LT1785/LT1785A/ LT1791/LT1791A 60V Fault Protected RS485/RS422 Transceivers FEATURES DESCRIPTION n 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. n n n n n n n n n n 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 Guaranteed Operation to 125C 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. APPLICATIONS n n n Data rates to 250kbaud on networks of up to 128 nodes are supported. Controlled slew rates on the driver outputscontrol EMI emissions and improve data transmission integrity on improperly terminated lines. Drivers are specified to operate with inexpensive cables as low as 72 characteristic impedance. Industrial Control Data Networks CAN Bus Applications HVAC Controls L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. The LT1785/LT1785A are available in 8-lead DIP and SO packages and the LT1791/LT1791A in 14-lead DIP and SO packages. TYPICAL APPLICATION Normal Operation Waveforms at 250kBaud VCC1 RO1 RE1 DE1 DI1 RX RO LT1785 RTERM TX Y-Z GND1 RO2 RE2 DE2 DI2 DI VCC2 RX LT1785 RTERM 178591 TA02 TX GND2 178591 TA01 178591fc 1 LT1785/LT1785A/ LT1791/LT1791A ABSOLUTE MAXIMUM RATINGS (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.................................... 0C to 70C LT1785I/LT1791I/ LT1785AI/LT1791AI .................................. -40C to 85C LT1785H/LT1791H/ LT1785AH/LT1791AH ............................. -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C PIN CONFIGURATION TOP VIEW TOP VIEW RO 1 R RE 2 DI 4 8 7 DE 3 6 D 5 R 13 NC VCC RO 2 B RE 3 12 A A DE 4 11 B GND DI 5 GND 6 N8 PACKAGE 8-LEAD PDIP 14 VCC NC 1 S8 PACKAGE 8-LEAD PLASTIC SO GND 7 TJMAX = 150C, JA = 130C/W (N8) TJMAX = 150C, JA = 150C/W (S8) N PACKAGE 14-LEAD PDIP 10 Z D 9 Y 8 NC S PACKAGE 14-LEAD PLASTIC SO TJMAX = 150C, JA = 130C/W (N) TJMAX = 150C, JA = 150C/W (S) ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1785CN8#PBF LT1785CN8#TRPBF 1785 8-Lead PDIP 0C to 70C LT1785CS8#PBF LT1785CS8#TRPBF 1785 8-Lead Plastic SO 0C to 70C LT1785IN8#PBF LT1785IN8#TRPBF 1785I 8-Lead PDIP -40C to 85C LT1785IS8#PBF LT1785IS8#TRPBF 1785I 8-Lead Plastic SO -40C to 85C LT1785ACN8#PBF LT1785ACN8#TRPBF 1785A 8-Lead PDIP 0C to 70C LT1785ACS8#PBF LT1785ACS8#TRPBF 1785A 8-Lead Plastic SO 0C to 70C LT1785AIN8#PBF LT1785AIN8#TRPBF 1785AI 8-Lead PDIP -40C to 85C LT1785AIS8#PBF LT1785AIS8#TRPBF 1785AI 8-Lead Plastic SO -40C to 85C LT1785HN8#PBF LT1785HN8#TRPBF 1785H 8-Lead PDIP -40C to 125C LT1785HS8#PBF LT1785HS8#TRPBF 1785H 8-Lead Plastic SO -40C to 125C LT1785AHN8#PBF LT1785AHN8#TRPBF 1785AH 8-Lead PDIP -40C to 125C LT1785AHS8#PBF LT1785AHS8#TRPBF 1785AH 8-Lead Plastic SO -40C to 125C LT1791CN#PBF LT1791CN#TRPBF 1791 14-Lead PDIP 0C to 70C LT1791CS#PBF LT1791CS#TRPBF 1791 14-Lead Plastic SO 0C to 70C 178591fc 2 LT1785/LT1785A/ LT1791/LT1791A ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1791IN#PBF LT1791IN#TRPBF 1791I 14-Lead PDIP -40C to 85C LT1791IS#PBF LT1791IS#TRPBF 1791I 14-Lead Plastic SO -40C to 85C LT1791ACN#PBF LT1791ACN#TRPBF 1791A 14-Lead