1
LTC1484
Low Power
RS485 Transceiver
with Receiver Fail-Safe
■
No Damage or Latchup to
±
15kV ESD (Human
Body Model), IEC-1000-4-2 Level 4 Contact (
±
8kV)
and Level 3 (
±
8kV) Air Gap Specifications
■
Guaranteed High Receiver Output State for Floating,
Shorted or Terminated Inputs with No Signal
Present
■
Drives Low Cost Residential Telephone Wires
■
Low Power: I
CC
= 700µA Max with Driver Disabled
■
I
CC
= 900µA Max for Driver Enable with No Load
■
20µA Max Quiescent Current in Shutdown Mode
■
Single 5V Supply
■
–7V to 12V Common Mode Range Permits ±7V
Ground Difference Between Devices on the Data Line
■
Power Up/Down Glitch-Free Driver Outputs
■
Up to 32 Transceivers on the Bus
■
Pin Compatible with the LTC485
■
Available in 8-Lead MSOP, PDIP and SO Packages
The LTC
®
1484 is a low power RS485 compatible trans-
ceiver. In receiver mode, it offers a fail-safe feature which
guarantees a high receiver output state when the inputs
are left open, shorted together or terminated with no
signal present. No external components are required to
ensure the high receiver output state.
Both driver and receiver feature three-state outputs with
separate receiver and driver control pins. The driver
outputs maintain high impedance over the entire com-
mon mode range when three-stated. Excessive power
dissipation caused by bus contention or faults is pre-
vented by a thermal shutdown circuit that forces the
driver outputs into a high impedance state.
Enhanced ESD protection allows the LTC1484 to with-
stand ±15kV (human body model), IEC-1000-4-2 level 4
(±8kV) contact and level 3 (±8kV) air discharge ESD
without latchup or damage.
The LTC1484 is fully specified over the commercial and
industrial temperature ranges and is available in 8-lead
MSOP, PDIP and SO packages.
■
Battery-Powered RS485/RS422 Applications
■
Low Power RS485/RS422 Transceiver
■
Level Translator
, LTC and LT are registered trademarks of Linear Technology Corporation.
RO1
RE1
DE1
DI1
R
V
CC1
LTC1484
GND1
B1
A1
B2
A2
120Ω120Ω
D
V
CC2
GND2
1484 TA01
R
D
RO2
RE2
DE2
DI2
LTC1484
RS485 Interface
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
Driving a 2000 Foot STP Cable
Dl1 ↑↓ DE1 = V
CC
1484 TA01a
Dl2 = 0 DE2 = 0
RE1 = RE2 = 0
Dl1
B2
A2
RO2
2
LTC1484
ABSOLUTE MAXIMUM RATINGS
W
WW
U
(Note 1)
Supply Voltage (V
CC
)............................................... 6.5V
Control Input Voltages ................. –0.3V to (V
CC
+ 0.3V)
Driver Input Voltage ..................... –0.3V to (V
CC
+ 0.3V)
Driver Output Voltages ................................. –7V to 10V
Receiver Input Voltages (Driver Disabled) .. –12V to 14V
Receiver Output Voltage............... –0.3V to (V
CC
+ 0.3V)
Junction Temperature .......................................... 125°C
Operating Temperature Range
LTC1484C .........................................0°C ≤ T
A
≤ 70°C
LTC1484I...................................... –40°C ≤ T
A
≤ 85°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
OD1
Differential Driver Output Voltage (Unloaded) I
OUT
= 0 ●V
CC
V
V
OD2
Differential Driver Output Voltage (with Load) R = 50Ω (RS422) ●2V
R = 27Ω (RS485) Figure 1 ●1.5 5 V
R = 22Ω, Figure 1 ●1.5 5 V
V
OD3
Differential Driver Output Voltage V
TST
= –7V to 12V, Figure 2 ●1.5 5 V
(with Common Mode)
∆V
OD
Change in Magnitude of Driver Differential R = 22Ω, 27Ω or R = 50Ω, Figure 1 ●0.2 V
Output Voltage for Complementary Output States V
TST
= –7V to 12V, Figure 2
V
OC
Driver Common Mode Output Voltage R = 22Ω, 27Ω or R = 50Ω, Figure 1 ●3V
∆|V
OC
| Change in Magnitude of Driver Common Mode R = 22Ω, 27Ω or R = 50Ω, Figure 1 ●0.2 V
Output Voltage for Complementary Output States
V
IH
Input High Voltage DE, DI, RE ●2.0 V
V
IL
Input Low Voltage DE, DI, RE ●0.8 V
I
IN1
Input Current DE, DI, RE ●±2µA
I
IN2
Input Current (A, B) DE = 0, V
CC
= 0 or 5V, V
IN
= 12V ●1.0 mA
DE = 0, V
CC
= 0 or 5V, V
IN
= –7V ●–0.8 mA
V
TH
Differential Input Threshold Voltage for Receiver –7V ≤ V
CM
≤ 12V, DE = 0 ●–0.20 –0.015 V
ELECTRICAL CHARACTERISTICS
PACKAGE/ORDER INFORMATION
W
UU
ORDER PART
NUMBER ORDER PART
NUMBER
LTC1484CMS8 LTC1484CN8
LTC1484CS8
LTC1484IN8
LTC1484IS8
S8 PART MARKING
1484
1484I
MS8 PART MARKING
LTDX
T
JMAX
= 125°C, θ
JA
= 200°C/ W
T
JMAX
= 125°C, θ
JA
= 130°C/ W (N8)
T
JMAX
= 125°C, θ
JA
= 135°C/W (S8)
Consult factory for Military grade parts.
