LTC2861IDE-TRPBF

FEATURES ■ ■ ■ ■ ■ ■ LTC2859/LTC2861 20Mbps RS485 Transceivers with Integrated Switchable Termination DESCRIPTION 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. ■ ■ ■ ■ ■ ■ 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 ■ ■ ■ Low Power RS485/RS422 Transceiver Level Translator Backplane Transceiver PRODUCT SELECTION GUIDE PART NUMBER LTC2859 LTC2861 DUPLEX Half Full PACKAGE DFN-10 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 RO RE TE DE DI SLO 2859/61 TA01 LTC2859 R RO RE TE DE Y D DI SLO LTC2859 120Ω 2V/DIV 20ns/DIV Z Y–Z R LTC2859 at 20Mbps DI 120Ω D 120Ω 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 RO RO RE DE DI TE 1 2 3 4 5 11 10 VCC 9B 8A 7 SLO 6 GND RE DE DI TE 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 1 2 3 4 5 6 13 12 VCC 11 A 10 B 9 8 7 Z Y SLO RO RE DE DI TE GND NC NC 1 2 3 4 5 6 7 8 TOP VIEW 16 VCC 15 A 14 B 13 Z 12 Y 11 SLO 10 NC 9 NC 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 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 LTC2861CDE#PBF LTC2861IDE#PBF LTC2861CGN#PBF LTC2861IGN#PBF LTC2859CDD#PBF LTC2859IDD#PBF LEAD BASED FINISH LTC2861CDE LTC2861IDE LTC2861CGN LTC2861IGN TAPE AND REEL LTC2861CDE#TRPBF LTC2861IDE#TRPBF LTC2861CGN#TRPBF LTC2861IGN#TRPBF LTC2859CDD#TRPBF LTC2859IDD#TRPBF TAPE AND REEL LTC2861CDE#TR LTC2861IDE#TR LTC2861CGN#TR LTC2861IGN#TR PART MARKING* 2861 2861 2861 2861I LBNX LBNX PART MARKING* 2861 2861 2861 2861I PACKAGE DESCRIPTION 12-Lead (4mm × 3mm) Plastic DFN 12-Lead (4mm × 3mm) Plastic DFN 16-Lead Plastic SSOP 16-Lead Plastic SSOP 10-Lead (3mm × 3mm) Plastic DFN 10-Lead (3mm × 3mm) Plastic DFN PACKAGE DESCRIPTION 12-Lead (4mm × 3mm) Plastic DFN 12-Lead (4mm × 3mm) Plastic DFN 16-Lead Plastic SSOP 16-Lead Plastic SSOP TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C 0°C to 70°C –40°C to 85°C 0°C to 70°C –40°C to 85°C TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C 0°C to 70°C –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 SYMBOL Driver |VOD| 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) R = 27Ω or R = 50Ω (Figure 1) ● ● ● ● 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). PARAMETER CONDITIONS MIN TYP MAX VCC VCC VCC 0.2 UNITS V V V V 1.5 2.0 Δ|VOD| Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common Mode Output Voltage Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States Driver Three-State (High Impedance) Output Current on Y and Z Maximum Driver Short-Circuit Current Receiver Input Current (A, B) VOC Δ|VOC| R = 27Ω or R = 50Ω (Figure 1) R = 27Ω or R = 50Ω (Figure 1) ● ● 3.0 0.2 V V IOZD IOSD Receiver IIN2 DE = OV, VO = –7V, +12V (LTC2861 Only) –7V ≤ (Y or Z) ≤ 12 (Figure 2) DE = TE = 0V, VCC = 0V or 5V, VA or VB = 12V, Other at 0V DE = TE = 0V, VCC = 0V or 5V, VA or VB = –7V, Other at 0V ● ● ±10 ±120 ±250 125 –100 ±0.2 25 μA mA μA μA V mV V ● ● ● VTH