Page 1
U
FEATURES
■
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
■
Industrial Control Data Networks
■
CAN Bus Applications
■
HVAC Controls
LT1785/LT1785A
LT1791/LT1791A
60V Fault Protected
RS485/RS422 Transceivers
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.
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.
TYPICAL APPLICATIO
RO1
RE1
DE1
DI1
RO2
RE2
DE2
DI2
RX
LT1785
TX
RX
LT1785
TX
V
CC1
R
GND1
V
CC2
R
GND2
U
TERM
TERM
Normal Operation Waveforms at 250kBaud
RO
Y-Z
DI
1785/91 TA02
1785/91 TA01
1
Page 2
LT1785/LT1785A
TOP VIEW
N PACKAGE
14-LEAD PDIP
S PACKAGE
14-LEAD PLASTIC SO
1
2
3
4
5
6
7
14
13
12
11
10
9
8
NC
RO
RE
DE
DI
GND
GND
V
CC
NC
A
B
Z
Y
NC
R
D
LT1791/LT1791A
A
W
O
LUTEXI TIS
S
A
WUW
U
ARB
G
(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)
WU
/
1
2
3
4
O
RDER I FOR ATIO
ORDER PART
TOP VIEW
R
D
S8 PACKAGE
8-LEAD PLASTIC SO
V
8
CC
B
7
A
6
GND
5
LT1785CN8
LT1785CS8
LT1785IN8
LT1785IS8
LT1785ACN8
LT1785ACS8
NUMBER
PACKAGE
RO
RE
DE
DI
N8 PACKAGE
8-LEAD PDIP
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
ORDER PART
NUMBER
LT1791CN
LT1791CS
LT1791IN
LT1791IS
LT1791ACN
LT1791ACS
T
= 150°C, θ
JMAX
= 150°C, θ
T
JMAX
Consult factory for Military grade parts.
= 130°C/ W (N8)
JA
= 150°C/ W (S8)
JA
2
S8 PART MARKING
1785
1785I
1785A
T
T
JMAX
JMAX
= 150°C, θ
= 150°C, θ
= 130°C/ W (N)
JA
= 150°C/ W (S)
JA
Page 3
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 MIN TYP MAX UNITS
V
OD1
V
OD2
∆V
V
OC
∆V
V
IH
V
IL
I
IN1
I
IN2
V
TH
∆V
V
OH
V
OL
R
IN
I
SC
I
CC
OD
TH
Differential Driver Output Voltage (Unloaded) IO = 0 ● 4.1 5 V
Differential Driver Output Voltage (With Load) R = 50Ω (RS422), Figure 1 ● 2.0 2.70 V
R = 27Ω (RS485), Figure 1
R = 18Ω
● 1.5 2.45 V
● 1.2 2.2 V
Change in Magnitude of Driver Differential Output R = 27Ω or R = 50Ω, Figure 1 ● 0.2 V
Voltage for Complementary Output States
Driver Common Mode Output Voltage R = 27Ω or R = 50Ω, Figure 1 ● 2 2.5 3 V
Change in Magnitude of Driver Common Mode R = 27Ω or R = 50Ω, Figure 1 ● 0.2 V
OC
Output Voltage for Complementary Output States
Input High Voltage DI, DE, RE ● 2V
Input Low Voltage DI, DE, RE ● 0.8 V
Input Current DI, DE, RE ● 5 µA
Input Current (A, B); (LT1791 or LT1785 with VIN = 12V ● 0.15 0.3 mA
DE = 0V) V
= –7V ● –0.15 –0.08 mA
IN
–60V ≤ V
≤ 60V ● –6 6 mA
IN
Differential Input Threshold Voltage for Receiver LT1785/LT1791: –7V ≤ VCM ≤ 12V ● –0.2 0.2 V
LT1785A/LT1791A: –7V ≤ V
≤ 12V ● –0.2 0 V
CM
Receiver Input Hysteresis –7V < VCM < 12V 20 mV
Receiver Output High Voltage IO = –400µA, VID = 200mV ● 3.5 4 V
Receiver Output Low Voltage IO = 1.6mA, VID = –200mV ● 0.3 0.5 V
Three-State (High Impedance) Output Current RE > 2V or Power Off ● –1 1 µA
at Receiver 0V < V
OUT
< 6V
Receiver Input Resistance (LT1791) –7V ≤ VCM ≤ 12V ● 85 125 kΩ
– 60V ≤ V
≤ 60V 125 kΩ
CM
LT1785 –7V ≤ VCM ≤ 12V ● 50 90 kΩ
RS485 Unit Load 0.25
Driver Short-Circuit Current V
= HIGH, Force VO = –7V ● 35 250 mA
OUT
= LOW, Force VO = 12V ● 35 250 mA
V
OUT
Driver Output Fault Current VO = 60V ● 6mA
= –60V ● –6 mA
V
O
Receiver Short-Circuit Current 0V ≤ VO ≤ V