1
2
3
4
RO
RE
DE
DI
8
7
6
5
V
CC
B
A
GND
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
1
2
3
4
8
7
6
5
TOP VIEW
RO
RE
DE
DI
V
CC
B
A
GND
N8 PACKAGE
8-LEAD PDIP S8 PACKAGE
8-LEAD PLASTIC SO
R
D
3
LTC1484
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
∆V
TH
Receiver Input Hysteresis V
CM
= 0V, DE = 0 ●±30 mV
V
OH
Receiver Output High Voltage I
OUT
= –4mA, (V
A
– V
B
) = 200mV ●3.5 V
V
OL
Receiver Output Low Voltage I
OUT
= 4mA, (V
A
– V
B
) = –200mV ●0.4 V
I
OZR
Three-State (High Impedance) Output Current V
CC
= Max, 0.4V ≤ V
OUT
≤ 2.4V, ●±1µA
at Receiver DE = 0
R
IN
Receiver Input Resistance –7V ≤ V
CM
≤ 12V ●12 22 kΩ
I
CC
Supply Current No Load, Output Enabled (DE = V
CC
)●600 900 µA
No Load, Output Disabled (DE = 0) ●400 700 µA
I
SHDN
Supply Current in Shutdown Mode DE = 0, RE = V
CC
, DI = 0 ●120 µA
I
OSD1
Driver Short-Circuit Current, V
OUT
= High (Note 4) –7V ≤ V
OUT
≤ 10V 35 250 mA
I
OSD2
Driver Short-Circuit Current, V
OUT
= Low (Note 4) –7V ≤ V
OUT
≤ 10V 35 250 mA
I
OSR
Receiver Short-Circuit Current 0V ≤ V
OUT
≤ V
CC
●785mA
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SWITCHING CHARACTERISTICS
U
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
PLH
Driver Input to Output R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF ●10 28.5 60 ns
(Figures 4, 6)
t
PHL
Driver Input to Output R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF ●10 31 60 ns
(Figures 4, 6)
t
SKEW
Driver Output to Output R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF ●2.5 10 ns
(Figures 4, 6)
t
r
, t
f
Driver Rise or Fall Time R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF ●31540 ns
(Figures 4, 6)
t
ZH
Driver Enable to Output High C
L
= 100pF (Figures 5, 7) S2 Closed ●40 70 ns
t
ZL
Driver Enable to Output Low C
L
= 100pF (Figures 5, 7) S1 Closed ●40 100 ns
t
LZ
Driver Disable Time from Low C
L
= 15pF (Figures 5, 7) S1 Closed ●40 70 ns
t
HZ
Driver Disable Time from High C
L
= 15pF (Figures 5, 7) S2 Closed ●40 70 ns
t
PLH
Receiver Input to Output R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF, ●30 160 200 ns
(Figures 4, 8)
t
PHL
Receiver Input to Output R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF, ●30 140 200 ns
(Figures 4, 8)
t
SKD
|t
PLH
– t
PHL
| Differential Receiver Skew R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF, 20 ns
(Figures 4, 8)
t
ZL
Receiver Enable to Output Low C
RL
= 15pF (Figures 3, 9) S1 Closed ●20 50 ns
t
ZH
Receiver Enable to Output High C
RL
= 15pF (Figures 3, 9) S2 Closed ●20 50 ns
t
LZ
Receiver Disable from Low C
RL
= 15pF (Figures 3, 9) S1 Closed ●20 50 ns
t
HZ
Receiver Disable from High C
RL
= 15pF (Figures 3, 9) S2 Closed ●20 50 ns
t
DZR
Driver Enable to Receiver Valid R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF ●1600 3000 ns
(Figures 4, 10)
f
MAX
Maximum Data Rate (Note 5) ●4 5 Mbps
t
SHDN
Time to Shutdown (Note 6) DE = 0, RE↑●50 300 600 ns
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
4
LTC1484
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
ZH(SHDN)
Driver Enable from Shutdown to Output High C
L
= 100pF (Figures 5, 7) S2 Closed, ●40 100 ns
DI = DE
t
ZL(SHDN)
Driver Enable from Shutdown to Output Low C
L
= 100pF (Figures 5, 7) S1 Closed, ●40 100 ns
DI = 0
t
ZH(SHDN)
Receiver Enable from Shutdown to Output High C
L
= 15pF (Figures 3, 9) S2 Closed, ●10 µs
DE = 0
t
ZL(SHDN)
Receiver Enable from Shutdown to Output Low C
L
= 15pF (Figures 3, 9) S1 Closed, ●10 µs
DE = 0
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: All typicals are given for V
CC
= 5V and T
A
= 25°C.
