LINER LTC1484C

LTC1484
Low Power
RS485 Transceiver
with Receiver Fail-Safe
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DESCRIPTIO
FEATURES
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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
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.
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APPLICATIO S
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Battery-Powered RS485/RS422 Applications
Low Power RS485/RS422 Transceiver
Level Translator
, LTC and LT are registered trademarks of Linear Technology Corporation.
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The LTC1484 is fully specified over the commercial and
industrial temperature ranges and is available in 8-lead
MSOP, PDIP and SO packages.
TYPICAL APPLICATIO
Driving a 2000 Foot STP Cable
RS485 Interface
LTC1484
VCC1
RO1
R
RE1
B2
120Ω
120Ω
D
DI1
RO2
VCC2
B1
A1
DE1
Dl1
LTC1484
R
A2
D
GND1
RE2
B2
DE2
A2
DI2
GND2
RO2
1484 TA01
Dl1 ↑↓
Dl2 = 0
RE1 = RE2 = 0
DE1 = VCC
DE2 = 0
1484 TA01a
1
LTC1484
W W
U
W
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)
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
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W
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PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
RO
RE
DE
DI
1
2
3
4
8
7
6
5
LTC1484CMS8
VCC
B
A
GND
MS8 PACKAGE
8-LEAD PLASTIC MSOP
ORDER PART
NUMBER
TOP VIEW
RO 1
R
RE 2
DE 3
D
DI 4
MS8 PART MARKING
TJMAX = 125°C, θJA = 200°C/ W
N8 PACKAGE
8-LEAD PDIP
8
VCC
7
B
6
A
5
GND
LTC1484CN8
LTC1484CS8
LTC1484IN8
LTC1484IS8
S8 PACKAGE
8-LEAD PLASTIC SO
S8 PART MARKING
TJMAX = 125°C, θJA = 130°C/ W (N8)
TJMAX = 125°C, θJA = 135°C/ W (S8)
LTDX
1484
1484I
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
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
VOD1
Differential Driver Output Voltage (Unloaded)
IOUT = 0
●
MIN
VOD2
Differential Driver Output Voltage (with Load)
R = 50Ω (RS422)
R = 27Ω (RS485) Figure 1
R = 22Ω, Figure 1
●
●
●
TYP
MAX
UNITS
VCC
V
2
1.5
1.5
5
5
V
V
V
1.5
5
V
VOD3
Differential Driver Output Voltage
(with Common Mode)
VTST = – 7V to 12V, Figure 2
●
∆VOD
Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
R = 22Ω, 27Ω or R = 50Ω, Figure 1
VTST = – 7V to 12V, Figure 2
●
0.2
V
VOC
Driver Common Mode Output Voltage
R = 22Ω, 27Ω or R = 50Ω, Figure 1
●
3
V
∆|VOC|
Change in Magnitude of Driver Common Mode
Output Voltage for Complementary Output States
R = 22Ω, 27Ω or R = 50Ω, Figure 1
●
0.2
V
VIH
Input High Voltage
DE, DI, RE
●
VIL
Input Low Voltage
DE, DI, RE
●
0.8
V
IIN1
Input Current
DE, DI, RE
●
±2
µA
IIN2
Input Current (A, B)
DE = 0, VCC = 0 or 5V, VIN = 12V
DE = 0, VCC = 0 or 5V, VIN = – 7V
●
●
1.0
– 0.8
mA
mA
VTH
Differential Input Threshold Voltage for Receiver
– 7V ≤ VCM ≤ 12V, DE = 0
●
2
2.0
– 0.20
V
– 0.015
V
LTC1484
ELECTRICAL CHARACTERISTICS
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
∆VTH
Receiver Input Hysteresis
VCM = 0V, DE = 0
●
VOH
Receiver Output High Voltage
IOUT = – 4mA, (VA – VB) = 200mV
●
VOL
Receiver Output Low Voltage
IOUT = 4mA, (VA – VB) = – 200mV
