LT1785ACN8-PBF [Linear]
60V Fault Protected RS485/RS422 Transceivers; 60V故障保护RS485 / RS422收发器
| 型号： | LT1785ACN8-PBF |
| 厂家： | 
Linear |
| 描述： | 60V Fault Protected RS485/RS422 Transceivers |
| 文件： | 总16页 (文件大小：195K) |
| 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
DESCRIPTION
TheLT®1785/LT1791arehalf-duplexandfull-duplexdiffer-
ential bus transceivers for RS485 and RS422 applications
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 ±±60 with
respect to ground with no damage to the device. Faults
may occur while the transceiver is active, shut down or
powered off.
n
Protected from Overvoltage Line Faults to ±±0ꢀ
n
Pin Compatible with LTC485 and LTC491
n
High Input Impedance Supports Up to 128 Nodes
No Damage or Latchup to ESD
n
IEC-1666-4-2 Level 4: ±15k0 Air Discharge
IEC-1666-4-2 Level 2: ±4k0 Contact Discharge
n
Controlled Slew Rates for EMI Emissions Control
n
Guaranteed High Receiver Output State for Floating,
Shorted or Inactive Inputs
Data rates to 256kbaud on networks of up to 128 nodes
are supported. Controlled slew rates on the driver out-
putscontrol EMI emissions and improve data transmis-
sion integrity on improperly terminated lines. Drivers are
specified to operate with inexpensive cables as low as
72Ω characteristic impedance.
n
Outputs Assume a High Impedance When Off or
Powered Down
n
Drives Low Cost, Low Impedance Cables
n
Short-Circuit Protection on All Outputs
n
Thermal Shutdown Protection
Guaranteed Operation to 125°C
n
The LT1785A/LT1791A devices have “fail-safe” receiver
inputstoguaranteeareceiveroutputhighforshorted,open
or inactive data lines. On-chip ESD protection eliminates
need for external protection devices.
APPLICATIONS
n
Industrial Control Data Networks
n
CAN Bus Applications
The LT1785/LT1785A are available in 8-lead DIP and SO
packages and the LT1791/LT1791A in 14-lead DIP and
SO packages.
n
H0AC Controls
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Normal Operation Waveforms at 250kBaud
0
CC1
RO1
RX
RO
RE1
R
TERM
LT1785
DE1
DI1
TX
Y-Z
GND1
DI
0
CC2
RO2
RX
RE2
R
TERM
LT1785
178591 TA62
DE2
DI2
TX
GND2
178591 TA61
178491fb
1
LT1785/LT1785A/
LT1791/LT1791A
(Note 1)
ABSOLUTE MAXIMUM RATINGS
Supply 0oltage (0 ) ................................................180
Operating Temperature Range
CC
Receiver Enable Input 0oltage...................... –6.30 to ±0
Driver Enable Input 0oltage.......................... –6.30 to ±0
Driver Input 0oltage................................... –6.30 to 180
Receiver Input 0oltage................................ –±60 to ±60
Driver Output 0oltage.................................. –±60 to ±60
LT1785C/LT1791C/
LT1785AC/LT1791AC.................................... 6°C to 76°C
