LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 20Mbps and Slew Rate Limited 15kV RS485/RS422 Transceivers DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 20Mbps or Low EMI 250kbps Maximum Data Rate No Damage or Latchup to ESD: ±15kV HBM High Input Impedance Supports 256 Nodes (C, I-Grade) Operation Up to 125°C (H-Grade) Guaranteed Failsafe Receiver Operation Over the Entire Common Mode Range Current Limited Drivers and Thermal Shutdown Delayed Micropower Shutdown: 5μA Maximum (C, I-Grade) Power Up/Down Glitch-Free Driver Outputs Low Operating Current: 900μA Maximum in Receive Mode Compatible with TIA/EIA-485-A Specifications Available in 8-Lead and 10-Lead 3mm × 3mm DFN and 8-Lead and 10-Lead MSOP Packages APPLICATIONS ■ ■ ■ Low Power RS485/RS422 Transceiver Level Translator Backplane Transceiver , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. The LTC®2856-1, LTC2856-2, LTC2857-1, LTC2857-2, LTC2858-1 and LTC2858-2 are low power, RS485/RS422 transceivers operating on 5V supplies at maximum data rates of 20Mbps or 250kbps for low EMI. The receiver has a one-eighth unit load, supporting up to 256 nodes per bus (C, I-Grade), and a failsafe feature that guarantees a high output state under conditions of floating or shorted inputs. The driver maintains a high output impedance over the entire common mode range when disabled or when the supply is removed. Excessive power dissipation caused by bus contention or a fault is prevented by current limiting all outputs and by thermal shutdown. Enhanced ESD protection allows these parts to withstand ±15kV (human body model) on the transceiver interface pins without latchup or damage. PART NUMBER MAX DATA RATE (Mbps) DUPLEX PACKAGE LTC2856-1 20 Half MSOP-8, DFN-8 LTC2856-2 0.25 Half MSOP-8, DFN-8 LTC2857-1 20 Full MSOP-8, DFN-8 LTC2857-2 0.25 Full MSOP-8, DFN-8 LTC2858-1 20 Full MSOP-10, DFN-10 LTC2858-2 0.25 Full MSOP-10, DFN-10 TYPICAL APPLICATION LTC2858-1 at 20Mbps LTC2856-1 RO1 RE1 R VCC1 DE1 D Y GND1 Z 2V/DIV DI1 DI RT LTC2856-1 RO2 RE2 R VCC2 Y-Z RT DE2 DI2 D GND2 285678 TA01a 20ns/DIV 2856 TA01b 285678fe 1 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC) ................................... –0.3V to 7V Logic Input Voltages (RE, DE, DI) ................ –0.3V to 7V Interface I/O (A, B, Y, Z) ....................(VCC – 15V) to 15V Receiver Output Voltage (RO) .......–0.3V to (VCC + 0.3V) Operating Temperature Range (Note 4) LTC285xC ................................................ 0°C to 70°C LTC285xI.............................................. –40°C to 85°C LTC285xH .......................................... –40°C to 125°C Storage Temperature Range MSOP ................................................ –65°C to 150°C DFN.................................................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) MSOP ............................................................... 