LTC1487
Ultra-Low Power RS485
with Low EMI, Shutdown
and High Input Impedance
FEATURES
s
s
s
s
s
s
s
DESCRIPTIO
s
s
s
s
s
High Input Impedance: Up to 256 Transceivers
on the Bus
Low Power: I
CC
= 120µA Max with Driver Disabled
I
CC
= 200µA Max with Driver Enabled, No Load
1µA Quiescent Current in Shutdown Mode
Controlled Slew Rate Driver for Reduced EMI
Single 5V Supply
ESD Protection to
±10kV
On Receiver Inputs and
Driver outputs
– 7V to 12V Common-Mode Range Permits
±7V
Ground Difference Between Devices on the Data Line
Thermal Shutdown Protection
Power Up/Down Glitch-Free Driver Outputs Permit
Live Insertion or Removal of Transceiver
Driver Maintains High Impedance in Three-State
or with the Power Off
Pin Compatible with the LTC485
The LTC
®
1487 is an ultra-low power differential line trans-
ceiver designed with high impedance inputs allowing up to
256 transceivers to share a single bus. It meets the
requirements of RS485 and RS422. The LTC1487 features
output drivers with controlled slew rate, decreasing the
EMI radiated from the RS485 lines, and improving signal
fidelity with misterminated lines. The CMOS design offers
significant power savings without sacrificing ruggedness
against overload or ESD damage. Typical quiescent cur-
rent is only 80µA while operating and 1µA in shutdown.
The driver and receiver feature three-state outputs, with
the driver outputs maintaining high impedance over the
entire common-mode range. Excessive power dissipation
caused by bus contention or faults is prevented by a
thermal shutdown circuit which forces the driver outputs
into a high impedance state. The receiver has a fail-safe
feature which guarantees a high output state when the
inputs are left open. I/O pins are protected against multiple
ESD strikes of over
±10kV
using the Human Body Model.
The LTC1487 is fully specified over the commercial tem-
perature range and is available in 8-pin DIP and SO
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATI
s
s
s
S
Battery-Powered RS485/RS422 Applications
Low Power RS485/RS422 Transceiver
Level Translator
TYPICAL APPLICATI
LTC1487
1
RO
2
RE
3
DE
4
DI
R
7
D
6
120Ω
LTC1487
2000 FEET OF TWISTED-PAIR WIRE
7
120Ω
6
D
R
1
RO
2
RE
3
DE
4
DI
DI
RECEIVER INPUT
A
B
330Ω
4.7nF
RO
EQUIVALENT LOAD OF 256
LTC1487 TRANSCEIVERS
LTC1487 • TA01
U
LTC1487 • TA02
UO
UO
sn1487 1487fs
1
LTC1487
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RO 1
RE 2
DE 3
DI 4
N8 PACKAGE
8-LEAD PDIP
D
R
8
7
6
5
V
CC
B
A
GND
Supply Voltage (V
CC
) .............................................. 12V
Control Input Voltage ..................... – 0.5V to V
CC
+ 0.5V
Driver Input Voltage ....................... – 0.5V to V
CC
+ 0.5V
Driver Output Voltage ...........................................
±14V
Receiver Input Voltage ..........................................
±14V
Receiver Output Voltage ................ – 0.5V to V
CC
+ 0.5V
Operating Temperature Range ............. 0°C
≤
T
A
≤
70°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LTC1487CN8
LTC1487CS8
S8 PART MARKING
1487
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 130°C/ W (N8)
T
JMAX
= 125°C,
θ
JA
= 150°C/ W (S8)
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
OD1
V
OD2
∆V
OD
V
OC
∆
V
OC
V
IH
V
IL
I
IN1
I
IN2
V
TH
∆V
TH
V
OH
V
OL
I
OZR
R
IN
I
CC
I
SHDN
I
OSD1
I
OSD2
I
OSR
PARAMETER
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (with Load)
Change in Magnitude of Driver Differential Output
Voltage for Complementary Output States
Driver Common-Mode Output Voltage
Change in Magnitude of Driver Common-Mode
Output Voltage for Complementary Output States
Input High Voltage
Input Low Voltage
Input Current
Input Current (A, B)
Differential Input Threshold Voltage for Receiver
Receiver Input Hysteresis
Receiver Output High Voltage
Receiver Output Low Voltage
Three-State (High Impedance) Output
Current at Receiver
Receiver Input Resistance
Supply Current
Supply Current in Shutdown Mode
Driver Short-Circuit Current, V
OUT
= HIGH
Driver Short-Circuit Current, V
OUT
= LOW
Receiver Short-Circuit Current
0°C
≤
T
A
≤
70°C, V
CC
= 5V (Notes 2, 3) unless otherwise noted.
