LTC2859/LTC2861 20Mbps RS485 Transceivers with Integrated Switchable Termination DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Integrated, Logic-Selectable 120Ω Termination Resistor 20Mbps Max Data Rate No Damage or Latchup to ESD: ±15kV HBM High Input Impedance Supports 256 Nodes 250kbps Low-EMI Mode Guaranteed Failsafe Receiver Operation Over the Entire Common Mode Range Current Limited Drivers and Thermal Shutdown Delayed Micropower Shutdown (5μA Max) Power Up/Down Glitch-Free Driver Outputs Low Operating Current (900μA Max in Receive Mode) Meets All TIA/EIA-485-A Specifications Available in 10-Pin 3mm × 3mm DFN, 12-Pin 4mm × 3mm DFN and 16-Pin SSOP Packages APPLICATIONS ■ ■ ■ The LTC®2859 and LTC2861 are low power, 20Mbps RS485/422 transceivers operating on 5V supplies. The receiver includes a logic-selectable 120Ω termination, one-eighth unit load supporting up to 256 nodes per bus, and a failsafe feature that guarantees a high output state under conditions of floating or shorted inputs. The driver features a logic-selectable low-EMI 250kbps operating mode, and 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 a thermal shutdown. Enhanced ESD protection allows the LTC2859 and LTC2861 to withstand ±15kV (human body model) on the transceiver interface pins without latchup or damage. PRODUCT SELECTION GUIDE Low Power RS485/RS422 Transceiver Level Translator Backplane Transceiver PART NUMBER DUPLEX PACKAGE LTC2859 Half DFN-10 LTC2861 Full SSOP-16, DFN-12 L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION LTC2859 LTC2859 R R RO RE TE DE 120Ω 120Ω LTC2859 at 20Mbps RO RE TE DI DE Y DI D D DI Z SLO SLO Y–Z 2859/61 TA01 LTC2859 120Ω 2V/DIV 20ns/DIV 285961 TA02 R D RO RE TE DE DI SLO 285961fb 1 LTC2859/LTC2861 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC) ................................... –0.3V to 7V Logic Input Voltages (RE, DE, DI, TE, SLO) ... –0.3V to 7V Interface I/O: A, B, Y, Z ...................................... (VCC –15V) to +15V (A-B) or (B-A) with Terminat or Enabled .................6V Receiver Output Voltage (RO) ........ –0.3V to (VCC +0.3V) Operating Temperature (Note 4) LTC2859C, LTC2861C .............................. 0°C to 70°C LTC2859I, LTC2861I ............................. –40°C to 85°C Storage Temperature Range................... –65°C to 125°C Lead Temperature (Soldering, 10 sec) GN Package ...................................................... 300°C PIN CONFIGURATION TOP VIEW TOP VIEW TOP VIEW RO 1 RE 2 11 RO 1 12 VCC 10 VCC RE 2 11 A 9 B DE 3 DI 4 9 Z TE 5 8 Y GND 6 7 SLO DE 3 8 A DI 4 7 SLO TE 5 6 GND DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN EXPOSED PAD (PIN 11) PCB GND CONNECTION TJMAX = 125°C, θJA = 43°C/W θJC = 3°C/W 13 10 B DE PACKAGE 12-LEAD (4mm × 3mm) PLASTIC DFN EXPOSED PAD (PIN 13) PCB GND CONNECTION TJMAX = 125°C, θJA = 43°C/W θJC = 4.3°C/W RO 1 16 VCC RE 2 15 A DE 3 14 B DI 4 13 Z TE 5 12 Y GND 6 11 SLO NC 7 10 NC NC 8 9 NC GN PACKAGE 16-LEAD (NARROW 0.150) PLASTIC SSOP TJMAX = 125°C, θJA = 110°C/W θJC = 40°C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2861CDE#PBF LTC2861CDE#TRPBF 2861 