Note 3: 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 4: For higher ambient temperatures, the part may enter thermal
shutdown during short-circuit conditions.
Note 5: Guaranteed by design.
Note 6: Time for I
CC
to drop to I
CC
/2 when the receiver is disabled.
SWITCHING CHARACTERISTICS
U
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
INPUT VOLTAGE (V)
–0.2 –0.16 –0.12 –0.08 –0.04 0
RECEIVER OUTPUT VOLTAGE (V)
1484 G01
6
5
4
3
2
1
0
TA = 25°C
VCC = 5V
VTH(HIGH)
VTH(LOW)
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER INPUT THRESHOLD VOLTAGE (V)
1484 G02
0
–0.05
–0.10
–0.15
–0.20
–0.25
V
CC
= 5V
V
TH(HIGH)
V
CM
= –7V
V
CM
= 12V
V
CM
= 0V
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER INPUT THRESHOLD VOLTAGE (V)
1484 G03
0
–0.05
–0.10
–0.15
–0.20
–0.25
V
CC
= 5V
V
TH(LOW)
V
CM
= –7V
V
CM
= 12V
V
CM
= 0V
Receiver Output Voltage vs Input
Voltage
Receiver Input Threshold Voltage
(Output High) vs Temperature
Receiver Input Threshold Voltage
(Output Low) vs Temperature
5
LTC1484
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER INPUT OFFSET VOLTAGE (mV)
1484 G04
0
–20
–40
–60
–80
–100
–120
–140
–160
–180
–200
V
CC
= 5V
V
CM
= –7V
V
CM
= 12V
V
CM
= 0V
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER HYSTERESIS (mV)
1484 G05
100
90
80
70
60
50
40
30
20
10
0
VCC = 5V
VTH(HIGH) – VTH(LOW)
VCM = –7V TO 12V
SUPPLY VOLTAGE (V)
4.5 4.75 5 5.25
RECEIVER INPUT THRESHOLD VOLTAGE (V)
1484 G06
0
–0.02
–0.04
–0.06
–0.08
–0.10
–0.12
–0.14
–0.16
–0.18
–0.20
TA = 25°C
VCM = 0V
VTH(HIGH)
VTH(LOW)
Receiver Input Offset Voltage vs
Temperature
Receiver Hysteresis vs
Temperature
Receiver Input Threshold Voltage
vs Supply Voltage
Receiver Output High Voltage vs
Output Current
Receiver Output Low Voltage vs
Output Current
Receiver Output High Voltage vs
Temperature
OUTPUT CURRENT (mA)
–25 –20 –15 –10 –5 0
RECEIVER OUTPUT HIGH VOLTAGE (V)
1484 G07
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
VCC = 4.75V
OUTPUT CURRENT (mA)
05 10 15 20 25
RECEIVER OUTPUT LOW VOLTAGE (V)
1484 G08
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
VCC = 4.75V
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER OUTPUT HIGH VOLTAGE (V)
1484 G09
4.5
4.4
4.3
4.2
4.1
4.0
3.9
3.8
3.7
3.6
3.5
VCC = 4.75V
IOUT = –8mA
Receiver Output Low Voltage vs
Temperature
Input Current (A, B) vs
Temperature
Receiver Input Resistance vs
Temperature
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER OUTPUT LOW VOLTAGE (V)
1484 G10
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
V
CC
= 4.75V
I
OUT
= 8mA
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
INPUT CURRENT (µA)
1484 G11
600
500
400
300
200
100
0
–100
–200
–300
–400
V
CC
= 0V OR 5V
V
CM
= 12V
V
CM
= –7V
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER INPUT RESISTANCE (kΩ)
1484 G12
26.0
25.5
25.0
24.5
24.0
23.5
23.0
22.5
22.0
V
CC
= 0V OR 5V
V
CM
= 12V
V
CM
= –7V
6
LTC1484
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Receiver Short-Circuit Current vs
Temperature
Receiver Propagation Delay vs
Temperature Receiver Skew vs Temperature
Receiver Propagation Delay vs
Supply Voltage
Shutdown Supply Current vs
Temperature
Shutdown Supply Current vs
Supply Voltage
Supply Current vs Temperature Supply Current vs Supply Voltage
Logic Input Threshold vs
Temperature
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER SHORT-CIRCUIT CURRENT (mA)
1484 G13
100
90
80
70
60
50
40
30
20
10
0
VCC = 5.25V
OUTPUT LOW
SHORT TO VCC
OUTPUT HIGH
SHORT TO GROUND
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER PROPAGATION DELAY (ns)
1484 G14
200