CC
● ±30 mA
Driver Three-State Output Current –7V ≤ VO ≤ 12V ● –0.2 0.3 mA
–60V ≤ V
≤ 60V ● –6 6 mA
O
Supply Current No Load, RE = 0V, DE = 5V ● 5.5 9 mA
No Load, RE = 5V, DE = 5V
No Load, RE = 0V, DE = 0V
No Load, RE = 5V, DE = 0V
● 5.5 9 mA
● 4.5 8 mA
● 0.2 0.3 mA
3
Page 4
LT1785/LT1785A
TEMPERATURE (°C)
–40
DELAY (ns)
1000
800
600
400
200
0
0
40
60
1785/91 G03
–20
20
80
100
t
PLH
t
PHL
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
t
PLH
t
PHL
t
SKEW
tr, t
f
t
ZH
t
ZL
t
LZ
t
HZ
t
PLH
t
PHL
t
SKD
t
ZL
t
ZH
t
LZ
t
HZ
f
MAX
t
SHDN
t
ZH(SHDN)
t
ZL(SHDN)
t
ZH(SHDN)
t
ZL(SHDN)
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Driver Input to Output Figures 3, 5 ● 700 2000 ns
Driver Input to Output Figures 3, 5 ● 700 2000 ns
Driver Output to Output Figures 3, 5 100 ns
Driver Rise or Fall Time Figures 3, 5 ● 200 800 2000 ns
Driver Enable to Output High Figures 4, 6 ● 500 3000 ns
Driver Enable to Output Low Figures 4, 6 ● 800 3000 ns
Driver Disable Time from Low 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
Receiver Input to Output Figures 3, 7 ● 400 900 ns
Differential Receiver Skew 200 ns
Receiver Enable to Output Low Figures 2, 8 ● 300 1000 ns
Receiver Enable to Output High Figures 2, 8 ● 300 1000 ns
Receiver Disable from Low Figures 2, 8 ● 400 1000 ns
Receiver Disable from High Figures 2, 8 ● 400 1000 ns
Maximum Data Rate ● 250 kbps
Time to Shut Down Figures 2, 6, 8 3 µs
Driver Enable from Shutdown to Output High Figures 2, 6; RE = 5V 12 µs
Driver Enable from Shutdown to Output Low Figures 2, 6; RE = 5V 12 µs
Receiver Enable from Shutdown to Output High Figures 2, 8; DE = 0V 4 µs
Receiver Enable from Shutdown to Output Low Figures 2, 8; DE = 0V 4 µs
UW
TYPICAL PERFORMANCE CHARACTERISTICS
Driver Differential Output Voltage
vs Load Resistance
4
TA = 25°C
3
2
OUTPUT VOLTAGE (V)
4
1
0
10
LOAD RESISTANCE (Ω)
100 1k
1785/91 G01
Driver Differential Output Voltage
vs Temperature
3.0
2.5
2.0
1.5
1.0
DIFFERENTIAL VOLTAGE (V)
0.5
R = 27Ω
0
–40
–20
0
TEMPERATURE (°C)
40
20
60
80
1785/91 G03
Receiver Propagation Delay
vs Temperature
100
Page 5
UW
TYPICAL PERFORMANCE CHARACTERISTICS
LT1785/LT1785A
LT1791/LT1791A
Driver Propagation Delay
vs Temperature
1000
900
800
700
600
500
400
300
PROPAGATION DELAY (ns)
200
100
0
–40
–20
LH
HL
0
TEMPERATURE (°C)
40
20
60
LT1785 Input Characteristics
Pins A or B; DE = RE = 0V
1mA/DIV
–60V 60V
1785/91 G07
V
A, VB
80
1785/91 G04
100
LT1791 Driver Output Leakage
DE = 0V
1mA/DIV
–60V 60V
V
1785/91 G05
OUT
Supply Current vs Temperature
7
DRIVER AND
6
RECEIVER ON
5
RECEIVER ONLY
4
(mA)
CC
3
I
2
1
STANDBY
0
–40
0
–20
TEMPERATURE (°C)
40
20
LT1791 Receiver Input Current
vs V
IN
200µA/DIV
–60V 60V
1785/91 G06
V
IN
Receiver Propagation Delay
vs Differential Input Voltage
700
600
LH VCM = 12V
0
0
HL VCM = 12V
1
VIN DIFFERENTIAL (V)
500
400
300
DELAY (ns)
200
100
80
1785/91 G08
100
60
HL VCM = –7V
LH VCM = –7V
2
34
1785/91 G09
5
UUU
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
Page 6
LT1785/LT1785A
LT1791/LT1791A
UUU
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.
