V
±5%,
unless otherwise noted. (Notes 2 and 3)
MIN
q
q
q
q
CONDITIONS
I
O
= 0
R = 50Ω (RS422)
R = 27Ω (RS485), Figure 1
R = 27Ω or R = 50Ω, Figure 1
TYP
MAX
5
UNITS
V
V
V
V
2
1.5
5
0.2
V
OC
∆
V
OC
R = 27Ω or R = 50Ω, Figure 1
R = 27Ω or R = 50Ω, Figure 1
q
q
3
0.2
V
IH
V
IL
I
IN1
I
IN2
V
TH
∆V
TH
V
OH
V
OL
I
OZR
R
IN
I
CC
I
OSD1
I
OSD2
I
OSR
DE, DI, RE
DE, DI, RE
DE, DI, RE
DE = 0, V
CC
= 0V
or 5.25V
– 7V
≤
V
CM
≤
12V
V
CM
= 0V
I
O
= – 4mA, V
ID
= 200mV
I
O
= 4mA, V
ID
= – 200mV
V
CC
= Max, 0.4V
≤
V
O
≤
2.4V
– 7V
≤
V
CM
≤
12V
No Load, Pins 2,
3, 4 = 0V or 5V
V
O
= – 7V
V
O
= 10V
0V
≤
V
O
≤
V
CC
Outputs Enabled
Outputs Disabled
V
IN
= 12V
V
IN
= – 7V
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
2
0.8
±2
±1
– 0.8
– 0.2
70
3.5
0.4
±1
12
500
300
35
35
7
100
100
900
500
250
250
85
0.2
2
U
V
V
V
V
µA
mA
mA
V
mV
V
V
µA
kΩ
µA
µA
mA
mA
mA
W
U
U
W W
W
LTC485
SWITCHI G CHARACTERISTICS
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
t
PLH
– t
PHL
Differential Receiver Skew
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 Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Receiver Disable from High
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.
TEST CIRCUITS
A
R
V
OD
R
B
LTC485 • F01
3V
DE
A
DI
B
R
DIFF
C
L2
C
L1
A
RO
B
RE
15pF
C
L
LTC485 • F02
Figure 3. Driver/Receiver Timing Test Circuit
U
V
CC
= 5V
±5%,
unless otherwise noted. (Notes 2 and 3)
MIN
q
q
q
q
CONDITIONS
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
(Figures 3 and 5)
TYP
30
30
5
15
40
40
40
40
MAX
50
50
10
25
70
70
70
70
200
200
50
50
50
50
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
10
10
3
C
L
= 100pF (Figures 4 and 6) S2 Closed
C
L
= 100pF (Figures 4 and 6) S1 Closed
C
L
= 15pF (Figures 4 and 6) S1 Closed
C
L
= 15pF (Figures 4 and 6) S2 Closed
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
(Figures 3 and 7)
q
q
q
q
q
q
q
30
30
90
90
13
20
20
20
20
C
RL
= 15pF (Figures 2 and 8) S1 Closed
C
RL
= 15pF (Figures 2 and 8) S2 Closed
C
RL
= 15pF (Figures 2 and 8) S1 Closed
C
RL
= 15pF (Figures 2 and 8) S2 Closed
q
q
q
q
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 POINT
RECEIVER
OUTPUT
S1
1k
V
CC
V
OC
C
RL
15pF
1k
S2
LTC485 • F02
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
S1
OUTPUT
UNDER TEST
500Ω
S2
V
CC
LTC485 • F03
Figure 4. Driver Timing Test Load #2
3
LTC485
SWITCHI G TI E WAVEFOR S
3V
DI
0V
t
PLH
B
V
O
A
1/2 V
O
V
O
0V
–V
O
10%
t
r
t
SKEW
80%
90%
V
DIFF
= V(A) – V(B)
t
f
20%
LTC485 • F05
1.5V
Figure 5. Driver Propagation Delays
3V
DI
0V
5V
A, B
V
OL
V
OH
A, B
0V
t
ZH
t
HZ
LTC485 • F06
1.5V
t
ZL
2.3V
2.3V
Figure 6. Driver Enable and Disable Times
V
OH
R
V
OL
t
PHL
V
OD2
A, B
–V
OD2
0V
1.5V
OUTPUT
f = 1MHz, t
r
≤
10ns, t
f
≤
10ns
INPUT
t
PLH
1.5V
Figure 7. Receiver Propagation Delays
3V
RE
0V
5V
R
t
ZL
1.5V
OUTPUT NORMALLY LOW
t
LZ
0.5V
1.5V
f = 1MHz, t
r
≤
10ns, t
f
≤
10ns
1.5V
R
0V
t
ZH
Figure 8. Receiver Enable and Disable Times
4
W
1.5V
W
U
f = 1MHz, t
r
≤
10ns, t
f
≤
10ns
t
PLH
1.5V
1/2 V
O
t
SKEW
f = 1MHz, t
r
≤
10ns, t
f
≤
10ns
t
LZ
OUTPUT NORMALLY LOW
1.5V
0.5V
OUTPUT NORMALLY HIGH
0.5V
LTC485 • F07
OUTPUT NORMALLY HIGH
t
HZ
0.5V
LTC485 • F08
LTC485
FU CTIO TABLES
LTC485 Transmitting
INPUTS
RE
X
X
X
X
DE
1
1
0
1
DI
1
0
X
X
LINE
CONDITION
No Fault
No Fault
X
Fault
OUTPUTS
B
0
1
Z
Z
A
1
0
Z
Z
PI FU CTIO S
PIN #
1
NAME
RO
DESCRIPTION
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.
Receiver Output Enable. A low enables the
receiver output, RO. A high input forces the
receiver output into a high impedance state.
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.
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.
Ground Connection.
Driver Output/Receiver Input.
Driver Output/Receiver Input.
Positive Supply; 4.75 < V
CC
< 5.25
2
RE
3
DE
LTC485 Receiving
INPUTS
RE
0
0
0
1
DE
0
0
0
0
A–B
≥0.2V
≤
– 0.2V
Inputs Open
X
OUTPUTS
R
1
0
1
Z
5
6
7
8
GND
A
B
V
CC
4
DI
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Output Low Voltage
vs Output Current
36
32
T
A
= 25°C
–18
–16
T
A
= 25°C
Receiver Output High Voltage
vs Output Current
4.8
4.6
4.4
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
28
24
20
16
12
8
4
0
0
0.5
1.5
1.0
OUTPUT VOLTAGE (V)
2.0
LTC485 • TPC01
–14
–12
–10
–8
–6
–4
–2
0
5
4
3
OUTPUT VOLTAGE (V)
2
LTC485 • TPC02
OUTPUT VOLTAGE (V)
U
U
U
U W
U
U
Receiver Output High Voltage
vs Temperature
I = 8mA
4.2
4.0
3.8
3.6
3.4
3.2
3.0
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
125
LTC485 • TPC03
5
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