12-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C LTC2861IDE#PBF LTC2861IDE#TRPBF 2861 12-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C LTC2861CGN#PBF LTC2861CGN#TRPBF 2861 16-Lead Plastic SSOP 0°C to 70°C LTC2861IGN#PBF LTC2861IGN#TRPBF 2861I 16-Lead Plastic SSOP –40°C to 85°C LTC2859CDD#PBF LTC2859CDD#TRPBF LBNX 10-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2859IDD#PBF LTC2859IDD#TRPBF LBNX 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2861CDE LTC2861CDE#TR 2861 12-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C LTC2861IDE LTC2861IDE#TR 2861 12-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C LTC2861CGN LTC2861CGN#TR 2861 16-Lead Plastic SSOP 0°C to 70°C LTC2861IGN LTC2861IGN#TR 2861I 16-Lead Plastic SSOP –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. 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/ 285961fb 2 LTC2859/LTC2861 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 = ∞, IO = 0mA, VCC = 4.5V (Figure 1) R = 27Ω (RS485), VCC = 4.5V (Figure 1) R = 50Ω (RS422), VCC = 4.5V (Figure 1) ● ● ● TYP MAX UNITS VCC VCC VCC V V V Driver |VOD| 1.5 2.0 Δ|VOD| Change in Magnitude of Driver Differential Output Voltage for Complementary Output States R = 27Ω or R = 50Ω (Figure 1) ● 0.2 V VOC Driver Common Mode Output Voltage R = 27Ω or R = 50Ω (Figure 1) ● 3.0 V Δ|VOC| Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States R = 27Ω or R = 50Ω (Figure 1) ● 0.2 V IOZD Driver Three-State (High Impedance) Output Current on Y and Z DE = OV, VO = –7V, +12V (LTC2861 Only) ● ±10 μA IOSD Maximum Driver Short-Circuit Current –7V ≤ (Y or Z) ≤ 12 (Figure 2) ● ±250 mA Receiver Input Current (A, B) DE = TE = 0V, VCC = 0V or 5V, VA or VB = 12V, Other at 0V ● 125 μA DE = TE = 0V, VCC = 0V or 5V, VA or VB = –7V, Other at 0V ● ● ±120 Receiver IIN2 –100 μA VTH Receiver Differential Input Threshold Voltage –7V ≤ VCM ≤ 12 ±0.2 ΔVTH Receiver Input Hysteresis VCM = 0V VOH Receiver Output HIGH Voltage I0 = –4mA, VID = 200mV, VCC = 4.5V ● VOL Receiver Output LOW Voltage I0 = 4mA, VID = –200mV, VCC = 4.5V ● 0.4 V IOZR Receiver Three-State (High Impedance) Output Current on RO RE = 5V, 0V ≤ VO ≤ VCC ● ±1 μA RIN Receiver Input Resistance RE = 5V or 0V, DE = TE = 0V ● 96 125 RTERM Receiver Input Terminating Resistor TE = 5V, VAB = 2V, VB = –7, 0, 10V (Figure 7) ● 108 120 VIH Logic Input High Voltage DE, DI, RE, TE, SLO, VCC = 4.5V ● 2 VIL Logic Input Low Voltage DE, DI, RE, TE, SLO, VCC = 4.5V ● IIN1 Logic Input Current DE, DI, RE, TE, SLO ● ISHDN Supply Current in Shutdown Mode DE = 0V, RE = VCC, TE = 0V ● ICCR Supply Current in Receive Mode No Load, DE = 0V, RE = 0V, TE = 0V ● ICCT Supply Current in Transmit Mode No Load, DE = VCC, RE = VCC, SLO = VCC, TE = 0V ● ICCTS Supply Current in Transmit SLO Mode No Load, DE = VCC, RE = VCC, SLO = 0V, TE = 0V ICCL Supply Current in Loopback Mode (Both No Load, DE = VCC, RE= 0V, SLO = VCC, TE Driver and Receiver Enabled) = 0V ICCRT Supply Current in Termination Mode 25 V mV 2.4 V kΩ –7V ≤ VA = VB ≤ 12V 156 Ω Logic V 0.8 V ±10 μA 0 5 μA 540 900 μA 630 1000 μA ● 670 1100 μA ● 660 1100 μA ● 640 1180 μA 0 Supplies DE = 0V, RE = VCC, TE = VCC, SLO = VCC 285961fb 