Page 1
FEATURES
■
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: ICC = 700µA Max with Driver Disabled
■
ICC = 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
U
APPLICATIO S
■
Battery-Powered RS485/RS422 Applications
■
Low Power RS485/RS422 Transceiver
■
Level Translator
LTC1484
Low Power
RS485 Transceiver
with Receiver Fail-Safe
U
DESCRIPTIO
The LTC®1484 is a low power RS485 compatible transceiver. 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 common mode range when three-stated. Excessive power
dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit that forces the
driver outputs into a high impedance state.
Enhanced ESD protection allows the LTC1484 to withstand ±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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
RS485 Interface
RO1
RE1
DE1
DI1
LTC1484
R
D
B1
A1
V
CC1
120Ω 120Ω
GND1
U
V
CC2
GND2
Driving a 2000 Foot STP Cable
LTC1484
B2
A2
R
D
RO2
RE2
DE2
DI2
1484 TA01
Dl1
B2
A2
RO2
Dl1 ↑↓ DE1 = V
Dl2 = 0 DE2 = 0
RE1 = RE2 = 0
CC
1484 TA01a
1
Page 2
LTC1484
WW
W
U
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (VCC)............................................... 6.5V
Control Input Voltages ................. –0.3V to (VCC + 0.3V)
Driver Input Voltage ..................... –0.3V to (VCC + 0.3V)
Driver Output Voltages ................................. –7V to 10V
Receiver Input Voltages (Driver Disabled) .. –12V to 14V
Receiver Output Voltage ............... – 0.3V to (VCC + 0.3V)
U
W
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
RO
1
RE
2
DE
3
DI
4
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
= 125°C, θJA = 200°C/ W
JMAX
8
V
CC
7
B
6
A
5
GND
LTC1484CMS8 LTC1484CN8
MS8 PART MARKING
LTDX
Junction Temperature .......................................... 125°C
Operating Temperature Range
LTC1484C ......................................... 0°C ≤ TA ≤ 70°C
LTC1484I...................................... –40°C ≤ TA ≤ 85°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
U
ORDER PART
TOP VIEW
RO
1
RE
2
DE
3
DI
N8 PACKAGE
8-LEAD PDIP
T
JMAX
T
JMAX
D
4
= 125°C, θJA = 130°C/ W (N8)
= 125°C, θJA = 135°C/W (S8)
V
8
R
8-LEAD PLASTIC SO
CC
B
7
A
6
GND
5
S8 PACKAGE
NUMBER
LTC1484CS8
LTC1484IN8
LTC1484IS8
S8 PART MARKING
1484
1484I
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at T
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
OD1
V
OD2
V
OD3
∆V
OD
V
OC
∆|VOC| Change in Magnitude of Driver Common Mode R = 22Ω, 27Ω or R = 50Ω, Figure 1 ● 0.2 V
V
IH
V
IL
I
IN1
I
IN2
V
TH
Differential Driver Output Voltage (Unloaded) I
Differential Driver Output Voltage (with Load) R = 50Ω (RS422) ● 2V
Differential Driver Output Voltage V
(with Common Mode)
Change in Magnitude of Driver Differential R = 22Ω, 27Ω or R = 50Ω, Figure 1 ● 0.2 V
Output Voltage for Complementary Output States V
Driver Common Mode Output Voltage R = 22Ω, 27Ω or R = 50Ω, Figure 1 ● 3V
Output Voltage for Complementary Output States
Input High Voltage DE, DI, RE ● 2.0 V
Input Low Voltage DE, DI, RE ● 0.8 V
Input Current DE, DI, RE ● ±2 µA
Input Current (A, B) DE = 0, VCC = 0 or 5V, VIN = 12V ● 1.0 mA
Differential Input Threshold Voltage for Receiver –7V ≤ VCM ≤ 12V, DE = 0 ● –0.20 –0.015 V
The ● denotes the specifications which apply over the full operating
= 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted.
A
= 0 ● V
OUT
R = 27Ω (RS485) Figure 1
R = 22Ω, Figure 1
= –7V to 12V, Figure 2 ● 1.5 5 V
TST
= –7V to 12V, Figure 2
TST
DE = 0, V
= 0 or 5V, VIN = –7V ● –0.8 mA
CC
● 1.5 5 V
● 1.5 5 V
CC
V
2
Page 3
LTC1484
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at T
The ● denotes the specifications which apply over the full operating
= 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted.
