View LT1791_295168.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

Final Electrical Specifications
LT1785/LT1791 60V Fault Protected RS485/RS422 Transceivers
December 1998
FEATURES
s s s s
DESCRIPTIO
s s
s s
Protected from Overvoltage Line Faults to 60V Pin Compatible with LTC485 and LTC491 High Input Impedance Supports Up to 64 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 Outputs Assume a High Impedance When Off or Powered Down Short-Circuit Protection on All Outputs Thermal Shutdown Protection
The LT(R)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 64 nodes are supported. Controlled slew rates on the driver outputs control EMI emissions and improve data transmission integrity on improperly terminated lines. On-chip ESD protection eliminates need for external protection devices. The LT1785 is available in 8-lead DIP and SO packages and the LT1791 in 14-lead DIP and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATI
s s s
S
Industrial Control Data Networks CAN Bus Applications HVAC Controls
TYPICAL APPLICATI
VCC1 RO1 RE1 DE1 DI1 RX LT1785 RTERM
Normal Operation Waveforms at 250kBaud
TX GND1
VCC2 RO2 RE2 DE2 DI2 RX LT1785 RTERM
TX GND2
1785/91 TA01
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.
U
1785/91 TA02
UO
UO
1
LT1785/LT1791 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
PACKAGE/ORDER I FOR ATIO
TOP VIEW RO 1 RE 2 DE 3 DI 4 N8 PACKAGE 8-LEAD PDIP D R 8 7 6 5 VCC B A GND
ORDER PART NUMBER LT1785CN8 LT1785CS8 LT1785IN8 LT1785IS8 S8 PART MARKING 1785 1785I
NC 1 RO 2 RE 3 DE 4 DI 5 GND 6 GND 7 N PACKAGE 14-LEAD PDIP
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 130C/ W (N8) TJMAX = 125C, JA = 150C/ W (S8)
Consult factory for Military grade parts.
2
U
U
W
WW
U
W
(Note 1)
Receiver Output Voltage ............................. - 0.3V to 6V Operating Temperature Range LT1785C/LT1791C ................................. 0C to 70C LT1785I/LT1791I ............................... - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
TOP VIEW 14 VCC R 13 NC 12 A 11 B 10 Z D 9 8 Y NC
ORDER PART NUMBER LT1791CN LT1791CS LT1791IN LT1791IS
S PACKAGE 14-LEAD PLASTIC SO
TJMAX = 125C, JA = 130C/ W (N) TJMAX = 125C, JA = 150C/ W (S)
LT1785/LT1791
DC ELECTRICAL CHARACTERISTICS
SYMBOL VOD1 VOD2 PARAMETER Differential Driver Output Voltage (Unloaded) Differential Driver Output Voltage (With Load) IO = 0
VCC = 5V, TA = 25C unless otherwise specified.
MIN
q q q q q q q q q q q q q q
CONDITIONS R = 50 (RS422), Figure 1 R = 27 (RS485), Figure 1 R = 18 R = 27 or R = 50, Figure 1 R = 27 or R = 50, Figure 1 R = 27 or R = 50, Figure 1 DI, DE, RE DI, DE, RE DI, DE, RE VIN = 12V VIN = - 7V - 60V VIN 60V - 7V VCM 12V - 7V < VCM < 12V IO = - 400A, VID = 200mV IO = 1.6mA, VID = - 200mV RE > 2V or Power Off - 7V VCM 12V - 60V VCM 60V - 7V VCM 12V No Load, RE = 0V, DE = 5V No Load, RE = 5V, DE = 5V No Load, RE = 0V, DE = 0V No Load, RE = 5V, DE = 0V VOUT = HIGH, Force VO = - 7V VOUT = LOW, Force VO = 12V VO = 60V VO = - 60V 0V VO VCC -7V VO 12V - 60V VO 60V
q q q q q q
TYP 4.1 2.70 2.45 2.2
MAX 5
UNITS V V V V
2.0 1.5 1.2
VOD VOC VOC VIH VIL IIN1 IIN2
Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common Mode Output Voltage Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States Input High Voltage Input Low Voltage Input Current Input Current (A, B); (LT1791 or LT1785 with DE = 0V) Differential Input Threshold Voltage for Receiver Receiver Input Hysteresis Receiver Output High Voltage Receiver Output Low Voltage Three-State (High Impedance) Output Current at Receiver 0V < VOUT < VCC + 6V