ΔVTH VOH VOL IOZR RIN RTERM Logic VIH VIL IIN1 Supplies ISHDN ICCR ICCT ICCTS ICCL ICCRT Receiver Differential Input Threshold Voltage Receiver Input Hysteresis Receiver Output HIGH Voltage Receiver Output LOW Voltage Receiver Three-State (High Impedance) Output Current on RO Receiver Input Resistance Receiver Input Terminating Resistor –7V ≤ VCM ≤ 12 VCM = 0V I0 = –4mA, VID = 200mV, VCC = 4.5V I0 = 4mA, VID = –200mV, VCC = 4.5V RE = 5V, 0V ≤ VO ≤ VCC RE = 5V or 0V, DE = TE = 0V –7V ≤ VA = VB ≤ 12V TE = 5V, VAB = 2V, VB = –7, 0, 10V (Figure 7) DE, DI, RE, TE, SLO, VCC = 4.5V DE, DI, RE, TE, SLO, VCC = 4.5V DE, DI, RE, TE, SLO DE = 0V, RE = VCC, TE = 0V No Load, DE = 0V, RE = 0V, TE = 0V No Load, DE = VCC, RE = VCC, SLO = VCC, TE = 0V No Load, DE = VCC, RE = VCC, SLO = 0V, TE = 0V ● ● ● ● 2.4 0.4 ±1 96 108 125 120 156 V μA kΩ Ω ● Logic Input High Voltage Logic Input Low Voltage Logic Input Current Supply Current in Shutdown Mode Supply Current in Receive Mode Supply Current in Transmit Mode Supply Current in Transmit SLO Mode ● ● ● 2 0.8 0 0 540 630 670 660 640 ±10 5 900 1000 1100 1100 1180 V V μA μA μA μA μA μA μA ● ● ● ● ● ● Supply Current in Loopback Mode (Both No Load, DE = VCC, RE= 0V, SLO = VCC, TE Driver and Receiver Enabled) = 0V Supply Current in Termination Mode DE = 0V, RE = VCC, TE = VCC, SLO = VCC 285961fb 3 LTC2859/LTC2861 SWITCHING CHARACTERISTICS SYMBOL fMAX tPLHD, tPHLD ΔtPD tSKEWD tRD, tFD tZLD, tZHD, tLZD, tHZD tZHSD, tZLSD tSHDN PARAMETER Maximum Data Rate Driver Input to Output Driver Input to Output Difference |tPLHD-tPHLD| Driver Output Y to Output Z Driver Rise or Fall Time Driver Enable or Disable Time Driver Enable from Shutdown Time to Shutdown Driver in Normal Mode (SLO HIGH) Note 3 RDIFF = 54Ω, CL = 100pF (Figure 3) RDIFF = 54Ω, CL = 100pF (Figure 3) RDIFF = 54Ω, CL = 100pF (Figure 3) RDIFF = 54Ω, CL = 100pF (Figure 3) RL = 500Ω, CL = 50pF RE = 0 (Figure 4) , RL = 500Ω, CL = 50pF RE = VCC (Figure 4) , (DE = ↓, RE = VCC) or (DE = 0, RE ↑) (Figure 4) Note 3 RDIFF = 54Ω, CL = 100pF (Figure 3) RDIFF = 54Ω, CL = 100pF (Figure 3) RDIFF = 54Ω, CL = 100pF (Figure 3) RDIFF = 54Ω, CL = 100pF (Figure 3) RL = 500Ω, CL = 50pF RE = 0 (Figure 4) , RL = 500Ω, CL = 50pF RE = 0 (Figure 4) , RL = 500Ω, CL = 50pF RE = VCC (Figure 4) , (DE = 0, RE = ↑) or (DE = ↓, RE = VCC) (Figure 4) CL = 15pF VCM = 1.5V, |VAB| = 1.5V, tR and , tF < 4ns (Figure 5) CL = 15pF (Figure 5) CL = 15pF (Figure 5) RL = 1kΩ, CL =15pF DE = VCC (Figure 6) , DI = 0 or VCC RL = 1kΩ, CL = 15pF DE = 0V (Figure 6) , DI = 0 or VCC VB = 0V, VAB = 2V, RE = VCC, DE = 0V (Figure 7) ● ● ● ● ● ● ● ● 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). CONDITIONS MIN 20 10 1 1 4 50 6 ±6 12.5 70 8 100 TYP MAX UNITS Mbps ns ns ns ns ns μs ns Driver in SLO Mode (SLO LOW) fMAXS tPLHDS, tPHLDS ΔtPDS tSKEWDS tRDS, tFDS tZHDS, tZLDS tLZDS, tHZDS