LTC2876/LTC2877 60V Rugged PROFIBUS RS485 Transceivers Features Description PROFIBUS IEC 61158-2 Compliant nn Protected from Overvoltage Line Faults to 60V nn 52kV ESD Interface Pins, 15kV All Other Pins nn 2kV (Level 4) IEC61000-4-4 Fast Transient Burst nn 25V Working Common Mode Range nn 20Mbps Maximum Baud Rate nn 1.65V to 5.5V Logic Supply Pin for Flexible Digital Interfacing (LTC2877) nn 5V Supply Can Operate Down to 3V for Low Power, Low Swing Applications nn Fully Balanced Differential Receiver Thresholds with 240mV Hysteresis for Superior Noise Tolerance and Low Duty Cycle Distortion nn Receiver Failsafe for Open, Shorted and Terminated Conditions nn Wide Operating Temperature Range: -40C to 125C nn Available in Small DFN and MSOP Packages The LTC(R)2876 and LTC2877 are PROFIBUS RS485 transceivers designed to meet the test specifications for PROFIBUS-DP masters and PROFIBUS-DP slaves, fully compatible with IEC 61158-2, type 3: medium attachment unit (MAU). With operation up to 20Mbps, the LTC2876/ LTC2877 supports all PROFIBUS data rates up to 12Mbps. nn The LTC2876 and LTC2877 are exceptionally robust, tolerating 60V faults on the bus pins and protected to 52kV ESD. These devices are suitable for harsh environments or where 24V power might be inadvertently connected. Extended 25V input common mode range and full failsafe operation improve data communication reliability in noisy systems. The LTC2876 and LTC2877 meet PROFIBUS and RS485 specifications with a supply voltage of 4.5V to 5.5V but can operate down to 3V with reduced supply current. Product Selection Guide Applications PROFIBUS-DP Industrial Communication Networks nn RS485 and RS422 Systems nn 3V Low Voltage Differential Signaling nn PART NUMBER LOGIC SUPPLY PIN PACKAGE LTC2876 NO DFN-8, MSOP-8 LTC2877 YES DFN-10, MSOP-10 nn L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application 1.8V 0.1F VL 5V LTC2877 VCC 5V 1F 390 RO PB C SENSOR PB RE PROFIBUS CABLE 220 PA ZO = 150 390 DE 390 B PB-PA 2V/DIV NEAR END 220 PA DI Eye Diagram of 12Mbps Signal at the Near and Far End of a 100m PROFIBUS Cable Driven by the LTC2877 Using 28 -1 PRBS Pattern A 390 B- A 2V/DIV FAR END GND 28767 TA01a 20ns/DIV 28767 TA01b 28767fa For more information www.linear.com/LTC2876 1 LTC2876/LTC2877 Absolute Maximum Ratings (Notes 1, 2) Supply Voltages (VCC, VL)............................. -0.3V to 6V Logic Input Voltages (RE, DE, DI)................. -0.3V to 6V Line Interface I/O (PA, PB)........................... -60V to 60V Line Interface I/O Difference (PB-PA)...... -120V to 120V Receiver Output (RO) LTC2876.......................................-0.3V to VCC + 0.3V LTC2877........................................ -0.3V to VL + 0.3V Operating Ambient Temperature Range (Note 3) LTC287xC................................................. 0C to 70C LTC287xI..............................................-40C to 85C LTC287xH........................................... -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10sec).................... 300C Pin Configuration LTC2876 LTC2876 TOP VIEW RO 1 RE 2 DE 3 DI 4 TOP VIEW 8 VCC 9 GND RO RE DE DI 7 PA 6 PB 5 GND 1 2 3 4 9 GND 8 7 6 5 VCC PA PB GND MS8E PACKAGE 8-LEAD PLASTIC MSOP DD PACKAGE 8-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 150C, JA = 40C/W, JC = 10C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB TJMAX = 150C, JA = 43C/W, JC = 5.5C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB LTC2877 LTC2877 TOP VIEW RO 1 RE 2 DE 3 DI 4 VL 5 TOP VIEW 10 VCC 11 GND RO RE DE DI VL 9 PA 8 PB 7 NC 6 GND 11 GND 10 9 8 7 6 VCC PA PB NC GND MSE PACKAGE 10-LEAD PLASTIC MSOP DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 150C, JA = 43C/W, JC = 5.5C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB 2 1 2 3 4 5 TJMAX = 150C, JA = 40C/W, JC = 10C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Order Information http://www.linear.com/product/LTC2876#orderinfo Lead Free Finish TUBE TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2876CMS8E#PBF LTC2876IMS8E#PBF LTC2876HMS8E#PBF LTC2876CMS8E#TRPBF LTC2876IMS8E#TRPBF LTC2876HMS8E#TRPBF LTGTN LTGTN LTGTN 8-Lead Plastic MSOP 8-Lead Plastic MSOP 8-Lead Plastic MSOP 0C to 70C -40C to 85C -40C to 125C LTC2876CDD#PBF LTC2876IDD#PBF LTC2876HDD#PBF LTC2876CDD#TRPBF LTC2876IDD#TRPBF LTC2876HDD#TRPBF LGTM LGTM LGTM 8-Lead Plastic DFN 8-Lead Plastic DFN 8-Lead Plastic DFN 0C to 70C -40C to 85C -40C to 125C LTC2877CMSE#PBF LTC2877IMSE#PBF LTC2877HMSE#PBF LTC2877CMSE#TRPBF LTC2877IMSE#TRPBF LTC2877HMSE#TRPBF LTGTQ LTGTQ LTGTQ 10-Lead Plastic MSOP 10-Lead Plastic MSOP 10-Lead Plastic MSOP 0C to 70C -40C to 85C -40C to 125C LTC2877CDD#PBF LTC2877IDD#PBF LTC2877HDD#PBF LTC2877CDD#TRPBF LTC2877IDD#TRPBF LTC2877HDD#TRPBF LGTP LGTP LGTP 10-Lead Plastic DFN 10-Lead Plastic DFN 10-Lead Plastic DFN 0C to 70C -40C to 85C -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on nonstandard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = VL = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN Primary Power Supply PROFIBUS, RS485 l 4.5 Low Voltage RS485 (Note 6) l 3.0 1.65 TYP MAX UNITS Supplies VCC 5.5 V V VL Logic Interface Power Supply LTC2877 Only l VCC V ICCS LTC2876 Supply Current in Shutdown Mode DE = 0V, RE = VCC, DI = VCC l 0 5 A DE = 0V, RE = VCC, DI = 0V l 12 25 A LTC2877 Supply Current in Shutdown Mode DE = 0V, RE = VL = VCC , DI = 0V or VL l 0 5 A ICCR Supply Current with Only Receiver Enabled No Load, DE = 0V, RE = 0V l 600 900 A ICCD Supply Current with Only Driver Enabled No Load, DE = RE = VCC = VL l 700 1100 A ICCDR Supply Current with Both Driver and Receiver Enabled No Load, DE = VCC = VL, RE = 0V l 750 1200 A LTC2877 Logic Supply Current in Shutdown Mode DE = 0V, RE = VL, DI = VL l 0 5 A DE = 0V, RE = VL, DI = 0V l 12 25 A DE = VL, RE = 0V, DI = VL l 30 60 A DE = VL, RE = 0V, DI = 0V l 65 120 A LTC2877 Logic Supply Current with Both Driver and Receiver Enabled 28767fa For more information www.linear.com/LTC2876 3 LTC2876/LTC2877 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = VL = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Driver VOD(PP) Differential Bus Output Voltage (B-A) PROFIBUS LOAD (Figure 1) with PROFIBUS Load RCABLE = 0, VCC = 4.5V to 5.5V RCABLE = 5.5, VCC = 4.5V to 5.5V RCABLE = 11, VCC = 4.75V to 5.5V l l l VBPP-APP Single-Ended Bus Output Amplitude Difference (BPP - APP) All of the Conditions Above l VBPP+APP Single-Ended Bus Output Amplitude Sum |BPP + APP| All of the Conditions Above l |VOD(485)| RS485 Differential Driver Output Voltage, in Either Logic State Figure 2 with No Load l |VOD(422)| RS422 Differential Driver Output Voltage, Either Logic State 4 4 4 7 7 7 0.5 4 VP-P(DIFF) VP-P(DIFF) VP-P(DIFF) V V VCC V RL = 27,VCC = 4.5V to 5.5V (Figure 2) l 1.5 3.4 V RL = 27,VCC = 3.0V to 3.6V (Figure 2) l 0.8 1.8 V Figure 2 with No Load l VCC V RL = 50,VCC = 4.5V to 5.5V (Figure 2) l 2 4 V RL = 50,VCC = 3.0V to 3.6V (Figure 2) l 1 2 V |VOD(485)|, RS485, RS422 Change in Magnitude of RL = 27 (RS485) or |VOD(422)| Driver Differential Output Voltage RL = 50 (RS422) (Figure 2) l 0.2 V VOC(485), VOC(422) RL = 27 (RS485) or RL = 50 (RS422) (Figure 2) l 3 V |VOC(485)|, RS485, RS422 Change in Magnitude of RL = 27 (RS485) or |VOC(422)| Driver Common-Mode Output Voltage RL = 50 (RS422) (Figure 2) l 0.2 V RS485, RS422 Driver Common-Mode Output Voltage Maximum Driver Short-Circuit Current -60V (PB or PA) 60V (Figure 3) l IIN Input Current (PA, PB) VCC = 0V or 5V, VBUS = 12V (Figure 4) VCC = 0V or 5V, VBUS = -7V (Figure 4) l l -100 RIN Input Resistance VBUS = -25V or 25V (Figure 4) l 75 VCM Common Mode Input Voltage (PA+PB)/2 for Data Reception VTS+ Differential Input Signal Threshold Voltage (PB-PA) Rising -25V VCM 25V, Edge Rates > 100mV/s (Note 5) (Figure 13) l 50 VTS- Differential Input Signal Threshold Voltage (PB-PA) Falling -25V VCM 25V, Edge Rates > 100mV/s (Note 5) (Figure 13) l -50 IOSD 150 250 mA 160 A A Receiver 112 135 k 25 V 120 200 mV -120 -200 mV l VTS Differential Input Signal Hysteresis Edge Rates > 100mV/s (Note 5) (Figure 13) VTFS+ Differential Input Failsafe Threshold Voltage (PB-PA) Rising -25V VCM 25V, DC Bus Voltages (Figure 13) l -20 -75 -200 mV VTFS- Differential Input Failsafe Threshold Voltage (PB-PA) Falling -25V VCM 25V, DC Bus Voltages (Figure 13) l -50 -120 -200 mV VTFS Differential Input Failsafe Hysteresis DC Bus Voltages (Figure 13) VOH Receiver Output High Voltage VCC 4.5V, I(RO) = -3mA (LTC2876) VL 2.25V, I(RO) = -3mA (LTC2877) VL < 2.25V, I(RO) = -2mA (LTC2877) l l l VOL Receiver Output Low Voltage VL 1.65V, I(RO) = 3mA (LTC2877) VCC 3.0V, I(RO) = 3mA (LTC2876) l l 4 240 mV 45 mV VCC - 0.4V VL - 0.4V VL - 0.4V V V V 0.4 0.4 V V Receiver Three-State (High Impedance) RE = High, RO = 0V Output Current on RO l -20 -40 A Receiver Three-State (High Impedance) RE = High, RO = VCC (LTC2876) or VL Output Current on RO (LTC2877) l 0 5 A 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = VL = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS Receiver Short-Circuit Current RE = Low, RO = 0V or VCC (LTC2876) or VL (LTC2877) l MIN Low Level Input Voltage (DE, DI, RE) LTC2876, 3.0 VCC 5.5V l LTC2877, 1.65 VL 5.5V l LTC2876, 3.0 VCC 5.5V l 0.75 * VCC 0.75 * VL TYP MAX UNITS 12 20 mA Logic High Level Input Voltage (DE, DI, RE) LTC2877, 1.65 VL 5.5V l Logic Input Current Low (DE) DE = 0V l Logic Input Current Low (DI, RE) DI or RE = 0V l 0.25 * VCC V 0.25 * VL V V V 0 -5 A -3 -10 -20 A 3 10 20 A 0 5 A Logic Input Current High (DE) DE = VCC (LTC2876) or VL (LTC2877) l Logic Input Current High (DI, RE) (DI, RE) = VCC (LTC2876) or VL (LTC2877) l ESD Protection Level of Interface Pins (PA, PB) Human Body Model to GND or VCC, or VL , Powered or Unpowered Human Body Model to GND, Unpowered 52 kV ESD Protection Level of All Other Pins (DE, DI, RE, VCC, VL) Human Body Model 15 kV ESD (Note 4) 26 kV Switching Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = VL = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS fMAX Maximum Data Rate (Note 4) l MIN TYP MAX tPLHD, tPHLD Driver Input to Output VCC = 3.3V or 5V (Figure 5) l 13 50 ns tPD Driver Input to Output Difference |tPLHD - tPHLD| (Figure 5) l 2 9 ns tSKEWD Driver Output PB to Output PA (Figure 5) l 9 ns tRD, tFD Driver Rise or Fall Time VCC = 3.3V or 5V (Figure 5) l tZLD, tZHD, tLZD, tHZD Driver Enable or Disable Time RE = 0V (Figure 6) l tZHSD, tZLSD Driver Enable from Shutdown RE = High (Figure 6) l 15 s tSHDND Time to Shutdown with DE RE = High (Figure 6) l 180 ns tPLHR, tPHLR Receiver Input to Output VCM = 2.25V, (PB-PA) = 1.5V, tR and tF < 4ns, VCC = 3.3V or 5V (Figure 7) l 50 70 ns tPR Receiver Input to Output Difference |tPLHR - tPHLR| (Figure 7) l 2 14 ns tRR, tFR Receiver Output Rise or Fall Time (Figure 7) l 3 15 ns tZLR, tZHR, tLZR, tHZR Receiver Enable/Disable Time DE = High (Figure 8) l 40 ns tZHSR, tZLSR Receiver Enable from Shutdown DE = 0V, (Figure 9) l 9 s tSHDNR Time to Shutdown with RE DE = 0V, (Figure 9) l 40 ns 20 UNITS Mbps Driver 4 15 ns 180 ns Receiver 28767fa For more information www.linear.com/LTC2876 5 LTC2876/LTC2877 Electrical Characteristics 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. Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to device ground unless otherwise specified. Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature exceeds 150C when overtemperature protection is active. Continuous operation above the specified maximum operating temperature may result in device degradation or failure. 6 Note 4: Not tested in production. Note 5: The dependency on edge rate is tested indirectly. Note 6: Does not meet RS485 or PROFIBUS specifications. See the Applications Information section for more information about running with a 3V supply. 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Typical Performance Characteristics TA = 25C. VCC = VL = 5V, unless otherwise noted. (Note 2) 5 750 ICCDR ICCD ICCS (nA) 2 600 ICCR 550 3 3.5 4 4.5 5 VCC SUPPLY VOLTAGE (V) ICCS (nA) 0 5.5 575 28767 G01 7 3 Driver Output Low/High Voltage vs Output Current 5 3 3.5 4 4.5 VCC (V) 5 0 -50 -25 5.5 OUTPUT CURRENT (mA) 4 20 30 40 OUTPUT CURRENT (mA) 80 28767 G07 25 50 75 100 125 150 TEMPERATURE (C) Driver and Receiver Propagation Delay vs VCC RECEIVER 50 OUTPUT LOW 40 0 -40 -80 -160 -60 0 28767 G06 60 OUTPUT HIGH -120 50 20 28767 G05 120 VOL (VCC = 5.0V) 10 15 DATA RATE (Mbps) 1 160 VOH (VCC = 5.0V) 1 5 VOD(PP) PROFI LOAD (Fig. 1), VCC = 5V VOD(422) (Fig. 2, RL = 50), VCC = 5V VOD(485) (Fig. 2, RL = 27), VCC = 5V VOD(422) (Fig. 2, RL = 50), VCC = 3.3V VOD(485) (Fig. 2, RL = 27), VCC = 3.3V 3 Driver Output Short-Circuit Current vs Voltage VOL (VCC = 3.3V) 0 2 28767 G04 2 No Load, VCC = 3.3V 4 4 0 20 VOH (VCC = 3.3V) No Load, VCC = 5V 10 5 1 10 RS485 54/100pF Load (Fig. 5) VCC = 3.3V 20 6 VOD (V) VOD (V) VL SUPPLY CURRENT (mA) 0.5 0 30 Driver Differential Output Voltage vs Temperature 2 3 PROFI 100m cable w/term (Fig.1) VCC = 5V 28767 G03 5 10 15 DATA RATE (Mbps) 40 0 VOD(PP) PROFIBUS LOADS (Fig. 1) VOD(422) (Fig. 2, RL = 50) VOD(485) (Fig. 2, RL = 27) 6 1.0 5 RS485 54/100pF Load (Fig. 5) VCC = 5V 28767 G02 VL = 5V, CRO = 15pF VL = 5V, CRO = 0pF VL = 1.65V, CRO = 15pF VL = 1.65V, CRO = 0pF 0 50 Driver Differential Output Voltage vs Supply Voltage 1.5 DRIVER OUTPUT VOLTAGE (V) 1 0.1 0 25 50 75 100 125 150 TEMPERATURE (C) 500 -50 -25 2.0 0 10 ICCR 3.0 0 100 ICCD 650 VL Supply Current vs Data Rate 2.5 1k ICCDR PROPAGATION DELAY (ns) 500 1 725 ICCS (nA) 3 650 ICCDR, ICCD, ICCR (A) 4 700 VCC Supply Current vs Data Rate 10k 800 ICCS (nA) VCC SUPPLY CURRENT (A) VCC Supply Current vs Temperature for Various Modes, No Load VCC SUPPLY CURRENT (mA) VCC Supply Current vs Voltage for Various Modes, No Load -40 -20 0 20 OUTPUT VOLTAGE (V) 40 40 30 20 DRIVER 10 60 28767 G08 0 3 3.5 4 4.5 VCC 5 5.5 28767 G09 28767fa For more information www.linear.com/LTC2876 7 LTC2876/LTC2877 Typical Performance Characteristics TA = 25C. VCC = VL = 5V, unless otherwise noted. (Note 2) Driver Output Skew vs Temperature Driver Output Propagation Delay Difference vs Temperature 30 5 5 27 4 4 24 3 21 2 15 VCC = 5V 12 3 2 VCC = 5V 1 tPD (ns) VCC = 3.3V 18 tSKEWD (ns) PROPAGATION DELAY (ns) Driver Propagation Delay vs Temperature 0 -1 VCC = 3.3V 1 -1 9 -2 6 -3 -3 3 -4 -4 0 -50 -25 -5 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) 0 28767 G10 VCC = 5V 0 VCC = 3.3V -2 -5 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 28767 G12 Receiver Propagation Delay Difference vs Temperature Receiver Output Voltage vs Output Current (Source and Sink) 5 60 6 VL = 5.5V RECEIVER OUTPUT VOLTAGE (V) 3 55 2 tPR (ns) PROPAGATION DELAY (ns) 4 50 VCC = 3.3V VCC = 3.3V 1 0 VCC = 5V -1 -2 45 -3 -4 40 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) 25 50 75 100 125 150 TEMPERATURE (C) 28767 G11 Receiver