0.2 2 2.5 3 0.2 2 0.8 5 - 0.15 -6 - 0.2 20 3.5 -1 85 85 25 0.5 5.5 5.5 4.5 0.2 35 35 -6 30 - 0.2 -6 0.6 6 9 9 8 0.3 250 250 6 125 125 4 0.3 0.5 1 0.3 - 0.08 0.6 6 0.2
V V V V V A mA mA mA V mV V V A k k k mA mA mA mA mA mA mA mA mA mA mA
VTH VTH VOH VOL
RIN
Receiver Input Resistance (LT1791) LT1785 RS485 Unit Load Supply Current
q q q q q q q q q q q
ISC
Driver Short-Circuit Current Driver Output Fault Current Receiver Short-Circuit Current Driver Three-State Output Current
3
LT1785/LT1791
SWITCHI G CHARACTERISTICS
SYMBOL tPLH tPHL tSKEW tr, tf tZH tZL tLZ tHZ tPLH tPHL tSKD tZL tZH tLZ tHZ fMAX tSHDN tZH(SHDN) tZL(SHDN) tZH(SHDN) tZL(SHDN) PARAMETER Driver Input to Output Driver Input to Output Driver Output to Output Driver Rise or Fall Time Driver Enable to Output High Driver Enable to Output Low Driver Disable Time from Low Driver Disable Time from High Receiver Input to Output Receiver Input to Output Differential Receiver Skew Receiver Enable to Output Low Receiver Enable to Output High Receiver Disable from Low Receiver Disable from High Maximum Data Rate Time to Shut Down 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
The q denotes specifications which apply over the full operating temperature range.
TYPICAL PERFORMANCE CHARACTERISTICS
Driver Differential Output Voltage vs Load Resistance
4 TA = 25C
2.5 3.0
OUTPUT VOLTAGE (VP)
3
DIFFERENTIAL VOLTAGE (V)
2
1.5 1.0 0.5
DELAY (ns)
1
0 10 100 LOAD RESISTANCE () 1k
1785/91 G01
4
UW
U
VCC = 5V, TA = 25C unless otherwise specified.
MIN
q q
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 Figures 2, 8 Figures 2, 8 Figures 2, 8 Figures 2, 8 Figures 2, 6, 8 Figures 2, 6; RE = 5V Figures 2, 6; RE = 5V Figures 2, 8; DE = 0V Figures 2, 8; DE = 0V
q q q q q q q
TYP 700 700 100
MAX 2000 2000 2000 3000 3000 3000 3000 900 900 1000 1000 1000 1000
UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns kbps s s s s s
200
800 500 800 200 800 400 400 200 300 300 400 400
q q q q q
250 3 12 12 4 4
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
Driver Differential Output Voltage vs Temperature
1000
Receiver Propagation Delay vs Temperature
800
tPHL
2.0
600 tPLH
400
200
R = 27 0 -40 -20
40 20 0 60 TEMPERATURE (C)
80
100
0 -40
-20
40 0 60 20 TEMPERATURE (C)
80
100
1785/91 G03
1785/91 G03
LT1785/LT1791 TYPICAL PERFORMANCE CHARACTERISTICS
Driver Propagation Delay vs Temperature
1000 900
PROPAGATION DELAY (ns)
800 700 600 500 400 300 200 100 0 -40 -20 40 0 60 20 TEMPERATURE (C) 80 100 LH
LT1791 Receiver Input Current vs VIN
200A/DIV
- 60V VIN
Supply Current vs Temperature
7 6 5 DRIVER AND RECEIVER ON
ICC (mA)
4 3 2 1
DELAY (ns)
RECEIVER ONLY
0 -40
STANDBY -20 40 0 60 20 TEMPERATURE (C) 80 100
UW
HL
LT1791 Driver Output Leakage DE = 0V
1mA/DIV
- 60V VOUT
60V
1785/91 G05
1785/91 G04
LT1785 Input Characteristics Pins A or B; DE = RE = 0V
1mA/DIV
60V
1785/91 G06
- 60V VA, VB
60V
1785/91 G07
Receiver Propagation Delay vs Differential Input Voltage
700 600 HL VCM = -7V 500 400 300 200 100 0 0 1 3 4 2 VIN DIFFERENTIAL (V) 5
1785/91 G09
HL VCM = 12V LH VCM = -7V LH VCM = 12V
1785/91 G08
5
LT1785/LT1791
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 VCC + 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 3s 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 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 3s 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 64 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]. 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 64 LT1785 or LT1791 transceivers on one RS485 data bus. 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 0.1F low ESR capacitor.
