1
LTC1690
Differential Driver and
Receiver Pair with Fail-Safe
Receiver Output
, LTC and LT are registered trademarks of Linear Technology Corporation.
The LTC
®
1690 is a low power receiver/driver pair that is
compatible with the requirements of RS485 and RS422.
The receiver offers a fail-safe feature that 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.
Separate driver output and receiver input pins allow full
duplex operation. Excessive power dissipation caused by
bus contention or faults is prevented by a thermal shut-
down circuit which forces the driver outputs into a high
impedance state.
The LTC1690 is fully specified over the commercial and
industrial temperature ranges. The LTC1690 is available in
8-Pin SO, MSOP and PDIP packages.
s
Battery-Powered RS485/RS422 Applications
s
Low Power RS485/RS422 Transceiver
s
Level Translator
s
Line Repeater
120
3
5
6
D1
120
2
8
7
R2
DRIVER
LTC1690
LTC1690
RECEIVER
120
2
7
8
Y1
Z1
B1
A1
A2
B2
Z2
Y2
R1
120
3
6
5
D2
RECEIVER
DRIVER
1690 TA01
s
No Damage or Latchup to
±
15kV ESD (Human Body
Model), IEC1000-4-2 Level 4 (
±
8kV) Contact and
Level 3 (
±
8kV) Air Discharge
s
Guaranteed High Receiver Output State for
Floating, Shorted or Terminated Inputs with No
Signal Present
s
Drives Low Cost Residential Telephone Wires
s
I
CC
= 600
µ
A Max with No Load
s
Single 5V Supply
s
7V to 12V Common Mode Range Permits
±
7V
Ground Difference Between Devices on the Data Line
s
Power-Up/Down Glitch-Free Driver Outputs Permit
Live Insertion or Removal of Transceiver
s
Driver Maintains High Impedance with the Power Off
s
Up to 32 Transceivers on the Bus
s
Pin Compatible with the SN75179 and LTC490
s
Available in SO, MSOP and PDIP Packages
D1
B2
A2
R2
1690 TA01a
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
Driving a 1000 Foot STP Cable
2
LTC1690
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OD1
Differential Driver Output Voltage (Unloaded)
I
O
= 0
q
V
CC
V
V
OD2
Differential Driver Output Voltage (with Load)
R = 50
; (RS422)
q
2
V
R = 22
or 27
; (RS485), Figure 1
q
1.5
5
V
V
OD3
Differential Driver Output Voltage (with Common Mode)
V
TST
= 7V to 12V, Figure 2
1.5
5
V
V
OD
Change in Magnitude of Driver Differential Output
R = 22
, 27
or 50
, Figure 1
q
0.2
V
Voltage for Complementary Output States
V
TST
= 7V to 12V, Figure 2
V
OC
Driver Common Mode Output Voltage
R = 22
, 27
or 50
, Figure 1
q
3
V
|V
OC
|
Change in Magnitude of Driver Common Mode
R = 22
, 27
or 50
, Figure 1
q
0.2
V
Output Voltage for Complementary Output States
V
IH
Input High Voltage
Driver Input (D)
q
2
V
V
IL
Input Low Voltage
Driver Input (D)
q
0.8
V
I
IN1
Input Current
Driver Input (D)
q
±
2
µ
A
I
IN2
Input Current (A, B)
V
CC
= 0V or 5.25V, V
IN
= 12V
q
1
mA
V
CC
= 0V or 5.25V, V
IN
= 7V
q
0.8
mA
V
TH
Differential Input Threshold Voltage for Receiver
7V
V
CM
12V
q
0.20
0.01
V
V
TH
Receiver Input Hysteresis
V
CM
= 0V
±
30
mV
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
Supply Voltage (V
CC
) .............................................. 6.5V
Driver Input Voltage ..................... 0.3V to (V
CC
+ 0.3V)
Driver Output Voltages ................................. 7V to 10V
Receiver Input Voltages .........................................