3 LTC2859/LTC2861 SWITCHING CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 5V, TE = 0 unless otherwise noted (Note 2). SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Driver in Normal Mode (SLO HIGH) fMAX Maximum Data Rate Note 3 ● tPLHD, tPHLD Driver Input to Output RDIFF = 54Ω, CL = 100pF (Figure 3) ● 10 50 ns ΔtPD Driver Input to Output Difference |tPLHD-tPHLD| RDIFF = 54Ω, CL = 100pF (Figure 3) ● 1 6 ns tSKEWD Driver Output Y to Output Z RDIFF = 54Ω, CL = 100pF (Figure 3) ● 1 ±6 ns tRD, tFD Driver Rise or Fall Time RDIFF = 54Ω, CL = 100pF (Figure 3) ● 4 12.5 ns tZLD, tZHD, tLZD, tHZD Driver Enable or Disable Time RL = 500Ω, CL = 50pF, RE = 0 (Figure 4) ● 70 ns tZHSD, tZLSD Driver Enable from Shutdown RL = 500Ω, CL = 50pF, RE = VCC (Figure 4) ● 8 μs tSHDN Time to Shutdown (DE = ↓, RE = VCC) or (DE = 0, RE ↑) (Figure 4) ● 100 ns 20 Mbps Driver in SLO Mode (SLO LOW) fMAXS Maximum Data Rate Note 3 ● tPLHDS, tPHLDS Driver Input to Output RDIFF = 54Ω, CL = 100pF (Figure 3) ● 0.95 1.5 μs ΔtPDS Driver Input to Output Difference |tPLHR-tPHLR| RDIFF = 54Ω, CL = 100pF (Figure 3) ● 50 500 ns tSKEWDS Driver Output A to Output B RDIFF = 54Ω, CL = 100pF (Figure 3) ● 200 ±500 ns tRDS, tFDS Driver Rise or Fall Time RDIFF = 54Ω, CL = 100pF (Figure 3) ● 0.9 1.5 μs tZHDS, tZLDS Driver Enable Time RL = 500Ω, CL = 50pF, RE = 0 (Figure 4) ● 300 ns tLZDS, tHZDS Driver Disable Time RL = 500Ω, CL = 50pF, RE = 0 (Figure 4) ● 70 ns tZHSDS, tZLSDS Driver Enable from Shutdown RL = 500Ω, CL = 50pF, RE = VCC (Figure 4) ● 8 μs tSHDNS Time to Shutdown (DE = 0, RE = ↑) or (DE = ↓, RE = VCC) (Figure 4) ● 500 ns tPLHR, tPHLR Receiver Input to Output CL = 15pF, VCM = 1.5V, |VAB| = 1.5V, tR and tF < 4ns (Figure 5) ● 50 70 ns tSKEWR Differential Receiver Skew |tPLHR-tPHLR| CL = 15pF (Figure 5) ● 1 6 ns tRR, tFR Receiver Output Rise or Fall Time CL = 15pF (Figure 5) ● 3 12.5 ns tZLR, tZHR, tLZR, tHZR Receiver Enable/Disable RL = 1kΩ, CL =15pF, DE = VCC (Figure 6) DI = 0 or VCC ● 50 ns tZHSR, tZLSR Receiver Enable from Shutdown RL = 1kΩ, CL = 15pF, DE = 0V (Figure 6) DI = 0 or VCC ● 8 μs tRTEN, tRTZ Termination Enable or Disable Time VB = 0V, VAB = 2V, RE = VCC, DE = 0V (Figure 7) ● 100 μs 250 kbps Receiver 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: 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. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. 285961fb 4 LTC2859/LTC2861 TEST CIRCUITS Y GND DI OR VCC DRIVER Z Y R + VOD – R GND OR DI VCC + VOC – IOSD DRIVER Z + – –7V to +12V 2859/61 F01-2 Figure 1. Driver DC Characteristics Figure 2. Driver Output Short-Circuit Current DI Y DI tSKEWD, tSKEWDS RDIFF CL Y, Z tPHLD, tPHLDS tPLHD, tPLHDS OV CL DRIVER VCC VO 1/2 VO Z 90% 10% (Y-Z) 0 0 tRD, tRDS 90% 10% tFD, tFDS 2859/61 F03 Figure 3. Driver Timing Measurement RL Y VCC OR DI GND CL GND OR VCC VCC DE 1/2 VCC OV VCC DRIVER Y or Z Z RL DE CL VCC OR GND Z or Y tZLD, tZLDS, tZLSD, tZLSDS 1/2 VCC VO tLZD, tLZDS 0.5V VOL VOH 1/2 VCC OV tZHD, tZHDS, tZHSD, tZHSDS 0.5V tHZD, tHZDS, tSHDN, tSHDNS 2859/61 F04 Figure 4. Driver Enable and Disable Timing Measurement 285961fb 5 LTC2859/LTC2861 TEST CIRCUITS ±VAB/2 A-B A