LTC2855

FEATURES ■ ■ ■ ■ ■ LTC2854/LTC2855 3.3V 20Mbps RS485/RS422 Transceivers with Integrated Switchable Termination DESCRIPTION The LTC®2854 and LTC2855 are low power, 20Mbps RS485/RS422 transceivers operating on 3.3V supplies. The receiver includes a logic-selectable 120Ω termination, 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 a thermal shutdown. Enhanced ESD protection allows the LTC2854 to withstand ±25kV (human body model) and the LTC2855 to withstand ±15kV on the transceiver interface pins without latchup or damage. ■ ■ ■ ■ ■ ■ ■ ■ Integrated, Logic-Selectable 120Ω Termination Resistor 3.3V Supply Voltage 20Mbps Maximum Data Rate No Damage or Latchup Up to ±25kV 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: 370μA Typical in Receive Mode Compatible with TIA/EIA-485-A Specifications Available in 10-Pin 3mm × 3mm DFN, 12-Pin 4mm × 3mm DFN and 16-Pin SSOP Packages PRODUCT SELECTION GUIDE PART NUMBER LTC2854 LTC2855 DUPLEX HALF FULL PACKAGE DFN-10 SSOP-16, DFN-12 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. TYPICAL APPLICATION LTC2854 RO RE TE DE DI D R LTC2854 R RO RE TE DE D DI LTC2854 at 20Mbps into 54Ω DI 120Ω 120Ω A B 2V/DIV A-B LTC2854 120Ω 285455 TA01 R D 20ns/DIV 285455 TA01b RO RE TE DE DI 285455fa 1 LTC2854/LTC2855 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC) ................................... –0.3V to 7V ⎯⎯ Logic Input Voltages (RE, DE, DI, TE)............ –0.3V to 7V Interface I/O: A, B, Y, Z ...................................... (VCC –15V) to +15V (A-B) or (B-A) with Terminator Enabled ..................6V Receiver Output Voltage (RO) ........ –0.3V to (VCC +0.3V) Operating Temperature (Note 4) LTC2854C, LTC2855C .............................. 0°C to 70°C LTC2854I, LTC2855I ............................ –40°C to 85°C LTC2854H, LTC2855H........................ –40°C to 125°C Storage Temperature Range................... –65°C to 150°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 NC 6 GND RE DE DI TE GND DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN 1 2 3 4 5 6 13 12 V CC 11 A 10 B 9 8 7 Z Y NC 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 NC 10 NC 9 NC EXPOSED PAD (PIN 11) PCB GND CONNECTION TJMAX = 125°C, θJA = 43°C/W θJC = 2.96°C/W DE PACKAGE 12-LEAD (4mm × 3mm) PLASTIC DFN EXPOSED PAD (PIN 13) PCB GND CONNECTION TJMAX = 125°C, θJA = 44°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 TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2854CDD#PBF LTC2854CDD#TRPBF LCQG 10-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2854IDD#PBF LTC2854IDD#TRPBF LCQG 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2854HDD#PBF LTC2854HDD#TRPBF LCQG 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LTC2855CDE#PBF LTC2855CDE#TRPBF 2855 12-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C LTC2855IDE#PBF LTC2855IDE#TRPBF 2855 12-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C LTC2855HDE#PBF LTC2855HDE#TRPBF 2855 12-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C LTC2855CGN#PBF LTC2855CGN#TRPBF 2855 16-Lead (Narrow 0.150) Plastic SSOP 0°C to 70°C LTC2855IGN#PBF LTC2855IGN#TRPBF 2855I 16-Lead (Narrow 0.150) Plastic SSOP –40°C