LT1785I/LT1791I/
LT1785AI/LT1791AI.................................. –46°C to 85°C
LT1785H/LT1791H/
LT1785AH/LT1791AH.............................–46°C to 125°C
Storage Temperature Range...................–±5°C to 156°C
Lead Temperature (Soldering, 16 sec) .................. 366°C
Receiver Output 0oltage...................–6.30 to (0 + ±0)
CC
PIN CONFIGURATION
TOP 0IEW
TOP 0IEW
NC
RO
1
2
3
4
5
±
7
14
13
12
11
16
9
0
CC
R
NC
A
RO
RE
DE
DI
1
2
3
4
0
B
A
8
7
±
5
CC
R
RE
DE
B
D
DI
Z
GND
D
GND
GND
Y
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
8
NC
T
= 156°C, θ = 136°C/W (N8)
JMAX
JA
N PACKAGE
S PACKAGE
T
= 156°C, θ = 156°C/W (S8)
14-LEAD PDIP 14-LEAD PLASTIC SO
JMAX
JA
T
= 156°C, θ = 136°C/W (N)
JA
JMAX
T
= 156°C, θ = 156°C/W (S)
JMAX
JA
ORDER INFORMATION
LEAD FREE FINISH
LT1785CN8#PBF
LT1785CS8#PBF
LT1785IN8#PBF
LT1785IS8#PBF
LT1785ACN8#PBF
LT1785ACS8#PBF
LT1785AIN8#PBF
LT1785AIS8#PBF
LT1785HN8#PBF
LT1785HS8#PBF
LT1785AHN8#PBF
LT1785AHS8#PBF
LT1791CN#PBF
TAPE AND REEL
PART MARKING*
1785
PACKAGE DESCRIPTION
8-Lead PDIP
TEMPERATURE RANGE
6°C to 76°C
LT1785CN8#TRPBF
LT1785CS8#TRPBF
LT1785IN8#TRPBF
LT1785IS8#TRPBF
LT1785ACN8#TRPBF
LT1785ACS8#TRPBF
LT1785AIN8#TRPBF
LT1785AIS8#TRPBF
LT1785HN8#TRPBF
LT1785HS8#TRPBF
LT1785AHN8#TRPBF
LT1785AHS8#TRPBF
LT1791CN#TRPBF
LT1791CS#TRPBF
1785
8-Lead Plastic SO
8-Lead PDIP
6°C to 76°C
1785I
–46°C to 85°C
–46°C to 85°C
6°C to 76°C
1785I
8-Lead Plastic SO
8-Lead PDIP
1785A
1785A
1785AI
1785AI
1785H
1785H
1785AH
1785AH
1791
8-Lead Plastic SO
8-Lead PDIP
6°C to 76°C
–46°C to 85°C
–46°C to 85°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
6°C to 76°C
8-Lead Plastic SO
8-Lead PDIP
8-Lead Plastic SO
8-Lead PDIP
8-Lead Plastic SO
14-Lead PDIP
LT1791CS#PBF
1791
14-Lead Plastic SO
6°C to 76°C
178591fb
2
LT1785/LT1785A/
LT1791/LT1791A
ORDER INFORMATION
LEAD FREE FINISH
LT1791IN#PBF
LT1791IS#PBF
LT1791ACN#PBF
LT1791ACS#PBF
LT1791AIN#PBF
LT1791AIS#PBF
LT1791HN#PBF
LT1791HS#PBF
LT1791AHN#PBF
LT1791AHS#PBF
LEAD BASED FINISH
LT1785CN8
TAPE AND REEL
LT1791IN#TRPBF
LT1791IS#TRPBF
LT1791ACN#TRPBF
LT1791ACS#TRPBF
LT1791AIN#TRPBF
LT1791AIS#TRPBF
LT1791HN#TRPBF
LT1791HS#TRPBF
LT1791AHN#TRPBF
LT1791AHS#TRPBF
TAPE AND REEL
LT1785CN8#TR
LT1785CS8#TR
LT1785IN8#TR
PART MARKING*
1791I
PACKAGE DESCRIPTION
14-Lead PDIP
TEMPERATURE RANGE
–46°C to 85°C
–46°C to 85°C
6°C to 76°C
1791I
14-Lead Plastic SO
14-Lead PDIP
1791A
1791A
14-Lead Plastic SO
14-Lead PDIP
6°C to 76°C
1791AI
1791AI
1791H
1791H
1791AH
1791AH
PART MARKING*
1785
–46°C to 85°C
–46°C to 85°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
TEMPERATURE RANGE
6°C to 76°C
14-Lead Plastic SO
14-Lead PDIP
14-Lead Plastic SO
14-Lead PDIP
14-Lead Plastic SO
PACKAGE DESCRIPTION
8-Lead PDIP