CONDITIONS
I
O
= 0
R = 50Ω (RS422)
R = 27Ω (RS485), Figure 1
R = 27Ω or R = 50Ω, Figure 1
R = 27Ω or R = 50Ω, Figure 1
R = 27Ω or R = 50Ω, Figure 1
DE, DI, RE
DE, DI, RE
DE, DI, RE
DE = 0, V
CC
= 0V or 5.25V, V
IN
= 12V
DE = 0, V
CC
= 0V or 5.25V, V
IN
= – 7V
– 7V
≤
V
CM
≤
12V
V
CM
= 0V
I
O
= – 4mA, V
ID
= 200mV
I
O
= 4mA, V
ID
= – 200mV
V
CC
= Max, 0.4V
≤
V
O
≤
2.4V
– 7V
≤
V
CM
≤
12V
No Load, Output Enabled
No Load, Output Disabled
DE = 0V, RE = V
CC
– 7V
≤
V
O
≤
12V
– 7V
≤
V
O
≤
12V
0V
≤
V
O
≤
V
CC
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
MIN
2.0
1.5
TYP
MAX
5
5
0.2
3
0.2
UNITS
V
V
V
V
V
V
V
2
0.8
±2
0.30
– 0.15
– 0.2
45
3.5
0.4
±1
70
96
120
80
1
35
35
7
200
120
10
250
250
85
0.2
sn1487 1487fs
2
U
V
µA
mA
mA
V
mV
V
V
µA
kΩ
µA
µA
µA
mA
mA
mA
W
U
U
W W
W
LTC1487
ELECTRICAL CHARACTERISTICS
SYMBOL
V
OD1
V
OD2
V
OC
V
TH
∆V
TH
I
CC
I
SHDN
t
PLH
t
PHL
t
SKEW
t
r
, t
f
t
PLH
t
PHL
t
SKD
f
MAX
PARAMETER
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (with Load)
Driver Common-Mode Output Voltage
Differential Input Threshold Voltage for Receiver
Receiver Input Hysteresis
Supply Current
Supply Current in Shutdown Mode
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
Receiver Input to Output
Receiver Input to Output
t
PLH
– t
PHL
Differential Receiver Skew
– 40°C
≤
T
A
≤
85°C, V
CC
= 5V (Note 4) unless otherwise noted.
CONDITIONS
I
O
= 0
R = 50Ω (RS422)
R = 27Ω (RS485), Figure 1
R = 27Ω or R = 50Ω, Figure 1
– 7V
≤
V
CM
≤
12V
V
CM
= 0V
No Load, Output Enabled
No Load, Output Disabled
DE = 0V, RE = V
CC
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
(Figures 3, 5)
q
q
q
q
q
q
q
q
q
q
q
q
MIN
2.0
1.5
– 0.2
TYP
MAX
5
5
3
0.2
UNITS
V
V
V
V
V
mV
µA
µA
µA
ns
ns
ns
ns
ns
ns
ns
kbps
45
120
80
1
150
150
100
150
30
30
250
140
140
13
200
120
10
1200
1200
600
2000
250
250
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
(Figures 3, 7)
q
q
q
q
Maximum Data Rate
SWITCHI G CHARACTERISTICS
SYMBOL
t
PLH
t
PHL
t
SKEW
t
r
, t
f
t
ZH
t
ZL
t
LZ
t
HZ
t
PLH
t
PHL
t
SKD
t
ZL
t
ZH
t
LZ
t
HZ
f
MAX
t
SHDN
PARAMETER
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
Receiver Input to Output
Receiver Input to Output
t
PLH
– t
PHL
Differential Receiver Skew
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Receiver Disable from High
Maximum Data Rate
Time to Shutdown
U
0°C
≤
T
A
≤
70°C, V
CC
= 5V (Notes 2, 3) unless otherwise noted.
MIN
q
q
q
q
CONDITIONS
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
(Figures 3, 5)
TYP
MAX
1200
1200
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
kbps
ns
150
150
250
150
100
100
150
150
30
30
140
140
13
20
20
20
20
250
50
200
600
1200
1500
1500
1500
1500
250
250
50
50
50
50
600
C
L
= 100pF (Figures 4, 6), S2 Closed
C
L
= 100pF (Figures 4, 6), S1 Closed
C
L
= 15pF (Figures 4, 6), S1 Closed
C
L
= 15pF (Figures 4, 6), S2 Closed
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF,
(Figures 3, 7)
q
q
q
q
q
q
q
C
RL
= 15pF (Figures 2, 8), S1 Closed
C
RL
= 15pF (Figures 2, 8), S2 Closed
C
RL
= 15pF (Figures 2, 8), S1 Closed
C
RL
= 15pF (Figures 2, 8), S2 Closed
DE = 0, RE =
q
q
q
q
q
q
sn1487 1487fs
3
LTC1487
SWITCHI G CHARACTERISTICS
SYMBOL
t
ZH(SHDN)
t
ZL(SHDN)
t
ZH(SHDN)
t
ZL(SHDN)
PARAMETER
Driver Enable from Shutdown to Output High
Driver Enable from Shutdown to Output Low
Receiver Enable from Shutdown to Output High
Receiver Enable from Shutdown to Output Low
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute maximum ratings are those beyond which the safety of
the device cannot be guaranteed.
