LT1785AHN8-TR

LT1785/LT1785A/ LT1791/LT1791A 60V Fault Protected RS485/RS422 Transceivers FEATURES n n n n DESCRIPTION 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 outputscontrol 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. 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 125°C APPLICATIONS n n n 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. TYPICAL APPLICATION Normal Operation Waveforms at 250kBaud VCC1 RO1 RE1 DE1 DI1 RX RO LT1785 RTERM TX GND1 Y-Z RO2 RE2 DE2 DI2 VCC2 RX LT1785 RTERM DI 178591 TA02 TX GND2 178591 TA01 178491fb 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.................................... 0°C to 70°C LT1785I/LT1791I/ LT1785AI/LT1791AI .................................. –40°C to 85°C LT1785H/LT1791H/ LT1785AH/LT1791AH ............................. –40°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C PIN CONFIGURATION TOP VIEW 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 NC 1 RO 2 RE 3 DE 4 DI 5 GND 6 S8 PACKAGE 8-LEAD PLASTIC SO GND 7 N PACKAGE 14-LEAD PDIP D R 14 VCC 13 NC 12 A 11 B 10 Z 9 8 Y NC TJMAX = 150°C, θJA = 130°C/W (N8) TJMAX = 150°C, θJA = 150°C/W (S8) S PACKAGE 14-LEAD PLASTIC SO TJMAX = 150°C, θJA = 130°C/W (N) TJMAX = 150°C, θJA = 150°C/W (S) ORDER INFORMATION LEAD FREE FINISH LT1785CN8#PBF LT1785CS8#PBF LT1785IN8#PBF LT1785IS8#PBF LT1785ACN8#PBF LT1785ACS8#PBF LT1785AIN8#PBF LT1785AIS8#PBF LT1785HN8#PBF LT1785HS8#PBF LT1785AHN8#PBF LT1785AHS8#PBF LT1791CN#PBF LT1791CS#PBF TAPE AND REEL LT1785CN8#TRPBF LT1785CS8#TRPBF LT1785IN8#TRPBF LT1785IS8#TRPBF LT1785ACN8#TRPBF LT1785ACS8#TRPBF LT1785AIN8#TRPBF LT1785AIS8#TRPBF LT1785HN8#TRPBF LT1785HS8#TRPBF LT1785AHN8#TRPBF LT1785AHS8#TRPBF LT1791CN#TRPBF LT1791CS#TRPBF PART MARKING* 1785 1785 1785I 1785I 1785A 1785A 1785AI 1785AI 1785H 1785H 1785AH 1785AH 1791 1791 PACKAGE DESCRIPTION 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO TEMPERATURE RANGE 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C 0°C to 70°C 0°C to 70°C 178591fb 2 LT1785/LT1785A/ LT1791/LT1791A ORDER INFORMATION LEAD FREE FINISH LT1791IN#PBF LT1791IS#PBF LT1791ACN#PBF LT1791ACS#PBF LT1791AIN#PBF LT1791AIS#PBF LT1791HN#PBF LT1791HS#PBF LT1791AHN#PBF LT1791AHS#PBF LEAD BASED FINISH LT1785CN8 LT1785CS8 LT1785IN8 LT1785IS8 LT1785ACN8 LT1785ACS8 LT1785AIN8 LT1785AIS8 LT1785HN8 LT1785HS8 LT1785AHN8 LT1785AHS8 LT1791CN LT1791CS LT1791IN LT1791IS LT1791ACN LT1791ACS LT1791AIN LT1791AIS LT1791HN LT1791HS LT1791AHN LT1791AHS TAPE AND REEL LT1791IN#TRPBF LT1791IS#TRPBF LT1791ACN#TRPBF LT1791ACS#TRPBF LT1791AIN#TRPBF LT1791AIS#TRPBF LT1791HN#TRPBF LT1791HS#TRPBF LT1791AHN#TRPBF LT1791AHS#TRPBF TAPE AND REEL LT1785CN8#TR LT1785CS8#TR LT1785IN8#TR LT1785IS8#TR LT1785ACN8#TR LT1785ACS8#TR LT1785AIN8#TR LT1785AIS8#TR LT1785HN8#TR LT1785HS8#TR LT1785AHN8#TR LT1785AHS8#TR LT1791CN#TR LT1791CS#TR LT1791IN#TR LT1791IS#TR LT1791ACN#TR LT1791ACS#TR LT1791AIN#TR LT1791AIS#TR LT1791HN#TR LT1791HS#TR LT1791AHN#TR LT1791AHS#TR PART MARKING* 1791I 1791I 1791A 1791A 1791AI 1791AI 1791H 1791H 1791AH 1791AH PART MARKING* 1785 1785 1785I 1785I 1785A 1785A 1785AI 1785AI 1785H 1785H 1785AH 1785AH 1791 1791 1791I 1791I 1791A 1791A 1791AI 