LT1785ACN8 [Linear]
60V Fault Protected RS485/RS422 Transceivers; 60V故障保护RS485 / RS422收发器
| 型号： | LT1785ACN8 |
| 厂家： | 
Linear |
| 描述： | 60V Fault Protected RS485/RS422 Transceivers |
| 文件： | 总12页 (文件大小：199K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1785/LT1785A
LT1791/LT1791A
60V Fault Protected
RS485/RS422 Transceivers
FEATURES
The LT®1785/LT1791 are half-duplex and full-duplex dif-
ferential bus transceivers for RS485 and RS422 applica-
tions which feature on-chip protection from overvoltage
faults on the data transmission lines. Receiver input and
driver output pins can withstand voltage faults up to ±60V
with respect to ground with no damage to the device.
Faultsmayoccurwhilethetransceiverisactive,shutdown
or powered off.
■
Protected from Overvoltage Line Faults to
±
60V
■
Pin Compatible with LTC485 and LTC491
■
High Input Impedance Supports Up to 128 Nodes
No Damage or Latchup to ESD
■
IEC-1000-4-2 Level 4: ±15kV Air Discharge
IEC-1000-4-2 Level 2: ±4kV Contact Discharge
Controlled Slew Rates for EMI Emissions Control
Guaranteed High Receiver Output State for Floating,
Shorted or Inactive Inputs
Outputs Assume a High Impedance When Off or
Powered Down
Drives Low Cost, Low Impedance Cables
Short-Circuit Protection on All Outputs
Thermal Shutdown Protection
■
■
Dataratesto250kbaudonnetworksofupto128nodesare
supported. Controlled slew rates on the driver outputs
control EMI emissions and improve data transmission
integrityonimproperlyterminatedlines.Driversarespeci-
fied to operate with inexpensive cables as low as 72Ω
characteristic impedance.
■
■
■
■
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APPLICATIO S
The LT1785A/LT1791A devices have “fail-safe” receiver
inputs to guarantee a receiver output high for shorted,
open or inactive data lines. On-chip ESD protection elimi-
nates need for external protection devices.
■
Industrial Control Data Networks
■
CAN Bus Applications
■
HVAC Controls
The LT1785/LT1785A are available in 8-lead DIP and SO
packagesand theLT1791/LT1791Ain14-leadDIPandSO
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATIO
Normal Operation Waveforms at 250kBaud
V
CC1
RO1
RX
RE1
DE1
R
TERM
LT1785
RO
DI1
TX
GND1
Y-Z
V
CC2
RO2
RX
RE2
DE2
DI
R
TERM
LT1785
DI2
TX
1785/91 TA02
GND2
1785/91 TA01
1
LT1785/LT1785A
LT1791/LT1791A
W W W
U
(Note 1)
ABSOLUTE AXI U RATI GS
Supply Voltage (VCC) .............................................. 18V
Receiver Enable Input Voltage .................... –0.3V to 6V
Driver Enable Input Voltage ........................ –0.3V to 6V
Driver Input Voltage.................................. –0.3V to 18V
Receiver Input Voltage............................... –60V to 60V
Driver Output Voltage ............................... – 60V to 60V
Receiver Output Voltage ................ –0.3V to (VCC + 6V)
Operating Temperature Range
LT1785C/LT1791C/
LT1785AC/LT1791AC ............................. 0°C to 70°C
LT1785I/LT1791I............................... –40°C to 85°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
W
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/O
PACKAGE RDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
LT1785CN8
LT1791CN
TOP VIEW
NC
RO
1
2
3
4
5
6
7
14
13
12
11
10
9
V
CC
LT1785CS8
LT1791CS
LT1791IN
LT1791IS
RO
RE
DE
DI
1
2
3
4
V
B
A
8
7
6
5
R
CC
NC
A
R
LT1785IN8
LT1785IS8
LT1785ACN8
LT1785ACS8
RE
DE
B
LT1791ACN
LT1791ACS
D
DI
Z
GND
D
GND
GND
Y
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
8
NC
N PACKAGE
S PACKAGE
14-LEAD PDIP 14-LEAD PLASTIC SO
S8 PART MARKING
TJMAX = 150°C, θJA = 130°C/ W (N8)
TJMAX = 150°C, θJA = 150°C/ W (S8)
TJMAX = 150°C, θJA = 130°C/ W (N)
T
JMAX = 150°C, θJA = 150°C/ W (S)
1785
1785I
1785A
Consult factory for Military grade parts.