to 85°C LTC2855HGN#PBF LTC2855HGN#TRPBF 2855H 16-Lead (Narrow 0.150) Plastic SSOP –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2854CDD LTC2854CDD#TR LCQG 10-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2854IDD LTC2854IDD#TR LCQG 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2854HDD LTC2854HDD#TR LCQG 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LTC2855CDE LTC2855CDE#TR 2855 12-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C LTC2855IDE LTC2855IDE#TR 2855 12-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C LTC2855HDE LTC2855HDE#TR 2855 12-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C LTC2855CGN LTC2855CGN#TR 2855 16-Lead (Narrow 0.150) Plastic SSOP 0°C to 70°C LTC2855IGN LTC2855IGN#TR 2855I 16-Lead (Narrow 0.150) Plastic SSOP –40°C to 85°C LTC2855HGN LTC2855HGN#TR 2855H 16-Lead (Narrow 0.150) Plastic SSOP –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 285455fa 2 LTC2854/LTC2855 ELECTRICAL CHARACTERISTICS SYMBOL Driver |VOD| Differential Driver Output Voltage R = ∞, VCC = 3V (Figure 1) R = 27Ω, VCC = 3V (Figure 1) R = 50Ω, VCC = 3.13V (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 = 3.3V unless otherwise noted (Note 2). PARAMETER CONDITIONS MIN TYP MAX VCC VCC VCC 0.2 UNITS V V V V 1.5 2 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 VOC Δ|VOC| R = 27Ω or R = 50Ω (Figure 1) R = 27Ω or R = 50Ω (Figure 1) ● ● 3 0.2 V V IOZD IOSD Receiver IIN DE = OV, (Y or Z) = –7V, 12V (LTC2855) –7V ≤ (Y or Z) ≤ 12V (Figure 2) ● ±10 180 ±250 300 125 –100 250 –145 96 125 μA mA mA μA μA μA μA kΩ ● –250 Receiver Input Current (A, B) DE = TE = 0V, VCC = 0V or 3.3V, VIN = 12V (Figure 3) (C, I-Grade) DE = TE = 0V, VCC = 0V or 3.3V, VIN = –7V, (Figure 3) (C, I-Grade) DE = TE = 0V, VCC = 0V or 3.3V, VIN = 12V (Figure 3) (H-Grade) DE = TE = 0V, VCC = 0V or 3.3V, 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 B = 0V I(RO) = –4mA, A-B = 200mV, VCC = 3V I(RO) = 4mA, A-B = –200mV, VCC = 3V ⎯R⎯E = VCC, 0V ≤ RO ≤ VCC 0V ≤ RO ≤ VCC TE = VCC, VAB = 2V, VB = –7V, 0V, 10V (Figure 8) VCC = 3.6V VCC = 3V ● ● ● ● ● RIN Receiver Input Resistance ● 48 125 kΩ VTH ΔVTH VOH VOL IOZR IOSR RTERM Logic VIH VIL IINL Supplies ICCS 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 Short-Circuit Current Receiver Input Terminating Resistor ● ±0.2 25 V mV V ● ● ● ● ● 2.4 0.4 ±1 ±85 108 120 156 V μA mA Ω Logic Input High Voltage Logic Input Low Voltage Logic Input Current Supply Current in Shutdown Mode ● ● ● 2 0.8 0 ±10 V V μA ICCR Supply Current in Receive Mode DE = 0V, ⎯R⎯E = VCC, TE = 0V (LTC2854C/LTC2854I, LTC2855C/LTC2855I) (LTC2854H, LTC2855H) ⎯⎯ DE = 0V, RE = 0V, TE = 0V ● ● ● 0 0 370 5 15 900 μA μA μA 285455fa 3 LTC2854/LTC2855 ELECTRICAL CHARACTERISTICS SYMBOL ICCT ICCTR ICCTERM ICCTERMR ICCTERMT ICCTERMTR ESD Protection ESD Protection for RS485/RS422 Pins A, B on LTC2854, Human Body Model Y, Z, A, B on LTC2855, Human Body Model ±25 ±15 kV kV PARAMETER Supply Current in Transmit Mode Supply Current with Both Driver and Receiver Enabled Supply Current in Termination Mode Supply Current in Receive and Termination Mode Supply Current in Transmit and Termination Mode Supply Current with