300°C PACKAGE INFORMATION LTC2856 TOP VIEW RO 1 RE 2 DE 3 9 DI 4 8 VCC 7 B 6 A 5 GND TOP VIEW RO RE DE DI 8 7 6 5 1 2 3 4 VCC B A GND MS8 PACKAGE 8-LEAD PLASTIC MSOP DD PACKAGE 8-LEAD (3mm s 3mm) PLASTIC DFN TJMAX = 150°C, θJA = 200°C/W, θJC = 40°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB TJMAX = 150°C, θJA = 43°C/W, θJC = 3°C/W LTC2857 TOP VIEW VCC 1 RO 2 DI 3 9 GND 4 8 A 7 B 6 Z 5 Y TOP VIEW VCC RO DI GND 8 7 6 5 1 2 3 4 A B Z Y MS8 PACKAGE 8-LEAD PLASTIC MSOP DD PACKAGE 8-LEAD (3mm s 3mm) PLASTIC DFN TJMAX = 150°C, θJA = 200°C/W, θJC = 40°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB TJMAX = 150°C, θJA = 43°C/W, θJC = 3°C/W LTC2858 TOP VIEW RO 1 10 VCC RE 2 9 A 11 DE 3 DI 4 7 Z GND 5 6 Y 8 B DD PACKAGE 10-LEAD (3mm s 3mm) PLASTIC DFN TOP VIEW RO RE DE DI GND 1 2 3 4 5 10 9 8 7 6 VCC A B Z Y MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 150°C, θJA = 120°C/W, θJC = 45°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB TJMAX = 150°C, θJA = 43°C/W, θJC = 3°C/W 285678fe 2 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 ORDER INFORMATION LTC2856 C DD -1 #TR PBF LEAD FREE DESIGNATOR TAPE AND REEL TR = Tape and Reel SPEED -1 = 20Mbps Max. Data Rate -2 = 250kbps Max. Data Rate PACKAGE TYPE DD = 8-Lead Plastic DFN (LTC2856, LTC2858) MS8 = 8-Lead Plastic MSOP (LTC2856, LTC2857) MS = 10-Lead Plastic MSOP (LTC2858) TEMPERATURE GRADE C = Commercial Temperature Range (0°C to 70°C) I = Industrial Temperature Range (–40°C to 85°C) H = Automotive Temperature Range (–40°C to 125°C) PRODUCT PART NUMBER LTC2856 = Half Duplex, with Enables LTC2857 = Full Duplex, no Enables LTC2858 = Full Duplex, with Enables Consult LTC Marketing for information on non-standard 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/ PRODUCT SELECTION GUIDE PART NUMBER PART MARKING MAX DATA RATE (Mbps) DUPLEX LOW POWER SHUTDOWN MODE PACKAGE LTC2856-1 LTCMF, LCMG 20 Half Yes MSOP-8, DFN-8 LTC2856-2 LTCMH, LCMJ 0.25 Half Yes MSOP-8, DFN-8 LTC2857-1 LTCMC, LCMD 20 Full No MSOP-8, DFN-8 LTC2857-2 LTCMK, LCMM 0.25 Full No MSOP-8, DFN-8 LTC2858-1 LTCGQ, LCGR 20 Full Yes MSOP-10, DFN-10 LTC2858-2 LTCMQ, LCMR 0.25 Full Yes MSOP-10, DFN-10 285678fe 3 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN Differential Driver Output Voltage R = ∞, VCC = 4.5V (Figure 1) ● R = 27Ω (RS485), VCC = 4.5V (Figure 1) ● R = 50Ω (RS422), VCC = 4.5V (Figure 1) ● Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common Mode Output Voltage R = 27Ω or R = 50Ω (Figure 1) Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States Driver Three-State (High Impedance) Output Current on Y and Z Maximum Driver Short-Circuit Current TYP MAX UNITS VCC V 1.5 VCC V 2 VCC V ● 0.2 V R = 27Ω or R = 50Ω (Figure 1) ● 3 V R = 27Ω or R = 50Ω (Figure 1) ● 0.2 V DE = 0V, (Y or Z) = –7V, 12V, LTC2858-1, LTC2858-2 –7V ≤ (Y or Z) ≤ 12V (Figure 2) ● ±10 μA ±250 mA ● 125 μA Driver |VOD| Δ|VOD| VOC Δ|VOC| IOZD IOSD ● ±120 Receiver VTH Receiver Differential Input Threshold Voltage DE = TE = 0V, VCC = 0V or 5V, VIN = 12V (Figure 3) (C, I-Grade) DE = TE = 0V, VCC = 0V or 5V, VIN = –7V, (Figure 3) (C, I-Grade) DE = TE = 0V, VCC = 0V or 5V, VIN = 12V (Figure 3) (H-Grade) DE = TE = 0V, VCC = 0V or 5V, VIN = –7V, (Figure 3) (H-Grade) RE = VCC or 0V, DE = TE = 0V, VIN = –7V, –3V, 3V, 7V, 12V (Figure 3) (C, I-Grade) RE = VCC or 0V, DE = TE = 0V, VIN = –7V, –3V, 3V, 7V, 12V (Figure 3) (H-Grade) –7V ≤ B ≤ 12V ΔVTH Receiver Input Hysteresis B = 0V VOH Receiver Output High Voltage I(RO) = –4mA, A-B = 200mV, VCC = 4.5V ● VOL Receiver Output Low Voltage I(RO) = 4mA, A-B = –200mV, VCC = 4.5V ● 0.4 V Receiver Three-State (High Impedance) Output Current on RO RE = 5V, 0V ≤ RO ≤ VCC, LTC2856-1, LTC2856-2, LTC2858-1, LTC2858-2 ● ±1 μA VIH Logic Input High Voltage