PDIP 0C to 70C LT1791ACS#PBF LT1791ACS#TRPBF 1791A 14-Lead Plastic SO 0C to 70C LT1791AIN#PBF LT1791AIN#TRPBF 1791AI 14-Lead PDIP -40C to 85C LT1791AIS#PBF LT1791AIS#TRPBF 1791AI 14-Lead Plastic SO -40C to 85C LT1791HN#PBF LT1791HN#TRPBF 1791H 14-Lead PDIP -40C to 125C LT1791HS#PBF LT1791HS#TRPBF 1791H 14-Lead Plastic SO -40C to 125C LT1791AHN#PBF LT1791AHN#TRPBF 1791AH 14-Lead PDIP -40C to 125C LT1791AHS#PBF LT1791AHS#TRPBF 1791AH 14-Lead Plastic SO -40C to 125C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1785CN8 LT1785CN8#TR 1785 8-Lead PDIP 0C to 70C LT1785CS8 LT1785CS8#TR 1785 8-Lead Plastic SO 0C to 70C LT1785IN8 LT1785IN8#TR 1785I 8-Lead PDIP -40C to 85C LT1785IS8 LT1785IS8#TR 1785I 8-Lead Plastic SO -40C to 85C LT1785ACN8 LT1785ACN8#TR 1785A 8-Lead PDIP 0C to 70C LT1785ACS8 LT1785ACS8#TR 1785A 8-Lead Plastic SO 0C to 70C LT1785AIN8 LT1785AIN8#TR 1785AI 8-Lead PDIP -40C to 85C LT1785AIS8 LT1785AIS8#TR 1785AI 8-Lead Plastic SO -40C to 85C LT1785HN8 LT1785HN8#TR 1785H 8-Lead PDIP -40C to 125C LT1785HS8 LT1785HS8#TR 1785H 8-Lead Plastic SO -40C to 125C LT1785AHN8 LT1785AHN8#TR 1785AH 8-Lead PDIP -40C to 125C LT1785AHS8 LT1785AHS8#TR 1785AH 8-Lead Plastic SO -40C to 125C LT1791CN LT1791CN#TR 1791 14-Lead PDIP 0C to 70C LT1791CS LT1791CS#TR 1791 14-Lead Plastic SO 0C to 70C LT1791IN LT1791IN#TR 1791I 14-Lead PDIP -40C to 85C LT1791IS LT1791IS#TR 1791I 14-Lead Plastic SO -40C to 85C LT1791ACN LT1791ACN#TR 1791A 14-Lead PDIP 0C to 70C LT1791ACS LT1791ACS#TR 1791A 14-Lead Plastic SO 0C to 70C LT1791AIN LT1791AIN#TR 1791AI 14-Lead PDIP -40C to 85C LT1791AIS LT1791AIS#TR 1791AI 14-Lead Plastic SO -40C to 85C LT1791HN LT1791HN#TR 1791H 14-Lead PDIP -40C to 125C LT1791HS LT1791HS#TR 1791H 14-Lead Plastic SO -40C to 125C LT1791AHN LT1791AHN#TR 1791AH 14-Lead PDIP -40C to 125C LT1791AHS LT1791AHS#TR 1791AH 14-Lead Plastic SO -40C to 125C 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/ 178591fc 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 = 25C, VCC = 5V. SYMBOL PARAMETER CONDITIONS MIN VOD1 Differential Driver Output Voltage (Unloaded) IO = 0 l VOD2 Differential Driver Output Voltage (With Load) R = 50 (RS422), Figure 1 R = 27 (RS485), Figure 1 R = 18 l l l VOD Change in Magnitude of Driver Differential Output Voltage for Complementary Output States R = 27 or R = 50, Figure 1 l VOC Driver Common Mode Output Voltage R = 27 or R = 50, Figure 1 l |VOC| Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States R = 27 or R = 50, Figure 1 l VIH Input High Voltage DI, DE, RE l VIL Input Low Voltage DI, DE, RE l IIN1 Input Current DI, DE, RE l IIN2 Input Current (A, B); (LT1791 or LT1785 with DE = 0V) VIN = 12V VIN = -7V -60V VIN 60V l l l -0.15 -6 l l -0.2 -0.2 2.0 1.5 1.2 2 TYP MAX 4.1 5 2.70 2.45 2.2 2.5 0.15 -0.08 3 V 0.2 V VTH Receiver Input Hysteresis -7V < VCM < 12V VOH Receiver Output High Voltage IO = -400A, VID = 200mV l VOL Receiver Output Low Voltage IO = 1.6mA, VID = -200mV l Three-State (High Impedance) Output Current at Receiver 0V < VOUT < 6V RE > 2V or Power Off l -1 Receiver Input Resistance (LT1791) -7V VCM 12V - 60V VCM 60V l 85 125 125 LT1785 -7V VCM 12V l 50 90 V 5 A 0.3 mA mA mA 6 LT1785/LT1791: -7V VCM 12V LT1785A/LT1791A: -7V VCM 12V 0.2 0 V V 20 mV 4 V 0.3 RS485 Unit Load ICC V 0.8 Differential Input Threshold Voltage for Receiver ISC 0.2 V VTH RIN V V V V 2 3.5 UNITS 0.5 V 1 A k k k 0.25 Driver Short-Circuit Current VOUT = HIGH, Force VO = -7V VOUT = LOW, Force VO = 12V l l 35 35 Driver Output Fault Current VO = 60V VO = -60V l l -6 Receiver Short-Circuit Current 0V VO VCC l Driver Three-State Output Current -7V VO 12V -60V VO 60V l l 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 l l l l -0.2 -6 5.5 5.5 4.5 0.2 250 250 mA mA 6 mA mA 35 mA 0.3 6 mA mA 9 9 8 0.3 mA mA mA mA 178591fc 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 = 25C, VCC = 5V. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS tPLH Driver Input to Output Figures 3, 5 tPHL Driver Input to Output Figures 3, 5 l 700 2000 ns l 700 2000 ns tSKEW Driver Output to Output Figures 3, 5 tr, tf Driver Rise or Fall Time Figures 3, 5 l tZH Driver Enable to Output High Figures 4, 6 tZL Driver Enable to Output Low tLZ Driver Disable Time from Low tHZ Driver Disable Time from High tPLH 100 200 ns 800 2000 ns l 500 3000 ns Figures 4, 6 l 800 3000 ns Figures 4, 6 l 200 5000 ns Figures 4, 6 l 800 5000 ns Receiver Input to Output Figures 3, 7 l 400 900 ns tPHL Receiver Input to Output Figures 3, 7 l 400 900 ns tSKD Differential Receiver Skew tZL Receiver Enable to Output Low Figures 2, 8 l 200 300 1000 ns tZH Receiver Enable to Output High Figures 2, 8 l 300 1000 ns tLZ Receiver Disable from Low Figures 2, 8 l 400 1000 ns tHZ Receiver Disable from High Figures 2, 8 l 400 1000 ns l 250 ns fMAX Maximum Data Rate tSHDN Time to Shut Down Figures 2, 6, 8 3 kbps s tZH(SHDN) Driver Enable from Shutdown to Output High Figures 2, 6; RE = 5V 12 s tZL(SHDN) Driver Enable from Shutdown to Output Low Figures 2, 6; RE = 5V 12 s tZH(SHDN) Receiver Enable from Shutdown to Output High Figures 2, 8; DE = 0V 4 s tZL(SHDN) Receiver Enable from Shutdown to Output Low Figures 2, 8; DE = 0V 4 s 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. 178591fc 5 LT1785/LT1785A/ LT1791/LT1791A TYPICAL PERFORMANCE CHARACTERISTICS Driver Differential Output Voltage vs Load Resistance Driver Differential Output Voltage vs Temperature 3.0 4 Receiver Propagation Delay vs Temperature 1000 OUTPUT VOLTAGE (V) 3 2 1 2.5 2.0 1.5 100 LOAD RESISTANCE () 10 tPLH 400 200 R = 27 0 -40 -20 1k 600 1.0 0.5 0 tPHL 800 DELAY (ns) DIFFERENTIAL VOLTAGE (V) TA = 25C 40 20 0 60 TEMPERATURE (C) 178591 G01 80 0 -40 100 40 20 0 60 TEMPERATURE (C) -20 178591 G02 Driver Propagation Delay vs Temperature 80 100 178591 G03 LT1791 Driver Output Leakage DE = 0V LT1791 Receiver Input Current vs VIN 1000 PROPAGATION DELAY (ns) 900 800 LH 700 600 200A/DIV 1mA/DIV HL 500 400 300 200 -60V 100 0 -40 -20 40 20 0 60 TEMPERATURE (C) 80 VIN 60V -60V VIN 178591 G05 60V 178591 