Driver, Receiver and Termination Enabled The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2). CONDITIONS No Load, DE = VCC, ⎯R⎯E = VCC, TE = 0V ⎯⎯ No Load, DE = VCC, RE = 0V, TE = 0V DE = 0V, ⎯R⎯E = VCC, TE = VCC DE = 0V, ⎯R⎯E = 0V, TE = VCC DE = VCC, ⎯R⎯E = VCC, TE = VCC DE = VCC, ⎯R⎯E = 0V, TE = VCC ● ● ● ● ● ● MIN TYP 450 450 110 450 470 470 MAX 1000 1000 180 950 1000 1000 UNITS μA μA μA μA μA μA SWITCHING CHARACTERISTICS SYMBOL Driver fMAX tPLHD, tPHLD ΔtPD tSKEWD tRD, tFD tZLD, tZHD, tLZD, tHZD tZHSD, tZLSD tSHDN 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 |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 PARAMETER The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2). CONDITIONS Note 3 RDIFF = 54Ω, CL = 100pF (Figure 4) RDIFF = 54Ω, CL = 100pF (Figure 4) RDIFF = 54Ω, CL = 100pF (Figure 4) RDIFF = 54Ω, CL = 100pF (Figure 4) ⎯⎯ RL = 500Ω, CL = 50pF, RE = 0 (Figure 5) ⎯⎯ RL = 500Ω, CL = 50pF, RE = VCC (Figure 5) ⎯⎯ (DE = ↓, RE = VCC) or (DE = 0, ⎯R⎯E ↑) (Figure 5) CL = 15pF, VCM = 1.5V, |VAB| = 1.5V, tR and tF < 4ns (Figure 6) CL = 15pF (Figure 6) CL = 15pF (Figure 6) RL = 1k, CL =15pF, DE = VCC (Figure 7) RL = 1k, CL = 15pF, DE = 0V (Figure 7) ⎯⎯ VB = 0V, VAB = 2V, RE = VCC, DE = 0V (Figure 8) ● ● ● ● ● ● ● ● MIN 20 TYP MAX UNITS Mbps 10 1 1 4 50 6 ±6 12.5 70 8 100 ns ns ns 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. Overtemperature protection activates at a junction temperature exceeding 150°C. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. 285455fa 4 LTC2854/LTC2855 TEST CIRCUITS Y GND DI OR VCC DRIVER Z + VOD – R Y GND OR DI VCC IOSD DRIVER Z R + VOC – + – 285455 F01-2 –7V to +12V Figure 1. Driver DC Characteristics Figure 2. Driver Output Short-Circuit Current IIN A OR B RECEIVER B OR A 285455 F03 VIN + – V RIN = IN IIN Figure 3. Receiver Input Current and Input Resistance VCC Y DI CL DRIVER RDIFF CL Z 285455 F04a DI 0V tPLHD tSKEWD tPHLD Y, Z VO 1/2 VO 90% Y-Z 10% 0 tRD 0 90% 10% tFD 285455 F04b Figure 4. Driver Timing Measurement VCC Y VCC OR GND DI CL DRIVER RL DE Z CL VCC OR GND 285455 F05a RL GND OR VCC DE 0V VCC Y OR Z VOL VOH Z OR Y 0V VO 1/2 VCC tZLD, tZLSD 1/2 VCC tLZD 0.5V 0.5V tHZD, tSHDN 285455 F05b 1/2 VCC tZHD, tZHSD Figure 5. Driver Enable and Disable Timing Measurements 285455fa 5 LTC2854/LTC2855 TEST CIRCUITS tR ±VAB/2 VCM ±VAB/2 B A RECEIVER RO CL 285455 F06a tF 90% 10% tPLHR tPHLR 1/2 VCC 90% 10% tFR 285455 F06b VAB A-B –VAB VCC RO 0 VO 90% 0 10% 90% 1/2 VCC 10% tRR tSKEWR = tPLHR – tPHLR Figure 6. Receiver Propagation Delay Measurements VCC RE 0V 0V OR VCC A RECEIVER VCC OR 0V B RE RO CL RL VCC OR GND VCC RO VOL VOH RO DI = 0V OR VCC 285455 F07a 1/2 VCC tZLR, tZLSR VO 1/2 VCC tLZR 0.5V 0.5V 285455 F05b 1/2 VCC 0V tZHR, tZHSR tHZR Figure 7. Receiver Enable and Disable Timing Measurements IA A RO RECEIVER RTERM = VAB IA TE VAB IA VCC 1/2 VCC 0V 90% 10% tRTEN tRTZ + – B TE + – VB 285455F07 Figure 8. Termination Resistance and Timing Measurements 285455fa 6 LTC2854/LTC2855 TYPICAL PERFORMANCE CHARACTERISTICS Receiver Skew vs Temperature 2 VAB = 1.5V CL = 15pF RECEIVER SKEW (ns) 1 DRIVER SKEW (ns) TA = 25°C, VCC = 3.3V, unless otherwise noted. Driver Propagation