tZHSDS, tZLSDS tSHDNS Receiver tPLHR, tPHLR tSKEWR tRR, tFR tZLR, tZHR, tLZR, tHZR tZHSR, tZLSR tRTEN, tRTZ Receiver Input to Output Differential Receiver Skew |tPLHR-tPHLR| Receiver Output Rise or Fall Time Receiver Enable/Disable Receiver Enable from Shutdown Termination Enable or Disable Time ● ● ● ● ● ● Maximum Data Rate Driver Input to Output Driver Input to Output Difference |tPLHR-tPHLR| Driver Output A to Output B Driver Rise or Fall Time Driver Enable Time Driver Disable Time Driver Enable from Shutdown Time to Shutdown ● ● ● ● ● ● ● ● ● 250 0.95 50 200 0.9 1.5 500 ±500 1.5 300 70 8 500 kbps μs ns ns μs ns ns μs ns 50 1 3 70 6 12.5 50 8 100 ns ns ns ns μs μs 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 + VOD – Y GND OR DI VCC IOSD DRIVER Z R R + VOC – + – 2859/61 F01-2 –7V to +12V Figure 1. Driver DC Characteristics Figure 2. Driver Output Short-Circuit Current Y DI CL DRIVER Z RDIFF CL DI VCC OV tPLHD, tPLHDS tSKEWD, tSKEWDS VO 1/2 VO tPHLD, tPHLDS Y, Z (Y-Z) 90% 10% 0 tRD, tRDS 0 90% 10% tFD, tFDS 2859/61 F03 Figure 3. Driver Timing Measurement RL Y VCC OR DI GND DRIVER Z DE CL RL CL GND OR VCC VCC DE 1/2 VCC OV VCC Y or Z VO VOL VOH tZLD, tZLDS, tZLSD, tZLSDS 1/2 VCC tLZD, tLZDS 0.5V 0.5V tHZD, tHZDS, tSHDN, tSHDNS 2859/61 F04 VCC OR GND Z or Y 1/2 VCC OV tZHD, tZHDS, tZHSD, tZHSDS Figure 4. Driver Enable and Disable Timing Measurement 285961fb 5 LTC2859/LTC2861 TEST CIRCUITS ±VAB/2 VCM ±VAB/2 A B RECEIVER RO CL RO 0V A-B VAB 0V –VAB VCC VO 90% 10% tPLHR 1/2 VCC tRR tSKEWR = tPLHR – tPHLR 2859/61 F05 1/2 VCC tPHLR 90% 10% tFR Figure 5. Receiver Propagation Delay Measurements 0V OR VCC A RECEIVER RO CL RE RE RL VCC OR GND VCC 0V VCC VO VOL VOH tZLR, tZLSR 1/2 VCC tLZR 1/2 VCC 0.5V 0.5V tHZR 2859/61 F06 VCC OR 0V B RO DI = 0V OR VCC RO 0V tZHR, tZHSR 1/2 VCC Figure 6. Receiver Enable/Disable Time Measurements A RO RECEIVER RTERM = VAB IA VCC TE 1/2 VCC 0V IA 90% 10% tRTEN tRTZ + – B VAB TE + – VB 2859/61 F07 Figure 7. Termination Resistance and Timing Measurements 285961fb 6 LTC2859/LTC2861 TYPICAL PERFORMANCE CHARACTERISTICS Receiver Skew vs Temperature VAB = 1.5V CL = 15pF 2 RECEIVER SKEW (ns) 2 DRIVER SKEW (ns) 3 TA = 25°C, VCC = 5V, unless otherwise noted. Driver Propagation Delay vs Temperature 18 16 DRIVER PROP DELAY (ns) 14 12 10 8 6 RDIFF = 54Ω CL = 100pF SLO = VCC Driver Skew vs Temperature RDIFF = 54Ω CL = 100pF SLO = VCC 1 1 0 0 –1 –40 –20 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 285961 G01 0 20 40 60 80 TEMPERATURE (°C) 100 120 285961 G02 4 –40 –20 0 20 40 60 80 100 120 285961 G03 TEMPERATURE (°C) RTERM vs Temperature 135 130 4 OUTPUT VOLTAGE (V) 125 RESISTANCE (Ω) 120 115 110 105 100 95 –40 –20 0 0 20 40 60 80 TEMPERATURE (°C) 100 120 285961 G04 Driver Output Low/High Voltage vs Output Current 5 VOH 4 OUTPUT VOLTAGE (V) 5 Driver Differential Output Voltage vs Temperature R=∞ 