G06 100 178591 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 VA, VB 60V HL VCM = 12V 500 0 -40 LH VCM = -7V 300 LH VCM = 12V 200 1 178591 G07 400 100 STANDBY 0 -20 40 20 0 60 TEMPERATURE (C) 80 100 178591 G08 0 1 3 4 2 VIN DIFFERENTIAL (V) 5 178591 G09 178591fc 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 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 circuitgoes 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 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 inputthresholds -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 0.1F low ESR capacitor directly at Pin 8 (VCC). 178591fc 7 LT1785/LT1785A/ LT1791/LT1791A TEST CIRCUITS A R VOD 1k VCC VOC R S1 TEST POINT RECEIVER OUTPUT 1k CRL S2 B 1785/91 F02 1785/91 F01 Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load 5V DE A A CL1 DI RO RDIFF B S1 CL2 RE 15pF VCC 500 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 FUNCTION TABLES LT1785 Transmitting LT1791 INPUTS OUTPUTS INPUTS OUTPUTS RE DE DI A B RO RE DE DI A-B Y Z RO 0 1 0 0 1 0 0 0 X -200mV Hi-Z Hi-Z 0 0 1 1 1 0 1 0 0 X 200mV* Hi-Z Hi-Z 1 1 0 X Hi-Z Hi-Z Hi-Z 0 0 X Open Hi-Z Hi-Z 1 1 1 0 0 1 Hi-Z 0 1 0 -200mV 0 1 0 1 1 1 1 0 Hi-Z 0 1 0 200mV* 0 1 1 0 1 0 Open 0 1 1 0 1 1 -200mV 1 0 0 1 200mV* 1 0 1 LT1785 Receiving OUTPUT 0 1 RE DE INPUTS DI A-B RO 0 1 1 Open 1 0 1 0 0 X -200mV 0 1 0 X X Hi-Z Hi-Z Hi-Z 0 0 X 200mV* 1 1 1 0 X 0 1 Hi-Z 0 0 X Open 1 1 1 1 X 1 0 Hi-Z 1 0 X X Hi-Z * 0mV for LT1791A * 0mV for LT1785A 178591fc 8 LT1785/LT1785A/ LT1791/LT1791A SWITCHING TIME WAVEFORMS 5V f = 125kHz, tr 10ns, tf 10ns 1.5V DI 1.5V 0V tPLH 1/2 VO tPHL B VO A VO 0V -VO tSKEW 1/2 VO tSKEW 90% 90% 10% VDIFF = V(A) - V(B) 10% tr tf 1785/91 F05 Figure 5. Driver Propagation Delays 5V f = 125kHz, tr 10ns, tf 10ns 1.5V DE 1.5V 0V tLZ tZL(SHDN), tZL 5V A, B 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOL VOH A, B 0V tHZ tZH(SHDN), tZH 178591 F06 Figure 6. Driver Enable and Disable Times VOH 1.5V RO tPHL VOD2 A-B -VOD2 1.5V OUTPUT VOL tPLH f = 125kHz, tr 10ns, tf 10ns 0V 0V INPUT 178591 F07 Figure 7. Receiver Propagation Delays 5V RE 1.5V 5V 1.5V f = 125kHz, tr 10ns, tf 10ns 0V tZL(SHDN), tZL tLZ RO 1.5V OUTPUT NORMALLY LOW 0.5V RO 1.5V OUTPUT NORMALLY HIGH 0.5V 0V tZH(SHDN), tZH tHZ 178591 F08 Figure 8. Receiver Enable and Disable Times 178591fc 9 LT1785/LT1785A/ LT1791/LT1791A APPLICATIONS INFORMATION 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 the120VAC 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. 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 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 in to 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. 178591fc 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 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. 