±
14V
Receiver Output Voltage .............. 0.3V to (V
CC
+ 0.3V)
Junction Temperature ........................................... 125
°
C
Operating Temperature Range
LTC1690C ........................................ 0
°
C
T
A
70
°
C
LTC1690I ..................................... 40
°
C
T
A
85
°
C
Storage Temperature Range ................. 65
°
C to 150
°
C
Lead Temperature (Soldering, 10 sec).................. 300
°
C
(Note 1)
ORDER PART
NUMBER
MS8 PART MARKING
ORDER PART
NUMBER
LTC1690CMS8
LTDA
S8 PART MARKING
1690
1690I
LTC1690CN8
LTC1690IN8
LTC1690CS8
LTC1690IS8
Consult factory for Military Grade Parts
1
2
3
4
8
7
6
5
TOP VIEW
V
CC
R
D
GND
A
B
Z
Y
N8 PACKAGE
8-LEAD PLASTIC DIP
S8 PACKAGE
8-LEAD PLASTIC SO
D
R
T
JMAX
= 125
°
C,
JA
= 130
°
C/W (N)
T
JMAX
= 125
°
C,
JA
= 135
°
C/W (S)
1
2
3
4
8
7
6
5
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
V
CC
R
D
GND
A
B
Z
Y
T
JMAX
= 125
°
C,
JA
= 200
°
C/W
PACKAGE/ORDER I
N
FOR
M
ATIO
N
W
U
U
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
°
C. V
CC
= 5V
±
5% (Notes 2, 3)
DC ELECTRICAL CHARACTERISTICS
3
LTC1690
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
°
C. V
CC
= 5V
±
5% (Notes 2, 3)
DC ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OH
Receiver Output High Voltage
I
O
= 4mA, V
ID
= 200mV
q
3.5
V
V
OL
Receiver Output Low Voltage
I
O
= 4mA, V
ID
= 200mV
q
0.4
V
R
IN
Receiver Input Resistance
7V
V
CM
12V
q
12
22
k
I
CC
Supply Current
No Load
q
260
600
µ
A
I
OSD1
Driver Short-Circuit Current, V
OUT
= HIGH
7V
V
O
10V
35
250
mA
I
OSD2
Driver Short-Circuit Current, V
OUT
= LOW
7V
V
O
10V
35
250
mA
I
OZ
Driver Three-State Current (Y, Z)
7V
V
O
10V, V
CC
= 0V
q
5
200
µ
A
I
OSR
Receiver Short-Circuit Current
0V
V
O
V
CC
q
7
85
mA
t
PLH
Driver Input to Output, Figure 3, Figure 4
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
10
22.5
60
ns
t
PHL
Driver Input to Output, Figure 3, Figure 4
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
10
25
60
ns
t
SKEW
Driver Output to Output, Figure 3, Figure 4
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
2.5
15
ns
t
r
, t
f
Driver Rise or Fall Time, Figure 3, Figure 4
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
2
13
40
ns
t
PLH
Receiver Input to Output, Figure 3, Figure 5
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
30
94
160
ns
t
PHL
Receiver Input to Output, Figure 3, Figure 5
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
30
89
160
ns
t
SKD
|t
PLH
t
PHL
|, Differential Receiver Skew, Figure 3, Figure 5
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
5
ns
f
MAX
Maximum Data Rate, Figure 3, Figure 5
R
DIFF
= 54
, C
L1
= C
L2
= 100pF
q
5
Mbps
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: 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 3: All typicals are given for V
CC
= 5V and T
A
= 25
°
C.