3 3 R = 100Ω R = 54Ω 2 VOL 2 1 1 0 10 40 30 20 50 OUTPUT CURRENT (mA) 60 70 285961 G05 0 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 285961 G06 Receiver Output Voltage vs Output Current (Source and Sink) 5 SOURCE 65 4 OUTPUT VOLTAGE (V) 60 PROP DELAY (ns) 3 55 50 45 40 35 SINK 0 0 1 3 4 2 OUTPUT CURRENT (mA) 5 285961 G07 Receiver Propagation Delay vs Temperature 70 VAB = 1.5V CL = 15pF SUPPLY CURRENT (mA) 60 50 40 Supply Current vs Data Rate R = 54Ω R = 100Ω 30 20 10 R=∞ 0 0.1 2 1 30 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 285961 G08 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 0 0 0 0 1 1 1 1 RE 0 0 1 1 0 0 1 1 TE 0 1 0 1 0 1 0 1 MODE Receive Receive with Term Shutdown Term Only Transmit with Receive Transmit with Receive and Term Transmit Transmit with Term A, B RIN RIN RIN RIN Driven Driven Driven Driven RO Enabled Enabled Hi-Z Hi-Z Enabled Enabled Hi-Z Hi-Z TERMINATOR Off On Off On Off On Off On LTC2861 LOGIC INPUTS DE 0 0 0 0 1 1 1 1 RE 0 0 1 1 0 0 1 1 TE 0 1 0 1 0 1 0 1 MODE Receive Receive with Term Shutdown Term Only Transmit with Receive Transmit with Receive and Term Transmit Transmit with Term A, B RIN RIN RIN RIN RIN RIN RIN RIN YZ , Hi-Z Hi-Z Hi-Z Hi-Z Driven Driven Driven Driven RO Enabled Enabled Hi-Z Hi-Z Enabled Enabled Hi-Z Hi-Z TERMINATOR Off On Off On Off On Off On BLOCK DIAGRAMS LTC2859 A (15kV) 120Ω LTC2861 A (15kV) 120Ω RE DE SLEEP/SHUTDOWN LOGIC AND DELAY RE DE SLEEP/SHUTDOWN LOGIC AND DELAY TE TE RO RECEIVER B (15kV) RO RECEIVER B (15kV) SLO SLO Z (15kV) Y (15kV) 2859/61 BD DI DRIVER DI DRIVER 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 1.25MHz/DIV 285961 F08a Driver Output at 125kHz into 100Ω Resistor 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 1.25MHz/DIV 285961 F08b Driver Output at 125kHz into 100Ω Resistor Frequency Spectrum of the Same Signal 285961fb Figure 8b. Driver Output in SLO Mode 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 2859/61 F09 B >96k 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 The resistance is maintained over the entire RS485 common mode range of –7V to +12V as shown in Figure 11. RESISTANCE (Ω) 150 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. Supply Current 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). High Speed Considerations 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. 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. 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 140 130 120 110 –10 –5 5 10 0 COMMON MODE VOLTAGE (V) 15 285961 F11 Figure 11. Termination Resistance vs Common Mode Voltage 140 120 100 80 60 40 20 PHASE MAGNITUDE 0 –5 PHASE (DEGREES) MAGNITUDE (Ω) –10 –15 –20 –25 0 10–1 100 101 FREQUENCY (MHz) 102 285961 F12 Figure 12. Termination Magnitude and Phase vs Frequency 75 70 65 60 55 50 RDIFF = 54Ω CURRENT (mA) CL = 1000pF CL = 100pF 45 102 103 104 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. 