LTC488/LTC489 Quad RS485 Line Receiver FEATURES DESCRIPTION n The LTC®488 and LTC489 are low power differential bus/ line receivers designed for multipoint data transmission standard RS485 applications with extended common mode range (12V to –7V). They also meet the requirements of RS422. n n n n n n n n Low Power: ICC = 7mA Typ Designed for RS485 or RS422 Applications Single 5V Supply –7V to 12V Bus Common Mode Range Permits ±7V Ground Difference Between Devices on the Bus 60mV Typical Input Hysteresis Receiver Maintains High Impedance in Three-State or with the Power Off 28ns Typical Receiver Propagation Delay Pin Compatible with the SN75173 (LTC488) Pin Compatible with the SN75175 (LTC489) APPLICATIONS n n The CMOS design offers significant power savings over its bipolar counterpart without sacrificing ruggedness against overload or ESD damage. The receiver features three-state outputs, with the receiver output maintaining high impedance over the entire common mode range. The receiver has a fail-safe feature which guarantees a high output state when the inputs are left open. Low Power RS485/RS422 Receivers Level Translator Both AC and DC specifications are guaranteed 4.75V to 5.25V supply voltage range. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION EN EN EN 2 DI DRIVER 1/4 LTC486 120Ω 120Ω 1 EN 4 12 RECEIVER 1/4 LTC488 3 RO 4000 FT 24 GAUGE TWISTED PAIR EN12 EN12 2 DI DRIVER 1/4 LTC487 120Ω 120Ω 1 4000 FT 24 GAUGE TWISTED PAIR 4 RECEIVER 1/4 LTC489 3 RO 4889 TA01 4889fb 1 LTC488/LTC489 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC) ................................................12V Control Input Currents .......................... –25mA to 25mA Control Input Voltages ..................–0.5V to (VCC + 0.5V) Receiver Input Voltages ..........................................±14V Receiver Output Voltages ..............–0.5V to (VCC + 0.5V) Operating Temperature Range LTC488C/LTC489C ................................... 0°C to 70°C LTC488I/LTC489I.................................. –40°C to 85°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C PIN CONFIGURATION LTC488 LTC488 TOP VIEW B1 1 R TOP VIEW 16 VCC B1 1 15 B4 A1 2 RO1 3 A1 2 RO1 3 14 A4 EN 4 13 RO4 RO2 5 12 EN A2 6 B2 7 GND 8 R R A2 6 B2 7 11 RO3 R R 10 A3 9 B3 SW PACKAGE 16-LEAD PLASTIC (WIDE) SO TJMAX = 150°C, θJA = 90°C/W N PACKAGE 16-LEAD PLASTIC DIP TJMAX = 150°C, θJA = 70°C/W LTC489 14 A4 12 EN GND 8 B3 15 B4 13 RO4 RO2 5 10 A3 9 R EN 4 11 RO3 R 16 VCC R LTC489 TOP VIEW B1 1 TOP VIEW 16 VCC R B1 1 16 VCC R A1 2 15 B4 A1 2 RO1 3 14 A4 RO1 3 EN12 4 13 RO4 EN12 4 13 RO4 12 EN34 RO2 5 12 EN34 RO2 5 A2 6 B2 7 GND 8 R R R 11 RO3 A2 6 10 A3 B2 7 9 B3 N PACKAGE 16-LEAD PLASTIC DIP TJMAX = 150°C, θJA = 70°C/W GND 8 R 15 B4 14 A4 11 RO3 R R 10 A3 9 B3 SW PACKAGE 16-LEAD PLASTIC (WIDE) SO TJMAX = 150°C, θJA = 90°C/W 4889fb 2 LTC488/LTC489 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC488CN#PBF LTC488CN#TRPBF LTC488CN 16-Lead Plastic DIP 0°C to 70°C LTC488CSW#PBF LTC488CSW#TRPBF LTC488CSW 16-Lead Plastic SO 0°C to 70°C LTC488IN#PBF LTC488IN#TRPBF LTC488IN 16-Lead Plastic DIP –40°C to 85°C LTC488ISW#PBF LTC488ISW#TRPBF LTC488ISW 16-Lead Plastic SO –40°C to 85°C LTC489CN#PBF LTC489CN#TRPBF LTC489CN 16-Lead Plastic DIP 0°C to 70°C LTC489CSW#PBF LTC489CSW#TRPBF LTC489CSW 16-Lead Plastic SO 0°C to 70°C LTC489IN#PBF LTC489IN#TRPBF LTC489IN 16-Lead Plastic DIP –40°C to 85°C LTC489ISW#PBF LTC489ISW#TRPBF LTC489ISW 16-Lead Plastic SO –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. 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/ DC ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V (Notes 2, 3), unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN VINH Input High Voltage EN, EN, EN12, EN34 l VINL Input Low Voltage EN, EN, EN12, EN34 l TYP MAX UNITS 2.0 V 0.8 V IIN1 Input Current EN, EN, EN12, EN34 l ±2 μA IIN2 Input Current (A, B) VCC = 0V or 5.25V, VIN = 12V VCC = 0V or 5.25V, VIN = – 7V l l 1.0 –0.8 mA mA VTH Differential Input Threshold Voltage for Receiver –7V ≤ VCM ≤ 12V l –0.2 0.2 V 3.5 ΔVTH Receiver Input Hysteresis VCM = 0V VOH Receiver Output High Voltage IO = –4mA, VID = 0.2V l VOL Receiver Output Low Voltage IO = 4mA, VID = –0.2V l 0.4 V IOZR Three-State Output Current at Receiver VCC = Max 0.4V ≤ VO ≤ 2.4V l ±1 μA ICC Supply Current No Load, Digital Pins = GND or VCC l 10 mA RIN Receiver Input Resistance –7V ≤ VCM ≤ 12V, VCC = 0V l 7 60 mV V 7 12 kΩ IOSR Receiver Short-Circuit Current 0V ≤ VO ≤ VCC l 85 mA t PLH Receiver Input to Output CL = 15pF (Figures 1, 3) l 12 28 55 ns l 12 28 55 ns tPHL Receiver Input to Output CL = 15pF (Figures 1, 3) tSKD | t PLH – tPHL | Differential Receiver Skew CL = 15pF (Figures 1, 3) 4 ns The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ± 5% (Notes 2, 3), unless otherwise noted. SYMBOL PARAMETER CONDITIONS TYP MAX t ZL Receiver Enable to Output Low CL = 15pF (Figures 2, 4) S1 Closed l MIN 30 60 UNITS ns tZH Receiver Enable to Output High CL = 15pF (Figures 2, 4) S2 Closed l 30 60 ns tLZ Receiver Disable from Low CL = 15pF (Figures 2, 4) S1 Closed l 30 60 ns CL = 15pF (Figures 2, 4) S2 Closed l 30 60 ns t HZ Receiver Disable from High 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: All typicals are given for VCC = 5V and TA = 25°C. 4889fb 3 LTC488/LTC489 TYPICAL PERFORMANCE CHARACTERISTICS Receiver Output Low Voltage vs Temperature at I = 8mA Receiver Output High Voltage vs Temperature at I = 8mA –18 0.8 4.6 –16 0.7 4.4 –14 0.6 0.5 0.4 0.3 4.2 4.0 3.8 3.6 0.2 3.4 0.1 3.2 0 –50 –25 0 75 25 50 TEMPERATURE (°C) 100 125 OUTPUT CURRENT (mA) 4.8 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 0.9 Receiver Output High Voltage vs Output Current at TA = 25°C –12 –10 –8 –6 –4 –2 3.0 –50 –25 0 75 50 25 TEMPERATURE (°C) 100 4889 G01 125 0 5 4 3 OUTPUT VOLTAGE (V) 4889 G02 Receiver Output Low Voltage vs Output Current at TA = 25°C 2 4889 G03 TTL Input Threshold vs Temperature 36 1.63 INPUT THRESHOLD VOLTAGE (V) OUTPUT CURRENT (mA) 32 28 24 20 16 12 8 1.61 1.59 1.57 4 1.55 –50 0 0.5 0 1.5 1.0 OUTPUT VOLTAGE (V) 2.0 –25 0 75 25 50 TEMPERATURE (°C) Receiver | tPLH – tPHL| vs Temperature Supply Current vs Temperature 7.0 SUPPLY CURRENT (mA) 5 4 TIME (ns) 125 8889 G05 4889 G04 3 2 1 –50 100 –25 0 75 25 50 TEMPERATURE (°C) 100 125 4889 G06 6.6 6.2 5.8 5.4 –50 –25 0 75 25 50 TEMPERATURE (°C) 100 125 4889 G07 4889fb 4 LTC488/LTC489 PIN FUNCTIONS B 1 (Pin 1): Receiver 1 Input. GND (Pin 8): Ground Connection. A1 (Pin 2): Receiver 1 Input. B3 (Pin 9): Receiver 3 Input. RO1 (Pin 3): Receiver 1 Output. If the receiver output is enabled, then if A > B by 200mV, RO1 will be high. If A < B by 200mV, then RO1 will be low. A3 (Pin 10): Receiver 3 Input. EN (Pin 4) LTC488: Receiver Output Enabled. See Function Table for details. EN12 (Pin 4) LTC489: Receiver 1, Receiver 2 Output Enabled. See Function Table for details. RO3 (Pin 11): Receiver 3 Output. Refer to RO1. EN (Pin 12) LTC488: Receiver Output Disabled. See Function Table for details. EN34 (Pin 12) LTC489: Receiver 3, Receiver 4 output enabled. See Function Table for details. RO4 (Pin 13): Receiver 4 Output. Refer to RO1. RO2 (Pin 5): Receiver 2 Output. Refer to RO1. A4 (Pin 14): Receiver 4 Input. A2 (Pin 6): Receiver 2 Input. B4 (Pin 15): Receiver 4 Input. B2 (Pin 7): Receiver 2 Input. VCC (Pin 16): Positive Supply; 4.75V ≤ VCC ≤ 5.25V. FUNCTION TABLES LTC488 LTC489 DIFFERENTIAL ENABLES OUTPUT DIFFERENTIAL ENABLES OUTPUT A–B EN EN RO A–B EN12 or EN34 RO VID ≥ 0.2V H X X L H H VID ≥ 0.2V H H –0.2V < VID < 0.2V H ? –0.2V < VID < 0.2V H X X L ? ? VID ≤ 0.2V H L VID ≤ 0.2V H X X L L L X L Z X L H Z H: High Level L: Low Level X: Irrelevant ?: Indeterminate Z: High Impedance (Off) 4889fb 5 LTC488/LTC489 TEST CIRCUITS 100pF A D DRIVER RO RECEIVER 54Ω CL B 100pF 4889 F01 Figure 1. Receiver Timing Test Circuit Note: The input pulse is supplied by a generator having the following characteristics: f = 1MHz, Duty Cycle = 50%, tr < 10ns, tf ≤ 10ns, ZOUT = 50Ω S1 RECEIVER OUTPUT 1k VCC CL 1k S2 4889 F02 Figure 2. Receiver Enable and Disable Timing Test Circuit SWITCHING TIME WAVEFORMS INPUT VOD2 INPUT A, B f = 1MHz; tr ≤ 10ns; tf ≤ 10ns 0V 0V –VOD2 tPHL tPLH VOH RO 1.5V 1.5V VOL 4889 F03 Figure 3. Receiver Propagation Delays EN OR EN12 3V f = 1MHz; tr ≤ 10ns; tf ≤ 10ns 1.5V 1.5V 0V tZL tLZ 5V RO 1.5V VOL OUTPUT NORMALLY LOW tZH VOH RO 0.5V tHZ OUTPUT NORMALLY HIGH 0.5V 1.5V 0V 4889 F04 Figure 4. Receiver Enable and Disable Times 4889fb 6 LTC488/LTC489 APPLICATIONS INFORMATION Typical Application Cables and Data Rate A typical connection of the LTC488/LTC489 is shown in Figure 5. Two twisted-pair wires connect up to 32 driver/ receiver pairs for half-duplex data transmission. There are no restrictions on where the chips are connected to the wires, and it isn’t necessary to have the chips connected at the ends. However, the wires must be terminated only at the ends with a resistor equal to their characteristic impedance, typically 120Ω. The input impedance of a receiver is typically 20k to GND, or 0.5 unit RS485 load, so in practice 50 to 60 transceivers can be connected to the same wires. The optional shields around the twistedpair help reduce unwanted noise, and are connected to GND at one end. The transmission line of choice for RS485 applications is a twisted-pair. There are coaxial cables (twinaxial) made for this purpose that contain straight-pairs, but these are less flexible, more bulky, and more costly than twisted-pairs. Many cable manufacturers offer a broad range of 120Ω cables designed for RS485 applications. Losses in a transmission line are a complex combination of DC conductor loss, AC losses (skin effect), leakage, and AC losses in the dielectric. In good polyethylene cable such as the Belden 9841, the conductor losses and dielectric losses are of the same order of magnitude, leading to relatively low overall loss (Figure 6). When using low loss cables, Figure 7 can be used as a guideline for choosing the maximum line length for a given EN SHIELD SHIELD 4 DX 1 DX 1/4 LTC486 2 3 RX 1/4 LTC488 OR 1/4 LTC489 120Ω 120Ω 3 RX 1 12 1 EN 2 EN 12 DX 4 1/4 LTC486 1 DX 2 1/4 LTC488 OR 1/4 LTC489 RX 3 4889 F05 EN 3 RX Figure 5. Typical Connection 10k CABLE LENGTH (FT) LOSS PER 100 FT (dB) 10 1 0.1 0.1 1 10 FREQUENCY (MHz) 100 4889 F06 Figure 6. Attenuation vs Frequency for Belden 9841 1k 100 10 10k 100k 1M DATA RATE (bps) 2.5M 10M 4889 F07 Figure 7. Cable Length vs Data Rate 4889fb 7 LTC488/LTC489 APPLICATIONS INFORMATION data rate. With lower quality PVC cables, the dielectric loss factor can be 1000 times worse. PVC twisted-pairs have terrible losses at high data rates (> 100kbps), and greatly reduce the maximum cable length. At low data rates however, they are acceptable and much more economical. Cable Termination The proper termination of the cable is very important. If the cable is not terminated with its characteristic impedance, distorted waveforms will result. In severe cases, distorted (false) data and nulls will occur. A quick look at the output of the driver will tell how well the cable is terminated. It is best to look at a driver connected to the end of the cable, since this eliminates the possibility of getting reflections from two directions. Simply look at the driver output while transmitting square wave data. If the cable is terminated properly, the waveform will look like a square wave (Figure 8). If the cable is loaded excessively (47Ω), the signal initially sees the surge impedance of the cable and jumps to an initial amplitude. The signal travels down the cable and is reflected back out of phase because of the mistermination. PROBE HERE DX DRIVER Rt RECEIVER RX Rt = 120Ω When the reflected signal returns to the driver, the amplitude will be lowered. The width of the pedestal is equal to twice the electrical length of the cable (about 1.5ns/foot). If the cable is lightly loaded (470Ω), the signal reflects in phase and increases the amplitude at the drive output. An input frequency of 30kHz is adequate for tests out to 4000 ft. of cable. AC Cable Termination Cable termination resistors are necessary to prevent unwanted reflections, but they consume power. The typical differential output voltage of the driver is 2V when the cable is terminated with two 120Ω resistors, causing 33mA of DC current to flow in the cable when no data is being sent. This DC current is about 60 times greater than the supply current of the LTC488/LTC489. One way to eliminate the unwanted current is by AC coupling the termination resistors as shown in Figure 9. The coupling capacitor must allow high frequency energy to flow to the termination, but block DC and low frequencies. The dividing line between high and low frequency depends on the length of the cable. The coupling capacitor must pass frequencies above the point where the line represents an electrical one-tenth wavelength. The value of the coupling capacitor should therefore be set at 16.3pF per foot of cable length for 120Ω cables. With the coupling capacitors in place, power is consumed only on the signal edges, and not when the driver output is idling at a 1 or 0 state. A 100nF capacitor is adequate for lines up to 4000 feet in length. Be aware that the power savings start to decrease once the data rate surpasses 1/(120Ω)(C). Rt = 47Ω 120Ω RECEIVER RX C Rt = 470Ω C = LINE LENGTH (FT)(16.3pF) 4889 F08 488/9 F09 Figure 9. AC-Coupled Termination Figure 8. Termination Effects 4889fb 8 LTC488/LTC489 APPLICATIONS INFORMATION Receiver Open-Circuit Fail-Safe Some data encoding schemes require that the output of the receiver maintains a known state (usually a logic 