180
160
140
120
100
80
60
40
20
0
VCC = 5V
tPLH
tPHL
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
RECEIVER SKEW (ns)
1484 G15
30
25
20
15
10
5
0
VCC = 5V
SUPPLY VOLTAGE (V)
4.5 4.75 5 5.25 5.5
RECEIVER PROPAGATION DELAY (ns)
1484 G16
200
180
160
140
120
100
TA = 25°C
tPLH
tPHL
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125
SHUTDOWN SUPPLY CURRENT (µA)
1484 G17
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
VCC = 5V
DE = DI = 0
RE = 5V
SUPPLY VOLTAGE (V)
4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5
SHUTDOWN SUPPLY CURRENT (µA)
1484 G18
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
T
A
= 25°C
TEMPERATURE (°C)
–55 –30 –5 20 45 70 95 120 145 170
SUPPLY CURRENT (µA)
1484 G19
1000
900
800
700
600
500
400
300
200
100
0
VCC = 5V
DRIVER ENABLED
NO LOAD
THERMAL SHUTDOWN
WITH DRIVER
ENABLED
DRIVER DISABLED
SUPPLY VOLTAGE (V)
4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5
SUPPLY CURRENT (µA)
1484 G20
700
600
500
400
300
200
100
0
T
A
= 25°C
DRIVER ENABLED
NO LOAD
DRIVER DISABLED
TEMPERATURE (°C)
–55
LOGIC INPUT THRESHOLD VOLTAGE (V)
1484 G21
2.00
1.95
1.90
1.85
1.80
1.75
1.70
1.65
1.60
1.55
1.50
VCC = 5.25V
VCC = 4.75V
VCC = 5V
–35 –15 5 25 45 65 85 105 125
7
LTC1484
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Driver Differential Output Voltage
vs Temperature
Driver Differential Output Voltage
vs Temperature
Driver Differential Output Voltage
vs Temperature
Driver Common Mode Output
Voltage vs Temperature
Driver Common Mode Output
Voltage vs Temperature
Driver Common Mode Output
Voltage vs Temperature
Driver Differential Output Voltage
vs Temperature
Driver Differential Output Voltage
vs Temperature
Driver Differential Output Voltage
vs Output Current
TEMPERATURE (°C)
–55
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1484 G22
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
∆VOD, VCC = 4.5V TO 5.25V
RL = 44Ω
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1484 G23
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
∆VOD, VCC = 4.5V TO 5.25V
RL = 54Ω
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1484 G24
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
∆VOD, VCC = 4.5V TO 5.25V
RL = 100Ω
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER COMMON MODE VOLTAGE (V)
1484 G25
3.0
2.5
2.0
1.5
1.0
0.5
0∆VOC, VCC = 4.5V TO 5.25V
RL = 44Ω
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER COMMON MODE VOLTAGE (V)
1484 G26
3.0
2.5
2.0
1.5
1.0
0.5
0∆VOC, VCC = 4.5V TO 5.25V
RL = 54Ω
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER COMMON MODE VOLTAGE (V)
1484 G27
3.0
2.5
2.0
1.5
1.0
0.5
0∆VOC, VCC = 4.5V TO 5.25V
RL = 100Ω
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1484 G28
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
∆VOD3 FOR VCC = 4.5V TO 5.25V
SEE FIGURE 2 VCM = –7V
VOD3
DI HIGH
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1484 G29
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
∆VOD3 FOR VCC = 4.5V TO 5.25V
VCM = 12V
VOD3
DI HIGH
SEE FIGURE 2
VCC = 5V
VCC = 4.5V
VCC = 4.75V
VCC = 5.25V
–35 –15 5 25 45 65 85 105 125
OUTPUT CURRENT (mA)
010 20 30 40 50 60 70 80 90 100
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1484 G30
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
VCC = 5V
TA = 25°C
8
LTC1484
RO (Pin 1): Receiver Output. If the receiver output is en-
abled (RE low) and the part is not in shutdown, RO is high
if (A – B) > VTH(MAX) and low if (A – B) < VTH(MIN). RO is
also high if the receiver inputs are open or shorted to-
gether, with or without a termination resistor.