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER INPUT THRESHOLD VOLTAGE (mV)
1690 G01
0
20
40
60
80
100
120
140
160
180
200
V
CC
= 5V
V
CM
= 12V
V
CM
= 0V
V
CM
= 7V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER INPUT THRESHOLD VOLTAGE (mV)
1690 G02
0
20
40
60
80
100
120
140
160
180
200
V
CC
= 5V
V
CM
= 12V
V
CM
= 7V
V
CM
= 0V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER HYSTERESIS (mV)
1690 G03
100
90
80
70
60
50
40
30
20
10
0
V
CC
= 5V
V
CM
= 12V
V
CM
= 7V
V
CM
= 0V
Receiver Input Threshold Voltage
(Output High) vs Temperature
Receiver Input Threshold Voltage
(Output Low) vs Temperature
Receiver Hysteresis vs
Temperature
4
LTC1690
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER INPUT OFFSET VOLTAGE (mV)
1690 G04
0
20
40
60
80
100
120
140
160
180
200
V
CC
= 5V
V
CM
= 12V
V
CM
= 7V
V
CM
= 0V
SUPPLY VOLTAGE (V)
4.5
4.75
5
5.25
5.5
RECEIVER INPUT THRESHOLD VOLTAGE (mV)
1690 G05
40
60
80
100
120
140
160
T
A
= 25
°
C
OUTPUT HIGH
OUTPUT LOW
RECEIVER OUTPUT HIGH VOLTAGE (V)
5
RECEIVER OUTPUT CURRENT (mA)
3.5
2.5
1690 G06
4.5
4
3
25
20
15
10
5
0
2
T
A
= 25
°
C
V
CC
= 4.75V
RECEIVER OUTPUT LOW VOLTAGE (V)
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6 1.8
2
RECEIVER OUTPUT CURRENT (mA)
1690 G07
40
35
30
25
20
15
10
5
0
T
A
= 25
°
C
V
CC
= 4.75V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER OUTPUT HIGH VOLTAGE (V)
1690 G08
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
I = 8mA
V
CC
= 4.75V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER OUTPUT LOW VOLTAGE (V)
1690 G09
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
I = 8mA
V
CC
= 4.75V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER PROPAGATION DELAY (ns)
1690 G10
120
110
100
90
80
70
60
V
CC
= 5V
t
PLH
t
PHL
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER SKEW (ns)
1690 G11
10
9
8
7
6
5
4
3
2
V
CC
= 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
RECEIVER PROPAGATION DELAY (ns)
1690 G12
110
100
90
80
70
60
50
t
PLH
t
PHL
Receiver Input Offset Voltage 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
Receiver Output Low Voltage vs
Temperature
Receiver Propagation Delay vs
Temperature
Receiver Skew
t
PLH
t
PHL
vs
Temperature
Receiver Propagation Delay vs
Supply Voltage
5
LTC1690
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
SHORT-CIRCUIT CURRENT
(mA)
1690 G13
70
60
50
40
30
20
10
0
V
CC
= 5.25V
OUTPUT LOW
OUTPUT HIGH
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
SUPPLY CURRENT (
µ
A)
1690 G14
340
320
300
280
260
240
220
200
180
160
140
120
V
CC
= 5.25V
V
CC
= 4.75V
V
CC
= 5V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
LOGIC INPUT THRESHOLD VOLTAGE (V)
1690 G15
1.75
1.70
1.65
1.60
1.55
1.50
V
CC
= 5.25V
V
CC
= 4.75V
V
CC
= 5V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1690 G16
2.9
2.7
2.5
2.3
2.1
1.9
1.7
1.5
R
L
= 44
V
CC
= 5.25V
V
CC
= 5V
V
CC
= 4.5V
V
CC
= 4.75V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1690 G17
2.9
2.7
2.5
2.3
2.1
1.9
1.7
1.5
R
L
= 54
V
CC
= 5.25V
V
CC
= 5V
V
CC
= 4.5V
V
CC
= 4.75V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
1690 G18
3.4
3.2
3.0
2.8
2.6
2.4
2.2
R
L
= 100
V
CC
= 5.25V
V
CC
= 5V
V
CC
= 4.5V
V
CC
= 4.75V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER COMMON MODE OUTPUT VOLTAGE (V)