VCM 0V –VAB RO RECEIVER B VAB tPLHR VCC RO CL ±VAB/2 VO 0V 90% 10% 1/2 VCC 1/2 VCC tRR tPHLR 90% 10% tFR tSKEWR = tPLHR – tPHLR 2859/61 F05 Figure 5. Receiver Propagation Delay Measurements 0V OR VCC RE A RECEIVER VCC OR 0V RL RO CL B VCC OR GND RO VCC tZLR, tZLSR 0V VCC 1/2 VCC tLZR VO 1/2 VCC RO DI = 0V OR VCC 0.5V VOL VOH RE 0.5V 1/2 VCC 0V tZHR, tZHSR tHZR 2859/61 F06 Figure 6. Receiver Enable/Disable Time Measurements RTERM = VAB IA A RO + – RECEIVER VAB + – 1/2 VCC 0V IA B TE VCC TE tRTEN tRTZ 90% 10% VB 2859/61 F07 Figure 7. Termination Resistance and Timing Measurements 285961fb 6 LTC2859/LTC2861 TYPICAL PERFORMANCE CHARACTERISTICS Receiver Skew vs Temperature TA = 25°C, VCC = 5V, unless otherwise noted. Driver Propagation Delay vs Temperature Driver Skew vs Temperature 3 18 RDIFF = 54Ω CL = 100pF SLO = VCC 2 16 DRIVER PROP DELAY (ns) VAB = 1.5V CL = 15pF DRIVER SKEW (ns) RECEIVER SKEW (ns) 2 1 1 0 0 14 12 10 8 6 –40 –20 0 20 40 60 80 TEMPERATURE (°C) –1 –40 –20 100 120 0 285961 G01 20 40 60 80 TEMPERATURE (°C) 4 –40 –20 100 120 105 100 120 285961 G03 4 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 110 80 R=∞ 4 115 60 5 130 120 40 Driver Differential Output Voltage vs Temperature VOH 125 20 TEMPERATURE (°C) 5 135 0 285961 G02 Driver Output Low/High Voltage vs Output Current RTERM vs Temperature 3 2 VOL 1 3 R = 100Ω 2 R = 54Ω 1 100 0 95 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 0 100 120 10 40 30 20 50 OUTPUT CURRENT (mA) 285961 G04 Receiver Output Voltage vs Output Current (Source and Sink) 60 0 –40 –20 70 285961 G05 Receiver Propagation Delay vs Temperature 5 70 SOURCE 65 VAB = 1.5V CL = 15pF 50 SUPPLY CURRENT (mA) PROP DELAY (ns) 2 55 50 45 40 1 0 1 3 4 2 OUTPUT CURRENT (mA) 5 285961 G07 285961 G06 R = 54Ω 40 R = 100Ω 30 20 R=∞ SINK 30 –40 –20 100 120 10 35 0 20 40 60 80 TEMPERATURE (°C) Supply Current vs Data Rate 60 3 0 60 4 OUTPUT VOLTAGE (V) RESISTANCE (Ω) RDIFF = 54Ω CL = 100pF SLO = VCC 0 20 40 60 80 TEMPERATURE (°C) 100 120 285961 G08 0 0.1 10 1 DATA RATE (Mbps) 100 285961 G09 285961fb 7 LTC2859/LTC2861 PIN FUNCTIONS (DD/DE/GN) RO (Pin 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 (Pin 2): Receiver Enable. A low enables the receiver. A high input forces the receiver output into a high impedance state. DE (Pin 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 and TE LOW, the part will enter a low power shutdown state. DI (Pin 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. TE (Pin 5): Internal Termination Resistance Enable. A high input will connect a termination resistor (120Ω typical) between pins A and B. GND (Pins 6,11/6,13/6): Ground. Pins 11 and 13 are backside thermal pad, connected to Ground. SLO (Pins 7/7/11): Driver Slew Rate Control. A low input will force the driver into a reduced slew rate mode. Y (Pins -/8/12): Positive Driver Output for LTC2861. Z (Pins -/9/13): Negative Driver Output for LTC2861. B (Pins 9/10/14): Negative Receiver Input (and Negative Driver Output for LTC2859). A (Pins 8/11/15): Positive Receiver Input (and Positive Driver Output for LTC2859). VCC (Pins 10/12/16): Positive Supply. 4.5V < VCC < 5.5V. Bypass with 0.1μF ceramic capacitor. 