6
U
U
U
LT1785/LT1791
FU CTIO TABLES
LT1785 Transmitting
INPUTS RE 0 0 1 1 1 DE 1 1 0 1 1 DI 0 1 X 0 1 A 0 1 Hi-Z 0 1 OUTPUTS B 1 0 Hi-Z 1 0 RO 0 1 Hi-Z Hi-Z Hi-Z RE 0 0 0 0 0 0 0 INPUTS RE 0 0 0 1 DE 0 0 0 0 DI X X X X A-B - 200mV 200mV Open X OUTPUT RO 0 1 1 Hi-Z 0 0 1 1 1 DE 0 0 0 1 1 1 1 1 1 0 1 1
LT1785 Receiving
TEST CIRCUITS
A R VOD R B
1785/91 F01
5V DE A DI B RDIFF CL2 CL1 A RO B RE 15pF
OUTPUT UNDER TEST 500 S2 CL
1785/91 F04
Figure 3. Driver/Receiver Timing Test Circuit
U
U
LT1791
INPUTS DI X X X 0 0 0 1 1 1 X 0 1 A-B - 200mV 200mV Open - 200mV 200mV Open - 200mV 200mV Open X X X Y Hi-Z Hi-Z Hi-Z 0 0 0 1 1 1 Hi-Z 0 1 OUTPUTS Z Hi-Z Hi-Z Hi-Z 1 1 1 0 0 0 Hi-Z 1 0 RO 0 1 1 0 1 1 0 1 1 Hi-Z Hi-Z Hi-Z
RECEIVER OUTPUT
VOC
TEST POINT
S1
1k VCC
CRL
1k
S2
1785/91 F02
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
S1 VCC
1785/91 F03
Figure 4. Driver Timing Test Load
7
LT1785/LT1791
SWITCHI G TI E WAVEFOR S
5V DI 0V t PLH B VO A VO 0V -VO 1/2 VO 10% tr tSKEW 90% VDIFF = V(A) - V(B) tf t SKEW 90% 10%
1785/91 F05
1.5V
Figure 5. Driver Propagation Delays
5V DE 0V 5V A, B VOL VOH A, B 0V 2.3V 1.5V
Figure 6. Driver Enable and Disable Times
VOH RO VOL t PHL VOD2 A-B -VOD2 0V 1.5V OUTPUT f = 125kHz, t r 10ns, t f 10ns INPUT t PLH 0V
1785/91 F07
Figure 7. Receiver Propagation Delays
5V RE 0V 5V RO 1.5V f = 125kHz, tr 10ns, tf 10ns t ZL(SHDN), tZL 1.5V OUTPUT NORMALLY LOW t LZ 0.5V 1.5V
RO 0V
Figure 8. Receiver Enable and Disable Times
8
W
W
U
f = 125kHz, t r 10ns, t f 10ns t PHL
1.5V 1/2 VO
f = 125kHz, t r 10ns, t f 10ns t ZL(SHDN), t ZL t LZ
1.5V
2.3V
OUTPUT NORMALLY LOW
0.5V
OUTPUT NORMALLY HIGH t HZ
0.5V
1785/91 F06
t ZH(SHDN), t ZH
1.5V
1.5V
OUTPUT NORMALLY HIGH t HZ
0.5V
1785/91 F08
t ZH(SHDN), tZH
LT1785/LT1791
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 typically - 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. 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. 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
U
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 3s 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 12s. 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 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 may have characteristic impedance as low as 72. The LT1785/LT1791 output drivers are guaranteed to drive cables as low as 72.