LT1785CS8
1785
8-Lead Plastic SO
8-Lead PDIP
6°C to 76°C
LT1785IN8
1785I
–46°C to 85°C
–46°C to 85°C
6°C to 76°C
LT1785IS8
LT1785IS8#TR
1785I
8-Lead Plastic SO
8-Lead PDIP
LT1785ACN8
LT1785ACS8
LT1785AIN8
LT1785AIS8
LT1785HN8
LT1785ACN8#TR
LT1785ACS8#TR
LT1785AIN8#TR
LT1785AIS8#TR
LT1785HN8#TR
LT1785HS8#TR
LT1785AHN8#TR
LT1785AHS8#TR
LT1791CN#TR
1785A
1785A
8-Lead Plastic SO
8-Lead PDIP
6°C to 76°C
1785AI
1785AI
1785H
1785H
1785AH
1785AH
1791
–46°C to 85°C
–46°C to 85°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
6°C to 76°C
8-Lead Plastic SO
8-Lead PDIP
LT1785HS8
8-Lead Plastic SO
8-Lead PDIP
LT1785AHN8
LT1785AHS8
LT1791CN
8-Lead Plastic SO
14-Lead PDIP
LT1791CS
LT1791CS#TR
1791
14-Lead Plastic SO
14-Lead PDIP
6°C to 76°C
LT1791IN
LT1791IN#TR
1791I
–46°C to 85°C
–46°C to 85°C
6°C to 76°C
LT1791IS
LT1791IS#TR
1791I
14-Lead Plastic SO
14-Lead PDIP
LT1791ACN
LT1791ACN#TR
LT1791ACS#TR
LT1791AIN#TR
LT1791AIS#TR
1791A
LT1791ACS
1791A
14-Lead Plastic SO
14-Lead PDIP
6°C to 76°C
LT1791AIN
1791AI
1791AI
1791H
1791H
1791AH
1791AH
–46°C to 85°C
–46°C to 85°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
–46°C to 125°C
LT1791AIS
14-Lead Plastic SO
14-Lead PDIP
LT1791HN
LT1791HN#TR
LT1791HS
LT1791HS#TR
14-Lead Plastic SO
14-Lead PDIP
LT1791AHN
LT1791AHN#TR
LT1791AHS#TR
LT1791AHS
14-Lead Plastic SO
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
This product is only offered in trays. For more information go to: http://www.linear.com/packaging/
178491fb
3
LT1785/LT1785A/
LT1791/LT1791A
DC ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, ꢀCC = 5ꢀ.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
0
Differential Driver Output 0oltage (Unloaded)
Differential Driver Output 0oltage (With Load)
I = 6
4.1
5
0
OD1
OD2
O
l
l
l
0
R = 56ꢀ (RS422), Figure 1
R = 27ꢀ (RS485), Figure 1
R = 18ꢀ
2.6
1.5
1.2
2.76
2.45
2.2
0
0
0
l
0
0
Change in Magnitude of Driver Differential Output
0oltage for Complementary Output States
R = 27ꢀ or R = 56ꢀ, Figure 1
6.2
0
OD
l
l
Driver Common Mode Output 0oltage
R = 27ꢀ or R = 56ꢀ, Figure 1
R = 27ꢀ or R = 56ꢀ, Figure 1
2
2
2.5
3
0
0
OC
Δ|0
|
Change in Magnitude of Driver Common Mode Output
0oltage for Complementary Output States
6.2
OC
l
l
l
0
0
Input High 0oltage
DI, DE, RE
DI, DE, RE
DI, DE, RE
0
0
IH
Input Low 0oltage
6.8
5
IL
I
IN1
I
IN2
Input Current
μA
l
l
l
Input Current (A, B); (LT1791 or LT1785 with DE = 60)
0
0
= 120
= –70
6.15
–6.68
6.3
mA
mA
mA
IN
IN
–6.15
–±
–±60 ≤ 0 ≤ ±60
±
IN
l
l
0
TH
Differential Input Threshold 0oltage for Receiver
LT1785/LT1791: –70 ≤ 0 ≤ 120
–6.2
–6.2
6.2
6
0
0
CM
LT1785A/LT1791A: –70 ≤ 0 ≤ 120
CM
Δ0
Receiver Input Hysteresis
–70 < 0 < 120
26
4
m0
0
TH
CM
l
l
l
0
Receiver Output High 0oltage
I = –466μA, 0 = 266m0
3.5
OH
OL
O
ID
0
Receiver Output Low 0oltage
I = 1.±mA, 0 = –266m0
6.3
6.5
1
0
O
ID
Three-State (High Impedance) Output Current at
RE > 20 or Power Off
–1
85
56
μA
Receiver 60 < 0
< ±0
OUT
l
l
R
Receiver Input Resistance (LT1791)
–70 ≤ 0 ≤ 120
125
125
kΩ
kΩ
IN
CM
– ±60 ≤ 0 ≤ ±60
CM
LT1785
–70 ≤ 0 ≤ 120
96
kΩ
CM
RS485 Unit Load
Driver Short-Circuit Current
6.25
l
l
I
0
OUT
0
OUT
= HIGH, Force 0 = –70
35
35
256
256
mA
mA
SC
O
= LOW, Force 0 = 120
O
l
l
Driver Output Fault Current
0 = ±60
O
±
mA
mA
O
0 = –±60
–±
l
Receiver Short-Circuit Current
60 ≤ 0 ≤ 0
±35
mA
O
CC
l
l
Driver Three-State Output Current
–70 ≤ 0 ≤ 120
–6.2
–±
6.3
±
mA
mA
O
–±60 ≤ 0 ≤ ±60
O
l
l
l
l
I
CC
Supply Current
No Load, RE = 60, DE = 50
No Load, RE = 50, DE = 50
No Load, RE = 60, DE = 60
No Load, RE = 50, DE = 60
5.5
5.5
4.5
6.2
9
9
mA
mA
mA
mA
8
6.3
178591fb
4
LT1785/LT1785A/
LT1791/LT1791A
SWITCHING CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, ꢀCC = 5ꢀ.
SYMBOL
PARAMETER
CONDITIONS
Figures 3, 5
Figures 3, 5
Figures 3, 5
Figures 3, 5
Figures 4, ±
Figures 4, ±
Figures 4, ±
Figures 4, ±
Figures 3, 7
Figures 3, 7
MIN
TYP
766
766
166
866
566
866
266
866
466
466
266
366
366
466
466
MAX
2666
2666
UNITS
ns
l
l
t
t
t
Driver Input to Output
PLH
Driver Input to Output
ns
PHL
Driver Output to Output
ns
SKEW
l
l
l
l
l
l
l
t , t
Driver Rise or Fall Time
266
2666
3666
3666
5666
5666
966
ns
r
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
966
ns
PHL
Differential Receiver Skew
ns
SKD
l
l
l
l
l
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Receiver Disable from High
Maximum Data Rate
Figures 2, 8
Figures 2, 8
Figures 2, 8
Figures 2, 8
1666
1666
1666
1666
ns
ZL
ns
ZH
ns
LZ
ns
HZ
256
kbps
μs
MAX
Time to Shut Down
Figures 2, ±, 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, ±; RE = 50
Figures 2, ±; RE = 50
Figures 2, 8; DE = 60
Figures 2, 8; DE = 60
μs
μs
μs
4
μs
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
178491fb
5
LT1785/LT1785A/
LT1791/LT1791A
TYPICAL PERFORMANCE CHARACTERISTICS
Driver Differential Output ꢀoltage
vs Load Resistance
Driver Differential Output ꢀoltage
vs Temperature
Receiver Propagation Delay
vs Temperature
3.6
2.5
2.6
1.5
1.6
6.5
6
1666
866
±66
466
266
6
4
3
2
1
6
T
= 25°C
A
t
PHL
t
PLH
R = 27Ω
–46
6
26
46
±6
86 166
–46
6
26
46
±6
86 166
16
166
1k
–26
–26
TEMPERATURE (°C)
TEMPERATURE (°C)
LOAD RESISTANCE (ꢀ)
178591 G61
178591 G62
178591 G63
Driver Propagation Delay
vs Temperature
LT1791 Driver Output Leakage
DE = 0ꢀ
LT1791 Receiver Input Current
vs ꢀIN
1666
966
866
766
±66
566
466
366
266
166
6
LH
HL
1mA/DI0
266μA/DI0
±60
±60
–±60
–±60
0
0
IN
IN
178591 G65
178591 G6±
–46
6
26
46
±6
86 166
–26
TEMPERATURE (°C)
178591 G64