285961fb 8 LTC2859/LTC2861 FUNCTION TABLES LTC2859 LOGIC INPUTS DE RE TE MODE A, B RO TERMINATOR 0 0 0 Receive RIN Enabled Off 0 0 1 Receive with Term RIN Enabled On 0 1 0 Shutdown RIN Hi-Z Off 0 1 1 Term Only RIN Hi-Z On 1 0 0 Transmit with Receive Driven Enabled Off 1 0 1 Transmit with Receive and Term Driven Enabled On 1 1 0 Transmit Driven Hi-Z Off 1 1 1 Transmit with Term Driven Hi-Z On LTC2861 LOGIC INPUTS DE RE TE MODE A, B Y, Z RO TERMINATOR 0 0 0 Receive RIN Hi-Z Enabled Off 0 0 1 Receive with Term RIN Hi-Z Enabled On 0 1 0 Shutdown RIN Hi-Z Hi-Z Off 0 1 1 Term Only RIN Hi-Z Hi-Z On 1 0 0 Transmit with Receive RIN Driven Enabled Off 1 0 1 Transmit with Receive and Term RIN Driven Enabled On 1 1 0 Transmit RIN Driven Hi-Z Off 1 1 1 Transmit with Term RIN Driven Hi-Z On BLOCK DIAGRAMS LTC2859 RE DE SLEEP/SHUTDOWN LOGIC AND DELAY LTC2861 A (15kV) 120Ω RE DE SLEEP/SHUTDOWN LOGIC AND DELAY A (15kV) 120Ω TE RO TE RO RECEIVER RECEIVER B (15kV) SLO DI B (15kV) SLO DRIVER DI Z (15kV) DRIVER Y (15kV) 2859/61 BD 285961fb 9 LTC2859/LTC2861 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 device (LTC2861) and A-B is positive for the halfduplex device (LTC2859). When the driver is disabled, both outputs are highimpedance. For the full duplex LTC2861, 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 half-duplex LTC2859, 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. The LTC2859/LTC2861 also feature thermal shutdown protection that disables the driver, terminator, and receiver in case of excessive power dissipation. SLO Mode: Slew Limiting for EMI Emissions Control The LTC2859/LTC2861 feature a logic-selectable reducedslew mode (SLO mode) that softens the driver output edges to control the high frequency EMI emissions from equipment and data cables. The reduced slew rate mode is entered by taking the SLO pin low, where the data rate is limited to about 250kbps. Slew limiting also mitigates the adverse effects of imperfect transmission line termination caused by stubs or mismatched cables. Figures 8a and 8b show the LTC2861 driver outputs in normal and SLO mode with their corresponding frequency spectrums operating at 250kbps. SLO mode significantly reduces the high frequency harmonics. Y, Z Y–Z Y–Z 1V/DIV 2μs/DIV 10dB/DIV Driver Output at 125kHz into 100Ω Resistor 1.25MHz/DIV 285961 F08a Frequency Spectrum of the Same Signal Figure 8a. Driver Output in Normal Mode Y, Z Y–Z Y–Z 1V/DIV 2μs/DIV 10dB/DIV Driver Output at 125kHz into 100Ω Resistor 1.25MHz/DIV 285961 F08b Frequency Spectrum of the Same Signal Figure 8b. Driver Output in SLO Mode 285961fb 10 LTC2859/LTC2861 APPLICATIONS INFORMATION 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). The LTC2859/LTC2861 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 (externally or internally), 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 Hi-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 when the termination is disabled. This is 8X higher than the requirements for RS485 standard and thus this receiver represents a one-eighth unit load. This, in turn, means that 8X 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 