1791AI 1791H 1791H 1791AH 1791AH PACKAGE DESCRIPTION 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO PACKAGE DESCRIPTION 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 8-Lead PDIP 8-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO 14-Lead PDIP 14-Lead Plastic SO TEMPERATURE RANGE –40°C to 85°C –40°C to 85°C 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C TEMPERATURE RANGE 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://www.linear.com/packaging/ 178491fb 3 LT1785/LT1785A/ LT1791/LT1791A DC ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER VOD1 VOD2 Differential Driver Output Voltage (Unloaded) Differential Driver Output Voltage (With Load) The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 5V. CONDITIONS IO = 0 R = 50Ω (RS422), Figure 1 R = 27Ω (RS485), Figure 1 R = 18Ω R = 27Ω or R = 50Ω, Figure 1 R = 27Ω or R = 50Ω, Figure 1 R = 27Ω or R = 50Ω, Figure 1 DI, DE, RE DI, DE, RE DI, DE, RE VIN = 12V VIN = –7V –60V ≤ VIN ≤ 60V LT1785/LT1791: –7V ≤ VCM ≤ 12V LT1785A/LT1791A: –7V ≤ VCM ≤ 12V –7V < VCM < 12V IO = –400μA, VID = 200mV IO = 1.6mA, VID = –200mV RE > 2V or Power Off –7V ≤ VCM ≤ 12V – 60V ≤ VCM ≤ 60V –7V ≤ VCM ≤ 12V VOUT = HIGH, Force VO = –7V VOUT = LOW, Force VO = 12V VO = 60V VO = –60V 0V ≤ VO ≤ VCC –7V ≤ VO ≤ 12V –60V ≤ VO ≤ 60V 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 l l l l l l l l l l l l l l l l l l l l l l l l l l l MIN 2.0 1.5 1.2 TYP 4.1 2.70 2.45 2.2 MAX 5 UNITS V V V V VOD VOC Δ|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) 0.2 2 2.5 3 0.2 2 0.8 5 –0.15 –6 –0.2 –0.2 20 3.5 –1 85 50 35 35 –6 ±35 –0.2 –6 5.5 5.5 4.5 0.2 0.3 6 9 9 8 0.3 125 125 90 0.25 250 250 6 4 0.3 0.5 1 0.15 –0.08 0.3 6 0.2 0 V V V V V μA mA mA mA V V mV V V μA kΩ kΩ kΩ mA mA mA mA mA mA mA mA mA mA mA VTH ΔVTH VOH VOL 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 < 6V RIN Receiver Input Resistance (LT1791) LT1785 RS485 Unit Load ISC Driver Short-Circuit Current Driver Output Fault Current Receiver Short-Circuit Current Driver Three-State Output Current ICC Supply Current 178591fb 4 LT1785/LT1785A/ LT1791/LT1791A SWITCHING 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 Figures 2, 6, 8 Figures 2, 6; RE = 5V Figures 2, 6; RE = 5V Figures 2, 8; DE = 0V Figures 2, 8; DE = 0V Figures 2, 8 Figures 2, 8 Figures 2, 8 Figures 2, 8 l l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 5V. 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 l l l l l l l l l MIN TYP 700 700 100 MAX 2000 2000 2000 3000 3000 5000 5000 900 900 1000 1000 1000 1000 UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns kbps μs μs μs μs μs 200 800 500 800 200 800 400 400 200 300 300 400 400 250 3 12 12 4 4 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. 