W
U
U
9
LT1785/LT1791
APPLICATIO S I FOR ATIO
A 12 RO RE DE DI 2 3 4 5 LT1791 Z 10 TX 120 Y9 9Y 10 Z RX 2 LT1791 RX 120 B 11 11 B
Figure 9. Full-Duplex RS422
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 8 7 6 5
0.300 - 0.325 (7.620 - 8.255)
0.045 - 0.065 (1.143 - 1.651)
0.009 - 0.015 (0.229 - 0.381)
0.065 (1.651) TYP 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 0.003 (0.457 0.076)
(
+0.035 0.325 -0.015 8.255 +0.889 -0.381
)
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)
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP 0.053 - 0.069 (1.346 - 1.752) 0.189 - 0.197* (4.801 - 5.004) 0.004 - 0.010 (0.101 - 0.254) 8 7 6 5
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
*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 2 3 4
SO8 0996
10
U
12 A TX 5 4 3 DI DE RE RO
1785/91 F09
W
U
U
U
0.130 0.005 (3.302 0.127)
0.255 0.015* (6.477 0.381)
1
2
3
4
N8 1197
0.050 (1.270) TYP
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
LT1785/LT1791
PACKAGE DESCRIPTION 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 13 12 11 10 9 8
0.255 0.015* (6.477 0.381)
1 0.300 - 0.325 (7.620 - 8.255) 0.130 0.005 (3.302 0.127) 0.020 (0.508) MIN 0.009 - 0.015 (0.229 - 0.381)
2
3
4
5
6
7
0.045 - 0.065 (1.143 - 1.651)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.018 0.003 (0.457 0.076)
N14 1197
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)
(
+0.035 0.325 -0.015 +0.889 8.255 -0.381
)
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 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0 - 8 TYP
2
3
4
5
6
7
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
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
11
LT1785/LT1791
TYPICAL APPLICATIONS
RO RE DE DI 1 2 3 4 LT1785 A6 6 A 7 B 6 A 7 B 6A LT1785 RX B7 RT 120 RT 120 7B RX 1 2 3 4 RO RE DE DI
1785/91 F10
TX
RO RE DE DI
1 2 3 4
RX LT1785
TX
Figure 11. RS485 Network with 120V AC Line Fault Protection
RELATED PARTS
PART NUMBER LTC485 LTC491 LTC1483 LTC1485 LTC1487 LTC1520 LTC1685 LTC1687 DESCRIPTION Low Power RS485 Interface Transceiver Differential Driver and Receiver Pair Ultralow Power RS485 Low EMI Transceiver Differential Bus Transceiver Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance 50Mbps Precision Quad Line Receiver 52Mbps RS485 Half-Duplex Transceiver 52Mbps RS485 Full-Duplex Transceiver COMMENTS ICC = 300A (Typ) ICC = 300A Controlled Driver Slew Rate 10Mbaud Operation Up to 256 Transceivers on the Bus Channel-to-Channel Skew 400ps (Typ) Propagation Delay Skew 500ps (Typ) Propagation Delay Skew 500ps (Typ)
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
U
TX
4 DI
3
2
1 RO
4 DI
3
2
1 RO
DE RE
DE RE
Figure 10. Half-Duplex RS485 Network Operation
8 B7
VCC
RAYCHEM POLYSWITCH TR600-150 x2 47 RT,120
A6 5 47 CARBON COMPOSITE 5W 1.5KE36CA 0.1F 300V
1785/91 F11
178791i LT/TP 1298 4K * PRINTED IN THE USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

▲Up To Search▲

Price & Availability of LT1791

	To Download LT1791 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .