LINER LT1785I 60v fault protected rs485/rs422 transceiver Datasheet

LT1785/LT1785A
LT1791/LT1791A
60V Fault Protected
RS485/RS422 Transceivers
U
FEATURES
■
■
■
■
■
■
■
■
■
■
DESCRIPTIO
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
U
APPLICATIO S
■
■
■
The LT®1785/LT1791 are half-duplex and full-duplex differential 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 ±60V
with respect to ground with no damage to the device.
Faults may occur while the transceiver is active, shut down
or powered off.
Data rates to 250kbaud on networks of up to 128 nodes are
supported. Controlled slew rates on the driver outputs
control EMI emissions and improve data transmission
integrity on improperly terminated lines. Drivers are specified to operate with inexpensive cables as low as 72Ω
characteristic impedance.
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 eliminates 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
packages and the LT1791/LT1791A in 14-lead DIP and SO
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATIO
Normal Operation Waveforms at 250kBaud
VCC1
RO1
RE1
DE1
RX
LT1785
RTERM
RO
DI1
TX
GND1
Y-Z
VCC2
RO2
RE2
DE2
DI2
RX
LT1785
DI
RTERM
TX
1785/91 TA02
GND2
1785/91 TA01
1
LT1785/LT1785A
LT1791/LT1791A
W W
W
AXI U
U
ABSOLUTE
RATI GS
(Note 1)
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
U
W
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
RO 1
R
RE 2
DE 3
DI 4
N8 PACKAGE
8-LEAD PDIP
D
8
VCC
7
B
6
A
5
GND
LT1785CN8
LT1785CS8
LT1785IN8
LT1785IS8
LT1785ACN8
LT1785ACS8
S8 PACKAGE
8-LEAD PLASTIC SO
ORDER PART
NUMBER
TOP VIEW
RO 2
Consult factory for Military grade parts.
2
R
13 NC
RE 3
12 A
DE 4
11 B
10 Z
DI 5
GND 6
GND 7
N PACKAGE
14-LEAD PDIP
TJMAX = 150°C, θJA = 130°C/ W (N8)
TJMAX = 150°C, θJA = 150°C/ W (S8)
14 VCC
NC 1
D
9
Y
8
NC
S PACKAGE
14-LEAD PLASTIC SO
S8 PART MARKING
1785
1785I
1785A
TJMAX = 150°C, θJA = 130°C/ W (N)
TJMAX = 150°C, θJA = 150°C/ W (S)
LT1791CN
LT1791CS
LT1791IN
LT1791IS
LT1791ACN
LT1791ACS
LT1785/LT1785A
LT1791/LT1791A
DC ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C, VCC = 5V.
SYMBOL
PARAMETER
CONDITIONS
VOD1
Differential Driver Output Voltage (Unloaded)
IO = 0
●
VOD2
Differential Driver Output Voltage (With Load)
R = 50Ω (RS422), Figure 1
R = 27Ω (RS485), Figure 1
R = 18Ω
●
●
●
∆VOD
Change in Magnitude of Driver Differential Output
Voltage for Complementary Output States
R = 27Ω or R = 50Ω, Figure 1
●
VOC
Driver Common Mode Output Voltage
R = 27Ω or R = 50Ω, Figure 1
●
∆VOC
Change in Magnitude of Driver Common Mode
Output Voltage for Complementary Output States
R = 27Ω or R = 50Ω, Figure 1
●
VIH
Input High Voltage
DI, DE, RE
●
VIL
Input Low Voltage
DI, DE, RE
●
IIN1
Input Current
DI, DE, RE
●
IIN2
Input Current (A, B); (LT1791 or LT1785 with
DE = 0V)
VIN = 12V
VIN = – 7V
– 60V ≤ VIN ≤ 60V
●
●
●
– 0.15
–6
VTH
Differential Input Threshold Voltage for Receiver
LT1785/LT1791: – 7V ≤ VCM ≤ 12V
LT1785A/LT1791A: – 7V ≤ VCM ≤ 12V
●
●
– 0.2
– 0.2
∆VTH
Receiver Input Hysteresis
– 7V < VCM < 12V
VOH
Receiver Output High Voltage
IO = – 400µA, VID = 200mV
●
VOL
Receiver Output Low Voltage
IO = 1.6mA, VID = – 200mV
●
Three-State (High Impedance) Output Current
at Receiver 0V < VOUT < 6V
RE > 2V or Power Off
●
–1
Receiver Input Resistance (LT1791)
– 7V ≤ VCM ≤ 12V
– 60V ≤ VCM ≤ 60V
●
85
125
125
LT1785
– 7V ≤ VCM ≤ 12V
●
50