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
∆V
V
V
I
TH
OH
OL
OZR
Receiver Input Hysteresis VCM = 0V, DE = 0 ● ±30 mV
Receiver Output High Voltage I
Receiver Output Low Voltage I
Three-State (High Impedance) Output Current VCC = Max, 0.4V ≤ V
= –4mA, (VA – VB) = 200mV ● 3.5 V
OUT
= 4mA, (VA – VB) = –200mV ● 0.4 V
OUT
≤ 2.4V, ● ±1 µA
OUT
at Receiver DE = 0
R
IN
I
CC
I
SHDN
I
OSD1
I
OSD2
I
OSR
Receiver Input Resistance –7V ≤ VCM ≤ 12V ● 12 22 kΩ
Supply Current No Load, Output Enabled (DE = VCC) ● 600 900 µA
No Load, Output Disabled (DE = 0)
● 400 700 µA
Supply Current in Shutdown Mode DE = 0, RE = VCC, DI = 0 ● 120 µA
Driver Short-Circuit Current, V
Driver Short-Circuit Current, V
Receiver Short-Circuit Current 0V ≤ V
= High (Note 4) –7V ≤ V
OUT
= Low (Note 4) – 7V ≤ V
OUT
≤ 10V 35 250 mA
OUT
≤ 10V 35 250 mA
OUT
OUT
≤ V
CC
● 785mA
U
SWITCHING CHARACTERISTICS
temperature range, otherwise specifications are at T
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
PLH
t
PHL
t
SKEW
tr, t
t
ZH
t
ZL
t
LZ
t
HZ
t
PLH
t
PHL
t
SKD
t
ZL
t
ZH
t
LZ
t
HZ
t
DZR
f
MAX
t
SHDN
f
Driver Input to Output R
Driver Input to Output R
Driver Output to Output R
Driver Rise or Fall Time R
Driver Enable to Output High CL = 100pF (Figures 5, 7) S2 Closed ● 40 70 ns
Driver Enable to Output Low CL = 100pF (Figures 5, 7) S1 Closed ● 40 100 ns
Driver Disable Time from Low CL = 15pF (Figures 5, 7) S1 Closed ● 40 70 ns
Driver Disable Time from High CL = 15pF (Figures 5, 7) S2 Closed ● 40 70 ns
Receiver Input to Output R
Receiver Input to Output R
|t
– t
PLH
| Differential Receiver Skew R
PHL
Receiver Enable to Output Low CRL = 15pF (Figures 3, 9) S1 Closed ● 20 50 ns
Receiver Enable to Output High CRL = 15pF (Figures 3, 9) S2 Closed ● 20 50 ns
Receiver Disable from Low CRL = 15pF (Figures 3, 9) S1 Closed ● 20 50 ns
Receiver Disable from High CRL = 15pF (Figures 3, 9) S2 Closed ● 20 50 ns
Driver Enable to Receiver Valid R
Maximum Data Rate (Note 5) ● 4 5 Mbps
Time to Shutdown (Note 6) DE = 0, RE↑ ● 50 300 600 ns
The ● denotes the specifications which apply over the full operating
= 25°C.
A
= 54Ω, CL1 = CL2 = 100pF ● 10 28.5 60 ns
DIFF
(Figures 4, 6)
= 54Ω, CL1 = CL2 = 100pF ● 10 31 60 ns
DIFF
(Figures 4, 6)
= 54Ω, CL1 = CL2 = 100pF ● 2.5 10 ns
DIFF
(Figures 4, 6)
= 54Ω, CL1 = CL2 = 100pF ● 31540 ns
DIFF
(Figures 4, 6)
= 54Ω, CL1 = CL2 = 100pF, ● 30 160 200 ns
DIFF
(Figures 4, 8)
= 54Ω, CL1 = CL2 = 100pF, ● 30 140 200 ns
DIFF
(Figures 4, 8)
= 54Ω, CL1 = CL2 = 100pF, 20 ns
DIFF
(Figures 4, 8)
= 54Ω, CL1 = CL2 = 100pF ● 1600 3000 ns
DIFF
(Figures 4, 10)
3
Page 4
LTC1484
U
SWITCHING CHARACTERISTICS
temperature range, otherwise specifications are at T
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
ZH(SHDN)
t
ZL(SHDN)
t
ZH(SHDN)
t
ZL(SHDN)
Driver Enable from Shutdown to Output High CL = 100pF (Figures 5, 7) S2 Closed, ● 40 100 ns
Driver Enable from Shutdown to Output Low CL = 100pF (Figures 5, 7) S1 Closed, ● 40 100 ns
Receiver Enable from Shutdown to Output High CL = 15pF (Figures 3, 9) S2 Closed, ● 10 µs
Receiver Enable from Shutdown to Output Low CL = 15pF (Figures 3, 9) S1 Closed, ● 10 µs
The ● denotes the specifications which apply over the full operating
= 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted.