●
0.4
V
IOZR
Three-State (High Impedance) Output Current
at Receiver
VCC = Max, 0.4V ≤ VOUT ≤ 2.4V,
DE = 0
●
±1
µA
RIN
Receiver Input Resistance
–7V ≤ VCM ≤ 12V
●
ICC
Supply Current
No Load, Output Enabled (DE = VCC)
No Load, Output Disabled (DE = 0)
●
●
ISHDN
Supply Current in Shutdown Mode
DE = 0, RE = VCC, DI = 0
●
20
µA
IOSD1
Driver Short-Circuit Current, VOUT = High (Note 4)
– 7V ≤ VOUT ≤ 10V
35
250
mA
IOSD2
Driver Short-Circuit Current, VOUT = Low (Note 4)
– 7V ≤ VOUT ≤ 10V
35
250
mA
IOSR
Receiver Short-Circuit Current
0V ≤ VOUT ≤ VCC
7
85
mA
●
TYP
MAX
±30
mV
3.5
12
UNITS
V
22
600
400
1
kΩ
900
700
µA
µA
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SWITCHING CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
tPLH
Driver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF
(Figures 4, 6)
●
10
28.5
60
ns
tPHL
Driver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF
(Figures 4, 6)
●
10
31
60
ns
tSKEW
Driver Output to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF
(Figures 4, 6)
●
2.5
10
ns
tr, tf
Driver Rise or Fall Time
RDIFF = 54Ω, CL1 = CL2 = 100pF
(Figures 4, 6)
●
15
40
ns
tZH
Driver Enable to Output High
CL = 100pF (Figures 5, 7) S2 Closed
●
40
70
ns
tZL
Driver Enable to Output Low
CL = 100pF (Figures 5, 7) S1 Closed
●
40
100
ns
tLZ
Driver Disable Time from Low
CL = 15pF (Figures 5, 7) S1 Closed
●
40
70
ns
tHZ
Driver Disable Time from High
CL = 15pF (Figures 5, 7) S2 Closed
●
40
70
ns
tPLH
Receiver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF,
(Figures 4, 8)
●
30
160
200
ns
tPHL
Receiver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF,
(Figures 4, 8)
●
30
140
200
ns
tSKD
|tPLH – tPHL| Differential Receiver Skew
RDIFF = 54Ω, CL1 = CL2 = 100pF,
(Figures 4, 8)
tZL
Receiver Enable to Output Low
CRL = 15pF (Figures 3, 9) S1 Closed
●
20
50
ns
tZH
Receiver Enable to Output High
CRL = 15pF (Figures 3, 9) S2 Closed
●
20
50
ns
tLZ
Receiver Disable from Low
CRL = 15pF (Figures 3, 9) S1 Closed
●
20
50
ns
tHZ
Receiver Disable from High
CRL = 15pF (Figures 3, 9) S2 Closed
●
20
50
ns
tDZR
Driver Enable to Receiver Valid
RDIFF = 54Ω, CL1 = CL2 = 100pF
(Figures 4, 10)
●
1600
3000
ns
fMAX
Maximum Data Rate (Note 5)
tSHDN
Time to Shutdown (Note 6)
DE = 0, RE↑
3
20
●
4
5
●
50
300
UNITS
ns
Mbps
600
ns
3
LTC1484
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SWITCHING CHARACTERISTICS
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
TYP
MAX
UNITS
tZH(SHDN)
Driver Enable from Shutdown to Output High
CL = 100pF (Figures 5, 7) S2 Closed,
DI = DE
●
40
100
ns
tZL(SHDN)
Driver Enable from Shutdown to Output Low
CL = 100pF (Figures 5, 7) S1 Closed,
DI = 0
●
40
100
ns
tZH(SHDN)
Receiver Enable from Shutdown to Output High
CL = 15pF (Figures 3, 9) S2 Closed,
DE = 0
●
10
µs
tZL(SHDN)
Receiver Enable from Shutdown to Output Low
CL = 15pF (Figures 3, 9) S1 Closed,
DE = 0
●
10
µs
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 VCC = 5V and TA = 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.
MIN
Note 5: Guaranteed by design.
Note 6: Time for ICC to drop to ICC/2 when the receiver is disabled.