2
LT1785/LT1785A
LT1791/LT1791A
DCELECTRICALCHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25°C, VCC = 5V.
A
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (With Load)
I = 0
●
4.1
5
V
OD1
OD2
O
R = 50Ω (RS422), Figure 1
R = 27Ω (RS485), Figure 1
R = 18Ω
●
●
●
2.0
1.5
1.2
2.70
2.45
2.2
V
V
V
∆V
OD
Change in Magnitude of Driver Differential Output
Voltage for Complementary Output States
R = 27Ω or R = 50Ω, Figure 1
●
0.2
V
V
Driver Common Mode Output Voltage
R = 27Ω or R = 50Ω, Figure 1
R = 27Ω or R = 50Ω, Figure 1
●
●
2
2
2.5
3
V
V
OC
∆ V
Change in Magnitude of Driver Common Mode
Output Voltage for Complementary Output States
0.2
OC
V
V
Input High Voltage
Input Low Voltage
Input Current
DI, DE, RE
DI, DE, RE
DI, DE, RE
●
●
●
V
V
IH
IL
0.8
5
I
I
µA
IN1
IN2
Input Current (A, B); (LT1791 or LT1785 with
DE = 0V)
V
V
= 12V
= –7V
●
●
●
0.15
–0.08
0.3
mA
mA
mA
IN
IN
–0.15
–6
–60V ≤ V ≤ 60V
6
IN
V
Differential Input Threshold Voltage for Receiver
LT1785/LT1791: –7V ≤ V ≤ 12V
●
●
–0.2
–0.2
0.2
0
V
V
TH
CM
LT1785A/LT1791A: –7V ≤ V ≤ 12V
CM
∆V
Receiver Input Hysteresis
–7V < V < 12V
20
4
mV
V
TH
CM
V
V
Receiver Output High Voltage
I = –400µA, V = 200mV
●
●
●
3.5
OH
OL
O
ID
Receiver Output Low Voltage
I = 1.6mA, V = –200mV
0.3
0.5
1
V
O
ID
Three-State (High Impedance) Output Current
RE > 2V or Power Off
–1
85
50
µA
at Receiver 0V < V
< 6V
OUT
R
IN
Receiver Input Resistance (LT1791)
–7V ≤ V ≤ 12V
●
●
125
125
kΩ
kΩ
CM
– 60V ≤ V ≤ 60V
CM
LT1785
–7V ≤ V ≤ 12V
90
kΩ
CM
RS485 Unit Load
Driver Short-Circuit Current
0.25
I
I
V
V
= HIGH, Force V = –7V
●
●
35
35
250
250
mA
mA
SC
OUT
OUT
O
= LOW, Force V = 12V
O
Driver Output Fault Current
V = 60V
V = –60V
●
●
6
mA
mA
O
–6
O
Receiver Short-Circuit Current
0V ≤ V ≤ V
●
±30
mA
O
CC
Driver Three-State Output Current
–7V ≤ V ≤ 12V
–60V ≤ V ≤ 60V
●
●
–0.2
–6
0.3
6
mA
mA
O
O
Supply Current
No Load, RE = 0V, DE = 5V
No Load, RE = 5V, DE = 5V
No Load, RE = 0V, DE = 0V
No Load, RE = 5V, DE = 0V
●
●
●
●
5.5
5.5
4.5
0.2
9
9
8
mA
mA
mA
mA
CC
0.3
3
LT1785/LT1785A
LT1791/LT1791A
U
SWITCHI G CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25°C, VCC = 5V.