DE, DI, RE, VCC = 5.5V ● VIL Logic Input Low Voltage DE, DI, RE, VCC = 4.5V ● IINL Logic Input Current DE, DI, RE ● Supply Current in Shutdown Mode DE = 0V, RE = VCC, LTC2856, LTC2858 (C and I-Grade) LTC2856, LTC2858 (H-Grade) No Load, DE = 0V, RE = 0V, LTC2856-1, LTC2856-2, LTC2858-1, LTC2858-2 IIN RIN IOZR Receiver Input Current (A, B) Receiver Input Resistance ● –100 μA ● 250 μA ● –145 ● 96 125 kΩ ● 48 125 kΩ μA ● ±0.2 25 V mV 2.4 V Logic 2 V 0.8 V 0 ±10 μA ● 0 5 μA ● 0 540 15 900 μA μA Supplies ICCS ICCR Supply Current in Receive Mode ● 285678fe 4 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 SWITCHING CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS ICCT Supply Current in Transmit Mode No Load, DE = VCC, RE = VCC ICCTR Supply Current with Both Driver and Receiver Enabled No Load, DE = VCC, RE = 0V MIN LTC2856-1 LTC2858-1 LTC2856-2 LTC2858-2 LTC2856-1 LTC2857-1 LTC2858-1 LTC2856-2 LTC2857-2 LTC2858-2 TYP MAX UNITS ● 630 1000 μA ● 670 1100 μA ● 660 1100 μA ● 700 1200 μA Driver in LTC2856-1, LTC2857-1, LTC2858-1 fMAX Maximum Data Rate (Note 3) ● tPLHD, tPHLD Driver Input to Output RDIFF = 54Ω, CL = 100pF (Figure 4) ● 10 50 ns ΔtPD Driver Input to Output Difference |tPLHD – tPHLD| RDIFF = 54Ω, CL = 100pF (Figure 4) ● 1 6 ns tSKEWD Driver Output Y to Output Z RDIFF = 54Ω, CL = 100pF (Figure 4) ● 1 ±6 ns tRD, tFD Driver Rise or Fall Time RDIFF = 54Ω, CL = 100pF (Figure 4) ● 4 12.5 ns tZLD, tZHD, tLZD, tHZD Driver Enable or Disable Time RL = 500Ω, CL = 50pF, RE = 0V, LTC2856-1, LTC2858-1 (Figure 5) ● 70 ns tZHSD, tZLSD Driver Enable from Shutdown RL = 500Ω, CL = 50pF, RE = VCC, LTC2856-1, LTC2858-1 (Figure 5) ● 8 μs tSHDN Time to Shutdown (DE = ↓, RE = VCC) or (DE = 0V, RE = ↑), LTC2856-1, LTC2858-1 (Figure 5) ● 100 ns (Note 3) ● RDIFF = 54Ω, CL = 100pF (Figure 4) ● ΔtPDS Driver Input to Output Difference |tPLHD – tPHLD| RDIFF = 54Ω, CL = 100pF (Figure 4) ● tSKEWDS Driver Output A to Output B RDIFF = 54Ω, CL = 100pF (Figure 4) ● tRDS, tFDS Driver Rise or Fall Time RDIFF = 54Ω, CL = 100pF (Figure 4) ● 0.90 tZHDS, tZLDS Driver Enable Time RL = 500Ω, CL = 50pF, RE = 0V, LTC2856-2, LTC2858-2 (Figure 5) tLZDS, tHZDS Driver Disable Time 20 Mbps Driver in LTC2856-2, LTC2857-2, LTC2858-2 fMAXS Maximum Data Rate tPLHDS, tPHLDS Driver Input to Output 250 kbps 0.95 1.5 μs 50 500 ns 200 ±500 ns 1.5 μs ● 300 ns RL = 500Ω, CL = 50pF, RE = 0V, LTC2856-2, LTC2858-2 (Figure 5) ● 70 ns tZHSDS, tZLSDS Driver Enable from Shutdown RL = 500Ω, CL 50pF, RE = VCC, LTC2856-2, LTC2858-2 (Figure 5) ● 8 μs tSHDNS Time to Shutdown (DE = 0V, RE↑) or (DE = ↓, RE = VCC), LTC2856-2, LTC2858-2 (Figure 5) ● 500 ns tPLHR, tPHLR Receiver Input to Output ● 50 70 ns Receiver tSKEWR Differential Receiver Skew, |tPLHR – tPHLR| CL = 15pF, VCM = 1.5V, |VAB| = 1.5V, tR and tF < 4ns (Figure 6) CL = 15pF (Figure 6) ● 1 6 ns tRR, tFR Receiver Output Rise or Fall Time CL = 15pF (Figure 6) ● 3 12.5 ns tZLR, tZHR, tLZR, tHZR Receiver Enable/Disable ● 50 ns tZHSR, tZLSR Receiver Enable from Shutdown RL = 1k, CL = 15pF, DE = VCC, LTC2856-1, LTC2856-2, LTC2858-1, LTC2858-2 (Figure 7) RL = 1k, CL = 15pF, DE = 0V, LTC2856-1, LTC2856-2, LTC2858-1, LTC2858-2 (Figure 7) ● 8 μs 285678fe 5 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 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. High temperatures degrade operating lifetimes. Operating lifetime is derated at temperatures greater than 105°C. 