90
RIN
MIN
2.0
1.5
1.2
2
TYP
MAX
4.1
5
2.70
2.45
2.2
2.5
ICC
0.2
V
3
V
0.2
V
V
0.8
0.15
– 0.08
5
µA
mA
mA
mA
6
20
V
V
mV
4
0.3
V
0.3
0.2
0
RS485 Unit Load
ISC
V
V
V
V
2
3.5
UNITS
V
0.5
V
1
µA
kΩ
kΩ
kΩ
0.25
Driver Short-Circuit Current
VOUT = HIGH, Force VO = – 7V
VOUT = LOW, Force VO = 12V
●
●
35
35
Driver Output Fault Current
VO = 60V
VO = – 60V
●
●
–6
Receiver Short-Circuit Current
0V ≤ VO ≤ VCC
●
Driver Three-State Output Current
–7V ≤ VO ≤ 12V
– 60V ≤ VO ≤ 60V
●
●
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
●
●
●
●
– 0.2
–6
5.5
5.5
4.5
0.2
250
250
mA
mA
6
mA
mA
±30
mA
0.3
6
mA
mA
9
9
8
0.3
mA
mA
mA
mA
3
LT1785/LT1785A
LT1791/LT1791A
U
SWITCHI G CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C, VCC = 5V.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
tPLH
Driver Input to Output
Figures 3, 5
●
700
2000
ns
tPHL
Driver Input to Output
Figures 3, 5
tSKEW
Driver Output to Output
Figures 3, 5
●
700
2000
ns
tr, tf
Driver Rise or Fall Time
Figures 3, 5
●
tZH
Driver Enable to Output High
Figures 4, 6
tZL
Driver Enable to Output Low
Figures 4, 6
tLZ
Driver Disable Time from Low
tHZ
tPLH
100
200
ns
800
2000
ns
●
500
3000
ns
●
800
3000
ns
Figures 4, 6
●
200
5000
ns
Driver Disable Time from High
Figures 4, 6
●
800
5000
ns
Receiver Input to Output
Figures 3, 7
●
400
900
ns
tPHL
Receiver Input to Output
Figures 3, 7
●
400
900
ns
tSKD
Differential Receiver Skew
tZL
Receiver Enable to Output Low
Figures 2, 8
●
300
1000
ns
tZH
Receiver Enable to Output High
Figures 2, 8
●
300
1000
ns
tLZ
Receiver Disable from Low
Figures 2, 8
●
400
1000
ns
tHZ
Receiver Disable from High
Figures 2, 8
●
400
1000
ns
fMAX
Maximum Data Rate
tSHDN
Time to Shut Down
Figures 2, 6, 8
3
µs
tZH(SHDN)
Driver Enable from Shutdown to Output High
Figures 2, 6; RE = 5V
12
µs
tZL(SHDN)
Driver Enable from Shutdown to Output Low
Figures 2, 6; RE = 5V
12
µs
tZH(SHDN)
Receiver Enable from Shutdown to Output High
Figures 2, 8; DE = 0V
4
µs
tZL(SHDN)
Receiver Enable from Shutdown to Output Low
Figures 2, 8; DE = 0V
4
µs
200
ns
250
●
kbps
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
Receiver Propagation Delay
vs Temperature
Driver Differential Output Voltage
vs Temperature
3.0
4
1000
TA = 25°C
2
1
2.0
1.5
10
100
LOAD RESISTANCE (Ω)
1k
600
tPLH
400
1.0
200
0.5
0
tPHL
800
DELAY (ns)
DIFFERENTIAL VOLTAGE (V)
OUTPUT VOLTAGE (V)
2.5
3
R = 27Ω
0
–40 –20
40
20
0
60
TEMPERATURE (°C)
80
100
0
–40
–20
40
0
60
20
TEMPERATURE (°C)
80
100
1785/91 G01
1785/91 G03
4
1785/91 G03
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
PROPAGATION DELAY (ns)
900
800
LH
700
1mA/DIV
600
200µA/DIV
HL
500
400
300
200
– 60V
100
0
–40
60V
VOUT
40
0
60
20
TEMPERATURE (°C)
–20
80
– 60V
60V
VIN
1785/91 G05
1785/91 G06
100
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
700
DRIVER AND
RECEIVER ON
600
HL VCM = –7V
5
4
RECEIVER ONLY
DELAY (ns)
ICC (mA)
1mA/DIV
3
2
– 60V
60V
VA, VB
HL VCM = 12V
500
0
–40
LH VCM = –7V
300
LH VCM = 12V
200
1
1785/91 G07
400
100
STANDBY
–20
40
0
60
20
TEMPERATURE (°C)
80
100
1785/91 G08
0
0
1
3
4
2
VIN DIFFERENTIAL (V)
5
1785/91 G09
U
U
U
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.
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
toggling between transmit and receive modes of operation. For CAN bus applications, RE should be tied low to
prevent the circuit from entering shutdown.