Propagation Delay vs Temperature VCC = 5V 0 -5 -50 -25 5 4 VL = 3.3V 3 VL = 2.25V 2 VL = 1.65V 1 VL = 1.65V TO 5.5V 0 25 50 75 100 125 150 TEMPERATURE (C) 0 28767 G14 28767 G13 0 4 6 8 2 OUTPUT CURRENT (ABSOLUTE VALUE, mA) 28767 G15 Receiver Output Voltage vs VL Voltage (LTC2877) PROFIBUS Operation at 12Mbps VCC = 5V RS485 Operation at 20Mbps VCC = 3.3V 400 VOL VL-VOH VOL VL-VOH VOL OR VOH (mV) 300 for I(RO) = +2mA for I(RO) = -2mA for I(RO) = +3mA for I(RO) = -3mA DI 2V/DIV DI 5V/DIV PB 1V/DIV 200 PB 0.5V/DIV PA 1V/DIV DOUBLE PROFIBUS TERMINATION RCABLE = 0 (Fig. 1) 100 50ns/DIV 0 1.5 8 PA 0.5V/DIV 2.5 3.5 VL (V) 4.5 RLDIFF = 54; CL=100pF (Fig. 5) 28767 G17 20ns/DIV 28767 G18 5.5 28767 G16 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Pin Functions (LTC2876/LTC2877) RO (Pin 1): Receiver Output. Supplied by VCC in the LTC2876 or VL in the LTC2877. If the receiver is enabled (RE low) and PB-PA > 200mV, then RO will be high. If PB-PA < -200mV, then RO will be low. If the receiver inputs are open, shorted, or terminated without being driven for more than about 1.5s, RO will be high. Integrated 250k pull-up resistor to supply. RE (Pin 2): Receiver Enable. Logic levels defined by the VCC supply in the LTC2876 or the VL supply in the LTC2877. A low input enables the receiver. A high input forces the receiver output into a high impedance state. If RE is high with DE low, the device enters a low power shutdown state. Integrated 500k pull-up resistor to supply. DE (Pin 3): Driver Enable. Logic levels defined by the VCC supply in the LTC2876 or the VL supply in the LTC2877. A high input on DE enables the driver. A low input forces the driver outputs into a high impedance state. If DE is low with RE high, the device enters a low power shutdown state. Integrated 500k pull-down resistor to ground. DI (Pin 4): Driver Input. Logic levels defined by the VCC supply in the LTC2876 or the VL supply in the LTC2877. If the driver outputs are enabled (DE high), then a low on DI drives a negative differential voltage between PB and PA. A high on DI, with the driver outputs enabled, drives a positive differential voltage between PB and PA. Integrated 500k pull-up resistor to supply. VL (NA/Pin 5): Logic supply: 1.65V VL VCC. Powers RO, RE, DE, and DI on LTC2877 only. Bypass with 0.1F ceramic capacitor to GND. GND (Pin 5, 9/Pin 6,11): Ground NC (NA/Pin 7): Not Internally Connected. PB (Pin 6/Pin 8): PROFIBUS B. Non-inverting receiver input and non-inverting driver output. Connect this to the B wire (positive) in a PROFIBUS network. In most non-PROFIBUS applications, this should connect to the A terminal. See the Applications Information section for more information on A vs B naming conventions. PA (Pin 7/Pin 9): PROFIBUS A. Inverting receiver input and inverting driver output. Connect this to the A wire (negative) in a PROFIBUS network. In most non-PROFIBUS applications, this should connect to the B terminal. See the Applications Information section for more information on A vs B naming conventions. VCC (Pin 8/Pin 10): Power Supply. 4.5V VCC 5.5V for PROFIBUS and RS485 compliant applications; 3.0V VCC 5.5V for a wide range of usage. See 3.3V Operation in the Applications Information section for details. Bypass with 1F ceramic capacitor to GND. Exposed Pad (Pin 9/Pin 11): Must be connected to GND. 28767fa For more information www.linear.com/LTC2876 9 LTC2876/LTC2877 Block Diagram 3V TO 5.5V LTC2876 VCC VCC VCC RO RECEIVER RE PB MODE CONTROL PA DE VCC DI DRIVER GND 28767 BD1 3V TO 5.5V 1.65V TO VCC LTC2877 VCC VL VCC RO RECEIVER RE PB MODE CONTROL PA DE VCC DI DRIVER GND 28767 BD2 10 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Test Circuits VCC VCC LTC2876/LTC2877 BPP VCC APP B RO HIGH HIGH 390 PB RE DE 220 PA DI 390 RCABLE B VOD(PP) A 390 + - B- A 0 220 RCABLE A 0 VBPP-APP = |BPP - APP| VBPP+APP = BPP + APP 390 MEASUREMENTS TAKEN AT STEADY STATE 28767 F01 Figure 1. Driver Differential Output Voltages for PROFIBUS Load VOD(485)+ VOD(485)- VCC |VOC(485)| PB LTC2876/LTC2877 CM PA RO HIGH HIGH RE PB RL VOD(485) DE PA CM PB-PA 0 RL DI VOD(485) = PB-PA VOC(485) + - |VOD(485)| = |VOD(485)+ - VOD(485)- | FOR RS422 MEASUREMENTS, SUBSTITUTE 485 WITH 422 IN THIS FIGURE. MEASUREMENTS TAKEN AT STEADY STATE 28767 F02 Figure 2. Driver Output Voltages in RS485 and RS422 Configurations VCC LTC2876/LTC2877 RO HIGH HIGH HIGH OR LOW RE DE PB PA DI IOSD + - -60V TO +60V 28767 F03 Figure 3. Drive Output Short-Circuit Current 28767fa For more information www.linear.com/LTC2876 11 LTC2876/LTC2877 Test Circuits VCC LTC2876/LTC2877 RO HIGH OR LOW LOW LOW RE PB DE IIN PA + - DI RIN = VBUS VBUS IIN 28767 F04 Figure 4. Receiver Input Current and Input Resistance VCC VCC* LTC2876/LTC2877 tPLHD DI RO tSKEWD PA HIGH HIGH RE PB DE 100pF 54 PA DI tPHLD 0V 100pF VO 1/2VO PB 90% PB-PA 10% 0 0 tRD 90% 10% tFD *FOR THE LTC2877, SUBSTITUTE VL FOR VCC 28767 F05 Figure 5. Driver Timing Measurement 12 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Test Circuits VCC VCC* DE LTC2876/LTC2877 RO 500 PB RE LOW OR HIGH 50pF VCC WHEN DI LOW GND WHEN DI HIGH VCC PA OR PB DE 500 PA DI LOW OR HIGH 1/2VCC* 0V 50pF tZLD, tZLSD tLZD 1/2VCC VOL 0.5V VOH GND WHEN DI LOW VCC WHEN DI HIGH PB OR PA 0.5V 1/2VCC 0V tZHD, tZHSD tHZD, tSHDND *FOR THE LTC2877, SUBSTITUTE VL FOR VCC 28767 F06 Figure 6. Driver Enable, Disable and Shutdown Timing Measurements VCC tPR = |tPLHR - tPHLR| LTC2876/LTC2877 1.5V RO 15pF LOW LOW LOW PB-PA PB RE DE PA VCM (PB-PA)/2 0V -1.5V (PB-PA)/2 tPLHR VCC* 90% 1/2VCC* 10% RO 0 tPHLR 1/2VCC* tRR DI 90% 10% tFR *FOR THE LTC2877, SUBSTITUTE VL FOR VCC 28767 F07 Figure 7. Receiver Propagation Delay Measurements 28767fa For more information www.linear.com/LTC2876 13 LTC2876/LTC2877 Test Circuits VCC FOR DI LOW GND FOR DI HIGH VCC 1k VCC* tZLR RE LTC2876/LTC2877 15pF RO RE LOW OR HIGH tLZR VCC RO HIGH 1/2VCC* 0V PB DE 1/2VCC* VOL 0.5V VOH PA RO DI 0.5V 1/2VCC* 0V tZHR tHZR *FOR THE LTC2877, SUBSTITUTE VL FOR VCC 28767 F08 Figure 8. Receiver Enable and Disable Timing Measurements VCC FOR CASE1 GND FOR CASE2 VCC 1k VCC* LTC2876/LTC2877 15pF LOW DE DI tSHDNR VCC* CASE 1 CASE 2 LOW 1/2VCC* 0V RO RE tZLSR RE PB PA 0V VCC VCC 0V RO 1/2VCC* VOL 0.5V VOH RO 0.5V 1/2VCC* 0V tZHSR *FOR THE LTC2877, SUBSTITUTE VL FOR VCC tSHDNR 28767 F09 Figure 9. Receiver Shutdown Timing Measurements 14 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Applications Information Note: Specifications in this section represent typical values unless otherwise noted. be compliant to PROFIBUS requirements. The LTC2876/ LTC2877 was designed specifically to meet PROFIBUS and RS485 requirements and is tested in a way that ensures this. PROFIBUS-DP and RS485 Cable and Termination Differences from RS485 PROFIBUS-DP can communicate over a variety of media, including copper wires, fiber optics, and even air in an infrared communicator. By far, the most commonly used media is a twisted pair of wires connecting devices that communicate with TIA/EIA-485-A (RS485) transceivers. The cable and termination network used for PROFIBUS is different than for RS485 as illustrated in Figure 10. The PROFIBUS network includes bus biasing resistors that are used in conjunction with the differential termination resistors on each end of the bus. The cable is a shielded twisted pair with an impedance of 150. Oddly enough, the effective differential resistance of the specified