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: Maximum data rate is guaranteed by other measured parameters and is not tested directly. Note 4: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Overtemperature protection actives at a junction temperature exceeding 150°C. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. TEST CIRCUITS Y GND OR VCC DI Y + DRIVER R GND OR VCC VOD – Z R + – DI IOSD DRIVER VOC Z 285678 F01 –7V TO +12V 285678 F02 Figure 1. Driver DC Characteristics Figure 2. Driver Output Short-Circuit Current IIN VIN + – + – A OR B RECEIVER B OR A 285678 F03 V RIN = IN IIN Figure 3. Receiver Input Current and Input Resistance 285678fe 6 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 TEST CIRCUITS VCC Y DI tPHLD, tPHLDS tPLHD, tPLHDS DI 0V tSKEWD,tSKEWDS CL DRIVER RDIFF Y, Z VO 1/2 VO CL Z 90% 285678 F04a Y-Z 10% 90% 0 0 10% 285678 F04b tRD, tRDS tFD, tFDS Figure 4. Driver Timing Measurement VCC RL Y VCC OR GND DI CL GND OR VCC DRIVER DE 1/2 VCC 0V VCC tZLD, tZLDS, tZLSD, tZLSDS VO Y OR Z tLZD, tLZDS 1/2 VCC 0.5V VOL RL DE Z CL VCC OR GND 285678 F05a VOH 0.5V 1/2 VCC Z OR Y 0V tZHD, tZHDS, tZHSD, tZHSDS tHZD, tHZDS, tSHDN, tSHDNS 285678 F05b Figure 5. Driver Enable and Disable Timing Measurement 285678fe 7 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 TEST CIRCUITS VAB A-B –VAB A ±VAB/2 VCM RECEIVER RO B ±VAB/2 0 tPLHR VCC VO RO CL 0 90% 1/2 VCC 10% tPHLR 90% 10% 1/2 VCC tRR 285678 F06 tFR 285678 F06b tSKEWR = tPLHR – tPHLR Figure 6. Receiver Propagation Delay Measurements VCC RE 0V OR VCC RECEIVER VCC OR 0V 1/2 VCC 0V A B RE RL RO CL VCC OR GND tZLR, tZLSR VCC VO RO tLZR 1/2 VCC 0.5V VOL VOH 0.5V 1/2 VCC RO DI = 0V OR VCC 0V 285678 F07a 285678 F05b tZHR, tZHSR tHZR Figure 7. Receiver Enable/Disable Time Measurements FUNCTION TABLES LTC2856-1, LTC2856-2 LTC2858-1, LTC2858-2 LOGIC INPUTS DE RE LOGIC INPUTS MODE A, B RO DE RE MODE A, B Y, Z RO 0 0 Receive RIN Driven 0 0 Receive RIN High-Z Driven 0 1 Shutdown RIN High-Z 0 1 Shutdown RIN High-Z High-Z 1 0 Transceive Driven Driven 1 0 Transceive RIN Driven Driven 1 1 Transmit Driven High-Z 1 1 Transmit RIN Driven High-Z 285678fe 8 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 TYPICAL PERFORMANCE CHARACTERISTICS Receiver Skew vs Temperature Driver Propagation Delay vs Temperature Driver Skew vs Temperature 2 2 18 RDIFF = 54Ω CL = 100pF 1 0 RDIFF = 54Ω CL = 100pF 16 DRIVER PROP DELAY (ns) DRIVER SKEW (ns) VAB = 1.5V CL = 15pF RECEIVER SKEW (ns) TA = 25°C, VCC = 5V unless otherwise noted. 1 0 14 12 10 8 6 –1 –40 –20 0 20 40 60 80 TEMPERATURE (°C) –1 –40 –20 100 120 0 20 40 60 80 TEMPERATURE (°C) 385678 G01 20 40 60 80 100 120 TEMPERATURE (°C) 285678 G03 Driver Output Low/High Voltage vs Output Current Driver Differential Output Voltage vs Temperature 5 160 5 RDIFF = ∞ VOH OUTPUT VOLTAGE (V) 120 SINK (VOUT = 5V) 100 4 OUTPUT VOLTAGE (V) 4 SOURCE (VOUT = 0V) 140 3 2 VOL 1 80 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 0 100 120 0 10 40 30 20 50 OUTPUT CURRENT (mA) 60 0 –40 –20 70 5 70 SOURCE 65 VAB = 1.5V CL = 15pF 0 SUPPLY CURRENT (mA) PROP DELAY (ns) 55 50 45 40 0 1 3 4 2 OUTPUT CURRENT (mA) 285678 G07 30 –40 –20 RDIFF = 54Ω 40 RDIFF = 100Ω 30 20 10 35 5 100 120 CL = 100pF 50 60 SINK 20 40 60 