Delay vs Temperature 18 16 14 12 10 9 RDIFF = 54Ω CL = 100pF Driver Skew vs Temperature RDIFF = 54Ω CL = 100pF 1 0 0 –1 –1 –40 –20 PROP DELAY (ns) 6 4 –40 –20 0 20 40 60 80 100 120 285455 G01 –40 –20 0 20 40 60 80 100 120 285455 G02 0 20 40 60 80 100 120 285455 G03 TEMPERATURE (˚C) TEMPERATURE (˚C) TEMPERATURE (˚C) RTERM vs Temperature 135 130 125 120 115 110 105 100 –40 –20 0 0 20 40 60 80 100 120 285455 G04 Driver Output Low/High Voltage vs Output Current 3 OUTPUT VOLTAGE (V) VOH OUTPUT VOLTAGE (V) 3 Driver Differential Output Voltage vs Temperature RDIFF = ∞ RDIFF = 100Ω 2 RDIFF = 54Ω RESISTANCE (Ω) 2 1 VOL 1 0 10 20 30 40 50 60 70 0 –40 –20 0 20 40 60 80 100 120 285455 G06 TEMPERATURE (˚C) OUTPUT CURRENT (mA) 285455 G05 TEMPERATURE (˚C) Receiver Output Voltage vs Output Current (Source and Sink) 70 SOURCE 3 OUTPUT VOLTAGE (V) 65 60 55 50 45 40 SINK 0 0 1 2 3 4 5 6 285455 G07 Receiver Propagation Delay vs Temperature VAB = 1.5V CL = 15pF SUPPLY CURRENT (mA) 60 50 40 30 20 10 Supply Current vs Data Rate CL = 100pF 2 PROP DELAY (ns) RDIFF = 54Ω RDIFF = 100Ω 1 RDIFF = ∞ 0 20 40 60 80 100 120 285455 G08 35 –40 –20 0 0.1 1 10 DATA RATE (Mbps) 100 285455 G09 OUTPUT CURRENT (mA) TEMPERATURE (˚C) 285455fa 7 LTC2854/LTC2855 PIN FUNCTIONS (DD/DE/GN) RO (Pin 1): Receiver Output. If the receiver output is enabled (⎯R⎯E 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 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 ⎯R⎯E 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. Y (Pins NA/8/12): Positive Driver Output for LTC2855. Z (Pins NA/9/13): Negative Driver Output for LTC2855. B (Pins 9/10/14): Negative Receiver Input (and Negative Driver Output for LTC2854). A (Pins 8/11/15): Positive Receiver Input (and Positive Driver Output for LTC2854). VCC (Pins 10/12/16): Positive Supply. VCC = 3.0V < VCC < 3.6V. Bypass with 0.1μF ceramic capacitor. 285455fa 8 LTC2854/LTC2855 FUNCTION TABLES LTC2854 DE 0 0 0 0 1 1 1 1 LOGIC INPUTS ⎯ R⎯E 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 RTERM RIN RTERM DRIVEN DRIVEN DRIVEN DRIVEN RO DRIVEN DRIVEN HIGH-Z HIGH-Z DRIVEN DRIVEN HIGH-Z HIGH-Z TERMINATOR OFF ON OFF ON OFF ON OFF ON LTC2855 DE 0 0 0 0 1 1 1 1 LOGIC INPUTS ⎯ R⎯E 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 RTERM RIN RTERM RIN RTERM RIN RTERM Y, Z HIGH-Z HIGH-Z HIGH-Z HIGH-Z DRIVEN DRIVEN DRIVEN DRIVEN RO DRIVEN DRIVEN HIGH-Z HIGH-Z DRIVEN DRIVEN HIGH-Z HIGH-Z TERMINATOR OFF ON OFF ON OFF ON OFF ON BLOCK DIAGRAMS LTC2854 VCC LTC2855 VCC RE DE SLEEP/SHUTDOWN LOGIC AND DELAY 120Ω RTERM A 25kV RE DE SLEEP/SHUTDOWN LOGIC AND DELAY 120Ω RTERM A (15kV) 125k RIN RO RECEIVER TE 125k RIN RO RECEIVER TE 125k RIN B 25kV 125k RIN B (15kV) DI DRIVER DI DRIVER Z (15kV) Y (15kV) GND GND 285455 BD 285455fa 9 LTC2854/LTC2855 APPLICATIONS INFORMATION Driver The driver provides full RS485/RS422 compatibility. When enabled, if DI is high, Y-Z is positive for the full-duplex device (LTC2855) and A-B is positive for the half-duplex device (LTC2854). When the driver is disabled, both outputs are highimpedance. For the full-duplex LTC2855, 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 LTC2854, 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 