termination network is 172, which is not a perfect match for the 150 cable, resulting in a slightly underdamped network. This manifests itself as a small bump, or increase in the signal voltage, at the receiving end of the cable, lasting twice as long as the cable propagation delay. RS485 offers high speed differential signaling that is robust for communication between multiple devices over long distances in noisy environments such as factory applications. Not All RS485 Transceivers Are Suitable for PROFIBUS Although the PROFIBUS standard specifies the use of RS485 devices at the physical layer, there are differences in the cable, termination, and driver requirements from RS485. A device meeting RS485 specifications may not 5V PROFIBUS MASTER In contrast, the RS485 network shows the preferred configuration with only differential termination resistors at each end of the bus, matching the 120 characteristic impedance of the cable. Profibus Multi-Node Network Twisted Pair Cable (ZO = 150) 5V 390 390 220 220 390 PROFIBUS STATION 390 PROFIBUS STATION PROFIBUS STATION RS485 Multi-Node Network Twisted Pair Cable (ZO = 120) RS485 MASTER 120 120 RS485 NODE RS485 NODE RS485 NODE 28767 F10 Figure 10. Cable and Termination Differences in RS485 and PROFIBUS Multi-Node Networks. PROFIBUS Type A Cable and Termination Shown in PROFIBUS Example (Top) 28767fa For more information www.linear.com/LTC2876 15 LTC2876/LTC2877 Applications Information Driver Output Requirement Differences from RS485 Driver Operation The driver requirements for PROFIBUS are specified differently than how the RS485 standard specifies them. A key difference is the terminated driver output voltage, VOD, as described below. The driver is enabled when the LTC2876/LTC2877 is powered up, DE is high, and there are no thermal faults. The polarity of PB-PA follows that of DI. That is, when DI is high, PB drives to a voltage that is greater than PA. If DI is low, PA is higher than PB. When the driver is disabled with DE low, both outputs are high impedance and the overall pin resistance is dominated by the receiver inputs sharing pins PA and PB. The PROFIBUS driver output levels are required to meet the following condition as stated in the "Test Specification for PROFIBUS DP Masters" and "Test Specification for PROFIBUS DP Slaves": * The differential voltage between A- and B-line shall be a minimum of 4V and a maximum of 7V, peak-to-peak differential. * This measurement shall be taken at the far end of the cable in use, with termination at each end. On the other hand, RS485 specifies the following: * The differential voltage between A- and B-line shall be a minimum of 1.5V and a maximum of 5V, peak differential. * This measurement shall be taken at the driver terminals with a 54 resistor between A and B. Clearly, these requirements are quite different. A common misunderstanding is that if an RS485 driver develops more than 2.1V across a 54 RS485 resistive load, then it will meet PROFIBUS requirements when used with a PROFIBUS termination network. This is not always the case. Furthermore, the strength of the driver can be too high, exceeding the upper limit of the PROFIBUS Specification (7VP-P). The best way to ensure PROFIBUS compliance is to test the device with a PROFIBUS load. The LTC2876 and LTC2877 are tested with a PROFIBUS load and with extra resistance added to represent cable losses for 100m and 200m to ensure they meet the PROFIBUS VOD requirement. The devices are also fully tested with RS485 loads to ensure they meet RS485 specifications. See the Electrical Characteristics section for details. 16 Driver Overvoltage and Overcurrent Protection The driver outputs PA and PB are protected from short circuits to any voltage within the absolute maximum range of -60V to +60V, with a maximum differential voltage of -120V to +120V. The maximum short-circuit current to any voltage within this range is 250mA. The driver includes a progressive foldback current limiting circuit that continuously reduces the driver current limit with increasing output short circuit voltage to better manage power dissipation and heating effects. The LTC2876/LTC2877 also features thermal shutdown protection that disables the driver and receiver in case of excessive power dissipation (see Note 3). Receiver The receiver provides full PROFIBUS and RS485 compatibility. When enabled, the state of RO reflects the polarity of (PB-PA). When the receiver is disabled, the output is high impedance and RO weakly pulled high through an internal 250k pull-up resistor. High Receiver Input Resistance Permits 200 Nodes The RS485 and PROFIBUS specifications allows for up to 32 receivers, each contributing one unit load, to be connected together in one network. The input resistance of the LTC2876/LTC2877 is guaranteed to be at least 6.25 times higher, and drawing proportionally less current, than a standard RS485 load, permitting a total of 200 receivers per contiguous network. The input load of the receiver is unaffected by enabling/disabling the receiver or by powering/depowering the device. 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Applications Information Balanced Signal Threshold LTC2876, LTC2877 - BALANCED THRESHOLDS The LTC2876/LTC2877 differential threshold is 120mV for rising input signals and -120mV for falling signals. This constitutes 240mV of hysteresis, which offers a high rejection to signal noise that can otherwise falsely trip a receiver. Since these thresholds are centered around zero volts (i.e. "balanced"), the duty cycle is preserved for small amplitude signals with slewed edges--typical of what is observed at the end of a long cable. Figure 11 illustrates this point. In contrast to this, some RS485 receivers have an unbalanced receiver threshold, used to address failsafe conditions (more on this below). That is, the rising and falling differential signal thresholds are both negative. Figure 12 illustrates an example where the rising threshold is -75mV and falling threshold is -120mV. This has two disadvantages. First, the hysteresis is only 45mV in this example, reducing the tolerance to noise, compared to the 240mV of hysteresis in the LTC2876/LTC2877. Secondly, these unbalanced thresholds cause a duty cycle or pulse width distortion at the receiver output relative to the input signal. Figure 12 illustrates how a competitor part, using the negative thresholds in this example introduces a duty cycle distortion that becomes increasingly worse with low input signal levels and slow input edge rates. Failsafe Operation The LTC2876 and LTC2877 have a failsafe feature that guarantees the receiver output will be in a logic 1 state (the idle state) when the inputs are shorted, left open, or terminated but not driven for more than about 1.5s. This failsafe feature is guaranteed to work for inputs spanning the entire common mode range of -25V to +25V. Many RS485 receivers simply employ a negative threshold (for rising and falling signals) to achieve failsafe operation. If the inputs are shorted together (0V differential), the receiver produces a high output, consistent with failsafe. However, this asymmetrical threshold comes with the disadvantages of pulse width distortion and sensitivity to signal noise as described in the section above. The LTC2876/LTC2877 achieves full failsafe operation, while reaping the benefits of a balanced receiver threshold. +200mV +120mV (PB-PA) VTS+ 0 -120mV VTS- -200mV RO 28767 F11 Figure 11. The LTC2876/LTC2877 Balanced Signal Threshold Voltages Preserve the Duty Cycle of an Incoming Signal. The Differential Signal Received (Top) Has a Duty Cycle of 50%, and Is Reflected In the Receiver Output, RO (Bottom) UNBALANCED THRESHOLDS +200mV (PB-PA) 0 -75mV -120mV VTS+ VTS- -200mV RO 28767 F12 Figure 12. Typical Competitor Unbalanced Signal Threshold Voltages Distort the Duty Cycle of an Incoming Signal. Input Is 50% Duty Cycle (Top) But the Receiver Output Is Not 50% Duty Cycle (Bottom) Failsafe operation is performed with a window comparator to determine when the differential input voltage falls between the rising and falling signal thresholds (VTS+, and VTS-). If this condition persists for more than about 1.5s then the receiver switches over to using the failsafe thresholds (VTFS-, VTFS+), as illustrated in Figure 13 and Figure 14. The delay allows normal data signals to transition through the threshold region without being interpreted as a failsafe condition, and thus maintaining the benefits of a balanced threshold receiver. However, for fault conditions (e.g., shorted, open, or undriven lines) that persist for more than 1.5s, the failsafe thresholds are engaged and the receiver output drives high, indicating this condition. The failsafe delay also prevents unwanted receiver output 28767fa For more information www.linear.com/LTC2876 17 LTC2876/LTC2877 Applications Information or RE goes low during this delay, the delay timer is reset and the chip does not enter shutdown. This reduces the chance of accidentally entering shutdown if DE and RE are driven in parallel by a slowly changing signal or if DE and RE are driven by two independent signals with a timing skew between them. VTS VTFS RO (PB-PA) VTS - , VTFS - -200mV -120mV VTFS + VTS + -75mV 0 +120mV +200mV 28767 F13 Figure 13. The LTC2876/LTC2877 Signal Thresholds (VTS-, VTS+) and Failsafe Thresholds (VTFS-, VTFS+) +200mV +120mV VTS+ (PB-PA) 0 -75mV -120mV VTFS+ VTS-, VTFS- -200mV 2 1 RO 3 4 28767 F14 Figure 14. LTC2876/LTC2877 Receiver Operation. Event 1: Signal Rises into Region Between Signal Thresholds, Resulting in the RO Transitioning to a Failsafe Condition After a Fixed Delay of About 1.5s. Event 2: Input Signal Falls Below Negative Signal Threshold, Resulting in an Immediate Fall on RO. Event 3: Signal Glitches into the Region Between Signal Thresholds for a Period Less Than the Failsafe Delay Time (~1.5s), Resulting in an Unchanged Output. Event 4: Signal Transitions Above Rising Signal Threshold, Resulting in an Immediate Rise in RO glitches resulting from receiver inputs that momentarily cross into the region between the signal rising and falling thresholds as illustrated in Figure 14, event 3. Shutdown Mode Delay The LTC2876 and LTC2877 feature a low power shutdown mode that is entered when both the driver and receiver are simultaneously disabled (pin DE low and RE high). A shutdown mode delay of approximately 250ns (not tested in production) is imposed after the state is received before the chip enters shutdown. If either DE goes high 18 This shutdown mode delay does not affect the outputs of the transmitter and receiver, which start to switch to the high impedance state upon the reception of their respective disable signals as defined by the parameters tSHDND and tSHDNR. The shutdown mode delay affects only the time when all the internal circuits that draw DC power from VCC are turned off. Power-Up/Down Glitch-Free Outputs The LTC2876 and LTC2877 employ an undervoltage detection circuit to control the activation of the on-chip circuitry. During power-up, PB, PA, and RO are undriven, until the VCC supply reaches a voltage sufficient to reliably operate the chip. In this mode, only the internal pull-up resistor on RO and the receiver input resistance to ground on PA and PB offer weak conduction paths at those pins. As the supply voltage rises above the undervoltage threshold, and if the device is configured for drive mode, the PB and PA pins become active and are driven to a state that reflects the input condition on DI. Likewise, if the device is configured for receive mode, the RO pin is driven high or low to reflect the state of the differential voltage across PB-PA. During power down, the reverse occurs; the supply undervoltage detection circuit senses low supply voltage and immediately puts the chip into shutdown. The driver and receiver outputs go to the undriven state. RO is pulled up through the internal 250k pull-up resistor and PA, PB are pulled low through the 125k receiver input resistors. If the LTC2876/LTC2877 is powered or depowered when configured for shutdown (RE = 0V and DE = VL (LTC2877) or VCC (LTC2876) then RO, PB, and PA will remain in the undriven state, without glitching high or low during the supply transition. This allows the powering and depowering of the LTC2876/LTC2877 when connected onto a live network without disturbing the lines. 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Applications Information 60V Fault Protection technology. The naturally high breakdown voltage of this technology provides protection in powered off and high impedance conditions. Figure 15 further illustrates how the driver and receiver inputs tolerate large voltages above the supply and below ground without excessive device currents. As shown, the driver outputs are reverse-diode protected from voltages back-driven above VCC or below ground. The receiver inputs use resistive dividers that tolerate large positive and negative voltages. The LTC2876/ LTC2877 is protected from 60V bus faults even with the loss of GND or VCC. TIA/EIA-485-A specifies that ground shifts between two devices on a network can be as large as -7V to +12V during operation. Most RS485 transceivers cannot safely tolerate voltages on their interface pins that are much higher than this range. However, industrial installations may encounter voltages much greater than this, causing damage to the devices. This requirement means that a driver and receiver sharing communication on a network must be able to operate with a signal common mode voltage difference of -7V to 12V. Competing PROFIBUS transceivers can be damaged by pin voltages exceeding these levels by only a few volts. The limited overvoltage tolerance makes implementation of effective external protection networks difficult without interfering with proper data network performance. Replacing standard RS485 transceivers with the LTC2876 or LTC2877 can eliminate field failures due to overvoltage faults without using costly external protection devices. The 60V fault protection of the LTC2876/LTC2877 is achieved by using a high voltage BiCMOS integrated circuit 25V Extended Common Mode Range The LTC2876/LTC2877 receiver features an extended common mode range of -25V to +25V. The wide common mode increases the reliability of operation in environments with high common mode voltages created by electrical noise or local ground potential differences due to ground loops. This extended common mode range allows the LTC2876/ LTC2877 to transmit and receive under conditions that would cause data errors or possible device damage in competing products. PB PA LTC2876/LTC2877 SIMPLIFIED DRIVER OUTPUT STAGE VCC VCC LTC2876/LTC2877 SIMPLIFIED RECEIVER INPUT STAGE 20:1 DIVIDE TO RO OUTPUT CIRCUITS FROM DI INPUT CIRCUITS 20:1 DIVIDE 28767 F15 Figure 15. Internal Circuit Structure at PA/PB Pins That Tolerates Large Positive and Negative Voltages 28767fa For more information www.linear.com/LTC2876 19 LTC2876/LTC2877 Applications Information Electrical Overstress Protection Equipment used in industrial environments is often exposed to extremely high levels of electrical overstress due to phenomena such as electrostatic discharges (ESD) from personnel or equipment, electrical fast transients (EFT) from switching high current inductive loads, and even lightning surges. The LTC2876/LTC2877 has been designed to thrive in these adverse conditions. ESD Perhaps the most common exposure to electrical overstress is ESD, which results from the build-up of electrical charge on one object, and discharged onto another in close proximity. The LTC2876/LTC2877 features exceptionally robust ESD protection. The bus interface pins (PB and PA) are protected to 52kV human body model (HBM) with respect to GND when unpowered and 26kV with respect to GND, VCC, or VL when powered, without latchup or damage, in any mode of operation. Every other pin on the device is protected to 15kV ESD (HBM) for all-around robustness. Figure 16 shows an unprotected LTC2876 struck repeatedly with 26kV from an ESD gun using air discharge to illustrate the strike energy. The device continues to function normally after the strikes, without damage or cycling the power. Figure 16. This Single Exposure Image Captures the Striking Robustness of an Unprotected LTC2876 Hit Repeatedly with 26kV ESD Discharges While Operating without Damage or Circuit Latchup 20 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Applications Information The IEC standard for ESD, IEC 61000-4-2, specifies a very fast (sub-nanosecond) edge transient stimulus intended for system level ESD testing and not specified at the device level. However, if it is applied directly to the bus interface pins, without any external protection devices, the LTC2876/ LTC2877 is protected to 4kV IEC when used in a typical application, powered or unpowered, and terminated with the standard PROFIBUS load. This is not tested in production. EFT Electrical fast transients can result from arcing contacts in switches and relays, common when switching inductive loads. The IEC standard for EFT is IEC61000-4-4 and specifies a repetitive burst pattern lasting 60 seconds. The LTC2876/LTC2877 is robust to EFT events and passes the highest level recognized in the IEC standard: level 4, 2kV on the PA and PB pins, without any external protection. Auxiliary Protection for Surge Surge events represent the most severe transient conditions caused by such things as load switching in power distribution systems, high current short circuit faults, and lighting strikes. These are addressed in standard IEC 61000-4-5, which specifies repetitive voltage and current waveforms used to deliver high power stimulus lasting tens of microseconds each. The LTC2876/LTC2877 is designed for high robustness against ESD and EFT, but the on-chip protection is not able to absorb the energy associated with the IEC 61000-4-5 surge transients. External protection is necessary to achieve a high level of surge protection, and can also extend the ESD and EFT protection to extremely high levels. In addition to providing transient protection, externally connected devices must preserve the ability of the LTC2876/ LTC2877 to operate over a wide common mode voltage and yet safely clamp the pin voltage low enough to avoid damage during the overstress event. The added protection must be low in capacitance to avoid excessively loading the transceiver bus, allowing operation at full data rate. The LTC2876/LTC2877's 60V pin rating makes it easy to find protection devices meeting these requirements. Figure 21 shows a solution providing 4kV protection of the bus Interface pins (PA and PB) for all three IEC 61000 standards as follows: IEC 61000-4-5 2nd Ed. 2005-11 Surge Level 4: 4kV (line to GND, 8/20s waveform, each line coupled to generator through 80 resistor per Figure 14 of the standard) IEC 61000-4-4 2nd Ed. 2004-07 EFT Level 4: 4kV (line to GND, 5kHz repetition rate, 15ms burst duration every 300ms, 60s test duration, discharge coupled to bus pins through 100pF capacitor per paragraph 7.3.2 of the standard) IEC 61000-4-2 2nd Ed. 2008-12 ESD Level 3: 4kV contact (line to GND, direct discharge to bus pins with transceiver and standard PROFIBUS resistor load and protection circuit mounted on a ground referenced test card per Figure 4 of the standard) The TVS devices in Figure 21 have a typical clamp voltage of about 36V, comfortably beyond the LTC2876/LTC2877's common mode operating range of 25V and well below the 60V rating. Since the LTC2876/LTC2877 bus pins are rated for 60V, the clamping device must maintain voltages less than this when conducting peak current during the overstress event. This relatively wide voltage window permits the use of smaller, more resistive clamps, which generally also have less capacitance. Two of these TVS devices are used in an antiparallel configuration because each can only protect in one polarity. The benefit of these uni-directional TVS devices is their low capacitance, offering a total load of only about 50pF to the signal lines in this configuration, permitting the LTC2876/ LTC2877 to communicate at maximum data rates with no significant performance degradation. 28767fa For more information www.linear.com/LTC2876 21 LTC2876/LTC2877 Applications Information Bus Pins PA & PB Naming Convention Table 1. PROFIBUS Type-A Cable Properties PROFIBUS communicates with RS485 signaling through a differential signal interface. These wires are labeled A and B. The PROFIBUS standard specifies that the bus wire B takes on a positive value with respect to bus wire A when no station is transmitting data (during the idle periods). However, the polarity convention of most RS485 devices uses the opposite convention. That is, with no transmission on the bus, the receiver reports a logic value that would result if A were higher than B--in this case a high on RO. From a practical standpoint, this means that if a general RS485 transceiver is connected to a PROFIBUS network, the transceiver's A pin must connect to the B wire and the B pin connect to the A wire. Certainly this can be confusing! PROPERTY VALUE Impedance 135 to 165 Capacitance < 30pF/m Loop Resistance < 110/km Conductor Area 0.34mm2 Color of Sheath (Non-IS) Violet Color of Inner Conductor A Green Color of Inner Conductor B Red Since the LTC2876/LTC2877 was designed specifically for PROFIBUS applications, the pin naming convention was made to match the PROFIBUS specification. To avoid confusion with other RS485 transceivers, the prefix "P" was added, meaning "PROFIBUS." If driver and receiver are enabled, a high level on DI, will drive the bus lines so that PB is higher than PA and the receiver will report a high level on RO. In PROFIBUS installations, connect PB to the B wire (red) and PA to the A wire (green). For non-PROFIBUS RS485 applications, the PB pin should be connected to the A signal and PA pin should be connect to the B signal to match the convention of most other RS485 devices. PROFIBUS Cables It is recommended that PROFIBUS installations use cable designed for PROFIBUS applications. Typically, Type A cable and termination is used. This is a shielded