LT1785 Input Characteristics Pins
A or B; DE = RE = 0ꢀ
Receiver Propagation Delay
vs Differential Input ꢀoltage
Supply Current vs Temperature
7
±
5
4
3
2
1
6
766
±66
566
466
366
266
166
6
DRI0ER AND
RECEI0ER ON
HL 0 = –70
CM
HL 0 = 120
CM
RECEI0ER ONLY
1mA/DI0
LH 0 = –70
CM
LH 0 = 120
CM
±60
178591 G67
–±60
0 , 0
A
B
STANDBY
6
3
4
5
1
2
–46
6
26
±6
86 166
46
–26
0
IN
DIFFERENTIAL (0)
TEMPERATURE (°C)
178591 G69
178591 G68
178591fb
6
LT1785/LT1785A/
LT1791/LT1791A
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 266m0. If A ≤ B by 266m0, 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 ±0.
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 ±±60 in both active and high
impedance modes. For CAN applications, output Y is the
CANL output node.
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-
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 tog-
gling between transmit and receive modes of operation.
ForCANbusapplications, REshouldbetiedlowtoprevent
the circuit from entering shutdown.
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 protected from shorts between ±±60 in both active and
high impedance modes. For CAN applications, output Z is
the CANH output node.
A:ReceiverInput.TheAreceiverinputforcesahighreceiver
outputwhen0(A)≥[0(B)+266m0].0(A)≤[0(B)–266m0]
forces a receiver output low. Receiver inputs A and B are
protected against voltage faults between ±±60. The high
input impedance allows up to 128 LT1785 or LT1791
transceivers on one RS485 data bus.
DE: Driver Output Enable. TTL level logic input. A logic
high on DE enables normal operation of the driver out-
puts (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 state. If receiver enable RE and driver enable
DE are both in the disable state, the circuit 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 operation. For CAN bus
operation the DE pin is used for signal input to place the
data bus in dominant or recessive states.
The LT1785A/LT1791A have guaranteed receiver input
thresholds –266m0 < 0 < 6. Receiver outputs are
TH
guaranteed to be in a high state for 60 inputs.
B: Receiver Input. The B receiver input forces a high
receiver output when 0(A) ≥ [0(B) + 266m0]. When
0(A) ≤ [0(B) – 266m0], the B receiver forces a receiver
output low. Receiver inputs A and B are protected against
voltage faults between ±±60. 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 –266m0 < 0 < 6. Receiver outputs are
TH
guaranteed to be in a high state for 60 inputs.
GND: Ground.
ꢀ :PositiveSupplyInput.ForRS422orRS485operation,
CC
4.750 ≤ 0 ≤ 5.250. Higher 0 input voltages increase
CC
CC
output drive swing. 0 should be decoupled with a 6.1μF
CC
low ESR capacitor directly at Pin 8 (0 ).