178491fb 5 LT1785/LT1785A/ LT1791/LT1791A TYPICAL PERFORMANCE CHARACTERISTICS Driver Differential Output Voltage vs Load Resistance 4 TA = 25°C 3 DIFFERENTIAL VOLTAGE (V) 2.5 2.0 DELAY (ns) 600 tPLH 1.5 1.0 0.5 0 10 100 LOAD RESISTANCE (Ω) 1k 178591 G01 Driver Differential Output Voltage vs Temperature 3.0 1000 Receiver Propagation Delay vs Temperature 800 tPHL OUTPUT VOLTAGE (V) 2 400 1 200 R = 27Ω 0 –40 –20 40 20 0 60 TEMPERATURE (°C) 80 100 0 –40 –20 40 20 0 60 TEMPERATURE (°C) 80 100 178591 G02 178591 G03 Driver Propagation Delay vs Temperature 1000 900 PROPAGATION DELAY (ns) 800 700 600 500 400 300 200 100 0 –40 –20 40 20 0 60 TEMPERATURE (°C) 80 100 LH HL 1mA/DIV LT1791 Driver Output Leakage DE = 0V LT1791 Receiver Input Current vs VIN 200μA/DIV –60V VIN 60V 178591 G05 –60V VIN 60V 178591 G06 178591 G04 LT1785 Input Characteristics Pins A or B; DE = RE = 0V 7 6 5 ICC (mA) 1mA/DIV 4 3 2 –60V VA, VB 60V 178591 G07 Supply Current vs Temperature 700 DRIVER AND RECEIVER ON 600 Receiver Propagation Delay vs Differential Input Voltage HL VCM = –7V 500 DELAY (ns) HL VCM = 12V LH VCM = –7V LH VCM = 12V RECEIVER ONLY 400 300 200 100 1 0 –40 STANDBY 0 –20 40 20 0 60 TEMPERATURE (°C) 80 100 0 1 3 4 2 VIN DIFFERENTIAL (V) 5 178591 G09 178591 G08 178591fb 6 LT1785/LT1785A/ LT1791/LT1791A PIN FUNCTIONS RO: Receiver Output. TTL level logic output. If the receiver is active (RE pin low), RO is high if receiver input A ≥ B by 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 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 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 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 0.1μF low ESR capacitor directly at Pin 8 (VCC). 178491fb 7 LT1785/LT1785A/ LT1791/LT1791A TEST CIRCUITS A R VOD R B 1785/91 F01 1785/91 F02 RECEIVER OUTPUT VOC TEST POINT S1 1k VCC CRL 1k S2 Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load 5V DE A DI B RDIFF CL2 CL1 A RO B RE 15pF 500Ω S2 CL 1785/91 F04 1785/91 F03 S1 VCC OUTPUT UNDER TEST Figure 3. Driver/Receiver Timing Test Circuit Figure 4. Driver Timing Test Load FUNCTION 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 OUTPUT DI X X X X A-B ≤ –200mV ≥ 200mV* Open X RO 0 1 1 Hi-Z 0 0 1 1 1 DE 0 0 0 1 1 1 1 1 1 0 1 1 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 LT1785 Receiving INPUTS RE 0 0 0 1 DE 0 0 0 0 * ≥ 0mV for LT1791A * ≥ 0mV for LT1785A 178591fb 8 LT1785/LT1785A/ LT1791/LT1791A SWITCHING TIME WAVEFORMS 5V DI 0V tPLH B VO A VO 0V –VO 1/2 VO 10% tr tSKEW 90% VDIFF = V(A) – V(B) tf tSKEW 90% 10% 1785/91 F05 1.5V f = 125kHz, tr ≤ 10ns, tf ≤ 10ns tPHL 1.5V 1/2 VO Figure 5. Driver Propagation Delays 5V DE 0V 5V A, B VOL VOH A, B 0V tZH(SHDN), tZH tHZ 178591 F06 1.5V f = 125kHz, tr ≤ 10ns, tf ≤ 10ns tZL(SHDN), tZL tLZ 1.5V 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V Figure 6. Driver Enable and Disable Times VOH RO VOL tPHL VOD2 A–B –VOD2 0V 1.5V OUTPUT f = 125kHz, tr ≤ 10ns, tf ≤ 10ns INPUT tPLH 0V 178591 F07 1.5V Figure 7. Receiver Propagation Delays 5V RE 0V 5V RO 1.5V f = 125kHz, tr ≤ 10ns, tf ≤ 10ns tZL(SHDN), tZL 1.5V OUTPUT NORMALLY LOW tLZ 0.5V 1.5V RO 0V 1.5V OUTPUT NORMALLY HIGH tHZ 0.5V 178591 F08 tZH(SHDN), tZH Figure 8. Receiver Enable and Disable Times 178491fb 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 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. 