80 TEMPERATURE (°C) Supply Current vs Data Rate 60 4 1 0 285678 G06 Receiver Propagation Delay vs Temperature 2 RDIFF = 54Ω 2 285678 G05 Receiver Output Voltage vs Output Current (Source and Sink) 3 RDIFF = 100Ω 3 1 285678 G04 OUTPUT VOLTAGE (V) 0 385678 G02 Driver Output Short-Circuit Current vs Temperature OUTPUT SHORT-CIRCUIT CURRENT (mA) 4 –40 –20 100 120 RDIFF = ∞ 0 0 20 40 60 80 TEMPERATURE (°C) 100 120 285678 G08 0.1 1 10 DATA RATE (Mbps) 100 285678 G09 285678fe 9 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 PIN FUNCTIONS PIN NUMBER PIN NAME LTC2856-1 LTC2856-2 LTC2857-1 LTC2857-2 LTC2858-1 LTC2858-2 RO 1 2 1 Receiver Output. If the receiver output is enabled (RE low) and A > B by 200mV, then RO will be high. If A < B by 200mV, then RO will be low. If the receiver inputs are open, shorted or terminated without a valid signal, RO will be high. RE 2 2 Receiver Enable. A low enables the receiver. A high input forces the receiver output into a high impedance state. DE 3 3 Driver Enable. A high on DE enables the driver. A low input will force the driver outputs into a high impedance. If RE is high with DE low, the part will enter a low power shutdown state. DI 4 3 4 Driver Input. If the driver outputs are enabled (DE high), then a low on DI forces the driver positive output low and negative output high. A high on DI, with the driver outputs enabled, forces the driver positive output high and negative output low. GND 5/9* 4/9* 5/11* Ground. *The Exposed Pad on the DFN packages should be connected to ground. Y 5 6 Noninverting Driver Output for the LTC2857-1, LTC2857-2, LTC2858-1 and LTC2858-2. High impedance when the driver is disabled (LTC2858-1) or unpowered. Z 6 7 Inverting Driver Output for the LTC2857-1, LTC2857-2, LTC2858-1 and LTC2858-2. High impedance when the driver is disabled (LTC2858-1) or unpowered. DESCRIPTION B 7 7 8 Inverting Receiver Input (and Inverting Driver Output for the LTC2856-1 and LTC2856-2). Impedance is > 96kΩ in receive mode or unpowered. A 6 8 9 Noninverting Receiver Input (and Noninverting Driver Output for the LTC2856-1 and LTC2856-2). Impedance is > 96kΩ in receive mode or unpowered. VCC 8 1 10 Positive Supply. 4.5V < VCC < 5.5V. Bypass with a 0.1μF ceramic capacitor. 285678fe 10 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 BLOCK DIAGRAMS LTC2856-1, LTC2856-2 LTC2857-1, LTC2857-2 A (15kV) RO RECEIVER RECEIVER RO B (15kV) RE DE A (15kV) SLEEP/SHUTDOWN LOGIC AND DELAY B (15kV) Z (15kV) DI DRIVER DRIVER DI Y (15kV) 2856 BD 2857 BD LTC2858-1, LTC2858-2 A (15kV) RO RECEIVER B (15kV) RE DE SLEEP/SHUTDOWN LOGIC AND DELAY Z (15kV) DI DRIVER Y (15kV) 2858 BD 285678fe 11 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 APPLICATIONS INFORMATION Driver The driver provides full RS485 and RS422 compatibility. When enabled, if DI is high, Y-Z is positive for the full-duplex devices and A-B is positive for the half-duplex device. When the driver is disabled, both outputs are high impedance. For the full-duplex devices, the leakage on the driver output pins is guaranteed to be less than 10μA over the entire common mode range of –7V to 12V. On the halfduplex device, the impedance is dominated by the receiver input resistance, RIN. Driver Overvoltage and Overcurrent Protection The driver outputs are protected from short circuits to any voltage