A
DI = DE
DI = 0
DE = 0
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
= 5V and TA = 25°C.
CC
Note 5: Guaranteed by design.
Note 6: Time for I
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.
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Output Voltage vs Input
Voltage
6
TA = 25°C
= 5V
V
CC
5
4
3
2
1
RECEIVER OUTPUT VOLTAGE (V)
0
–0.2
V
TH(LOW)
–0.16 –0.12 –0.08 –0.04 0
INPUT VOLTAGE (V)
V
TH(HIGH)
1484 G01
Receiver Input Threshold Voltage
(Output High) vs Temperature
0
VCC = 5V
V
–0.05
–0.10
–0.15
–0.20
RECEIVER INPUT THRESHOLD VOLTAGE (V)
–0.25
TH(HIGH)
VCM = –7V
VCM = 0V
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
VCM = 12V
to drop to ICC/2 when the receiver is disabled.
CC
Receiver Input Threshold Voltage
(Output Low) vs Temperature
0
VCC = 5V
V
TH(LOW)
VCM = 0V
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G02
–0.05
–0.10
–0.15
–0.20
RECEIVER INPUT THRESHOLD VOLTAGE (V)
–0.25
VCM = –7V
VCM = 12V
1484 G03
4
Page 5
UW
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1484
Receiver Input Offset Voltage vs
Temperature
0
VCC = 5V
–20
–40
–60
–80
–100
–120
–140
–160
–180
RECEIVER INPUT OFFSET VOLTAGE (mV)
–200
VCM = 0V
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
VCM = –7V
VCM = 12V
Receiver Output High Voltage vs
Output Current
5.0
VCC = 4.75V
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
RECEIVER OUTPUT HIGH VOLTAGE (V)
0.5
0
–20 –15 –10 –5 0
–25
OUTPUT CURRENT (mA)
1484 G04
1484 G07
Receiver Hysteresis vs
Temperature
100
VCC = 5V
90
80
70
60
V
50
40
30
RECEIVER HYSTERESIS (mV)
20
10
0
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
TH(HIGH)
= –7V TO 12V
V
CM
– V
TH(LOW)
Receiver Output Low Voltage vs
Output Current
1.0
VCC = 4.75V
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
RECEIVER OUTPUT LOW VOLTAGE (V)
0.1
0
5 10 15 20 25
0
OUTPUT CURRENT (mA)
Receiver Input Threshold Voltage
vs Supply Voltage
0
TA = 25°C
–0.02
–0.04
–0.06
–0.08
1484 G05
–0.10
–0.12
–0.14
–0.16
–0.18
RECEIVER INPUT THRESHOLD VOLTAGE (V)
–0.20
= 0V
V
CM
V
TH(HIGH)
V
TH(LOW)
4.5 4.75 5 5.25
SUPPLY VOLTAGE (V)
1484 G06
Receiver Output High Voltage vs
Temperature
4.5
VCC = 4.75V
1484 G08
4.4
4.3
4.2
4.1
4.0
3.9
3.8
3.7
RECEIVER OUTPUT HIGH VOLTAGE (V)
3.6
3.5
= –8mA
I
OUT
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G09
Receiver Output Low Voltage vs
Temperature
0.50
VCC = 4.75V
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
RECEIVER OUTPUT LOW VOLTAGE (V)
0.05
= 8mA
I
OUT
0
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G10
Input Current (A, B) vs
Temperature
600
500
400
300
200
VCC = 0V OR 5V
100
0
–100
INPUT CURRENT (µA)
–200
–300
–400
–55 –35 –15 5 25 45 65 85 105 125
VCM = 12V
VCM = –7V
TEMPERATURE (°C)
1484 G11
Receiver Input Resistance vs
Temperature
26.0
VCC = 0V OR 5V
25.5
25.0
24.5
24.0
23.5
23.0
RECEIVER INPUT RESISTANCE (kΩ)
22.5
22.0
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
VCM = 12V
VCM = –7V
1484 G12
5
Page 6
LTC1484