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.
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
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
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.
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
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
B
Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load
6
R
V
OD
V
OC
R
1785/91 F01
RECEIVER
OUTPUT
TEST POINT
C
RL
S1
1k
S2
1k
V
CC
1785/91 F02
Page 7
TEST CIRCUITS
5V
DE
DI
A
R
DIFF
B
Figure 3. Driver/Receiver Timing Test Circuit Figure 4. Driver Timing Test Load
UU
FU CTIO TABLES
LT1785/LT1785A
LT1791/LT1791A
A
C
L1
B
C
L2
RE
RO
15pF
1785/91 F03
OUTPUT
UNDER TEST
500Ω
C
L
S1
V
CC
S2
1785/91 F04
LT1785 Transmitting
INPUTS OUTPUTS
RE DE DI A B RO
0100 10
0111 01
1 0 X Hi-Z Hi-Z Hi-Z
1100 1Hi-Z
1111 0Hi-Z
LT1785 Receiving
INPUTS OUTPUT
RE DE DI A-B RO
00X≤–200mV 0
00X≥200mV* 1
0 0 X Open 1
1 0 X X Hi-Z
* ≥ 0mV for LT1785A
UW W
SWITCHI G TI E WAVEFOR S
LT1791
INPUTS OUTPUTS
RE DE DI A-B Y Z RO
00 X≤ –200mV Hi-Z Hi-Z 0
00 X≥200mV* Hi-Z Hi-Z 1
0 0 X Open Hi-Z Hi-Z 1
01 0≤ –200mV 0 1 0
01 0≥200mV* 0 1 1
0 1 0 Open 0 1 1
01 1≤ –200mV 1 0 0
01 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
* ≥ 0mV for LT1791A
5V
DI
0V
–V
B
A
V
O
0V
O
V
O
1/2 V
1.5V
O
10%
t
r
f = 125kHz, tr ≤ 10ns, tf ≤ 10ns
t
PLH
t
SKEW
90%
V
= V(A) – V(B)
DIFF
1.5V
1/2 V
t
PHL
t
SKEW
90%
10%
t
f
O
1785/91 F05
Figure 5. Driver Propagation Delays
7
Page 8
LT1785/LT1785A
LT1791/LT1791A
UW W
SWITCHI G TI E WAVEFOR S
A, B
A, B
RO
A – B
RO
5V
DE
0V
5V
V
OL
V
OH
0V
f = 125kHz, tr ≤ 10ns, tf ≤ 10ns
1.5V
t
ZL(SHDN), tZL
2.3V
2.3V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
t
ZH(SHDN), tZH
1.5V
t
LZ
0.5V
0.5V
t
HZ
1785/91 F06
Figure 6. Driver Enable and Disable Times
V
–V
OH
V
OL
V
OD2
OD2
t
PHL
1.5V
f = 125kHz, tr ≤ 10ns, tf ≤ 10ns
0V 0V
OUTPUT
INPUT
t
PLH
1.5V
1785/91 F07
Figure 7. Receiver Propagation Delays
5V
RE
0V
5V
1.5V
f = 125kHz, tr ≤ 10ns, tf ≤ 10ns
t
, t
ZL(SHDN)
1.5V
ZL
OUTPUT NORMALLY LOW
1.5V
t
LZ
0.5V
RO
0V
1.5V
OUTPUT NORMALLY HIGH
t
ZH(SHDN)
Figure 8. Receiver Enable and Disable Times
UU 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-
0.5V
, t
ZH
t
HZ
1785/91 F08
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.
8
Page 9
UU W U
APPLICATIO S I FOR ATIO
LT1785/LT1785A
LT1791/LT1791A
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.