U W
TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C
VCC = 5V
5
4
3
2
1
0
–0.2
VTH(LOW)
–0.16
VTH(HIGH)
–0.12
–0.08
–0.04
INPUT VOLTAGE (V)
0
1484 G01
4
0
VCC = 5V
VTH(HIGH)
–0.05
VCM = –7V
–0.10
VCM = 0V
VCM = 12V
–0.15
–0.20
–0.25
–55 –35 –15
Receiver Input Threshold Voltage
(Output Low) vs Temperature
RECEIVER INPUT THRESHOLD VOLTAGE (V)
RECEIVER OUTPUT VOLTAGE (V)
6
Receiver Input Threshold Voltage
(Output High) vs Temperature
RECEIVER INPUT THRESHOLD VOLTAGE (V)
Receiver Output Voltage vs Input
Voltage
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G02
0
VCC = 5V
VTH(LOW)
–0.05
–0.10
VCM = –7V
–0.15
VCM = 0V
–0.20
–0.25
–55 –35 –15
VCM = 12V
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G03
LTC1484
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Input Offset Voltage vs
Temperature
Receiver Hysteresis vs
Temperature
–60
–80
–100
VCM = –7V
–120
VCM = 0V
–140
VCC = 5V
90
–40
VCM = 12V
–160
–180
80
70
60
VTH(HIGH) – VTH(LOW)
VCM = –7V TO 12V
50
40
30
20
10
–200
–55 –35 –15
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
–0.06
–0.10
–0.12
3.5
3.0
2.5
2.0
1.5
1.0
0.5
–20
–15
–10
–5
OUTPUT CURRENT (mA)
–0.16
–0.18
4.75
5
SUPPLY VOLTAGE (V)
4.5
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
5
10
15
20
OUTPUT CURRENT (mA)
VCM = 12V
300
200
VCC = 0V OR 5V
100
0
–100
0.10
–200
0.05
–300
5 25 45 65 85 105 125
TEMPERATURE (°C)
3.9
3.8
3.7
3.6
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G09
RECEIVER INPUT RESISTANCE (kΩ)
0.15
4.0
Receiver Input Resistance vs
Temperature
400
INPUT CURRENT (µA)
0.40
0.20
4.1
26.0
500
0.25
4.2
3.5
–55 –35 –15
25
600
VCC = 4.75V
IOUT = 8mA
0.30
VCC = 4.75V
IOUT = –8mA
4.3
Input Current (A, B) vs
Temperature
0.50
0.35
4.4
1484 G08
Receiver Output Low Voltage vs
Temperature
5.25
Receiver Output High Voltage vs
Temperature
0.8
0
0
1484 G10
4.5
1484 G06
VCC = 4.75V
0.9
1484 G07
0
–55 –35 –15
VTH(LOW)
–0.14
RECEIVER OUTPUT HIGH VOLTAGE (V)
4.0
0
–25
VTH(HIGH)
–0.08
1.0
VCC = 4.75V
RECEIVER OUTPUT LOW VOLTAGE (V)
RECEIVER OUTPUT HIGH VOLTAGE (V)
–0.04
Receiver Output Low Voltage vs
Output Current
5.0
4.5
TA = 25°C
VCM = 0V
1484 G05
Receiver Output High Voltage vs
Output Current
RECEIVER OUTPUT LOW VOLTAGE (V)
0
–0.02
–0.20
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G04
0.45
RECEIVER INPUT THRESHOLD VOLTAGE (V)
100
VCC = 5V
–20
RECEIVER HYSTERESIS (mV)
RECEIVER INPUT OFFSET VOLTAGE (mV)
0
Receiver Input Threshold Voltage
vs Supply Voltage
–400
–55 –35 –15
VCM = –7V
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G11
25.5
VCC = 0V OR 5V
25.0
VCM = 12V
24.5
VCM = –7V
24.0
23.5
23.0
22.5
22.0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G12
5
LTC1484
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Short-Circuit Current vs
Temperature
Receiver Propagation Delay vs
Temperature
200
80
70
OUTPUT LOW
SHORT TO VCC
60
50
40
30
OUTPUT HIGH
SHORT TO GROUND
20
10
0
–55 –35 –15
180
30
VCC = 5V
160
140
tPHL
100
80
60
40
5
tPLH
tPHL
120
4.75
5
5.25
SUPPLY VOLTAGE (V)
0.8
0.7
1.00
0.6
0.5
0.4
0.3
0.2
0.1
0
–55 –35 –15
5.5
DRIVER ENABLED
NO LOAD
500
400
300
DRIVER DISABLED
0
–55 –30 –5
600
500
DRIVER ENABLED
NO LOAD
400
300
DRIVER DISABLED
200
100
20 45 70 95 120 145 170
TEMPERATURE (°C)
1484 G19
0.75
0.70
0.65
0.60
0.55
Logic Input Threshold vs
Temperature
2.00
TA = 25°C
200
100
0.80
1484 G18
LOGIC INPUT THRESHOLD VOLTAGE (V)
600
THERMAL SHUTDOWN
WITH DRIVER
ENABLED
SUPPLY CURRENT (µA)
700
0.85
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)
5 25 45 65 85 105 125