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Short-Circuit Current vs
Temperature
100
VCC = 5.25V
90
80
70
60
50
40
30
20
10
RECEIVER SHORT-CIRCUIT CURRENT (mA)
0
–55 –35 –15 5 25 45 65 85 105 125
OUTPUT LOW
SHORT TO V
OUTPUT HIGH
SHORT TO GROUND
TEMPERATURE (°C)
CC
Receiver Propagation Delay vs
Supply Voltage
200
TA = 25°C
180
t
160
140
120
RECEIVER PROPAGATION DELAY (ns)
100
4.5
4.75 5 5.25 5.5
PLH
t
PHL
SUPPLY VOLTAGE (V)
1484 G13
1484 G16
Receiver Propagation Delay vs
Temperature Receiver Skew vs Temperature
200
VCC = 5V
180
160
140
120
100
80
60
40
RECEIVER PROPAGATION DELAY (ns)
20
0
–55 –35 –15 5 25 45 65 85 105 125
t
PLH
t
PHL
TEMPERATURE (°C)
Shutdown Supply Current vs
Temperature
0.9
VCC = 5V
0.8
DE = DI = 0
RE = 5V
0.7
0.6
0.5
0.4
0.3
0.2
SHUTDOWN SUPPLY CURRENT (µA)
0.1
0
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G14
1484 G17
30
VCC = 5V
25
20
15
10
RECEIVER SKEW (ns)
5
0
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
Shutdown Supply Current vs
Supply Voltage
1.00
TA = 25°C
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
SHUTDOWN SUPPLY CURRENT (µA)
0.55
0.50
4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5
SUPPLY VOLTAGE (V)
1484 G15
1484 G18
Supply Current vs Temperature Supply Current vs Supply Voltage
1000
VCC = 5V
900
800
700
600
500
400
300
SUPPLY CURRENT (µA)
200
100
DRIVER ENABLED
NO LOAD
DRIVER DISABLED
0
–55
–30 –5 20 45 70 95 120 145 170
THERMAL SHUTDOWN
WITH DRIVER
ENABLED
TEMPERATURE (°C)
1484 G19
700
TA = 25°C
600
500
400
300
200
SUPPLY CURRENT (µA)
100
0
4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5
DRIVER ENABLED
NO LOAD
DRIVER DISABLED
SUPPLY VOLTAGE (V)
6
1484 G20
Logic Input Threshold vs
Temperature
2.00
1.95
1.90
1.85
1.80
1.75
1.70
1.65
1.60
1.55
LOGIC INPUT THRESHOLD VOLTAGE (V)
1.50
–55
VCC = 5.25V
VCC = 4.75V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
VCC = 5V
1484 G21
Page 7
UW
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1484
Driver Differential Output Voltage
vs Temperature
3.0
2.5
2.0
VCC = 5.25V
1.5
1.0
0.5
0
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
–0.5
–55
–35 –15 5 25 45 65 85 105 125
VCC = 5V
VCC = 4.75V
∆VOD, VCC = 4.5V TO 5.25V
TEMPERATURE (°C)
RL = 44Ω
VCC = 4.5V
Driver Common Mode Output
Voltage vs Temperature
3.0
2.5
2.0
1.5
VCC = 5.25V
VCC = 5V
RL = 44Ω
VCC = 4.75V
VCC = 4.5V
1484 G22
Driver Differential Output Voltage
vs Temperature
3.0
2.5
VCC = 5.25V
2.0
1.5
1.0
0.5
0
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
–0.5
–55
–35 –15 5 25 45 65 85 105 125
VCC = 5V
VCC = 4.75V
∆VOD, VCC = 4.5V TO 5.25V
TEMPERATURE (°C)
RL = 54Ω
VCC = 4.5V
Driver Common Mode Output
Voltage vs Temperature
3.0
2.5
2.0
1.5
VCC = 5.25V
VCC = 5V
RL = 54Ω
VCC = 4.75V
VCC = 4.5V
1484 G23
Driver Differential Output Voltage
vs Temperature
3.5
3.0
2.5
VCC = 5.25V
2.0
1.5
1.0
0.5
0
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
–0.5
–35 –15 5 25 45 65 85 105 125
–55
VCC = 5V
∆VOD, VCC = 4.5V TO 5.25V