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.
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.
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.
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.
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
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
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
Page 10
LT1785/LT1785A
LT1791/LT1791A
UU W U
APPLICATIO S I FOR ATIO
2
RO
RE
DE
DI
RX
3
4
5
TX
PACKAGE DESCRIPTION
0.300 – 0.325
(7.620 – 8.255)
(1.143 – 1.651)
12
A
120Ω
11
B
10
Z
9
Y
120Ω
12
A
11
10
9
TX
B
LT1791LT1791
Z
RX
Y
Figure 9. Full-Duplex RS422
U
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.045 – 0.065
0.130 ± 0.005
(3.302 ± 0.127)
5
DI
4
DE
3
RE
2
RO
1785/91 F09
0.400*
(10.160)
MAX
876
5
0.065
(1.651)
0.009 – 0.015
(0.229 – 0.381)
+0.035
0.325
–0.015
+0.889
8.255
()
–0.381
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
TYP
0.100 ± 0.010
(2.540 ± 0.254)
8-Lead Plastic Small Outline (Narrow 0.150)
0.010 – 0.020
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
*
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
× 45°
0.016 – 0.050
0.406 – 1.270
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.014 – 0.019
(0.355 – 0.483)
0.125
(3.175)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
S8 Package
(LTC DWG # 05-08-1610)
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
0.020
(0.508)
MIN
0.255 ± 0.015*
(6.477 ± 0.381)
0.228 – 0.244
(5.791 – 6.197)
0.189 – 0.197*
(4.801 – 5.004)
7
8
1
2
12
6
3
4
3
N8 1197
5
0.150 – 0.157**
(3.810 – 3.988)
4
SO8 0996
10
Page 11
PACKAGE DESCRIPTION
LT1785/LT1785A
LT1791/LT1791A
U
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
0.255 ± 0.015*
(6.477 ± 0.381)
11
1213
8910
2
0.300 – 0.325
(7.620 – 8.255)
0.009 – 0.015
(0.229 – 0.381)
+0.035
0.325
–0.015
+0.889
8.255
()
–0.381
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
0.020
(0.508)
MIN
0.130 ± 0.005
(3.302 ± 0.127)
0.125
(3.175)
MIN
0.005
(0.125)
MIN
0.100 ± 0.010
(2.540 ± 0.254)
S Package
14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
13
14
31
4
0.045 – 0.065
(1.143 – 1.651)
0.337 – 0.344*
(8.560 – 8.738)
12
11
6
9
7
0.065
(1.651)
TYP
0.018 ± 0.003
(0.457 ± 0.076)
N14 1197
8
5
10
0.228 – 0.244
(5.791 – 6.197)
0.010 – 0.020
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
*
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
× 45°
0° – 8° TYP
0.016 – 0.050
0.406 – 1.270
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.
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
0.150 – 0.157**
(3.810 – 3.988)
1
3
2
4
0.050
(1.270)
TYP
5
7
6
0.004 – 0.010
(0.101 – 0.254)
S14 0695
11
Page 12
LT1785/LT1785A
LT1791/LT1791A
U
TYPICAL APPLICATIONS
RO
1
RX
2
RE
DE
DI
LT1785
3
4
TX
R
T
120Ω
7
B
6
A
6
7
A
B
LT1785
4
DI
DE
1
3
2
RE
RO
6
7
A
B
LT1785
4
3
DI
DE
1
2
RE
RO
R
120Ω
T
7
6
RX
B
A
LT1785
1
RO
2
RE
3
DE
4
TX
DI
1785/91 F10
Figure 10. Half-Duplex RS485 Network Operation
RAYCHEM
POLYSWITCH
TR600-150
× 2
47Ω
47Ω
CARBON
COMPOSITE
5W
0.1µF
300V
RT,120Ω
1785/91 F11
RO
8
V
1
RX
2
RE
DE
DI
LT1785
3
4
TX
CC
7
B
6
A
5
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 2500V
LTC1685 52Mbps RS485 Half-Duplex Transceiver Propagation Delay Skew 500ps (Typ)
LTC1687 52Mbps RS485 Full-Duplex Transceiver Propagation Delay Skew 500ps (Typ)
Linear Technology Corporation
12
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear-tech.com
Isolation in Surface Mount Package
RMS
178591f LT/TP 0300 4K • PRINTED IN THE USA
LINEAR TECHNOLOGY CORPORATION 1998
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