CC
178491fb
7
LT1785/LT1785A/
LT1791/LT1791A
TEST CIRCUITS
A
S1
S2
TEST POINT
1k
R
RECEI0ER
OUTPUT
0
CC
0
OD
1k
0
C
RL
OC
R
B
1785/91 F62
1785/91 F61
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
50
DE
A
S1
A
B
C
C
L1
L2
DI
0
CC
RO
R
DIFF
566Ω
OUTPUT
UNDER TEST
B
S2
RE
15pF
C
L
1785/91 F64
1785/91 F63
Figure 3. Driver/Receiver Timing Test Circuit
Figure 4. Driver Timing Test Load
FUNCTION TABLES
LT1785 Transmitting
INPUTS
LT1791
OUTPUTS
INPUTS
DI
OUTPUTS
RE
6
DE
1
DI
6
A
6
B
1
RO
RE
6
6
6
6
6
6
6
6
6
1
1
1
DE
6
6
6
1
1
1
1
1
1
6
1
1
A-B
≤ –266m0
≥ 266m0*
Open
Y
Hi-Z
Hi-Z
Hi-Z
6
Z
RO
6
6
X
X
X
6
6
6
1
1
1
X
6
1
Hi-Z
Hi-Z
Hi-Z
1
6
1
1
1
6
1
1
1
6
X
6
Hi-Z
6
Hi-Z
1
Hi-Z
Hi-Z
Hi-Z
1
1
1
≤ –266m0
≥ 266m0*
Open
6
1
1
1
1
6
6
1
1
6
1
1
LT1785 Receiving
INPUTS
≤ –266m0
≥ 266m0*
Open
1
6
6
OUTPUT
1
6
1
RE
6
DE
6
DI
X
A-B
RO
6
1
6
1
≤ –266m0
≥ 266m0*
Open
X
Hi-Z
6
Hi-Z
1
Hi-Z
Hi-Z
Hi-Z
6
6
X
1
X
6
6
X
1
X
1
6
1
6
X
X
Hi-Z
* ≥ 6m0 for LT1791A
* ≥ 6m0 for LT1785A
178591fb
8
LT1785/LT1785A/
LT1791/LT1791A
SWITCHING TIME WAVEFORMS
50
f = 125kHz, t ≤ 16ns, t ≤ 16ns
DI
1.50
1.50
r
f
60
B
1/2 0
O
t
t
PHL
PLH
0
O
A
t
t
SKEW
1/2 0
SKEW
O
0
O
96%
16%
96%
0
DIFF
= 0(A) – 0(B)
60
16%
–0
O
t
r
t
f
1785/91 F65
Figure 5. Driver Propagation Delays
50
60
50
f = 125kHz, t ≤ 16ns, t ≤ 16ns
1.50
1.50
DE
A, B
A, B
r
f
t
t
, t
LZ
ZL(SHDN) ZL
2.30
OUTPUT NORMALLY LOW
6.50
6.50
0
OL
OH
60
0
OUTPUT NORMALLY HIGH
, t
2.30
t
t
178591 F6±
HZ
ZH(SHDN) ZH
Figure ±. Driver Enable and Disable Times
0
OH
1.50
1.50
RO
OUTPUT
0
OL
OD2
OD2
t
f = 125kHz, t ≤ 16ns, t ≤ 16ns
t
PHL
r
f
PLH
0
A – B
–0
60
60
INPUT
178591 F67
Figure 7. Receiver Propagation Delays
50
60
50
1.50
1.50
RE
RO
RO
f = 125kHz, t ≤ 16ns, t ≤ 16ns
r
f
t
, t
t
LZ
ZL(SHDN) ZL
1.50
OUTPUT NORMALLY LOW
6.50
6.50
OUTPUT NORMALLY HIGH
, t
1.50
t
60
t
HZ
178591 F68
ZH(SHDN) ZH
Figure 8. Receiver Enable and Disable Times
178491fb
9
LT1785/LT1785A/
LT1791/LT1791A
APPLICATIONS INFORMATION
Overvoltage Protection
LT1785 pins A and B and the LT1791 driver output pins Y
andZareprotectedtoIEC-1666-4-2level2.Thesepinswill
survivemultipleESDstrikesof±15k0airdischargeor±4k0
contactdischarge.Duetotheirveryhighinputimpedance,
the LT1791 receiver pins are protected to IEC-1666-4-2
level 2, or ±15k0 air and ±4k0 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.