A
SYMBOL PARAMETER
CONDITIONS
Figures 3, 5
Figures 3, 5
Figures 3, 5
Figures 3, 5
Figures 4, 6
Figures 4, 6
Figures 4, 6
Figures 4, 6
Figures 3, 7
Figures 3, 7
MIN
TYP
700
700
100
800
500
800
200
800
400
400
200
300
300
400
400
MAX
2000
2000
UNITS
ns
t
t
t
Driver Input to Output
●
●
PLH
Driver Input to Output
ns
PHL
Driver Output to Output
ns
SKEW
t , t
r
Driver Rise or Fall Time
●
●
●
●
●
●
●
200
2000
3000
3000
5000
5000
900
ns
f
t
t
t
t
t
t
t
t
t
t
t
f
t
t
t
t
t
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
Receiver Input to Output
ns
ZH
ZL
LZ
HZ
ns
ns
ns
ns
PLH
Receiver Input to Output
900
ns
PHL
Differential Receiver Skew
ns
SKD
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Figures 2, 8
Figures 2, 8
Figures 2, 8
Figures 2, 8
●
●
●
●
●
1000
1000
1000
1000
ns
ZL
ns
ZH
ns
LZ
Receiver Disable from High
Maximum Data Rate
ns
HZ
250
kbps
µs
MAX
Time to Shut Down
Figures 2, 6, 8
3
12
12
4
SHDN
ZH(SHDN)
ZL(SHDN)
ZH(SHDN)
ZL(SHDN)
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
Figures 2, 6; RE = 5V
Figures 2, 6; RE = 5V
Figures 2, 8; DE = 0V
Figures 2, 8; DE = 0V
µs
µs
µs
4
µs
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Driver Differential Output Voltage
vs Load Resistance
Driver Differential Output Voltage
vs Temperature
Receiver Propagation Delay
vs Temperature
4
3
2
1
0
3.0
2.5
2.0
1.5
1.0
0.5
0
1000
800
600
400
200
0
T
= 25°C
A
t
PHL
t
PLH
R = 27Ω
10
100
1k
80 100
–40
0
20
40
60
80 100
–40
0
20
TEMPERATURE (°C)
40
60
–20
–20
LOAD RESISTANCE (Ω)
TEMPERATURE (°C)
1785/91 G01
1785/91 G03
1785/91 G03
4
LT1785/LT1785A
LT1791/LT1791A
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Driver Propagation Delay
vs Temperature
LT1791 Receiver Input Current
vs VIN
LT1791 Driver Output Leakage
DE = 0V
1000
900
800
700
600
500
400
300
200
100
0
LH
HL
1mA/DIV
200µA/DIV
–60V
60V
–60V
60V
VOUT
1785/91 G05
VIN
1785/91 G06
–40
0
20
40
60
80 100
–20
TEMPERATURE (°C)
1785/91 G04
LT1785 Input Characteristics
Pins A or B; DE = RE = 0V
Receiver Propagation Delay
vs Differential Input Voltage
Supply Current vs Temperature
7
6
5
4
3
2
1
0
700
600
500
400
300
200
100
0
DRIVER AND
RECEIVER ON
HL V = –7V
CM
HL V = 12V
CM
RECEIVER ONLY
1mA/DIV
LH V = –7V
CM
LH V = 12V
CM
–60V
60V
1785/91 G07
VA, VB
STANDBY
–40
0
20
40
60
80 100
–20
0
3
4
5
1
2
TEMPERATURE (°C)
V
DIFFERENTIAL (V)
IN
1785/91 G08
1785/91 G09
U
U
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PIN FUNCTIONS
RO: Receiver Output. TTL level logic output. If the receiver
is active (RE pin low), RO is high if receiver input A ≥ B by
200mV. If A ≤ B by 200mV, then RO will be low. RO
assumes a high impedance output state when RE is high
or the part is powered off. RO is protected from output
shorts from ground to 6V.
goes to a low power shutdown state. Placing either RE or
DE into its active state brings the circuit out of shutdown.
Shutdown state is not entered until a 3µs delay after both
RE and DE are disabled, allowing for logic skews in
toggling between transmit and receive modes of opera-
tion. For CAN bus applications, RE should be tied low to
prevent the circuit from entering shutdown.
RE: Receiver Output Enable. TTL level logic input. A logic
low on RE enables normal operation of the receiver output
RO. A logic high level at RE places the receiver output pin
RO into a high impedance state. If receiver enable RE and
driver enable DE are both in the disable state, the circuit
DE: Driver Output Enable. TTL level logic input. A logic
high on DE enables normal operation of the driver outputs
(Y and Z on LT1791, A and B on LT1785). A logic low level
at DE places the driver output pins into a high impedance
5
LT1785/LT1785A
LT1791/LT1791A
U
U
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PIN FUNCTIONS
state. If receiver enable RE and driver enable DE are both
in the disable state, the circuit goes to a low power
shutdownstate.PlacingeitherREorDEintoitsactivestate
brings the circuit out of shutdown. Shutdown state is not
entereduntila3µsdelayafterbothREandDEaredisabled,
allowing for logic skews in toggling between transmit and
receive modes of operation. For CAN bus operation the DE
pin is used for signal input to place the data bus in
dominant or recessive states.
protected from shorts between ±60V in both active and
high impedance modes. For CAN applications, output Z is
the CANH output node.
A: Receiver Input. The A receiver input forces a high
receiveroutputwhenV(A)≥[V(B)+200mV]. V(A)≤[V(B)
– 200mV] forces a receiver output low. Receiver inputs A
and B are protected against voltage faults between ±60V.
The high input impedance allows up to 128 LT1785 or
LT1791 transceivers on one RS485 data bus.
DI: Driver Input. TTL level logic input. A logic high at DI
causes driver output A or Y to a high state, and output B
or Z to a low state. Complementary output states occur for
DI low. For CAN bus applications DI should be tied low.
The LT1785A/LT1791A have guaranteed receiver input
thresholds –200mV < VTH < 0. Receiver outputs are
guaranteed to be in a high state for 0V inputs.
B: Receiver Input. The B receiver input forces a high
receiver output when V(A) ≥ [V(B) + 200mV]. When V(A)
≤ [V(B) – 200mV], the B receiver forces a receiver output
low. Receiver inputs A and B are protected against voltage
faults between ±60V. The high input impedance allows up
to128LT1785orLT1791transceiversononeRS485 data
bus.
GND: Ground.
Y: Driver Output. The Y driver output is in phase with the
driver input DI. In the LT1785 driver output Y is internally
connected to receiver input A. The driver output assumes
a high impedance state when DE is low, power is off or
thermal shutdown is activated. The driver output is pro-
tected from shorts between ±60V in both active and high
impedance modes. For CAN applications, output Y is the
CANL output node.
The LT1785A/LT1791A have guaranteed receiver input
thresholds –200mV < VTH < 0. Receiver outputs are
guaranteed to be in a high state for 0V inputs.
Z: Driver Output. The Z driver output is opposite in phase
to the driver input DI. In the LT1785 driver output Z is
internally connected to receiver input B. The driver output
assumes a high impedance state when DE is low, power is
off or thermal shutdown is activated. The driver output is
VCC:PositiveSupplyInput.ForRS422orRS485 operation,
4.75V ≤ VCC ≤ 5.25V. Higher VCC input voltages increase
output drive swing. VCC should be decoupled with a 0.1µF
low ESR capacitor directly at Pin 8 (VCC).
TEST CIRCUITS
A
S1
TEST POINT
1k
R
RECEIVER
OUTPUT
V
CC
V
OD
1k
V
OC
C
RL
S2
R
B
1785/91 F02
1785/91 F01
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
6
LT1785/LT1785A
LT1791/LT1791A
TEST CIRCUITS
5V
DE
A
B
S1
A
C
C
L1
L2
V
DI
CC
RO
R
500Ω
DIFF
OUTPUT
UNDER TEST
B
S2
RE
15pF
C
L
1785/91 F04
1785/91 F03
Figure 3. Driver/Receiver Timing Test Circuit
Figure 4. Driver Timing Test Load
U
U
FU CTIO TABLES
LT1791
LT1785 Transmitting
INPUTS
OUTPUTS
INPUTS
OUTPUTS
RE
0
0
0
0
0
0
0
0
0
1
1
1
DE
0
0
0
1
1
1
1
1
1
0
1
1
DI
X
X
X
0
0
0
1
1
1
X
0
1
A-B
≤ –200mV
≥200mV*
Open
Y
Hi-Z
Hi-Z
Hi-Z
0
Z
Hi-Z
Hi-Z
Hi-Z
1
RO
0
RE
0
DE
1
DI
0
A
0
B
1
RO
0
1
0
1
1
1
0
1
1
1
0
X
0
Hi-Z
0
Hi-Z
1
Hi-Z
Hi-Z
Hi-Z
≤ –200mV
≥200mV*
Open
0
1
1
0
1
1
1
1
1
1
0
0
1
1
LT1785 Receiving
≤ –200mV
≥200mV*
Open
1
0
0
INPUTS
OUTPUT
1
0
1
RE
0
DE
0
DI
X
A-B
RO
0
1
0
1
≤–200mV
≥200mV*
Open
X
Hi-Z
0
Hi-Z
1
Hi-Z
Hi-Z
Hi-Z
0
0
X
1
X
0
0
X
1
X
1
0
1
0
X
X
Hi-Z
* ≥ 0mV for LT1791A
* ≥ 0mV for LT1785A
U
W
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SWITCHI G TI E WAVEFOR S
5V
f = 125kHz, t ≤ 10ns, t ≤ 10ns
DI
1.5V
1.5V
r
f
0V
B
1/2 V
O
t
t
PHL
PLH
V
O
A
t
t
1/2 V
SKEW
SKEW
O
V
O
90%
10%
90%
V
= V(A) – V(B)
0V
–V
DIFF
10%
O
t
t
f
1785/91 F05
r
Figure 5. Driver Propagation Delays
7
LT1785/LT1785A
LT1791/LT1791A
U
W
W
SWITCHI G TI E WAVEFOR S
5V
f = 125kHz, t ≤ 10ns, t ≤ 10ns
1.5V
1.5V
DE
A, B
A, B
r
f
0V
5V
t
t
, t
ZL(SHDN) ZL
LZ
2.3V
OUTPUT NORMALLY LOW
0.5V
0.5V
V
OL
OH
0V
V
OUTPUT NORMALLY HIGH
, t
2.3V
t
t
1785/91 F06
HZ
ZH(SHDN) ZH
Figure 6. Driver Enable and Disable Times
V
OH
1.5V
1.5V
RO
OUTPUT
V
OL
t
f = 125kHz, t ≤ 10ns, t ≤ 10ns
t
PLH
PHL
r
f
V
A – B
–V
OD2
OD2
0V
0V
INPUT
1785/91 F07
Figure 7. Receiver Propagation Delays
5V
0V
5V
1.5V
1.5V
RE
RO
RO
f = 125kHz, t ≤ 10ns, t ≤ 10ns
r
f
t
, t
t
LZ
ZL(SHDN) ZL
1.5V
OUTPUT NORMALLY LOW
0.5V
0.5V
OUTPUT NORMALLY HIGH
, t
1.5V
t
0V
t
1785/91 F08
HZ
ZH(SHDN) ZH
Figure 8. Receiver Enable and Disable Times
U U
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APPLICATIO S I FOR ATIO
cally –8V to 12.5V. Replacement of standard RS485
transceiver components with the LT1785 or LT1791
devices eliminates field failures due to overvoltage faults
ortheuseofcostlyexternalprotectiondevices.Thelimited
overvoltagetoleranceofCMOSRS485transceiversmakes
implementation of effective external protection networks
difficult without interfering with proper data network
performance within the –7V to 12V region of RS485
operation.