input resistance of the receivers is unaffected by enabling/disabling the receiver and by powering/unpowering the part. The equivalent input resistance looking into A and B is shown in Figure 9. The termination resistor cannot be enabled by TE if the device is unpowered or in thermal shutdown mode. Switchable 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. The LTC2859/LTC2861 are the first RS485 transceivers to offer integrated switchable termination resistors on the receiver input pins. This provides the tremendous advantage of being able to easily change, through logic control, the proper line termination for optimal performance when configuring transceiver networks. When the TE pin is high, the termination resistor is enabled and the differential resistance from A to B is 120Ω. Figure 10 shows the I/V characteristics between pins A and B with the termination resistor enabled and disabled. A >96k 60Ω TE 60Ω >96k 2859/61 F09 B Figure 9. Equivalent Input Resistance into A and B (on the LTC2859, Valid if Driver is Disabled) Figure 10. Curve Trace Between A and B with Termination Enabled and Disabled 285961fb 11 LTC2859/LTC2861 APPLICATIONS INFORMATION 150 The resistance is maintained over the entire RS485 common mode range of –7V to +12V as shown in Figure 11. 140 RESISTANCE (Ω) The integrated termination resistor has a high frequency response which does not limit performance at the maximum specified data rate. Figure 12 shows the magnitude and phase of the termination impedance vs frequency. 120 Supply Current 110 –10 –5 5 10 0 COMMON MODE VOLTAGE (V) 15 285961 F11 Figure 11. Termination Resistance vs Common Mode Voltage 140 0 MAGNITUDE MAGNITUDE (Ω) 120 –5 100 –10 PHASE 80 –15 60 40 High Speed Considerations PHASE (DEGREES) The unloaded static supply currents in the LTC2859/ LTC2861 are very low —typically under 700μA for all modes of operation without the internal terminator enabled. 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 current is 33mA, which is sourced by the positive voltage supply. This is true whether the terminators are external or internal such as in the LTC2859/ LTC2861. Power supply current increases with toggling data due to capacitive loading and this term can increase significantly at high data rates. Figure 13 shows supply current vs data rate for two different capacitive loads (for the circuit configuration of Figure 3). 130 –20 20 –25 0 10–1 A ground plane layout is recommended for the LTC2859/ LTC2861. 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 (LTC2861) 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. The logic inputs of the LTC2859/LTC2861 have 50mV 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 102 285961 F12 Figure 12. Termination Magnitude and Phase vs Frequency 75 RDIFF = 54Ω 70 CURRENT (mA) 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 LTC2861, DI and A/B should not be routed near the driver or receiver outputs. 