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 72. The LT1785/LT1791 output drivers are guaranteed to drive cables as low as 72. A 12 RO RE DE 2 RX 9 Y 120 B 11 10 Z 3 5 5 4 4 LT1791 LT1791 TX 3 11 B Z 10 DI TX 120 12 A Y 9 RX 2 DI DE RE RO 178591 F09 Figure 9. Full-Duplex RS422 178591fc 11 LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 .015* (6.477 0.381) .300 - .325 (7.620 - 8.255) .008 - .015 (0.203 - 0.381) ( +.035 .325 -.015 8.255 +0.889 -0.381 ) .045 - .065 (1.143 - 1.651) .130 .005 (3.302 0.127) .065 (1.651) TYP .100 (2.54) BSC .120 (3.048) .020 MIN (0.508) MIN .018 .003 (0.457 0.076) N8 1002 NOTE: 1. DIMENSIONS ARE INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) 178591fc 12 LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .189 - .197 (4.801 - 5.004) NOTE 3 .045 .005 .050 BSC 8 .245 MIN 7 6 5 .160 .005 .150 - .157 (3.810 - 3.988) NOTE 3 .228 - .244 (5.791 - 6.197) .030 .005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 0- 8 TYP .016 - .050 (0.406 - 1.270) NOTE: 1. DIMENSIONS IN .053 - .069 (1.346 - 1.752) .014 - .019 (0.355 - 0.483) TYP 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) 2 3 4 .004 - .010 (0.101 - 0.254) .050 (1.270) BSC SO8 0303 178591fc 13 LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION N Package 14-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) .770* (19.558) MAX 14 13 12 11 10 9 8 1 2 3 4 5 6 7 .255 .015* (6.477 0.381) .300 - .325 (7.620 - 8.255) .130 .005 (3.302 0.127) .045 - .065 (1.143 - 1.651) .020 (0.508) MIN .065 (1.651) TYP .008 - .015 (0.203 - 0.381) ( +.035 .325 -.015 +0.889 8.255 -0.381 NOTE: 1. DIMENSIONS ARE ) .120 (3.048) MIN .005 (0.127) .100 MIN (2.54) BSC .018 .003 (0.457 0.076) N14 1103 INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) 178591fc 14 LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION S Package 14-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .337 - .344 (8.560 - 8.738) NOTE 3 .045 .005 .050 BSC 14 N 12 11 10 9 8 N .245 MIN .160 .005 .150 - .157 (3.810 - 3.988) NOTE 3 .228 - .244 (5.791 - 6.197) 1 .030 .005 TYP 13 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 2 3 4 5 .053 - .069 (1.346 - 1.752) NOTE: 1. DIMENSIONS IN .014 - .019 (0.355 - 0.483) TYP 7 .004 - .010 (0.101 - 0.254) 0 - 8 TYP .016 - .050 (0.406 - 1.270) 6 .050 (1.270) BSC 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) S14 0502 178591fc 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 its circuits as described herein will not infringe on existing patent rights. 15 LT1785/LT1785A/ LT1791/LT1791A TYPICAL APPLICATION RO RE DE DI 1 RX RT 120 B 7 RT 120 RX 7 B 1 2 2 LT1785 3 4 6 A A 6 6 A TX 6 A 7 B LT1785 7 B TX 3 4 RO RE DE DI 178591 F10 LT1785 4 3 DI DE LT1785 2 RE 1 RO 4 DI 3 DE 2 RE 1 RO Figure 10. Half-Duplex RS485 Network Operation 8 RO RE DE DI 1 RX RAYCHEM POLYSWITCH TR600-150 x2 47 VCC B 7 2 3 4 RT,120 LT1785 A 6 47 CARBON COMPOSITE 5W 5 TX 178591 F11 0.1F 300V 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 = 300A (Typ) LTC491 Differential Driver and Receiver Pair ICC = 300A 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) 178591fc 16 Linear Technology Corporation LT 0409 REV C * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 1998