Overvoltage Protection
The LT1785/LT1791 RS485/RS422 transceivers answer
an applications need for overvoltage fault tolerance on
data networks. Industrial installations may encounter
common mode voltages between nodes far greater than
the –7V to 12V range specified for compliance to RS485
standards. CMOS RS485 transceivers can be damaged by
voltages above their absolute maximum ratings of typi-
8
LT1785/LT1785A
LT1791/LT1791A
U U
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APPLICATIO S I FOR ATIO
line. The DE logic input performs a similar function on the
driver outputs. A high state on DE activates the differential
driver outputs, a low state places both driver outputs into
high impedance. Tying the RE and DE logic inputs to-
gether may be done to allow one logic signal to toggle the
transceiver from receive to transmit modes. The DE input
is used as the data input in CAN bus applications.
The high overvoltage rating of the LT1785/LT1791 facili-
tates easy extension to almost any level. Simple discrete
component networks that limit the receiver input and
driver output voltages to less than ±60V can be added to
the device to extend protection to any desired level. Figure
11 shows a protection network against faults to the
120VAC line voltage.
TheLT1785/LT1791protectionisachievedbyusingahigh
voltage bipolar integrated circuit process for the trans-
ceivers. The naturally high breakdown voltages of the
bipolar process provides protection in powered-off and
high impedance conditions. The driver outputs use a
foldback current limit design to protect against overvolt-
age faults while still allowing high current output drive.
Disabling both the driver and receiver places the device
intoalowsupplycurrentshutdownmode.Aninternaltime
delay of 3µs minimum prevents entering shutdown due to
small logic skews when a toggle between receive and
transmit is desired. The recovery time from shutdown
mode is typically 12µs. The user must be careful to allow
for this wake-up delay from shutdown mode. To allow full
250kbaud data rate transmission in CAN applications, the
RE pin should be tied low to prevent entering shutdown
mode.
ESD Protection
The LT1785/LT1791 I/O pins have on-chip ESD protection
circuitry to eliminate field failures caused by discharges to
exposed ports and cables in application environments.
The LT1785 pins A and B and the LT1791 driver output
pins Y and Z are protected to IEC-1000-4-2 level 2. These
pins will survive multiple ESD strikes of ±15kV air dis-
charge or ±4kV contact discharge. Due to their very high
input impedance, the LT1791 receiver pins are protected
to IEC-1000-4-2 level 2, or ±15kV air and ±4kV contact
discharges. This level of ESD protection will guarantee
immunity from field failures in all but the most severe ESD
environments. The LT1791 receiver input ESD tolerance
may be increased to IEC level 4 compliance by adding 2.2k
resistors in series with these pins.
Slew Limiting for EMI Emissions Control
The LT1785/LT1791 feature controlled driver output slew
rates to control high frequency EMI emissions from
equipment and data cables. The slew limiting limits data
rate operation to 250kbaud. Slew limiting also mitigates
the adverse affects of imperfect transmission line termi-
nation caused by stubs or mismatched cable. In some low
speed, short distance networks, cable termination may be
eliminated completely with no adverse effect on data
transmission.
Data Network Cable Selection and Termination
Long distance data networks operating at high data trans-
mission rates should use high quality, low attenuation
cable with well-matched cable terminations. Short dis-
tance networks at low data rates may use much less
expensive PVC cable. These cables have characteristic
impedances as low as 72Ω. The LT1785/LT1791 output
drivers are guaranteed to drive cables as low as 72Ω.