typical peak current in this condition does not exceed 180mA. If a high driver output is shorted to a voltage just above VCC , a reverse current will flow into the supply. When this voltage exceeds VCC by about 1.4V, the reverse current turns off. Preventing the driver from turning off with outputs shorted to output voltages just above VCC keeps the driver active even for receiver loads that have a positive common mode with respect to the driver — a valid condition. The worst-case peak reverse short-circuit current can be as high as 300mA in extreme cold conditions. If this current cannot be absorbed by the supply, a 3.6V Zener diode can be added in parallel with the supply to sink this current. All devices also feature thermal shutdown protection that disables the driver and receiver in case of excessive power dissipation (see Note 4). 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 LTC2854/LTC2855 have a failsafe feature that guarantees the receiver output to be in a logic-high state when >96kΩ 285455 F09 the inputs are either shorted, left open, or terminated (externally or internally), but not driven. 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) when the termination is disabled. This is 8X higher than the requirements for the 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 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. 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. >96kΩ 60Ω TE 60Ω B A Figure 9. Equivalent Input Resistance into A and B (on the LTC2854, Valid if Driver is Disabled) 285455fa 10 LTC2854/LTC2855 APPLICATIONS INFORMATION 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 LTC2854/LTC2855 are the first 3.3V RS485/RS422 transceivers to offer integrated switchable termination resistors on the receiver input pins. This provides the advantage of being able to easily change, through logic control, the 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. The resistance is maintained over the entire RS485 common mode range of –7V to +12V as shown in Figure 11. 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. 150 VAB = 2V 140 RESISTANCE (Ω) 130 120 110 100 –10 Figure 10. Curve Trace Between A and B with Termination Enabled and Disabled –5 5 10 0 COMMON MODE VOLTAGE (V) 15 285455 F11 Figure 11. Typical Resistance of the Enabled Terminator vs Voltage on B Pin 185 170 MAGNITUDE (Ω) 155 140 125 110 95 80 10 –1 10 0 FREQUENCY (MHz) MAGNITUDE PHASE 30 15 0 PHASE (°) 285455fa –15 –30 – 45 – 60 – 75 101 285455 F12 Figure 12. Termination Magnitude and Phase vs Frequency 11 LTC2854/LTC2855 APPLICATIONS INFORMATION Supply Current The unloaded static supply currents in the LTC2854/ LTC2855 are very low —typically under 500μA 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 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 LTC2854/LTC2855. Power supply current increases with toggling rate 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 4. 