1690 G19
3.0
2.5
2.0
1.5
1.0
0.5
0
R
L
= 44
V
CC
= 5V
V
CC
= 4.5V
V
CC
= 4.75V
V
CC
= 5.25V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER COMMON MODE OUTPUT VOLTAGE (V)
1690 G20
3.0
2.5
2.0
1.5
1.0
0.5
0
R
L
= 54
V
CC
= 4.5V
V
CC
= 4.75V
V
CC
= 5V
V
CC
= 5.25V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER COMMON MODE OUTPUT VOLTAGE (V)
1690 G21
3.0
2.5
2.0
1.5
1.0
0.5
0
V
CC
= 4.5V
V
CC
= 4.75V
V
CC
= 5V
V
CC
= 5.25V
R
L
= 100
Receiver Short-Circuit Current vs
Temperature
Supply Current vs Temperature
Logic Input Threshold Voltage vs
Temperature
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
6
LTC1690
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V)
0
1
2
3
4
5
OUTPUT CURRENT (mA)
1690 G22
100
90
80
70
60
50
40
30
20
10
0
T
A
= 25
°
C
DRIVER OUTPUT HIGH VOLTAGE (V)
0
1
2
3
4
OUTPUT CURRENT (mA)
1690 G23
100
80
60
40
20
0
T
A
= 25
°
C
V
CC
= 5V
DRIVER OUTPUT LOW VOLTAGE (V)
0
0.5
1
1.5
2
2.5
3
OUTPUT CURRENT (mA)
1690 G24
100
90
80
70
60
50
40
30
20
10
0
T
A
= 25
°
C
V
CC
= 5V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER PROPAGATION DELAY (ns)
1690 G25
30
25
20
15
10
5
0
V
CC
= 5V
t
PHL
t
PLH
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER SKEW (ns)
1690 G26
4.0
3.5
3.0
2.5
2.0
1.5
1.0
V
CC
= 5V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
DRIVER SHORT-CIRCUIT CURRENT
(mA)
1690 G29
250
200
150
100
50
0
V
CC
= 5.25V
OUTPUT HIGH
SHORT TO 7V
OUTPUT LOW
SHORT TO 10V
TEMPERATURE (
°
C)
55 35 15
5
25
45
65
85 105 125
RECEIVER INPUT RESISTANCE (k
)
1690 G30
25
24
23
22
21
20
V
CC
= 5V
V
CM
= 12V
V
CM
= 7V
SUPPLY VOLTAGE (V)
4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5
DRIVER PROPAGATION DELAY (ns)
1690 G27
30
25
20
15
10
5
0
t
PHL
t
PLH
Driver Differential Output Voltage
vs Output Current
Driver Output High Voltage vs
Output Current
Driver Output Low Voltage vs
Output Current
Driver Propagation Delay vs
Temperature
Driver Skew vs Temperature
Driver Propagation Delay vs
Supply Voltage
Driver Short-Circuit Current vs
Temperature
Receiver Input Resistance vs
Temperature
7
LTC1690
SWITCHI G TI E WAVEFOR S
U
W
W
V
O
D
3V
0V
t
PLH
V
O
= V(A) V(B)
V
O
Z
Y
t
SKEW
t
SKEW
t
r
f = 1MHz, t
r
10ns, t
f
10ns
1.5V
90%
10%
50%
t
PHL
t
f
1.5V
90%
10%
50%
V
O
1/2 V
O
1690 F04
Figure 4. Driver Propagation Delays
f = 1MHz, t
r
10ns, t
f
10ns
NOTE: t
SKD
= |t
PHL
t
PLH
|
INPUT
OUTPUT
A B
R
V
OD2
V
OD2
5V
V
OL
t
PHL
0V
1.5V
t
PLH
0V
1.5V
1690 F05
Figure 5. Receiver Propagation Delays
FU
N
CTIO
N
TABLES
U
U
Driver
D
Z
Y
1
0
1
0
1
0
Receiver
A B
R
0.01V
1
0.20V
0
Inputs Open
1
Inputs Shorted
1
Note: Table valid with or without termination resistors.
1690 F01
Y
Z
R
R
V
OD2
V
OC
1690 F02
Y
Z
60
375
V
OD3
V
TST
7V TO 12V
375
1690 F03
D
Y
Z
R
DIFF
A
B
15pF
C
L1
C
L2
R
+
+
+
Figure 1. Driver
DC Test Load #1
Figure 2. Driver
DC Test Load #2
Figure 3. Driver/Receiver
Timing Test Load
TEST CIRCUITS
PI
N
FU
N
CTIO
N
S
U
U
U
V
CC
(Pin 1): Positive Supply. 4.75V < V
CC
< 5.25V.
R (Pin 2): Receiver Output. R is high if (A B)
10mV
and low if (A B)
200mV.
D (Pin 3): Driver Input. If D is high, Y is taken high and Z
is taken low. If D is low, Y is taken low and Z is taken high.
GND (Pin 4): Ground.
Y (Pin 5): Driver Output.
Z (Pin 6): Driver Output.
B (Pin 7): Receiver Input.