within the Absolute Maximum range of (VCC – 15V) to 15V. The maximum current in this condition is 250mA. If the pin voltage exceeds about ±10V, current limit folds back to about half of the peak value to reduce overall power dissipation and avoid damaging the part. All devices also feature thermal shutdown protection that disables the driver and receiver output in case of excessive power dissipation (see Note 4). Slew Limiting for EMI Emissions Control The LTC2856-2, LTC2857-2 and the LTC2858-2 feature reduced slew rate driver outputs to control the high frequency EMI emissions from equipment and data cables. These devices are limited to data rates of 250kbaud or less. Slew limiting also mitigates the adverse affects of imperfect transmission line termination caused by stubs or mismatched cable. Figures 10 and 11 show the output waveforms from the LTC2858-1 and its slew rate limited counterpart, the LTC2858-2, operating at 250kbps. The corresponding frequency spectrums show significant reduction in the high frequency harmonics for the slew rate limited device. Receiver and Failsafe With the receiver enabled, when the absolute value of the differential voltage between the A and B pins is greater than 200mV, the state of RO will reflect the polarity of (A-B). These parts have a failsafe feature that guarantees the receiver output to be in a logic-high state when the inputs are either shorted, left open or terminated, but not driven for more than about 3μs. The delay prevents signal zero crossings from being interpreted as shorted inputs and causing RO to go high inadvertently. This failsafe feature is guaranteed to work for inputs spanning the entire common mode range of –7V to 12V. The receiver output is internally driven high (to VCC) or low (to ground) with no external pull-up needed. When the receiver is disabled the RO pin becomes high-Z with leakage of less than ±1μA for voltages within the supply range. Receiver Input Resistance The receiver input resistance from A or B to ground is guaranteed to be greater than 96k (C, I-Grade). This is 8× higher than the requirements for the RS485 standard and thus this receiver represents a one-eighth unit load. This, in turn, means that 8× the standard number of receivers, or 256 total, can be connected to a line without loading it beyond what is called out in the RS485 standard. The receiver input resistance from A or B to ground on high temperature H-Grade parts is greater than 48k providing a one-quarter unit load. The input resistance of the receivers is unaffected by enabling/disabling the receiver and by powering/unpowering the part. Supply Current The unloaded static supply currents in these devices are very low—typically under 700μA for all modes of operation. In applications with resistively terminated cables, the supply current is dominated by the driver load. For example, when using two 120Ω terminators with a differential driver output voltage of 2V, the DC load current is 33mA, which is sourced by the positive voltage supply. Power supply current increases with toggling data due to capacitive loading and this term can increase significantly at high data rates. Figure 8 shows supply current vs data rate for two different capacitive loads for the circuit configuration of Figure 4. 