RE (Pin 2): Receiver Output Enabled. A high on this pin
three-states the receiver output (RO) and a low enables it.
DE (Pin 3): Driver Enable Input. DE = high enables the
output of the driver with the driver outputs determined by
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Driver Output High Voltage vs
Output Current
Driver Output Low Voltage vs
Output Current
Driver Propagation Delay vs
Temperature
Driver Short-Circuit Current vs
Temperature Driver Skew vs Temperature
Driver Propagation Delay vs
Supply Voltage
OUTPUT CURRENT (mA)
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10 0
DRIVER OUTPUT HIGH VOLTAGE (V)
1484 G31
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
VCC = 4.75V
OUTPUT CURRENT (mA)
010 20 30 40 50 60 70 80 90 100
DRIVER OUTPUT LOW VOLTAGE (V)
1484 G32
3.0
2.5
2.0
1.5
1.0
0.5
0
VCC = 4.75V
TEMPERATURE (°C)
–55
DRIVER PROPAGATION DELAY (ns)
1484 G33
50
45
40
35
30
25
20
15
10
5
0
VCC = 5V
tPHL
tPLH
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER SHORT-CIRCUIT CURRENT (mA)
1484 G34
250
200
150
100
50
0
VCC = 5.25V
DRIVER OUTPUT HIGH
SHORT TO –7V
DRIVER OUTPUT LOW
SHORT TO 10V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–55
DRIVER SKEW (ns)
1484 G35
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0–35 –15 5 25 45 65 85 105 125
SUPPLY VOLTAGE (V)
4.5 4.75 5 5.25 5.5
DRIVER PROPAGATION DELAY (ns)
1484 G36
40
35
30
25
20
15
10
5
0
TA = 25°C
tPHL
tPLH
PIN FUNCTIONS
UUU
the DI pin. DE = low forces the driver outputs into a high
impedance state. The LTC1484 enters shutdown when
both receiver and driver outputs are disabled (RE is high
and DE is low).
DI (Pin 4): Driver Input. When the driver outputs are
enabled (DE high), DI high takes the A output high and the
B output low. DI low takes the A output low and the B
output high.
GND (Pin 5): Ground.
9
LTC1484
PIN FUNCTIONS
UUU
A (Pin 6): Driver Output/Receiver Input. The input resis-
tance is typically 22k when the driver is disabled (DE = 0).
When the driver is enabled, the A output follows the logic
level at the DI pin.
B (Pin 7): Driver Output/Receiver Input. The input resis-
tance is typically 22k when the driver is disabled (DE = 0).
When the driver is enabled, the B output is inverted from
the logic level at the DI pin.
VCC (Pin 8): Positive Supply. 4.75V ≤ V CC ≤ 5.25V. A 0.1µF
bypass capacitor is recommended.
Driver
INPUTS OUTPUTS
RE DE DI B A
X1101
X1010
O0XZZ
10XZ*Z*
FU CTIO TABLES
UU
Receiver
INPUTS OUTPUTS
RE DE A – B RO
00 ≥V
TH(MAX)
1
00 ≤V
TH(MIN)
0
0 0 Inputs Open 1
0 0 Inputs Shorted 1
1X X Z
†
TEST CIRCUITS
OUTPUT
UNDER
TEST C
L
S1
S2
V
CC
500Ω
1484 F05
OUTPUT
UNDER
TEST
C
RL
1k
S1
S2
V
CC
1k
1484 F03
Figure 3
Figure 5
DE
RE
A
B
DI C
L1
R
DIFF
C
L2
RO
15pF
A
B
1484 F04
Figure 4
Note: Z = high impedance, X = don’t care
*Shutdown mode for LTC1484
†
Shutdown mode for LTC1484 if DE = 0. Table valid with or without
termination resistors.