TEMPERATURE (°C)
700
800
TA = 25°C
0.90
Supply Current vs Supply Voltage
1000
VCC = 5V
0.95
1484 G17
Supply Current vs Temperature
SUPPLY CURRENT (µA)
Shutdown Supply Current vs
Supply Voltage
VCC = 5V
DE = DI = 0
RE = 5V
1484 G16
900
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G15
SHUTDOWN SUPPLY CURRENT (µA)
SHUTDOWN SUPPLY CURRENT (µA)
RECEIVER PROPAGATION DELAY (ns)
180
6
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
0.9
TA = 25°C
4.5
10
Shutdown Supply Current vs
Temperature
200
140
15
1484 G14
Receiver Propagation Delay vs
Supply Voltage
160
20
20
1484 G13
100
25
120
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
VCC = 5V
tPLH
RECEIVER SKEW (ns)
VCC = 5.25V
90
RECEIVER PROPAGATION DELAY (ns)
RECEIVER SHORT-CIRCUIT CURRENT (mA)
100
Receiver Skew vs Temperature
0
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 G20
1.95
1.90
1.85
1.80
1.75
VCC = 5.25V
VCC = 5V
1.70
1.65
1.60
VCC = 4.75V
1.55
1.50
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G21
LTC1484
U W
TYPICAL PERFOR A CE CHARACTERISTICS
RL = 44Ω
2.5
1.5
VCC = 5V
VCC = 4.75V
VCC = 4.5V
1.0
0.5
∆VOD, VCC = 4.5V TO 5.25V
0
–0.5
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
2.5
2.0
VCC = 5.25V
VCC = 5V
VCC = 4.75V
1.5
VCC = 4.5V
1.0
0.5
∆VOD, VCC = 4.5V TO 5.25V
0
–0.5
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G22
Driver Common Mode Output
Voltage vs Temperature
2.0
3.0
RL = 44Ω
2.5
VCC = 5.25V
VCC = 5V
VCC = 4.75V
1.5
VCC = 4.5V
1.0
0.5
∆VOC, VCC = 4.5V TO 5.25V
0
–55 –35 –15
2.0
VCC = 5.25V
VCC = 5V
VCC = 4.75V
1.5
VCC = 4.5V
1.0
0.5
∆VOC, VCC = 4.5V TO 5.25V
2.5
2.0
VCC = 5.25V
1.5
0.5
VCC = 5V
VCC = 4.75V
VCC = 4.5V
1.0
∆VOD3 FOR VCC = 4.5V TO 5.25V
0
–0.5
–55 –35 –15
1.0
0.5
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G28
∆VOD, VCC = 4.5V TO 5.25V
0
–0.5
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3.0
5 25 45 65 85 105 125
TEMPERATURE (°C)
RL = 100Ω
2.5
VCC = 5.25V
2.0
3.0
2.5
2.0
1.5
1.0
VCC = 5.25V
VCC = 5V
VCM = 12V
VOD3
DI HIGH
SEE FIGURE 2
VCC = 4.75V
VCC = 4.5V
0.5
∆VOD3 FOR VCC = 4.5V TO 5.25V
0
–0.5
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G29
VCC = 5V
VCC = 4.75V
1.5
VCC = 4.5V
1.0
0.5
∆VOC, VCC = 4.5V TO 5.25V
0
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G27
Driver Differential Output Voltage
vs Temperature
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
3.0
VCC = 5V
VCC = 4.75V
VCC = 4.5V
1.5
1484 G26
Driver Differential Output Voltage
vs Temperature
VCM = –7V
VOD3
DI HIGH
VCC = 5.25V
2.0
Driver Common Mode Output
Voltage vs Temperature
2.5
1484 G25
SEE FIGURE 2
2.5
1484 G24
RL = 54Ω
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3.5
RL = 100Ω
3.0
Driver Common Mode Output
Voltage vs Temperature
DRIVER COMMON MODE VOLTAGE (V)
DRIVER COMMON MODE VOLTAGE (V)
3.0
3.5
1484 G23
DRIVER COMMON MODE VOLTAGE (V)
VCC = 5.25V
RL = 54Ω
Driver Differential Output Voltage
vs Output Current
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
2.0
3.0
Driver Differential Output Voltage
vs Temperature
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
3.0
Driver Differential Output Voltage
vs Temperature
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
Driver Differential Output Voltage
vs Temperature
5.0
VCC = 5V
TA = 25°C
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
1484 G30
7
LTC1484
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output High Voltage vs
Output Current
Driver Output Low Voltage vs
Output Current
3.0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10 0