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 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. 10k CABLE LENGTH (FT) 1k LOW-EMI MODE MAX DATA RATE 100 RS485 MAX DATA RATE 10 10k 100k NORMAL MODE MAX DATA RATE 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 0.675 ± 0.05 0.38 ± 0.10 10 3.50 ± 0.05 1.65 ± 0.05 2.15 ± 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 PIN 1 TOP MARK (SEE NOTE 6) 3.00 ± 0.10 (4 SIDES) 1.65 ± 0.10 (2 SIDES) (DD10) DFN 1103 5 0.200 REF 0.50 BSC 2.38 ± 0.05 (2 SIDES) 0.75 ± 0.05 2.38 ± 0.10 (2 SIDES) 1 0.25 ± 0.05 0.50 BSC 0.00 – 0.05 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) 0.70 ± 0.05 3.30 ± 0.05 1.70 ± 0.05 PIN 1 TOP MARK PACKAGE (NOTE 6) OUTLINE 0.25 ± 0.05 2.50 REF 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 0.00 – 0.05 0.200 REF 0.50 BSC 0.75 ± 0.05 R = 0.05 TYP 3.00 ± 0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 ± 0.10 12 3.60 ± 0.05 2.20 ± 0.05 3.30 ± 0.10 1.70 ± 0.10 PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER 1 0.50 BSC (UE12/DE12) DFN 0806 REV D 6 0.25 ± 0.05 2.50 REF BOTTOM VIEW—EXPOSED PAD 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) .045 ± .005 .189 – .196* (4.801 – 4.978) 16 15 14 13 12 11 10 9 .009 (0.229) REF .254 MIN .150 – .165 .229 – .244 (5.817 – 6.198) .150 – .157** (3.810 – 3.988) .0165 ± .0015 .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) 0° – 8° TYP .0532 – .0688 (1.35 – 1.75) 23 4 56 7 8 .004 – .0098 (0.102 – 0.249) .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE .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 285961fb 14 LTC2859/LTC2861 TYPICAL APPLICATIONS Multi-Node Network with End Termination Using LTC2859 TE = 0V TE = 0V D R R D LTC2859 LTC2859 LTC2859 R TE = 5V LTC2859 R 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 I1 R LTC2859 B "A" 120Ω DI I2 D A "B" 2859/61 TA03 RELATED PARTS PART NUMBER LTC485 LTC491 LTC1480 LTC1483 LTC1485 LTC1487 LTC1520 LTC1535 LTC1685 LT1785 DESCRIPTION Low Power RS485 Interface Transceiver Differential Driver and Receiver Pair 3.3V Ultralow Power RS485 Transceiver Ultralow Power RS485 Low EMI Transceiver Differential Bus Transceiver Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance 50Mbps Precision Quad Line Receiver Isolated RS485 Full-Duplex Transceiver 52Mbps RS485 Transceiver with Precision Delay 60V Fault Protected RS485 Transceiver COMMENTS ICC = 300μA (Typ) ICC = 300μA 3.3V Operation Controlled Driver Slew Rate 10Mbaud Operation Up to 256 Transceivers on the Bus Channel-to-Channel Skew 400ps (Typ) 2500VRMS Isolation in Surface Mount Package Propagation Delay Skew 500ps (Typ) 60V Tolerant, 15kV ESD 285961fb 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● LT 0108 REV B • PRINTED IN USA www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006