V
OD1
V
OD2
A
B
R
RV
OC
1484 F01
Figure 1
VOD3
A
B
375Ω
375Ω
60Ω–7V TO 12V
1484 F02
Figure 2
10
LTC1484
SWITCHI G TI E WAVEFOR S
UWW
Figure 6. Driver Propagation Delays
Figure 9. Receiver Enable and Shutdown Timing
Figure 8. Receiver Propagation Delays
1.5V
2.3V
2.3V
t
ZH(SHDN)
,
t
ZH
NOTE: A, B ARE THREE-STATED WHEN DE = 0, 1kΩ PULL-UP OR 1kΩ PULL-DOWN
t
ZL(SHDN)
,
t
ZL
1.5V
0.5V
0.5V
t
HZ
t
LZ
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V
0V
DE
5V
V
OL
V
OH
0V
A, B
A, B
1484 F07
f = 1MHz, t
r
≤ 10ns, t
f
≤ 10ns
Figure 7. Driver Enable and Disable Timing
1.5V
1.5V
1.5V
t
ZH(SHDN),
t
ZH
NOTE: DE = 0, RO IS THREE-STATED IN SHUTDOWN, 1kΩ PULL-UP FOR NORMALLY LOW OUTPUT,
1kΩ PULL-DOWN FOR NORMALLY HIGH OUTPUT
t
ZL(SHDN),
t
ZL
1.5V
0.5V
0.5V
t
HZ
t
LZ
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
RE
5V
0V
5V
0V
RO
RO
1484 F09
f = 1MHz, t
r
≤ 10ns, t
f
≤ 10ns
0V
t
PHL
A – B
VOL
RO 1.5V
NOTE: tSKD = |tPHL – tPLH|, RE = 0
1.5V
0V
tPLH
INPUT
OUTPUT
5V
–VOD2
VOD2
1484 F08
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
DI
3V
1.5V
t
PLH
t
r
t
SKEW
NOTE: DE = 1
1/2 V
O
V
O
f = 1MHz, t
r
≤ 10ns, t
f
≤ 10ns
90%
50% 50%
10%
0V
B
A
V
O
–V
O
90%
1.5V
t
PHL
t
SKEW
10%
t
f
V
O
= V(A) – V(B)
1484 F06
11
LTC1484
APPLICATIONS INFORMATION
WUUU
SWITCHI G TI E WAVEFOR S
UWW
1.5V
1.5V
NOTE: DI = 0, RE = 0, A AND B ARE THREE-STATED WHEN DE = 0
tDZR
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V
0V
DE
V(A) – V(B)
RO
1484 F10
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
Figure 10. Driver Enable to Receiver Valid Timing
Low Power Operation
The LTC1484 has a quiescent current of 900µA max when
the driver is enabled. With the driver in three-state, the
supply current drops to 700µA max. The difference in
these supply currents is due to the additional current
drawn by the internal 22k receiver input resistors when the
driver is enabled. Under normal operating conditions, the
additional current is overshadowed by the 50mA current
drawn by the external termination resistor.
Receiver Open-Circuit Fail-Safe
Some encoding schemes require that the output of the
receiver maintain a known state (usually a logic 1) when
data transmission ends and all drivers on the line are
forced into three-state. Earlier RS485 receivers with a
weak pull-up at the A input will give a high output only
when the inputs are floated. When terminated or shorted
together, the weak pull-up is easily defeated causing the
receiver output to go low. External components are needed
if a high receiver output is mandatory. The receiver of the
LTC1484 has a fail-safe feature which guarantees the
output to be in a logic 1 when the receiver inputs are left
open or shorted together, regardless of whether the termi-
nation resistor is present or not.
In encoding schemes where the required known state is a
low, external components are needed for the LTC1484 and
other RS485 parts.
Fail-safe is achieved by making the receiver trip points fall
within the V
TH(MIN)
to V
TH(MAX)
range. When any of the
listed receiver input conditions exist, the receiver inputs
are effectively at 0V and the receiver output goes high.
The receiver fail-safe mechanism is designed to reject fast
common mode steps (–7V to 12V in 10ns) switching at
100kHz typ. This is achieved through an internal carrier
detect circuit similar to the LTC1482. This circuit has built-
in delays to prevent glitches while the input swings be-
tween ±V
TH(MAX)
levels. When all the drivers connected to
the receiver inputs are three-stated, the internal carrier
detect signal goes low to indicate that no differential signal
is present. When any driver is taken out of three-state, the
carrier detect signal takes 1.6µs typ (see t
DZR
) to detect the
enabled driver. During this interval, the transceiver output
(RO) is forced to the fail-safe high state. After 1.6µs, the
receiver will respond normally to changes in driver output.
If the part is taken out of shutdown mode with the receiver
inputs floating, the receiver output takes about 10µs to
leave three-state (see t
ZL(SHDN)
). If the receiver inputs are
actively driven to a high state, the outputs go high after
about 5.5µs.