285678fe 12 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 APPLICATIONS INFORMATION Cable Length vs Data Rate RDIFF = 54Ω CURRENT (mA) 70 65 CL = 1000pF 60 55 CL = 100pF 50 45 102 104 103 DATA RATE (kbps) 105 285678 F08 Figure 8. Supply Current vs Data Rate High Speed Considerations A ground plane layout is recommended. A 0.1μF bypass capacitor less than one-quarter inch away from the VCC pin is also recommended. The PC board traces connected to signals A/B and Z/Y 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 outputs away from any sensitive inputs to reduce feedback effects that might cause noise, jitter or even oscillations. For example, in the full-duplex LTC2857-1, DI and A/B should not be routed near the driver or receiver outputs. The logic inputs have 100mV of hysteresis 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 1.5V), 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 through their thresholds by faster than 1V/μs when transitioning. Good supply decoupling and proper line termination also reduce glitches caused by driver transitions. For a given data rate, the maximum transmission distance is bounded by the cable properties. A typical curve of cable length vs data rate compliant with the RS485 standard is shown in Figure 9. Three regions of this curve reflect different performance limiting factors in data transmission. In the flat region of the curve, maximum distance is determined by resistive losses in the cable. The downward sloping region represents limits in distance and data rate due to AC losses in the cable. The solid vertical line represents the specified maximum data rate in the RS485 standard. The dashed line at 250kbps shows the maximum data rate of the low-EMI LTC2856-2, LTC2857-2, and LTC2858-2. The dashed line at 20Mbps shows the maximum data rates of the LTC2856-1, LTC2857-1 and LTC2858-1. 10k CABLE LENGTH (FT) 75 LOW-EMI MODE MAX DATA RATE 1k NORMAL MODE MAX DATA RATE 100 RS485 MAX DATA RATE 10 10k 100k 1M 10M DATA RATE (bps) 100M 285678 F09 Figure 9. Cable Length vs Data Rate (RS485 Standard Shown in Solid Vertical Lines) Cable Termination Proper cable termination is very important for good signal fidelity. If the cable is not terminated with its characteristic impedance, reflections will result in distorted waveforms. RS485 transceivers typically communicate over twistedpair cables with characteristic impedance ranging from 100Ω to 120Ω. Each end of the network should be terminated with a discrete resistor matching the characteristic impedance or with an LTC2859/LTC2861 transceiver with integrated termination capability. 285678fe 13 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 APPLICATIONS INFORMATION Time-Based Traces Frequency Spectrum Y, Z 1V/DIV Y-Z 10dB/DIV Y-Z 2V/DIV 2μs/DIV 285678 F10a 1.25MHz/DIV 285678 F10b Figure 10. LTC2858-1 Driver Output at 100kHz Into 100Ω Resistor 285678fe 14 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 APPLICATIONS INFORMATION Time-Based Traces Frequency Spectrum Y, Z 1V/DIV Y-Z 10dB/DIV Y-Z 2V/DIV 285678 F11a 2μs/DIV 1.2MHz/DIV 285678 F11b Figure 11. LTC2858-2 Driver Output at 100kHz Into 100Ω Resistor TYPICAL APPLICATIONS Failsafe “0” Application (Idle State = Logic “0”) VCC 100k I1 RO R B A DI I2 “A” “B” D LTC2856-1 285678 TA02 285678fe 15 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 PACKAGE DESCRIPTION DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) 0.675 p 0.05 3.5 p 0.05 1.65 p 0.05 2.15 p 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.38 p 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p 0.10 (4 SIDES) R = 0.115 TYP 5 0.38 p 0.10 8 1.65 p 0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) (DD) DFN 1203 0.200 REF 0.75 p 0.05 4 0.25 p 0.05 1 0.50 BSC 0.00 – 0.05 2.38 p 0.10 (2 SIDES) 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 285678fe 16 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 PACKAGE DESCRIPTION DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 0.38 p 0.10 6 10 5 1 0.675 p 0.05 3.50 p 0.05 1.65 p 0.05 2.15 p 0.05 (2 SIDES) 3.00 p 0.10 (4 SIDES) PACKAGE OUTLINE PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.25 p 0.05 1.65 p 0.10 (2 SIDES) 0.50 BSC 2.38 p 0.05 (2 SIDES) (DD) DFN 1103 0.25 p 0.05 0.50 BSC 0.75 p 0.05 0.00 – 0.05 2.38 p 0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 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 285678fe 17 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 PACKAGE DESCRIPTION MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660) 0.889 p 0.127 (.035 p .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.42 p 0.038 (.0165 p .0015) TYP 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.65 (.0256) BSC 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) DETAIL “A” 0° – 6° TYP GAUGE PLANE 1 0.53 p 0.152 (.021 p .006) DETAIL “A” 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) BSC 0.1016 p 0.0508 (.004 p .002) MSOP (MS8) 0307 REV F 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 285678fe 18 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 PACKAGE DESCRIPTION MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 p 0.127 (.035 p .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.50 0.305 p 0.038 (.0197) (.0120 p .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) DETAIL “A” 0.497 p 0.076 (.0196 p .003) REF 10 9 8 7 6 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 p 0.152 (.021 p .006) DETAIL “A” 0.86 (.034) REF 1.10 (.043) MAX 0.18 (.007) SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP 0.50 (.0197) BSC 0.1016 p 0.0508 (.004 p .002) MSOP (MS) 0307 REV E 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 285678fe 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. 19 LTC2856-1/LTC2856-2 LTC2857-1/LTC2857-2 LTC2858-1/LTC2858-2 TYPICAL APPLICATION Multi-Node Network and End Termination Using the LTC2856-1 R D R LTC2856-1 D LTC2856-1 R R TE = 5V TE = 5V D D LTC2859 LTC2859 285678 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC485 Low Power RS485 Interface Transceiver ICC = 300μA (Typ) LTC491 Differential RS485 Driver and Receiver Pair ICC = 300μA LTC1480 3.3V Ultralow Power RS485 Transceiver 3.3V Operation 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 Transceiver 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 Transceiver with Precision Delay Propagation Delay Skew 500ps (Typ) LT1785 60V Fault Protected RS485 Transceiver 60V Tolerant, ±15kV ESD LTC2859/ LTC2861 20Mbps RS485 Transceivers with Integrated Switchable Termination Integrated, Switchable, 120Ω Termination Resistor, ±15kV ESD 285678fe 20 Linear Technology Corporation LT 0308 REV E • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006