twisted pair with the following properties: 22 The three resistors that make up the termination network should be placed at both ends of the bus and must be powered during operation. If there are multiple nodes communicating on the bus, only the nodes at the ends should be terminated. The cable shield helps to improve electromagnetic compatibility (EMC). It is recommended to ground both ends of the shield, through the case of the connector, to the chassis of the connected station. In applications where ground potential differences exist between stations, for example long distance transmission between buildings, the shield should be grounded only at one end of the cable. If the potential difference exceeds several volts, galvanic isolation is recommended at one or more of the connected stations. In this case, consider using the LTM(R)2892 Module isolator (see 3500VRMS Isolated PROFIBUS Node with Termination on the last page). If the shield cannot be grounded through the connector case, pin 1 of the D-sub connector can be used as an alternative, although the added inductance makes this sub-optimal. In such a case, it is better to bare the cable shield at an appropriate point and ground it with a short cable or clamp to the metallic structure of the station. Unshielded cable can be used in PROFIBUS installations if there is no severe electromagnetic interference (EMI). Do not use cables that are untwisted pairs. 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Applications Information Maximum PROFIBUS Cable Length The following table gives the maximum cable segment lengths at PROFIBUS baud rates, as specified in IEC 61158-2: Table 2. PROFIBUS Maximum Cable Length BAUD RATE (kbits/s) MAX. SEGMENT LENGTH (m) The D-sub connector is specified for use up to 12Mbps. Inductors are often built into the cable connectors to reduce unwanted ringing and reflections at data rates above 1.5Mbits/s. Cable connectors are also available with termination resistors that can be switched in/out. Table 3. Pin Designation For D-Sub and M12 Connectors. (Connections in Bold are Mandatory) 9.6 1200 19.2 1200 45.45 1200 93.75 1200 187.5 1000 500 400 1500 200 3000 100 5 3 GND for Bus Termination 6000 100 6 1 VCC (+5V) for Bus Termination 12000 100 7 PIN NUMBER 9-PIN D-Sub M12 CONNECTION 1, Case Thread Cable Shield 2 3 GND for 24V Supply 4 4 8 CNTR-P (Repeater Direction Control) +24V Supply 2 9 Connectors 2 4 3 4 1 3 5 5 M12 PLUG 2 6 2 3 7 4 8 Not Used Operation in RS485 and RS422 Systems The LTC2876 and LTC2877 are completely compatible with standard RS485 and RS422 networks. In these installations, the PB pin should be treated as the A pin for compatibility with most RS485 transceivers. Likewise, the PA pin should be matched up with the B signal in RS485. Further discussion about this can be found in section "Bus Pins PA and PB Naming Convention." Twisted pair cables with characteristic impedance of 120 or 100 can be used. Shielded cable is recommended for the highest electromagnetic compatibility (EMC), but unshielded cable like CAT-5e works well. Untwisted pair cables (UTP) should be avoided. Both ends of a cable should be terminated differentially with resistors that match the cable's impedance, as illustrated in Figure 10. 1 M12 SOCKET 1 PA (A - Green Wire) CNTR-N (Repeater Direction Control) 5 The PROFIBUS standard only specifies the use of a 9-pin D-sub connector for stations and cables. A commonly used alternative is the 5-pin "B-coded" M12 circular connectors (IEC 947-5-2). In all cases, the female side of the connector is located in the station, while the cable uses the male end. Connector diagrams are shown in Figure 17 and pin designations are shown in Table 3. PB (B - Red Wire) 5 9 9-PIN D-SUB 28767 F16 Figure 17. Connector Pin Allocations Sometimes bus biasing resistors are used for nonPROFIBUS RS485 installations to introduce a high level (IDLE state) on the bus when nothing is driving it. An example of such a network is shown in Figure 181. Here the three resistors (620, 130, and 620) replace the single 120 differential resistor in one location only. 28767fa For more information www.linear.com/LTC2876 23 LTC2876/LTC2877 Applications Information 5V due to the overvoltage-tolerant design of the LTC2876/ LTC2877, as illustrated in Figure 15. 620 LTC2876 OR LTC2877 130 120 BUS BIAS RESISTORS AT ONE END 620 LTC2876 OR LTC2877 28767 F17 Figure 18. Using the LTC2876/LTC2877 in an RS485 Network (Not PROFIBUS) with Optional Bus Bias Resistors Unlike PROFIBUS, the biasing network is not part of the RS485 standard. Although the LTC2876 and LTC2877 are compatible with this biasing arrangement, the internal failsafe feature eliminates the need for it, since an undriven bus triggers a failsafe condition. In extremely noisy environments the resistor biasing helps reinforce the failsafe condition. VL Logic Supply A separate logic supply pin VL allows the LTC2877 to interface with any logic signal from 1.65V to 5.5V. All logic I/Os use VL as their high supply. It is recommended that VL does not exceed VCC during operation. If VL does exceed VCC, no damage will occur but the VL supply current could increase about 300A, depending on the operating configuration and the state of the device. If VL is not connected to VCC, bypass VL with a 0.1F capacitor to GND. The driver is disabled and pins PB and PA are undriven when VL or VCC is grounded or disconnected. 3.3V Operation The LTC2876 and LTC2877 can be used with a supply voltage as low as 3.0V in RS485 installations. Reducing the supply voltage reduces the driver output signal swing below what is specified in the RS485 standard but still produces signals much larger than the 200mV minimum signal swing required at the receiver input. A plot in the Typical Characteristics section shows the driver output signal for 3.3V and 5V supply voltages. 3.3V-powered LTC2876/LTC2877 devices can be mixed with other RS485 transceivers running from 5V on the same network as shown in Figure 20. There is no concern for the higher voltage of a 5V node overdriving the 3.3V node 24 One advantage to using a lower supply voltage is reduced VCC current draw. VCC supply currents are roughly proportional to the applied supply voltage when the LTC2876/ LTC2877 is driving loads. The Typical Characteristics section shows the typical power supply currents versus transmission rates for 3.3V and 5V supplies. PROFIBUS installations that use the LTC2876/LTC2877 with supply voltages less than 4.5V, may fall out of compliance to the PROFIBUS specification. High Speed Considerations A ground plane layout with a 1F bypass capacitor placed less than 7mm away from VCC is recommended. The PC board traces connected to signal PB and PA should be symmetrical and as short as possible to maintain good differential signal integrity. To minimize capacitive effects, the differential signals should be separated by more than the width of a trace and should not be routed on top of each other if they are on different signal planes. Care should be taken to route the outputs away from the sensitive inputs to reduce feedback effects that might cause noise, jitter, and even oscillations. For example, DI and RO should not be routed next to each other or next to PB and PA. Logic inputs have a typical hysteresis of about 150mV to provide noise immunity. Fast edges on the outputs can cause glitches in the ground and power supplies which are exacerbated by capacitive loading. If a logic input is held near its threshold (typically VCC /2 or VL/2), a noise glitch from a driver transition may exceed the hysteresis levels on the logic and data input pins, causing an unintended state change. This can be avoided by maintaining normal logic levels on the pins and by slewing inputs faster than 1V/s. Good supply decoupling and proper driver termination also reduces glitches caused by driver transitions. References 1 "Application Guidelines for TIA/EIA-485-A": TSB-89-A, TIA Telecommunications System Bulletin, January 2006. 