OUTPUT CURRENT (mA)
50
VCC = 4.75V
DRIVER PROPAGATION DELAY (ns)
VCC = 4.75V
4.5
DRIVER OUTPUT LOW VOLTAGE (V)
DRIVER OUTPUT HIGH VOLTAGE (V)
5.0
2.5
2.0
1.5
1.0
0.5
0
50
15
10
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G33
40
4.5
35
3.5
3.0
2.5
2.0
1.5
0.5
5 25 45 65 85 105 125
TEMPERATURE (°C)
20
5.0
1.0
0
–55 –35 –15
tPLH
25
Driver Propagation Delay vs
Supply Voltage
4.0
DRIVER SKEW (ns)
200
DRIVER OUTPUT LOW
SHORT TO 10V
30
0
–55 –35 –15
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
DRIVER PROPAGATION DELAY (ns)
VCC = 5.25V
100
tPHL
35
Driver Skew vs Temperature
250
150
40
1484 G32
Driver Short-Circuit Current vs
Temperature
DRIVER OUTPUT HIGH
SHORT TO –7V
VCC = 5V
45
5
0
1484 G31
DRIVER SHORT-CIRCUIT CURRENT (mA)
Driver Propagation Delay vs
Temperature
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1484 G34
1484 G35
TA = 25°C
tPHL
30
tPLH
25
20
15
10
5
0
4.5
4.75
5
5.25
SUPPLY VOLTAGE (V)
5.5
1484 G36
U
U
U
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) > VTH(MAX) and low if (A – B) < VTH(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.
LTC1484
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U
U
PIN FUNCTIONS
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.
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.
VCC (Pin 8): Positive Supply. 4.75V ≤ VCC ≤ 5.25V. A 0.1µF
bypass capacitor is recommended.
U
U
FU CTIO TABLES
Receiver
Driver
INPUTS
RE
DE
INPUTS
OUTPUTS
DI
B
OUTPUTS
A
RE
DE
A–B
RO
0
≥ VTH(MAX)
1
≤ VTH(MIN)
0
X
1
1
0
1
0
X
1
0
1
0
0
0
O
0
X
Z
Z
0
0
Inputs Open
1
1
0
X
Z*
Z*
0
0
Inputs Shorted
1
1
X
X
Z†
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.
TEST CIRCUITS
375Ω
A
A
VOD1
VOD2
60Ω
VOD3
R
S1
OUTPUT
UNDER
TEST
R
1k
VCC
–7V TO 12V
1k
CRL
VOC
S2
375Ω
B
1484 F02
B
1484 F03
1484 F01
Figure 1
Figure 2
Figure 3
DE
A
DI
CL1
S1
RO
RDIFF
B
A
B
CL2
15pF
OUTPUT
UNDER
TEST
VCC
500Ω
CL
RE
S2
1484 F05
1484 F04
Figure 4
Figure 5
9
LTC1484
U
W
W
SWITCHI G TI E WAVEFOR S
3V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
1.5V
DI
1.5V
0V
t PLH
VO
10%
–VO
t PHL
90%
50%
VO = V(A) – V(B)
50%
tr
90%
10%
tf
B
VO
A
tSKEW
1/2 VO
t SKEW
1484 F06
NOTE: DE = 1
Figure 6. Driver Propagation Delays
3V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
1.5V
DE
1.5V
0V
t ZL(SHDN), t ZL
5V
A, B
2.3V
OUTPUT NORMALLY LOW
VOL
VOH
A, B
t LZ
0.5V
0.5V
OUTPUT NORMALLY HIGH
2.3V
0V
t HZ
t ZH(SHDN), t ZH
1484 F07
NOTE: A, B ARE THREE-STATED WHEN DE = 0, 1kΩ PULL-UP OR 1kΩ PULL-DOWN
Figure 7. Driver Enable and Disable Timing
VOD2
A–B
– VOD2
0V
0V
INPUT
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
t PHL
t PLH
5V
RO
1.5V
1.5V
OUTPUT
VOL
1484 F08
NOTE: tSKD = |tPHL – tPLH|, RE = 0
Figure 8. Receiver Propagation Delays
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
1.5V
RE
5V
RO
t ZL(SHDN), tZL
1.5V
1.5V
t LZ
OUTPUT NORMALLY LOW
0V
0.5V
5V
RO
0.5V
OUTPUT NORMALLY HIGH
1.5V
0V
t ZH(SHDN), tZH
NOTE: DE = 0, RO IS THREE-STATED IN SHUTDOWN, 1kΩ PULL-UP FOR NORMALLY LOW OUTPUT,
1kΩ PULL-DOWN FOR NORMALLY HIGH OUTPUT
Figure 9. Receiver Enable and Shutdown Timing
10
t HZ
1484 F09
LTC1484
U
W
W
SWITCHI G TI E WAVEFOR S
3V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
1.5V
DE
0V
t DZR
V(A) – V(B)
OUTPUT NORMALLY LOW
RO
1.5V
OUTPUT NORMALLY HIGH
1484 F10
NOTE: DI = 0, RE = 0, A AND B ARE THREE-STATED WHEN DE = 0
Figure 10. Driver Enable to Receiver Valid Timing
U
W
U
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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.