A (Pin 8): Receiver Input.
8
LTC1690
3
1
5
6
D
120
2
1
8
7
R
DRIVER
LTC1690
5V
LTC1690
RECEIVER
120
SHIELD
2
4
7
8
R
3
4
6
5
D
RECEIVER
DRIVER
1690 F06
SHIELD
0.01
µ
F
5V
0.01
µ
F
Figure 6. Typical Application
APPLICATIO
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FOR
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ATIO
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A typical application is shown in Figure 6. Two twisted pair
wires connect two driver/receiver pairs for full duplex data
transmission. Note that the driver and receiver outputs are
always enabled. If the outputs must be disabled, use the
LTC491. There are no restrictions on where the chips are
connected, and it isn't necessary to have the chips con-
nected to the ends of the wire. However, the wires must be
terminated at the ends with a resistor equal to their
characteristic impedance, typically 120
. Because only
one driver can be connected on the bus, the cable need
only be terminated at the receiving end. The optional
shields around the twisted pair are connected to GND at
one end and help reduce unwanted noise.
The LTC1690 can be used as a line repeater as shown in
Figure 7. If the cable is longer that 4000 feet, the LTC1690
is inserted in the middle of the cable with the receiver
output connected back to the driver input.
Receiver Fail-Safe
Some encoding schemes require that the output of the
receiver maintains a known state (usually a logic 1) when
data transmission ends and all drivers on the line are
forced into three-state. The receiver of the LTC1690 has a
fail-safe feature which guarantees the output to be in a
logic 1 state when the receiver inputs are left floating or
shorted together. This is achieved without external com-
ponents by designing the trip-point of the LTC1690 to be
within 200mV to 10mV. If the receiver output must be
a logic 0 instead of a logic 1, external components are
required.
The LTC1690 fail-safe receiver is designed to reject fast
7V to 12V common mode steps at its inputs. The slew
rate that the receiver will reject is typically 400V/
µ
s, but
7V to 12V steps in 10ns can be tolerated if the frequency
of the common mode step is moderate (<600kHz).
Driver-Receiver Crosstalk
The driver outputs generate fast rise and fall times. If the
LTC1690 receiver inputs are not terminated and floating,
switching noise from the LTC1690 driver can couple into
the receiver inputs and cause the receiver output to glitch.
This can be prevented by ensuring that the receiver inputs
are terminated with a 100
or 120
resistor, depending
on the type of cable used. A cable capacitance that is
greater than 10pF (
1ft of cable) also prevents glitches if
no termination is present. The receiver inputs should not
be driven typically above 8MHz to prevent glitches.
9
LTC1690
APPLICATIO
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ATIO
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Fault Protection
When shorted to 7V or 10V at room temperature, the
short-circuit current in the driver outputs is limited by
internal resistance or protection circuitry to 250mA maxi-
mum. Over the industrial temperature range, the absolute
maximum positive voltage at any driver output should be
limited to 10V to avoid damage to the driver outputs. At
higher ambient temperatures, the rise in die temperature
due to the short-circuit current may trip the thermal
shutdown circuit.
The receiver inputs can withstand the entire 7V to 12V
RS485 common mode range without damage.
The LTC1690 includes a thermal shutdown circuit that
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 a maximum of 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.
If the outputs of two or more LTC1690 drivers are shorted
directly, the driver outputs cannot supply enough current
to activate the thermal shutdown. Thus, the thermal shut-
down circuit will not prevent contention faults when two
drivers are active on the bus at the same time.
3
5
6
D
DRIVER
LTC1690
120
2
8
7
R
RECEIVER
DATA
OUT
DATA
IN
1690 F07
Figure 7. Line Repeater
10
LTC1690
Cables and Data Rate
The transmission line of choice for RS485 applications is
a twisted pair. There are coaxial cables (twinaxial) made
for this purpose that contain straight pairs, but these are
less flexible, more bulky and more costly than twisted
pairs. Many cable manufacturers offer a broad range of
120
cables designed for RS485 applications.
Losses in a transmission line are a complex combination
of DC conductor loss, AC losses (skin effect), leakage and
AC losses in the dielectric. In good polyethylene cables
such as Belden 9841, the conductor losses and dielectric
losses are of the same order of magnitude, leading to
relatively low overall loss (Figure 8).