100 101 FREQUENCY (MHz) 65 60 CL = 1000pF 55 50 45 102 CL = 100pF 103 104 DATA RATE (kbps) 105 285961 F13 Figure 13. Supply Current vs Data Rate 285961fb 12 LTC2859/LTC2861 APPLICATIONS INFORMATION from a driver transition may exceed the hysteresis levels on the logic and data inputs 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 reduces glitches caused by driver transitions. represents the specified maximum data rate in the RS485 standard. The dashed lines at 250kbps and 20Mbps show the maximum data rates of the LTC2859/LTC2861 in LowEMI and normal modes, respectively. CABLE LENGTH (FT) 10k Cable Length vs Data Rate 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 14. 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 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 285961 F14 Figure 14. Cable Length vs Data Rate (RS485 Standard Shown in Solid Lines) PACKAGE DESCRIPTION DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD10) DFN 1103 5 0.25 ± 0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) 1 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.00 – 0.05 2.38 ±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 285961fb 13 LTC2859/LTC2861 PACKAGE DESCRIPTION DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 4.00 ±0.10 (2 SIDES) 7 0.70 ±0.05 3.60 ±0.05 2.20 ±0.05 12 R = 0.05 TYP 3.30 ±0.05 1.70 ± 0.05 0.40 ± 0.10 R = 0.115 TYP PIN 1 TOP MARK PACKAGE (NOTE 6) 3.30 ±0.10 3.00 ±0.10 (2 SIDES) 1.70 ± 0.10 0.75 ±0.05 6 0.25 ± 0.05 PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER OUTLINE 0.200 REF 0.25 ± 0.05 1 (UE12/DE12) DFN 0806 REV D 0.50 BSC 0.50 BSC 2.50 REF 2.50 REF BOTTOM VIEW—EXPOSED PAD 0.00 – 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 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 GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .045 ±.005 .009 (0.229) REF 16 15 14 13 12 11 10 9 .254 MIN .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ± .0015 .150 – .157** (3.810 – 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) .0532 – .0688 (1.35 – 1.75) 2 3 4 5 6 7 8 .004 – .0098 (0.102 – 0.249) 0° – 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) .008 – .012 (0.203 – 0.305) TYP .0250 (0.635) BSC GN16 (SSOP) 0204 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 3. DRAWING NOT TO SCALE 285961fb 14 LTC2859/LTC2861 TYPICAL APPLICATIONS Multi-Node Network with End Termination Using LTC2859 TE = 0V TE = 0V D R D R LTC2859 LTC2859 LTC2859 LTC2859 R R TE = 5V TE = 5V D D 2859/61 TA04 285961fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC2859/LTC2861 TYPICAL APPLICATION Failsafe “0” Application (Idle State = Logic “0”) VCC 100kΩ RO LTC2859 R I1 B 120Ω DI I2 A D "A" "B" 2859/61 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC485 Low Power RS485 Interface Transceiver ICC = 300μA (Typ) LTC491 Differential 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 Transceivers on the Bus LTC1520 50Mbps Precision Quad Line Receiver Channel-to-Channel Skew 400ps (Typ) LTC1535 Isolated RS485 Full-Duplex Transceiver 2500VRMS Isolation in Surface Mount Package LTC1685 52Mbps RS485 Transceiver with Precision Delay Propagation Delay Skew 500ps (Typ) LT1785 60V Fault Protected RS485 Transceiver 60V Tolerant, 15kV ESD 285961fb 16 Linear Technology Corporation LT 0108 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006