12
LTC1484
APPLICATIONS INFORMATION
WUUU
Shutdown Mode
The receiver output (RO) and the driver outputs (A, B) can
be three-stated by taking the RE and DE pins high and low
respectively. Taking RE high and DE low at the same time
puts the LTC1484 into shutdown mode and I
CC
drops to
20µA max.
In some applications (see CDMA), the A and B lines are
pulled to V
CC
or GND through external resistors to force
the line to a high or low state when all connected drivers
are disabled. In shutdown, the supply current will be
higher than 20µA due to the additional current drawn
through the external pull-up and the 22k input resistance
of the LTC1484.
ESD Protection
The ESD performance of the LTC1484 A and B pins is
characterized to meet ±15kV using the Human Body
Model (100pF, 1.5kΩ), IEC-1000-4-2 level (±8kV) contact
mode and IEC-1000-4-2 level 3 (±8kV) air discharge
mode.
This means that external voltage suppressors are not
required in many applications when compared with parts
that are only protected to ±2kV. Pins other than the A and
B pins are protected to ±4.5kV typical per the Human Body
Model.
When powered up, the LTC1484 does not latch up or
sustain damage when the A and B pins are tested using any
of the three conditions listed. The data during the ESD
event may be corrupted, but after the event the LTC1484
continues to operate normally. The additional ESD protec-
tion at the A and B pins is important in applications where
these pins are exposed to the external world via connec-
tions to sockets.
Fault Protection
When shorted to –7V or 10V at room temperature, the
short-circuit current in the driver pins is limited by
internal resistance or protection circuitry to 250mA. Over
the industrial temperature range, the absolute maximum
positive voltage at any driver pin should be limited to 10V
to avoid damage to the driver pins. At higher ambient
temperatures, the rise in die temperature due to the
short-circuit current may trip the thermal shutdown
circuit.
When the driver is disabled, the receiver inputs can
withstand the entire –7V to 12V RS485 common mode
range without damage.
The LTC1484 includes a thermal shutdown circuit which
protects the part against prolonged shorts at the driver
outputs. If a driver output is shorted to another output or
to V
CC
, the current will be limited to 250mA. If the die
temperature rises above 150°C, the thermal shutdown
circuit three-states the driver outputs to open the current
path. When the die cools down to about 130°C, the driver
outputs are taken out of three-state. If the short persists,
the part will heat again and the cycle will repeat. This
thermal oscillation occurs at about 10Hz and protects the
part from excessive power dissipation. The average fault
current drops as the driver cycles between active and
three-state. When the short is removed, the part will return
to normal operation.
Carrier Detect Multiple Access (CDMA) Application
In normal half-duplex RS485 systems, only one node can
transmit at a time. If an idle node suddenly needs to gain
access to the twisted pair while other communications are
in progress, it must wait its turn. This delay is unaccept-
able in safety-related applications. A scheme known as
Carrier Detect Multiple Access (CDMA) solves this prob-
lem by allowing any node to interrupt on-going communi-
cations.
Figure 11 shows four nodes in a typical CDMA communi-
cations system. In the absence of any active drivers, bias
resistors (1.2k) force a “1” across the twisted pair. All
drivers in the system are connected so that when enabled,
they transmit a “0”. This is accomplished by tying DI low
and using DE as the driver data input. A “1” is transmitted
by disabling the driver’s “0” output and allowing the bias
resistors to reestablish a “1” on the twisted pair.
Control over communications is achieved by asserting a
“0” during the time an active transmitter is sending a “1”.
Any node that is transmitting data watches its own
13
LTC1484
RD
1
1k RO4 DE4
67
2
58
5V
34
R
D
1
1k
RO2DE2
67
120Ω
2
585V
5V
34
1.2k
1484 F11
1.2k
120Ω
5V
1.2k
1.2k
R
D
1
1k
RO3
DE3
RO1 DE1
67
2
585V
34
RD
1
1k
67
2
5
8
5V
34
receiver output and expects to see perfect agreement
between the two data streams. (Note that the driver inverts
the data, so the transmitted and received data streams are
actually opposites.) If the simultaneously transmitted and
received data streams differ (usually detected by compar-
ing RO and DE with an XOR), it signals the presence of a
second, active driver. The first driver falls silent, and the
second driver seizes control.
If the LTC1484 is connected as shown in Figure 11, the
overhead of XORing the transmitted and received data in
hardware or software is eliminated. DE and RE are con-
nected together so the receiver is disabled and its output
three-stated whenever a “0” is transmitted. A 1k pull-up
ensures a “1” at the receiver output during this condition.