TheLT1785/LT1791RS485/RS422transceiversansweran
applications need for overvoltage fault tolerance on data
networks. Industrialinstallationsmayencountercommon
mode voltages between nodes far greater than the –70 to
120 range specified for compliance to RS485 standards.
CMOS RS485 transceivers can be damaged by voltages
above their absolute maximum ratings of typically –80
to 12.50. Replacement of standard RS485 transceiver
componentswiththeLT1785orLT1791deviceseliminates
field failures due to overvoltage faults or the use of costly
external protection devices. The limited overvoltage toler-
anceofCMOSRS485transceiversmakesimplementation
of effective external protection networks difficult without
interfering with proper data network performance within
the –70 to 120 region of RS485 operation.
Low Power Shutdown
TheLT1785/LT1791haveREandDElogicinputstocontrol
the receive and transmit modes of the transceivers. The
RE input allows normal data reception when in the low
state. The receiver output goes to a high impedance state
when RE is high, allowing multiplexing the RO data line.
TheDElogicinputperformsasimilarfunctiononthedriver
outputs. A high state on DE activates the differential driver
outputs, a low state places both driver outputs in to high
impedance. TyingtheREandDElogicinputstogethermay
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 ±±60 can be added
to the device to extend protection to any desired level.
Figure 11 shows a protection network against faults to
the1260AC line voltage.
The LT1785/LT1791 protection is achieved by using a high
voltagebipolarintegratedcircuitprocessforthetransceiv-
ers. 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 overvoltage faults
while still allowing high current output drive.
Disabling both the driver and receiver places the device
into a low supply current shutdown mode. An internal
time 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
256kbaud 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
exposedportsandcablesinapplicationenvironments.The
178591fb
10
LT1785/LT1785A/
LT1791/LT1791A
APPLICATIONS INFORMATION
Slew Limiting for EMI Emissions Control
Data Network Cable Selection and Termination
The LT1785/LT1791 feature controlled driver output slew
ratestocontrolhighfrequencyEMIemissionsfromequip-
ment and data cables. The slew limiting limits data rate
operation to 256kbaud. Slew limiting also mitigates the
adverse affects of imperfect transmission line termina-
tion 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.
Long distance data networks operating at high data trans-
mission rates should use high quality, low attenuation
cablewithwell-matchedcableterminations.Shortdistance
networks at low data rates may use much less expensive
P0C cable. These cables have characteristic impedances
as low as 72Ω. The LT1785/LT1791 output drivers are
guaranteed to drive cables as low as 72ꢀ.
12
11
A
B
12
11
A
B
5
2
126Ω
RX
DI
RO
TX
3
4
4
3
RE
DE
LT1791
LT1791
DE
RE
Z
16
9
16
9
Z
2
5
126Ω
TX
RO
DI
RX
Y
Y
178591 F69
Figure 9. Full-Duplex RS422
178491fb
11
LT1785/LT1785A/
LT1791/LT1791A
PACKAGE DESCRIPTION
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 65-68-1516)
.400*
(10.160)
MAX
8
7
6
5
4
.255 ± .015*
(6.477 ± 0.381)
1
2
3
.130 ± .005
.300 – .325
.045 – .065
(3.302 ± 0.127)
(1.143 – 1.651)
(7.620 – 8.255)
.065
(1.651)
TYP
.008 – .015
(0.203 – 0.381)
.120
.020
(0.508)
MIN
(3.048)
MIN
+.035
.325
–.015
.018 ± .003
(0.457 ± 0.076)