Note 2:
All currents into device pins are positive; all currents out ot device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
450
400
OUTPUT CURRENT (mA)
80
T
A
= 25°C
70
SUPPLY CURRENT (µA)
350
300
250
200
150
100
50
DRIVER ENABLED
WITH NO LOAD
DRIVER DISABLED WITH NO LOAD
0
25 50 75 100 125 150 175
TEMPERATURE (°C)
LTC1487 • TPC01
DIFFERENTIAL VOLTAGE (V)
THERMAL SHUTDOWN
WITH DRIVER ENABLED
AND NOMINAL LOAD
0
– 50 –25
Driver Output Low Voltage
vs Output Current
120
T
A
= 25°C
100
0
–10
–20
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
80
60
40
20
0
0
1
2
3
OUTPUT VOLTAGE (V)
4
TIME (ns)
4
U W
U
0°C
≤
TA
≤
70°C, V
CC
= 5V (Notes 2, 3) unless otherwise noted.
MIN
q
q
q
q
CONDITIONS
C
L
= 100pF (Figures 4, 6), S2 Closed
C
L
= 100pF (Figures 4, 6), S1 Closed
C
L
= 15pF (Figures 2, 8), S2 Closed
C
L
= 15pF (Figures 2, 8), S1 Closed
TYP
MAX
2000
2000
2000
2000
UNITS
ns
ns
ns
ns
Note 3:
All typicals are given for V
CC
= 5V and T
A
= 25°C.
Note 4:
The LTC1487 is not tested and is not quality-assurance sampled at
– 40°C and at 85°C. These specifications are guaranteed by design,
correlation, and/or inference from 0°C, 25°C and/or 70°C tests.
Driver Differential Output Voltage
vs Output Current
2.24
2.22
2.20
2.18
2.16
2.14
2.12
2.10
2.08
2.06
2.04
2.02
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
OUTPUT VOLTAGE (V)
LTC1487 • TPC02
Driver Differential Output Voltage
vs Temperature
R
L
= 54Ω
60
50
40
30
20
10
0
2.00
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
LTC1487 • TPC03
Driver Output High Voltage
vs Output Current
T
A
= 25°C
Driver Skew vs Temperature
500
450
400
350
300
250
200
150
–50 –25
–30
–40
–50
–60
–70
–80
–90
–100
0
1
3
4
2
OUTPUT VOLTAGE (V)
5
50
25
75
0
TEMPERATURE (°C)
100
125
LTC1487 • TPC04
LTC1487 • TPC05
LTC1487
• G06
sn1487 1487fs
LTC1487
PIN FUNCTIONS
RO (Pin 1):
Receiver Output. If the receiver output is
enabled (RE LOW), and A > B by 200mV, RO will be HIGH.
If A < B by 200mV, then RO will be LOW.
RE (Pin 2):
Receiver Output Enable. A LOW enables the
receiver output, RO. A HIGH input forces the receiver
output into a high impedance state.
DE (Pin 3):
Driver Outputs Enable. A HIGH on DE enables
the driver output. A and B and the chip will function as a line
driver. A LOW input will force the driver outputs into a high
impedance state and the chip will function as a line
receiver. If RE is HIGH and DE is LOW, the part will enter
a low power (1µA) shutdown state.
DI (Pin 4):
Driver Input. If the driver outputs are enabled
(DE HIGH) then a LOW on DI forces the outputs A LOW and
B HIGH. A HIGH on DI with the driver outputs enabled will
force A HIGH and B LOW.
GND (Pin 5):
Ground.
A (Pin 6):
Driver Output/Receiver Input.
B (Pin 7):
Driver Output/Receiver Input.
V
CC
(Pin 8):
Positive Supply. 4.75V < V
CC
< 5.25V.
FU CTIO TABLES
LTC1487 Transmitting
INPUTS
RE
X
X
0
1
DE
1
1
0
0
DI
1
0
X
X
0
1
Z
Z*
OUTPUTS
B
A
1
0
Z
Z*
RE
0
0
0
1
*Shutdown mode
TEST CIRCUITS
A
R
V
OD
R
B
LTC1487 • F01
LTC1487 • F02
Figure 1. Driver DC Test Load
3V
DE
A
DI
B
R
DIFF
C
L2
C
L1
A
Figure 3. Driver/Receiver Timing Test Circuit
U
U
U
U
U
LTC1487 Receiving
INPUTS
DE
0
0
0
0
A–B
≥
0.2V
≤
– 0.2V
Inputs Open
X
OUTPUTS
RO
1
0
1
Z*
*Shutdown mode
RECEIVER
OUTPUT
V
OC
TEST POINT
S1
1k
V
CC
C
RL
1k
S2
Figure 2. Receiver Timing Test Load
S1
RO
B
RE
LTC1487 • F03
LTC1487 • F04
15pF
OUTPUT
UNDER TEST
500Ω
S2
C
L
V
CC
Figure 4. Driver Timing Test Load
sn1487 1487fs
5
京公网安备 11010802033920号
EEWORLD