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
U
PIN FUNCTIONS
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.
protected from shorts between ±60V in both active and
high impedance modes. For CAN applications, output Z is
the CANH output node.
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.
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 protected from shorts between ±60V in both active and high
impedance modes. For CAN applications, output Y is the
CANL output node.
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
A: Receiver Input. The A receiver input forces a high
receiver output when V(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.
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
to 128 LT1785 or LT1791 transceivers on one RS485␣ data
bus.
The LT1785A/LT1791A have guaranteed receiver input
thresholds –200mV < VTH < 0. Receiver outputs are
guaranteed to be in a high state for 0V inputs.
VCC: Positive Supply Input. For RS422 or RS485␣ 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
R
RECEIVER
OUTPUT
VOD
R
VOC
S1
TEST POINT
1k
VCC
CRL
1k
S2
B
1785/91 F01
Figure 1. Driver DC Test Load
6
1785/91 F02
Figure 2. Receiver Timing Test Load
LT1785/LT1785A
LT1791/LT1791A
TEST CIRCUITS
5V
DE
A
S1
A
CL1
DI
RO
RDIFF
B
CL2
15pF
RE
VCC
500Ω
OUTPUT
UNDER TEST
B
S2
CL
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
RE
DE
INPUTS
OUTPUTS
DI
A
B
OUTPUTS
RO
RE
DE
DI
A-B
Y
Z
RO
0
X
≤ – 200mV
Hi-Z
Hi-Z
0
≥ 200mV*
Hi-Z
Hi-Z
1
0
1
0
0
1
0
0
0
1
1
1
0
1
0
0
X
1
0
X
Hi-Z
Hi-Z
Hi-Z
0
0
X
Open
Hi-Z
Hi-Z
1
1
0
≤ – 200mV
0
1
0
0
≥ 200mV*
0
1
1
1
1
0
0
1
Hi-Z
0
1
1
1
1
0
Hi-Z
0
1
0
1
0
Open
0
1
1
0
1
1
≤ – 200mV
1
0
0
0
1
1
≥ 200mV*
1
0
1
0
1
1
Open
1
0
1
1
0
X
X
Hi-Z
Hi-Z
Hi-Z
1
1
0
X
0
1
Hi-Z
1
1
1
X
1
0
Hi-Z
LT1785 Receiving
INPUTS
OUTPUT
RE
DE
DI
A-B
RO
0
0
X
≤ – 200mV
0
0
0
X
≥200mV*
1
0
0
X
Open
1
1
0
X
X
Hi-Z
* ≥ 0mV for LT1785A
* ≥ 0mV for LT1791A
U
W
W
SWITCHI G TI E WAVEFOR S
5V
f = 125kHz, t r ≤ 10ns, t f ≤ 10ns
1.5V
DI
1.5V
0V
t PLH
1/2 VO
t PHL
B
VO
A
VO
0V
–VO
tSKEW
1/2 VO
90%
10%
t SKEW
90%
10%
VDIFF = V(A) – V(B)
tr
tf
1785/91 F05
Figure 5. Driver Propagation Delays
7
LT1785/LT1785A
LT1791/LT1791A
U
W
W
SWITCHI G TI E WAVEFOR S
5V
f = 125kHz, t r ≤ 10ns, t f ≤ 10ns
1.5V
DE
1.5V
0V
t LZ
t ZL(SHDN), t ZL
5V
A, B
2.3V
OUTPUT NORMALLY LOW
0.5V
2.3V
OUTPUT NORMALLY HIGH
0.5V
VOL
VOH
A, B
0V
t HZ
t ZH(SHDN), t ZH
1785/91 F06
Figure 6. Driver Enable and Disable Times
VOH
1.5V
RO
VOL
f = 125kHz, t r ≤ 10ns, t f ≤ 10ns
t PHL
VOD2
A–B
–VOD2
1.5V
OUTPUT
0V
t PLH
0V
INPUT
1785/91 F07
Figure 7. Receiver Propagation Delays
5V
1.5V
RE
t ZL(SHDN), tZL
5V
1.5V
f = 125kHz, tr ≤ 10ns, tf ≤ 10ns
0V
t LZ
RO
1.5V
OUTPUT NORMALLY LOW
0.5V
RO
1.5V
OUTPUT NORMALLY HIGH
0.5V
0V
t ZH(SHDN), tZH
t HZ
1785/91 F08
Figure 8. Receiver Enable and Disable Times
U U
W
U
APPLICATIO S I FOR ATIO
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
cally – 8V to 12.5V. Replacement of standard RS485
transceiver components with the LT1785 or LT1791
devices eliminates field failures due to overvoltage faults
or the use of costly external protection devices. The limited
overvoltage tolerance of CMOS RS485 transceivers makes
implementation of effective external protection networks
difficult without interfering with proper data network
performance within the – 7V to 12V region of RS485
operation.