TEMPERATURE (°C)
RL = 100Ω
VCC = 4.75V
VCC = 4.5V
Driver Common Mode Output
Voltage vs Temperature
3.0
2.5
2.0
1.5
VCC = 5.25V
VCC = 5V
RL = 100Ω
VCC = 4.75V
VCC = 4.5V
1484 G24
1.0
0.5
DRIVER COMMON MODE VOLTAGE (V)
0
–55
∆VOC, VCC = 4.5V TO 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
Driver Differential Output Voltage
vs Temperature
3.5
SEE FIGURE 2
3.0
2.5
VCC = 5.25V
2.0
1.5
1.0
0.5
0
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
–0.5
–55
–35 –15 5 25 45 65 85 105 125
VCC = 5V
∆V
FOR VCC = 4.5V TO 5.25V
OD3
TEMPERATURE (°C)
VCC = 4.75V
VCM = –7V
V
OD3
DI HIGH
VCC = 4.5V
1484 G25
1484 G28
1.0
0.5
DRIVER COMMON MODE VOLTAGE (V)
0
–55
∆VOC, VCC = 4.5V TO 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
Driver Differential Output Voltage
vs Temperature
3.0
2.5
2.0
VCC = 5.25V
1.5
VCM = 12V
V
OD3
1.0
DI HIGH
SEE FIGURE 2
0.5
0
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
–0.5
–35 –15 5 25 45 65 85 105 125
–55
VCC = 5V
VCC = 4.75V
∆V
FOR VCC = 4.5V TO 5.25V
OD3
TEMPERATURE (°C)
VCC = 4.5V
1484 G26
1484 G29
1.0
0.5
DRIVER COMMON MODE VOLTAGE (V)
0
–55
∆VOC, VCC = 4.5V TO 5.25V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
Driver Differential Output Voltage
vs Output Current
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
0
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
VCC = 5V
= 25°C
T
A
1484 G27
1484 G30
7
Page 8
LTC1484
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output High Voltage vs
Output Current
5.0
VCC = 4.75V
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
DRIVER OUTPUT HIGH VOLTAGE (V)
0.5
0
–90 –80 –70 –60 –50 –40 –30 –20 –10 0
–100
OUTPUT CURRENT (mA)
1484 G31
Driver Output Low Voltage vs
Output Current
3.0
VCC = 4.75V
2.5
2.0
1.5
1.0
0.5
DRIVER OUTPUT LOW VOLTAGE (V)
0
10 20 30 40 50 60 70 80 90 100
0
OUTPUT CURRENT (mA)
Driver Short-Circuit Current vs
Temperature Driver Skew vs Temperature
250
200
150
100
50
DRIVER SHORT-CIRCUIT CURRENT (mA)
0
–55
DRIVER OUTPUT HIGH
SHORT TO –7V
DRIVER OUTPUT LOW
SHORT TO 10V
–35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
VCC = 5.25V
1484 G34
5.0
4.5
4.0
3.5
3.0
2.5
2.0
DRIVER SKEW (ns)
1.5
1.0
0.5
0
–35 –15 5 25 45 65 85 105 125
–55
TEMPERATURE (°C)
1484 G32
1484 G35
Driver Propagation Delay vs
Temperature
50
VCC = 5V
45
40
35
30
25
20
15
10
DRIVER PROPAGATION DELAY (ns)
5
0
–35 –15 5 25 45 65 85 105 125
–55
t
PHL
t
PLH
TEMPERATURE (°C)
Driver Propagation Delay vs
Supply Voltage
40
TA = 25°C
35
30
25
20
15
10
DRIVER PROPAGATION DELAY (ns)
5
0
4.5
4.75 5 5.25 5.5
t
PHL
t
PLH
SUPPLY VOLTAGE (V)
1484 G33
1484 G36
UUU
PIN FUNCTIONS
RO (Pin 1): Receiver Output. If the receiver output is enabled (RE low) and the part is not in shutdown, RO is high
if (A – B) > V
TH(MAX)
and low if (A – B) < V
TH(MIN)
. RO is
also high if the receiver inputs are open or shorted together, 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
8
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.