.100
(2.54)
BSC
+0.889
8.255
(
)
N8 1002
–0.381
NOTE:
INCHES
MILLIMETERS
1. DIMENSIONS ARE
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
178591fb
12
LT1785/LT1785A/
LT1791/LT1791A
PACKAGE DESCRIPTION
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 65-68-1±16)
.189 – .197
(4.801 – 5.004)
.045 ±.005
.160 ±.005
NOTE 3
.050 BSC
7
5
8
6
.245
MIN
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
3
4
2
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
INCHES
1. DIMENSIONS IN
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
SO8 0303
178491fb
13
LT1785/LT1785A/
LT1791/LT1791A
PACKAGE DESCRIPTION
N Package
14-Lead PDIP (Narrow 0.300)
(LTC DWG # 65-68-1516)
.770*
(19.558)
MAX
14
13
12
11
10
9
8
7
.255 ± .015*
(6.477 ± 0.381)
1
2
3
5
6
4
.300 – .325
(7.620 – 8.255)
.045 – .065
(1.143 – 1.651)
.130 ± .005
(3.302 ± 0.127)
.020
(0.508)
MIN
.065
(1.651)
TYP
.008 – .015
(0.203 – 0.381)
+.035
.325
.005
(0.127)
MIN
–.015
.120
(3.048)
MIN
.018 ± .003
.100
(2.54)
BSC
+0.889
8.255
(0.457 ± 0.076)
(
)
–0.381
N14 1103
NOTE:
INCHES
MILLIMETERS
1. DIMENSIONS ARE
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
178591fb
14
LT1785/LT1785A/
LT1791/LT1791A
PACKAGE DESCRIPTION
S Package
14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 65-68-1±16)
.337 – .344
.045 ±.005
(8.560 – 8.738)
.050 BSC
N
NOTE 3
13
12
11
10
8
14
N
9
.245
MIN
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
1
2
3
N/2
N/2
7
.030 ±.005
TYP
RECOMMENDED SOLDER PAD LAYOUT
1
2
3
4
5
6
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0° – 8° TYP
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
.016 – .050
(0.406 – 1.270)
S14 0502
NOTE:
1. DIMENSIONS IN
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
178491fb
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LT1785/LT1785A/
LT1791/LT1791A
TYPICAL APPLICATION
R
R
T
126Ω
1
1
T
RO
RO
RX
RX
126Ω
7
±
B
A
7
±
B
A
2
3
2
3
RE
RE
LT1785
LT1785
DE
DE
±
A
7
B
±
A
7
B
4
4
DI
DI
TX
TX
178591 F16
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
TR±66-156
0
CC
1
× 2
RO
47Ω
RX
7
B
A
2
3
R ,126Ω
T
RE
LT1785
DE
±
5
178591 F11
6.1μF
3660
47Ω
CARBON
4
DI
TX
COMPOSITE
5W
1.5KE3±CA
Figure 11. RS485 Network with 120ꢀ AC Line Fault Protection
RELATED PARTS
PART NUMBER
LTC485
DESCRIPTION
COMMENTS
Low Power RS485 Interface Transceiver
Differential Driver and Receiver Pair
I
CC
CC
= 366μA (Typ)
= 366μA
LTC491
I
LTC1483
LTC1485
LTC1487
LTC1526
LTC1535
LTC1±85
LTC1±87
Ultralow Power RS485 Low EMI Transceiver
Differential Bus Transceiver
Controlled Driver Slew Rate
16Mbaud Operation
Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance
56Mbps Precision Quad Line Receiver
Up to 25± Transceivers on the Bus
Channel-to-Channel Skew 466ps (Typ)
Isolated RS485 Full-Duplex Transceiver
52Mbps RS485 Half-Duplex Transceiver
52Mbps RS485 Full-Duplex Transceiver
25660
Isolation in Surface Mount Package
RMS
Propagation Delay Skew 566ps (Typ)
Propagation Delay Skew 566ps (Typ)
178591fb
LT 0608 REV B • PRINTED IN USA
LinearTechnology Corporation
1±36 McCarthy Blvd., Milpitas, CA 95635-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 1998
(468) 432-1966 FAX: (468) 434-6567 www.linear.com
相关型号：
LT1785AHN8#PBF
LT1785 - 60V Fault Protected RS485/RS422 Transceivers; Package: PDIP; Pins: 8; Temperature Range: -40°C to 125°C
Linear
LT1785AHN8#TR
IC LINE TRANSCEIVER, PDIP8, 0.300 INCH, PLASTIC, DIP-8, Line Driver or Receiver
Linear
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