LT1785/LT1785A
LT1791/LT1791A
U U
W
U
APPLICATIO S I FOR ATIO
The high overvoltage rating of the LT1785/LT1791 facilitates 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.
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 together 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 LT1785/LT1791 protection is achieved by using a high
voltage bipolar integrated circuit process for the transceivers. 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
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 discharge 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.
Low Power Shutdown
The LT1785/LT1791 have RE and DE logic inputs to
control 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
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 termination 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 transmission rates should use high quality, low attenuation
cable with well-matched cable terminations. Short distance 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.
9
LT1785/LT1785A
LT1791/LT1791A
U U
W
U
APPLICATIO S I FOR ATIO
A 12
RO
RE
DE
2
RX
12 A
120Ω
B 11
3
DI
4
4
LT1791
LT1791
5
TX
DE
3
RE
10 Z
Z 10
DI
5
TX
11 B
120Ω
Y 9
9 Y
2
RX
RO
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)
0.300 – 0.325
(7.620 – 8.255)
0.009 – 0.015
(0.229 – 0.381)
(
+0.035
0.325 –0.015
8.255
+0.889
–0.381
)
0.400*
(10.160)
MAX
0.130 ± 0.005
(3.302 ± 0.127)
0.045 – 0.065
(1.143 – 1.651)
0.065
(1.651)
TYP
8
7
6
5
1
2
3
4
0.255 ± 0.015*
(6.477 ± 0.381)
0.125
(3.175) 0.020
MIN
(0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
0.100 ± 0.010
(2.540 ± 0.254)
N8 1197
*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)
0.010 – 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)
0.189 – 0.197*
(4.801 – 5.004)
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
8
7
6
5
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
1
10
2
3
4
SO8 0996
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
1
2
3
4
5
6
7
0.255 ± 0.015*
(6.477 ± 0.381)
0.130 ± 0.005
(3.302 ± 0.127)
0.300 – 0.325
(7.620 – 8.255)
0.045 – 0.065
(1.143 – 1.651)
0.020
(0.508)
MIN
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
+0.035
0.325 –0.015
0.005
(0.125)
MIN
0.100 ± 0.010
(2.540 ± 0.254)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
(
+0.889
8.255
–0.381
)
0.018 ± 0.003
(0.457 ± 0.076)
0.125
(3.175)
MIN
N14 1197
S Package
14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.337 – 0.344*
(8.560 – 8.738)
14
13
12
11
10
9
8
0.228 – 0.244
(5.791 – 6.197)
0.150 – 0.157**
(3.810 – 3.988)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
2
3
4
5
6
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0° – 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
7
0.050
(1.270)
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
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 circuits as described herein will not infringe on existing patent rights.
S14 0695
11
LT1785/LT1785A
LT1791/LT1791A
U
TYPICAL APPLICATIONS
RO
RE
DE
DI
1
RX
RT
120Ω
B 7
RT
120Ω
7 B
RX
2
2
3
4
1
6 A
A 6
LT1785
6
A
TX
6
A
7
B
7
B
LT1785
TX
3
4
RO
RE
DE
DI
1785/91 F10
LT1785
4
3
DI
DE
LT1785
2
RE
1
RO
4
DI
3
DE
1
2
RE
RO
Figure 10. Half-Duplex RS485 Network Operation
8
RO
RE
DE
DI
1
RX
RAYCHEM
POLYSWITCH
TR600-150
×2
47Ω
VCC
B 7
2
3
4
RT,120Ω
LT1785
A 6
1785/91 F11
0.1µF
47Ω
300V
CARBON
COMPOSITE
5W
5
TX
1.5KE36CA
Figure 11. RS485 Network with 120V AC Line Fault Protection
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC485
Low Power RS485 Interface Transceiver
ICC = 300µA (Typ)
LTC491
Differential Driver and Receiver Pair
ICC = 300µA
LTC1483
Ultralow Power RS485 Low EMI Transceiver
Controlled Driver Slew Rate
LTC1485
Differential Bus Transceiver
10Mbaud Operation
LTC1487
Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance
Up to 256 Transceivers on the Bus
LTC1520
50Mbps Precision Quad Line Receiver
Channel-to-Channel Skew 400ps (Typ)
LTC1535
Isolated RS485 Full-Duplex Transceiver
2500VRMS Isolation in Surface Mount Package
LTC1685
52Mbps RS485 Half-Duplex Transceiver
Propagation Delay Skew 500ps (Typ)
LTC1687
52Mbps RS485 Full-Duplex Transceiver
Propagation Delay Skew 500ps (Typ)
12
Linear Technology Corporation
178591f LT/TP 0300 4K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1998