Page 9
UUU
OUTPUT
UNDER
TEST
C
RL
1k
S1
S2
V
CC
1k
1484 F03
PIN FUNCTIONS
LTC1484
A (Pin 6): Driver Output/Receiver Input. The input resistance 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.
U
U
FU CTIO TABLES
Driver
INPUTS OUTPUTS
RE DE DI B A
X1101
X1010
O0XZZ
10XZ*Z*
Note: Z = high impedance, X = don’t care
*Shutdown mode for LTC1484
B (Pin 7): Driver Output/Receiver Input. The input resistance 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.
V
(Pin 8): Positive Supply. 4.75V ≤ VCC ≤ 5.25V. A 0.1µF
CC
bypass capacitor is recommended.
Receiver
INPUTS OUTPUTS
RE DE A – B RO
00 ≥V
00 ≤V
TH(MAX)
TH(MIN)
0 0 Inputs Open 1
0 0 Inputs Shorted 1
1X X Z
†
Shutdown mode for LTC1484 if DE = 0. Table valid with or without
termination resistors.
1
0
†
TEST CIRCUITS
A
B
V
OD1
V
OD2
Figure 1
DI
DE
1484 F01
R
V
OC
R
A
R
DIFF
B
Figure 4
A
V
OD3
B
A
C
L1
B
C
L2
375Ω
60Ω
375Ω
Figure 2
RE
1484 F02
RO
15pF
1484 F04
–7V TO 12V
OUTPUT
UNDER
TEST
500Ω
C
L
Figure 3
S1
V
CC
S2
1484 F05
Figure 5
9
Page 10
LTC1484
UWW
SWITCHI G TI E WAVEFOR S
DI
–V
3V
0V
V
O
O
B
A
V
O
1/2 V
NOTE: DE = 1
1.5V
t
PLH
90%
10%
t
r
O
50%
t
SKEW
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
Figure 6. Driver Propagation Delays
3V
DE
0V
5V
A, B
V
OL
V
OH
A, B
0V
NOTE: A, B ARE THREE-STATED WHEN DE = 0, 1kΩ PULL-UP OR 1kΩ PULL-DOWN
1.5V
t
ZL(SHDN), tZL
2.3V
2.3V
t
ZH(SHDN), tZH
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
VO = V(A) – V(B)
t
PHL
t
t
HZ
50%
LZ
1.5V
90%
10%
t
f
1484 F06
t
SKEW
1.5V
0.5V
0.5V
1484 F07
A – B
RO
RO
RO
Figure 7. Driver Enable and Disable Timing
V
–V
OD2
OD2
V
5V
OL
NOTE: t
SKD
= |t
0V
PHL
– t
PLH
t
PHL
1.5V
|, RE = 0
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
INPUT
OUTPUT
Figure 8. Receiver Propagation Delays
RE
5V
0V
5V
0V
NOTE: DE = 0, RO IS THREE-STATED IN SHUTDOWN, 1kΩ PULL-UP FOR NORMALLY LOW OUTPUT,
1kΩ PULL-DOWN FOR NORMALLY HIGH OUTPUT
1.5V
t
ZL(SHDN), tZL
1.5V
1.5V
t
ZH(SHDN), tZH
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
t
PLH
t
0V
1.5V
1484 F08
1.5V
t
LZ
0.5V
0.5V
HZ
1484 F09
10
Figure 9. Receiver Enable and Shutdown Timing
Page 11
UWW
SWITCHI G TI E WAVEFOR S
LTC1484
V(A) – V(B)
RO
3V
DE
0V
NOTE: DI = 0, RE = 0, A AND B ARE THREE-STATED WHEN DE = 0
1.5V
U
t
DZR
1.5V
Figure 10. Driver Enable to Receiver Valid Timing
WUU
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
APPLICATIONS INFORMATION
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 termination resistor is present or not.
1484 F10
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 builtin delays to prevent glitches while the input swings between ±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
) to detect the
DZR
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.