80 70 SUPPLY CURRENT (mA) 60 50 40 30 20 0.1 1 10 DATA RATE (Mbps) 100 285455 F13 the full duplex LTC2855, DI and A/B should not be routed near the driver or receiver outputs. The logic inputs of the LTC2854/LTC2855 have 150mV 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 reduces glitches caused by driver transitions. Cable Length vs Data Rate RDIFF = 54Ω C L = 1000pF C L = 100pF 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/RS422 standards 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/RS422 standards. The dashed lines at 20Mbps show the maximum data rates of the LTC2854/LTC2855. 10k Figure 13. Supply Current vs Data Rate High Speed Considerations A ground plane layout is recommended for the LTC2854/ LTC2855. 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 (LTC2855) 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 CABLE LENGTH (FT) 1k LTC2854/LTC2855 MAX DATA RATE 100 RS485/RS422 MAX DATA RATE 10 10k 100k 1M 10M DATA RATE (bps) 100M 285455 F14 Figure 14. Cable Length vs Data Rate (RS485/ RS422 Standards Shown in Vertical Solid Line) 285455fa 12 LTC2854/LTC2855 TYPICAL APPLICATION Failsafe “0” Application (Idle State = Logic “0”) VCC 100kΩ RO I1 R LTC2854 B "A" A DI I2 D "B" 285455 TA03 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 0.50 BSC 2.38 ± 0.05 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 3.00 ± 0.10 (4 SIDES) 1.65 ± 0.10 (2 SIDES) (DD) DFN 1103 5 0.200 REF 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 285455fa 13 LTC2854/LTC2855 PACKAGE DESCRIPTION DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 0.70 ± 0.05 3.60 ± 0.05 1.70 ± 0.05 2.20 ± 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 3.30 ± 0.05 (2 SIDES) 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ± 0.10 (2 SIDES) R = 0.05 TYP 3.00 ± 0.10 (2 SIDES) 1.70 ± 0.05 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER 0.75 ± 0.05 6 0.25 ± 0.05 3.30 ± 0.05 (2 SIDES) 1 0.50 BSC (UE12/DE12) DFN 0905 REV C 7 R = 0.115 TYP 0.40 ± 0.10 12 PIN 1 TOP MARK (NOTE 6) 0.200 REF 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD 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 285455fa 14 LTC2854/LTC2855 PACKAGE DESCRIPTION GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) 16 15 14 13 12 11 10 9 .045 ± .005 .009 (0.229) REF .254 MIN .150 – .165 .229 – .244 (5.817 – 6.198) .150 – .157** (3.810 – 3.988) .0165 ± .0015 .0250 BSC 1 .015 ± .004 × 45° (0.38 ± 0.10) .0532 – .0688 (1.35 – 1.75) 23 4 56 7 8 .004 – .0098 (0.102 – 0.249) RECOMMENDED SOLDER PAD LAYOUT .007 – .0098 (0.178 – 0.249) 0° – 8° TYP .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 285455fa 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 LTC2854/LTC2855 TYPICAL APPLICATION Multi-Node Network with End Termination Using the LTC2854 TE = 0V TE = 0V D R R D LTC2854 LTC2854 LTC2854 R TE = 3.3V LTC2854 R TE = 3.3V D D 285455 TA04 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 10Mbps 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 Up to 256 Transceivers on the Bus 5V Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD LTC2856/LTC2857/ 20Mbps and Slew Rate-Limited, 15kV RS485/RS422 LTC2858 Transceiver LTC2859/LTC2861 20Mbps RS485 Transceiver with Integrated Switchable Termination 285455fa 16 Linear Technology Corporation (408) 432-1900 ● FAX: (408) 434-0507 ● LT 1107 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007