When using low loss cable, Figure 9 can be used as a
guideline for choosing the maximum length for a given
data rate. With lower quality PVC cables, the dielectric loss
factor can be 1000 times worse. PVC twisted pairs have
terrible losses at high data rates (>100kbits/s), reducing
the maximum cable length. At low data rates, they are
acceptable and are more economical. The LTC1690 is
tested and guaranteed to drive CAT 5 cable and termina-
tions as well as common low cost residential telephone
wire.
APPLICATIO
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FREQUENCY (MHz)
0.1
0.1
LOSS PER 100 FT (dB)
1.0
10
1.0
10
100
1690 F08
Figure 8. Attenuation vs Frequency for Belden 9841
DATA RATE (bps)
10k
10
CABLE LENGTH (FT)
100
1k
10k
100k
1M
10M
1690 F09
2.5M
Figure 9. RS485 Cable Length Recommended. Applies
for 24 Gauge, Polyethylene Dielectric Twisted Pair
ESD PROTECTION
The ESD performance of the LTC1690 driver outputs (Z, Y)
and the receiver inputs (A, B) is as follows:
a) Meets
±
15kV Human Body Model (100pF, 1.5k
).
b) Meets IEC1000-4-2 Level 4 (
±
8kV) contact mode speci-
fications.
c) Meets IEC1000-4-2 Level 3 (
±
8kV) air discharge speci-
fications.
This level of ESD performance means that external voltage
suppressors are not required in many applications, when
compared with parts that are only protected to
±
2kV. The
LTC1690 driver input (D) and receiver output are pro-
tected to
±
2kV per the Human Body Model.
When powered up, the LTC1690 does not latch up or
sustain damage when the Z, Y, A or B pins are subjected
to any of the conditions listed above. The data during the
ESD event may be corrupted, but after the event the
LTC1690 continues to operate normally.
The additional ESD protection at the LTC1690 Z, Y, A and
B pins is important in applications where these pins are
exposed to the external world via socket connections.
11
LTC1690
Dimensions in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTIO
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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
1
2
3
4
0.193
±
0.006
(4.90
±
0.15)
8
7 6
5
0.118
±
0.004*
(3.00
±
0.102)
0.118
±
0.004**
(3.00
±
0.102)
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
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
(
)
1
2
3
4
8
7
6
5
0.255
±
0.015*
(6.477
±
0.381)
0.400*
(10.160)
MAX
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
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
1
2
3
4
0.150 0.157**
(3.810 3.988)
8
7
6
5
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
*
**
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
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.
12
LTC1690
1690f LT/TP 0400 4K · PRINTED IN USA
©
LINEAR TECHNOLOGY CORPORATION 1998
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507
q
www.linear-tech.com
120
1.2k
5V
RX
1.2k
1690 TA02
RECEIVER
2.7k
2.7k
RS232 IN
RX
1690 TA03
RECEIVER
Receiver with Low Fail-Safe Output
RS232 Receiver
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC485
5V Low Power RS485 Interface Transceiver
Low Power
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
LTC1484
5V Low Power RS485 Transceiver with Fail-Safe Receiver Circuit
Low Power, High Output State when Inputs are Open,
Shorted or Terminated,
±
15kV ESD Protection
LTC1485
5V RS485 Transceiver
High Speed, 10Mbps
LTC1487
5V Ultralow Power RS485 with Low EMI, Shutdown and
Highest Input Impedance, Low EMI, Lowest Power
High Input Impedance
LTC490
5V Differential Driver and Receiver Pair
Low Power, Pin Compatible with LTC1690
LTC491
5V Low Power RS485 Full-Duplex Transceiver
Low Power
LTC1535
Isolated RS485 Transceiver
2500V
RMS
Isolation, Full Duplex
LTC1685
52Mbps, RS485 Fail-Safe Transceiver
Pin Compatible with LTC485
LTC1686/LTC1687
52Mbps, RS485 Fail-Safe Driver/Receiver
Pin Compatible with LTC490/LTC491
LT1785/LT1791
±
60V Fault Protected RS485 Half-/Full-Duplex Transceiver
±
15kV ESD Protection
TYPICAL APPLICATIO
N
S
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