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 VTH(MIN) to VTH(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 ±VTH(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 tDZR) 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 tZL(SHDN)). If the receiver inputs are
actively driven to a high state, the outputs go high after
about 5.5µs.
11
LTC1484
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W
U
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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.
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
12
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.
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
LTC1484
U
U
W
U
APPLICATIONS INFORMATION
1k
1 2 3
8
5V
4
D
5
1k
3 2 1
4
D
R
5V
1.2k
DE2 RO2
RO4 DE4
R
5V
5
8
6 7
120Ω
1.2k
5V
1.2k
7 6
120Ω
5V
6 7
8
R
1
5
D
2 3
4
7 6
5
8
5V
1.2k
R
D
4
3 2 1
1484 F11
1k
RO1 DE1
DE3 RO3
1k
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.
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 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)
1484 F12a
DE1
B2
A2
RO2
(b)
1484 F12b
Figure 12. LTC1484 Driving a 1000 Foot STP Cable
13
LTC1484
U
W
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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
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 tDZR 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 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.
Dimensions in inches (millimeters), unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.040 ± 0.006
(1.02 ± 0.15)
0.007
(0.18)
0.034 ± 0.004
(0.86 ± 0.102)
8
7 6
5
0° – 6° TYP
0.021 ± 0.006
(0.53 ± 0.015)
SEATING
PLANE 0.012
(0.30)
0.0256
REF
(0.65)
BSC
0.006 ± 0.004
(0.15 ± 0.102)
* 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
14
0.118 ± 0.004*
(3.00 ± 0.102)
0.118 ± 0.004**
(3.00 ± 0.102)
0.193 ± 0.006
(4.90 ± 0.15)
MSOP (MS8) 1098
1
2 3
4
LTC1484
U
PACKAGE DESCRIPTION
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
8
7
6
5
1
2
3
4
0.255 ± 0.015*
(6.477 ± 0.381)
0.300 – 0.325
(7.620 – 8.255)
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
(
+0.035
0.325 –0.015
8.255
+0.889
–0.381
0.130 ± 0.005
(3.302 ± 0.127)
0.045 – 0.065
(1.143 – 1.651)
)
0.125
(3.175) 0.020
MIN
(0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
0.100
(2.54)
BSC
N8 1098
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
8
7
6
5
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.014 – 0.019
(0.355 – 0.483)
TYP
*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
2
3
4
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
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.
SO8 1298
15
LTC1484
U
TYPICAL APPLICATIO
Fail-Safe “0” Application (Idle State = Logic “0”)
5V
I1
RO
RE
LTC1484
RE
R
DE
DE
DI
RO
I2
DI
VCC
B
A
“A”
“B”
D
GND
1484 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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LTC1480
3.3V Ultralow Power RS485 Transceiver with Shutdown
Lower Supply Voltage
LTC1481
5V Ultralow Power RS485 Transceiver with Shutdown
Lowest Power
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
LTC1487
5V Ultralow Power RS485 with Low EMI, Shutdown and
High Input Impedance
Highest Input Impedance, Low EMI, Lowest Power
LTC1535
Isolated RS485 Transceiver
2500VRMS Isolation
LTC1685
52Mbps RS485 Transceiver
Propagation Delay Skew 500ps (Typ)
LTC1690
5V Differential Driver and Receiver Pair with Fail-Safe Receiver Output
Low Power, ±15kV ESD Protection
LT1785
±60V Fault Protected RS485 Transceiver
±15kV ESD Protection, Industry Standard Pinout
16
Linear Technology Corporation
1484f LT/TP 0400 4K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1998