178591fb 10 LT1785/LT1785A/ LT1791/LT1791A APPLICATIONS INFORMATION 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. A 12 RO RE DE DI 2 3 4 5 LT1791 Z 10 TX 120Ω Y9 RX 120Ω B 11 12 A 11 B TX 5 4 LT1791 10 Z 9Y RX 2 3 DI DE RE RO 178591 F09 Figure 9. Full-Duplex RS422 178491fb 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 .255 ± .015* (6.477 ± 0.381) 1 .300 – .325 (7.620 – 8.255) 2 3 4 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .008 – .015 (0.203 – 0.381) +.035 .325 –.015 .065 (1.651) TYP .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 (0.457 ± 0.076) N8 1002 ( 8.255 +0.889 –0.381 ) .100 (2.54) BSC INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) NOTE: 1. DIMENSIONS ARE 178591fb 12 LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .050 BSC .045 ±.005 8 .189 – .197 (4.801 – 5.004) NOTE 3 7 6 5 .245 MIN .160 ±.005 .228 – .244 (5.791 – 6.197) .150 – .157 (3.810 – 3.988) NOTE 3 .030 ±.005 TYP RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN 0°– 8° TYP 1 2 3 4 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) 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) .014 – .019 (0.355 – 0.483) TYP .050 (1.270) BSC SO8 0303 178491fb 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 .255 ± .015* (6.477 ± 0.381) 1 .300 – .325 (7.620 – 8.255) .130 ± .005 (3.302 ± 0.127) .020 (0.508) MIN 2 3 4 5 6 7 .045 – .065 (1.143 – 1.651) .008 – .015 (0.203 – 0.381) +.035 .325 –.015 .065 (1.651) TYP .120 (3.048) MIN .005 (0.127) .100 MIN (2.54) BSC .018 ± .003 (0.457 ± 0.076) N14 1103 ( +0.889 8.255 –0.381 ) INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) NOTE: 1. DIMENSIONS ARE 178591fb 14 LT1785/LT1785A/ LT1791/LT1791A PACKAGE DESCRIPTION S Package 14-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .050 BSC N .045 ±.005 14 13 .337 – .344 (8.560 – 8.738) NOTE 3 12 11 10 9 8 .245 MIN N .160 ±.005 .228 – .244 (5.791 – 6.197) 1 2 3 N/2 N/2 .150 – .157 (3.810 – 3.988) NOTE 3 .030 ±.005 TYP RECOMMENDED SOLDER PAD LAYOUT 1 2 3 4 5 6 7 .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0° – 8° TYP .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .014 – .019 (0.355 – 0.483) TYP .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 178491fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no 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 2 3 4 LT1785 A6 6 A LT1785 7 B 6 A LT1785 7 B 6A LT1785 RX B7 RT 120Ω RT 120Ω 7B RX 1 2 3 4 RO RE DE DI 178591 F10 TX TX 4 DI DE 3 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 2 3 4 LT1785 A6 5 RX B7 VCC RAYCHEM POLYSWITCH TR600-150 ×2 47Ω RT,120Ω 0.1μF 300V 178591 F11 TX 47Ω CARBON COMPOSITE 5W 1.5KE36CA Figure 11. RS485 Network with 120V AC Line Fault Protection RELATED PARTS PART NUMBER LTC485 LTC491 LTC1483 LTC1485 LTC1487 LTC1520 LTC1535 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 Isolated RS485 Full-Duplex Transceiver 52Mbps RS485 Half-Duplex Transceiver 52Mbps RS485 Full-Duplex Transceiver COMMENTS ICC = 300μA (Typ) ICC = 300μA Controlled Driver Slew Rate 10Mbaud Operation Up to 256 Transceivers on the Bus Channel-to-Channel Skew 400ps (Typ) 2500VRMS Isolation in Surface Mount Package Propagation Delay Skew 500ps (Typ) Propagation Delay Skew 500ps (Typ) 178591fb 16 Linear Technology Corporation (408) 432-1900 ● FAX: (408) 434-0507 ● LT 0608 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com © LINEAR TECHNOLOGY CORPORATION 1998