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Applications Information VCC VL 4.5V to 5.5V LTC2876 VCC 9-PIN D-SUB CONNECTOR (FEMALE) 1F VCC RO PB C 1 PB 0.1F VL 3 PA VCC LTC2877 1F PB PB SENSOR 8 9-PIN D-SUB CONNECTOR (FEMALE) 1 6 RE PA DI PA 3 8 PA 5 DE 5 DE GND GND GND GND (a) 6 VCC RO C DI 4.5V to 5.5V 6 RE SENSOR VCC 1.65V to 5.5V (b) 1 390 3 220 PROFIBUS CABLE (ZO = 150) 390 6 1 B 8 220 8 A 5 9-PIN D-SUB CONNECTOR (MALE) SHIELD 390 390 TERMINATION RESISTOR STRINGS SWITCHED IN TO SIGNAL LINES IF LOCATED AT BUS END 3 5 9-PIN D-SUB CONNECTOR (MALE) (c) 28767 F18 Figure 19. Complete Configuration for PROFIBUS Operation Using the (a) LTC2876, or (b) LTC2877 and (c) the Cable with Termination Resistors 28767fa For more information www.linear.com/LTC2876 25 LTC2876/LTC2877 Applications Information 3V TO 5.5V 3V TO 5.5V VCC PB LTC2876/ LTC2877 A 120 3.3V OR 5V RS485 NODE 120 B PA 28767 F19 Figure 20. LTC2876/LTC2877 Operation as Low as 3V is Compatible with Other RS485 Devices, but with Reduced Output Signal Swing TVS TVS PB PB PA PA LTC2876/ LTC2877 TVS TVS: LITTLEFUSE SACB30 TVS 28767 F21 Figure 21. Exceptionally Robust, Low-Capacitance, 30V Tolerant, 4kV IEC 61000 Bus Protection Against Surge, EFT, and ESD. (See Auxiliary Protection for Surge, EFT, and ESD in the Applications Information Section for More Details) 26 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Package Description Please refer to http://www.linear.com/product/LTC2876#packaging for the most recent package drawings. DD Package 8-Lead Plastic DFN (3mm x 3mm) (Reference LTC # 05-08-1698 Rev C) DDDWG Package 8-Lead Plastic DFN (3mm x 3mm) (Reference LTC DWG # 05-08-1698 Rev C) 0.70 0.05 3.5 0.05 1.65 0.05 2.10 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED PIN 1 TOP MARK (NOTE 6) 0.200 REF 3.00 0.10 (4 SIDES) R = 0.125 TYP 5 0.40 0.10 8 1.65 0.10 (2 SIDES) 0.75 0.05 4 0.25 0.05 1 (DD8) DFN 0509 REV C 0.50 BSC 2.38 0.10 0.00 - 0.05 BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON TOP AND BOTTOM OF PACKAGE 28767fa For more information www.linear.com/LTC2876 27 LTC2876/LTC2877 Package Description Please refer to http://www.linear.com/product/LTC2876#packaging for the most recent package drawings. DD Package Package 10-Lead Plastic DFNDD (3mm x 3mm) 10-Lead DFN (3mm (Reference LTC DWGPlastic # 05-08-1699 Rev C)x 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 0.05 3.55 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 0.10 (4 SIDES) R = 0.125 TYP 6 0.40 0.10 10 1.65 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 5 0.75 0.05 0.00 - 0.05 1 (DD) DFN REV C 0310 0.25 0.05 0.50 BSC 2.38 0.10 (2 SIDES) BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 28 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Package Description Please refer to http://www.linear.com/product/LTC2876#packaging for the most recent package drawings. MS8E Package 8-Lead Plastic MSOP , Exposed Die Pad MS8E Package (Reference LTC MSOP, DWG # 05-08-1662 Rev Pad K) 8-Lead Plastic Exposed Die (Reference LTC DWG # 05-08-1662 Rev K) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 (.074) 1 1.88 0.102 (.074 .004) 0.29 REF 1.68 (.066) 0.889 0.127 (.035 .005) 0.05 REF 5.10 (.201) MIN DETAIL "B" CORNER TAIL IS PART OF DETAIL "B" THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 1.68 0.102 3.20 - 3.45 (.066 .004) (.126 - .136) 8 3.00 0.102 (.118 .004) (NOTE 3) 0.65 (.0256) BSC 0.42 0.038 (.0165 .0015) TYP 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 0.102 (.118 .004) (NOTE 4) 4.90 0.152 (.193 .006) DETAIL "A" 0 - 6 TYP GAUGE PLANE 0.53 0.152 (.021 .006) DETAIL "A" 1 2 3 4 1.10 (.043) MAX 0.86 (.034) REF 0.18 (.007) SEATING PLANE 0.22 - 0.38 (.009 - .015) TYP 0.65 (.0256) NOTE: BSC 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 0.1016 0.0508 (.004 .002) MSOP (MS8E) 0213 REV K 28767fa For more information www.linear.com/LTC2876 29 LTC2876/LTC2877 Package Description Please refer to http://www.linear.com/product/LTC2876#packaging for the most recent package drawings. MSE Package 10-Lead Plastic MSOP, Exposed Die Pad MSE Package (Reference LTC DWG # 05-08-1664 Rev I) 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 0.102 (.074 .004) 5.10 (.201) MIN 1 0.889 0.127 (.035 .005) 1.68 0.102 (.066 .004) 0.05 REF 10 0.305 0.038 (.0120 .0015) TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 0.102 (.118 .004) (NOTE 3) DETAIL "B" CORNER TAIL IS PART OF DETAIL "B" THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 10 9 8 7 6 DETAIL "A" 0 - 6 TYP 1 2 3 4 5 GAUGE PLANE 0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE 0.86 (.034) REF 1.10 (.043) MAX 0.17 - 0.27 (.007 - .011) TYP 0.50 (.0197) BSC NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 30 0.497 0.076 (.0196 .003) REF 3.00 0.102 (.118 .004) (NOTE 4) 4.90 0.152 (.193 .006) 0.254 (.010) 0.29 REF 1.68 (.066) 3.20 - 3.45 (.126 - .136) 0.50 (.0197) BSC 1.88 (.074) 0.1016 0.0508 (.004 .002) MSOP (MSE) 0213 REV I 28767fa For more information www.linear.com/LTC2876 LTC2876/LTC2877 Revision History REV DATE DESCRIPTION A 08/16 Changed test condition for tPLHR and tPHLR PAGE NUMBER 5 28767fa 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. For more information www.linear.com/LTC2876 31 LTC2876/LTC2877 Typical Application 3500VRMS Isolated PROFIBUS Node with Termination ISOLATED 5VIN 3V TO 5.5V RO D R DI A6 A5 A4 B1 B2 B3 A3 A2 A1 B4 B5 B6 VCC1 VL1 ON1 OUTD OUTE OUTF INC INB INA EOUTD GND1 GND1 ISOLATION BARRIER LTM2892-S VCC2 VL2 ON2 IND INE INF OUTC OUTB OUTA EOUTA GND2 GND2 J6 J5 J4 J1 J2 J3 H3 H2 H1 H4 H5 H6 8 VCC LTC2876 390 1 RO PB 4 6 3 2 RE 7 4 DI 3 DE 1 220 PA GND 2 M12 CONNECTOR (FEMALE) 390 5 ISOLATED GROUND 28767 TA02 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC2862/LTC2863/ 60V Fault Protected 3V to 5.5V RS485/RS422 Transceivers LTC2864/LTC2865 60V Tolerant, 15kV ESD, 250kbps or 20Mbps LTC2856/LTC2857/ 5V 20Mbps and Slew Rate Limited 15kV RS485/RS422 LTC2858 Transceivers 15kV ESD, 250kbps or 20Mbps LTC2850/LTC2851/ 3.3V 20Mbps RS485 Transceivers LTC2852 15kV ESD LTC2854/LTC2855 25kV ESD (LTC2854), 15kV ESD (LTC2855) 3.3V 20Mbps RS485 Transceivers with Integrated Switchable Termination LTC2859, LTC2861 5V 20Mbps and Slew Rate Limited RS485 Transceivers 15kV ESD LTM2881 Complete 3.3V or 5V Isolated RS485 Module Transceiver + Power, and Switchable Integrated Termination Resistor 2500VRMS Isolation, with Integrated Isolated DC/DC Converter, 1W Power, Low EMI, 15kV ESD, 30kV/s Transient Immunity LTM2892 3500VRMS 6-Channel Digital Isolator 3500VRMS Isolation in a Small Package with Temperature Ratings Up to 125C 32 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC2876 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC2876 28767fa LT 0816 REV A * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2016