11
Page 12
LTC1484
U
WUU
APPLICATIONS INFORMATION
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 ICC drops to
20µA max.
In some applications (see CDMA), the A and B lines are
pulled to VCC 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.
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 VCC, 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.
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 protection at the A and B pins is important in applications where
these pins are exposed to the external world via connections 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
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 unacceptable in safety-related applications. A scheme known as
Carrier Detect Multiple Access (CDMA) solves this problem by allowing any node to interrupt on-going communications.
Figure 11 shows four nodes in a typical CDMA communications 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
12
Page 13
LTC1484
U
WUU
APPLICATIONS INFORMATION
RO4 DE4
1k
2
1
34
67
D
58
5
5
1
67
2
DE1
R
D
34
1.2k
120Ω
1.2k
5V
5V
8
5V
R
1k
RO1
Figure 11. Transmit “0” CDMA Application
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 comparing 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 connected 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 communications.
RO2DE2
1k
1
2
34
D
5
67
DE3
R
2
34
RO3
D
R
8
67
8
5V
1
1484 F11
1k
5V
5V
1.2k
120Ω
1.2k
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
DE1
B2
A2
RO2
(a)
DE1
1484 F12a
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.
B2
A2
RO2
(b)
1484 F12b
Figure 12. LTC1484 Driving a 1000 Foot STP Cable
13
Page 14
LTC1484
U
WUU
APPLICATIONS INFORMATION
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 difference 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 maximum 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
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters), unless otherwise noted.
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
timing does not
DZR
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 VCC and
connecting the 1k resistor as a pull-down. In this configuration the driver is noninverting and the receiver output RO
truly follows DE.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.040
± 0.006
SEATING
PLANE
(1.02 ± 0.15)
0.012
(0.30)
0.0256
REF
(0.65)
BSC
0.007
(0.18)
0.021
± 0.006
(0.53 ± 0.015)
* 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
° – 6° TYP
0
0.034 ± 0.004
(0.86 ± 0.102)
0.006 ± 0.004
(0.15 ± 0.102)
0.118 ± 0.004*
(3.00 ± 0.102)
0.193 ± 0.006
(4.90 ± 0.15)
8
7
12
6
5
0.118 ± 0.004**
MSOP (MS8) 1098
4
3
(3.00 ± 0.102)
14
Page 15
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters), unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400*
(10.160)
MAX
876
0.255 ± 0.015*
(6.477 ± 0.381)
5
LTC1484
12
0.300 – 0.325
(7.620 – 8.255)
0.065
(1.651)
0.009 – 0.015
(0.229 – 0.381)
+0.035
0.325
–0.015
+0.889
8.255
()
–0.381
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
TYP
0.045 – 0.065
(1.143 – 1.651)
0.100
(2.54)
BSC
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
8
0.228 – 0.244
(5.791 – 6.197)
3
0.189 – 0.197*
(4.801 – 5.004)
7
6
4
0.130 ± 0.005
(3.302 ± 0.127)
0.125
(3.175)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
5
0.150 – 0.157**
(3.810 – 3.988)
0.020
(0.508)
MIN
N8 1098
0.010 – 0.020
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
*
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
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
×
°
45
0.016 – 0.050
(0.406 – 1.270)
0°– 8° TYP
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
TYP
1
3
2
4
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
SO8 1298
15
Page 16
LTC1484
U
TYPICAL APPLICATIO
Fail-Safe “0” Application (Idle State = Logic “0”)
5V
LTC1484
RO
RO
I1
RE
DE
DI
I2
RE
DE
D
DI
V
CC
GND
B
A
“A”
“B”
1484 TA02
R
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LTC1482 5V Low Power RS485 Transceiver with Carrier Detect Output Low Power, High Output State When Inputs are Open,
Shorted or Terminated, ±15kV ESD Protection
LTC1483 5V Ultralow Power RS485 Low EMI Transceiver with Shutdown Low EMI, Lowest Power
LTC1485 5V RS485 Transceiver High Speed, 10Mbps, ±15kV ESD Protection
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High Input Impedance
LTC1535 Isolated RS485 Transceiver 2500V
LTC1685 52Mbps RS485 Transceiver Propagation Delay Skew 500ps (Typ)
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RMS
Isolation
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear-tech.com
1484f LT/TP 0400 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
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