Low Power Shutdown
The LT1785/LT1791 have RE and DE logic inputs to
control the receive and transmit modes of the transceiv-
ers. TheREinputallowsnormaldatareceptionwheninthe
low state. The receiver output goes to a high impedance
state when RE is high, allowing multiplexing the RO data
9
LT1785/LT1785A
LT1791/LT1791A
U U
W
U
APPLICATIO S I FOR ATIO
12
11
A
B
12
11
A
B
5
2
120Ω
RX
DI
RO
TX
3
4
4
3
RE
DE
DE
RE
LT1791
LT1791
Z
10
9
10
9
Z
2
5
120Ω
TX
RO
DI
RX
Y
Y
1785/91 F09
Figure 9. Full-Duplex RS422
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
0.130 ± 0.005
0.300 – 0.325
0.045 – 0.065
(3.302 ± 0.127)
(1.143 – 1.651)
(7.620 – 8.255)
8
1
7
6
5
4
0.065
(1.651)
TYP
0.255 ± 0.015*
(6.477 ± 0.381)
0.009 – 0.015
(0.229 – 0.381)
0.125
0.020
(0.508)
MIN
(3.175)
MIN
+0.035
–0.015
2
3
0.325
0.100 ± 0.010
(2.540 ± 0.254)
0.018 ± 0.003
+0.889
8.255
(
)
(0.457 ± 0.076)
N8 1197
–0.381
*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)
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
8
7
6
5
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
0.150 – 0.157**
(3.810 – 3.988)
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
SO8 0996
1
3
4
2
10
LT1785/LT1785A
LT1791/LT1791A
U
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
N Package
14-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.770*
(19.558)
MAX
14
13
12
11
10
9
8
7
0.255 ± 0.015*
(6.477 ± 0.381)
1
2
3
5
6
4
0.300 – 0.325
(7.620 – 8.255)
0.045 – 0.065
(1.143 – 1.651)
0.130 ± 0.005
(3.302 ± 0.127)
0.020
(0.508)
MIN
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
+0.035
0.325
0.005
(0.125)
MIN
0.100 ± 0.010
(2.540 ± 0.254)
–0.015
0.125
(3.175)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
+0.889
8.255
(
)
–0.381
N14 1197
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
S Package
14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.337 – 0.344*
(8.560 – 8.738)
13
12
11 10
8
14
9
0.228 – 0.244
0.150 – 0.157**
(5.791 – 6.197)
(3.810 – 3.988)
1
2
3
4
5
6
7
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0° – 8° TYP
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
0.016 – 0.050
0.406 – 1.270
S14 0695
*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 represen-
tation that the interconnection of circuits as described herein will not infringe on existing patent rights.
11
LT1785/LT1785A
LT1791/LT1791A
U
TYPICAL APPLICATIONS
R
R
T
120Ω
1
1
T
RO
RO
RX
RX
120Ω
7
6
B
A
7
6
B
A
2
3
2
3
RE
DE
RE
DE
LT1785
LT1785
6
A
7
B
6
A
7
B
4
4
DI
DI
TX
TX
1785/91 F10
LT1785
LT1785
4
4
1
1
3
2
3
2
DI
DI
DE
DE
RE RO
RE RO
Figure 10. Half-Duplex RS485 Network Operation
RAYCHEM
POLYSWITCH
8
TR600-150
V
CC
1
× 2
RO
47Ω
RX
LT1785
7
B
A
2
3
R ,120Ω
T
RE
DE
6
5
1785/91 F11
0.1µF
300V
47Ω
CARBON
4
DI
TX
COMPOSITE
5W
1.5KE36CA
Figure 11. RS485 Network with 120V AC Line Fault Protection
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC485
Low Power RS485 Interface Transceiver
Differential Driver and Receiver Pair
I
I
= 300µA (Typ)
= 300µA
CC
CC
LTC491
LTC1483
LTC1485
LTC1487
LTC1520
LTC1535
LTC1685
LTC1687
Ultralow Power RS485 Low EMI Transceiver
Differential Bus Transceiver
Controlled Driver Slew Rate
10Mbaud Operation
Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance
50Mbps Precision Quad Line Receiver
Up to 256 Transceivers on the Bus
Channel-to-Channel Skew 400ps (Typ)
Isolated RS485 Full-Duplex Transceiver
52Mbps RS485 Half-Duplex Transceiver
52Mbps RS485 Full-Duplex Transceiver
2500V
Isolation in Surface Mount Package
RMS
Propagation Delay Skew 500ps (Typ)
Propagation Delay Skew 500ps (Typ)
178591f LT/TP 0300 4K • PRINTED IN THE USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 1998
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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