The receiver is enabled when the driver is disabled. During
this interval the receiver output should also be “1”. Thus,
under normal operation the receiver output is always “1”.
If a “0” is detected, it indicates the presence of a second
active driver attempting to seize control of communica-
tions.
The maximum frequency at which the system in Figure 11
can operate is determined by the cable capacitance, the
values of the pull-up and pull-down resistors and receiver
propagation delay. The external resistors take a longer
time to pull the line to a “1” state due to higher source
resistance compared to an active driver, thereby affecting
the duty cycle of the receiver output at the far end of the
line.
Figure 11. Transmit “0” CDMA Application
APPLICATIONS INFORMATION
WUUU
(b)
Figure 12a shows a 100kHz DE1 waveform for an LTC1484
driving a 1000-foot shielded twisted-pair (STP) cable and
the A2, B2 and RO2 waveforms of a receiving LTC1484 at
the far end of the cable. The propagation delay between
DE1 of the driver and RO2 at the far end of the line is 1.8µs
at the rising edge and 3.7µs at the falling edge of DE1. The
(a)
Figure 12. LTC1484 Driving a 1000 Foot STP Cable
1484 F12a
1484 F12b
B2
A2
RO2
DE1
DE1
B2
A2
RO2
14
LTC1484
longer delay for the falling edge is due to the larger voltage
range the line must swing (typically >2V compared to
370mV) before the receiver trips high again. The differ-
ence in delay affects the duty cycle of the received data and
depends on cable capacitance. For a 1-foot STP cable, the
delays drop to 0.13µs and 0.4µs. Using smaller valued
pull-up and pull-down resistors to equalize the positive
and negative voltage swings needed to trip the receivers
will reduce the difference in delay and increase the maxi-
mum data rate. With 220Ω resistors, both rising and
falling edge delays are 2.2µs when driving a 1000-foot STP
cable as shown in Figure 12b.
The fail-safe feature of the LTC1484 receiver allows a
CDMA system to function without the A and B pull-up and
pull-down resistors. However, if the resistors are left out,
noise margin will be reduced to as low as 15mV and
propagation delays will increase significantly. Operation in
this mode is not recommended.
Since DE and RE are tied together, the part never shuts
down. The receiver inputs are never floating (due to the
external bias resistors) so that the t
DZR
timing does not
apply to this application. The whole system can be changed
to actively transmit only a “1” by swapping the pull-up and
pull-down resistors in Figure 11, shorting DI to V
CC
and
connecting the 1k resistor as a pull-down. In this configu-
ration the driver is noninverting and the receiver output RO
truly follows DE.
APPLICATIONS INFORMATION
WUUU
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters), unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
MSOP (MS8) 1098
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
0.021 ± 0.006
(0.53 ± 0.015)
0° – 6° TYP
SEATING
PLANE
0.007
(0.18)
0.040 ± 0.006
(1.02 ± 0.15)
0.012
(0.30)
REF
0.006 ± 0.004
(0.15 ± 0.102)
0.034 ± 0.004
(0.86 ± 0.102)
0.0256
(0.65)
BSC 12
34
0.193 ± 0.006
(4.90 ± 0.15)
8765
0.118 ± 0.004*
(3.00 ± 0.102)
0.118 ± 0.004**
(3.00 ± 0.102)
15
LTC1484
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters), unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
N8 1098
0.100
(2.54)
BSC
0.065
(1.651)
TYP
0.045 – 0.065
(1.143 – 1.651)
0.130 ± 0.005
(3.302 ± 0.127)
0.020
(0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
0.125
(3.175)
MIN
12 34
8765
0.255 ± 0.015*
(6.477 ± 0.381)
0.400*
(10.160)
MAX
0.009 – 0.015
(0.229 – 0.381)
0.300 – 0.325
(7.620 – 8.255)
0.325 +0.035
–0.015
+0.889
–0.381
8.255
()
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.016 – 0.050
(0.406 – 1.270)
0.010 – 0.020
(0.254 – 0.508)× 45°
0°– 8° TYP
0.008 – 0.010
(0.203 – 0.254)
SO8 1298
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
TYP
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
1234
0.150 – 0.157**
(3.810 – 3.988)
8765
0.189 – 0.197*
(4.801 – 5.004)
0.228 – 0.244
(5.791 – 6.197)
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
16
LTC1484
1484f LT/TP 0400 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
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TYPICAL APPLICATIO
U
RO
RE
DE
DI
R
D
RO
RE
DE
DI
VCC
B
A
GND
1484 TA02
“A”
“B”
5V
LTC1484
I1
I2
Fail-Safe “0” Application (Idle State = Logic “0”)