1) when the data is finished transmitting and all drivers on the line are forced in three-state. The receiver of the LTC488/LTC489 has a fail-safe feature which guarantees the output to be in a logic 1 state when the receiver inputs are left floating (open-circuit). When the input is terminated with 120Ω and the receiver output must be forced to a known state, the circuits of Figure 10 can be used. 5V 110Ω 130Ω 130Ω RECEIVER RX RECEIVER RX 110Ω 5V 1.5k 120Ω The termination resistors are used to generate a DC bias which forces the receiver output to a known state, in this case a logic 0. The first method consumes about 208mW and the second about 8mW. The lowest power solution is to use an AC termination with a pullup resistor. Simply swap the receiver inputs for data protocols ending in logic 1. Fault Protection All of LTC’s RS485 products are protected against ESD transients up to 2kV using the human body model (100pF, 1.5k). However, some applications need more protection. The best protection method is to connect a bidirectional TransZorb® from each line side pin to ground (Figure 11). A TransZorb is a silicon transient voltage suppressor that has exceptional surge handling capabilities, fast response time, and low series resistance. They are available from General instruments, GSI, and come in a variety of breakdown voltages and prices. Be sure to pick a breakdown voltage higher than the common mode voltage required for your application (typically 12V). Also, don’t forget to check how much the added parasitic capacitance will load down the bus. 1.5k Y 5V 120Ω DRIVER 100k Z C 120Ω RECEIVER RX 4889 F11 Figure 11. ESD Protection with TransZorbs 4889 F10 Figure 10. Forcing “0” When All Drivers Are Off 4889fb 9 LTC488/LTC489 PACKAGE DESCRIPTION N Package 16-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .770* (19.558) MAX 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 .255 ± .015* (6.477 ± 0.381) .130 ± .005 (3.302 ± 0.127) .300 – .325 (7.620 – 8.255) .008 – .015 (0.203 – 0.381) ( +.035 .325 –.015 +0.889 8.255 –0.381 NOTE: 1. DIMENSIONS ARE ) .045 – .065 (1.143 – 1.651) .020 (0.508) MIN .065 (1.651) TYP .120 (3.048) MIN .100 (2.54) BSC INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) .018 ± .003 (0.457 ± 0.076) N16 1002 4889fb 10 LTC488/LTC489 PACKAGE DESCRIPTION SW Package 16-Lead Plastic Small Outline (Wide .300 Inch) (Reference LTC DWG # 05-08-1620) .050 BSC .045 ±.005 .030 ±.005 TYP .398 – .413 (10.109 – 10.490) NOTE 4 16 N 15 14 13 12 11 10 9 N .325 ±.005 .420 MIN .394 – .419 (10.007 – 10.643) NOTE 3 1 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .005 (0.127) RAD MIN .009 – .013 (0.229 – 0.330) .291 – .299 (7.391 – 7.595) NOTE 4 .010 – .029 × 45° (0.254 – 0.737) 3 4 5 6 7 .093 – .104 (2.362 – 2.642) 8 .037 – .045 (0.940 – 1.143) 0° – 8° TYP NOTE 3 .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN 2 .050 (1.270) BSC .004 – .012 (0.102 – 0.305) .014 – .019 (0.356 – 0.482) TYP INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS 4. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) S16 (WIDE) 0502 4889fb 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. 11 LTC488/LTC489 TYPICAL APPLICATION RS232 Receiver RS232 IN 5.6k RECEIVER 1/4 LTC488 OR 1/4 LTC489 RX 4889 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC485 Low Power RS485 Transceiver Low Power, Half-Duplex LTC490 Low Power RS485 Full-Duplex Transceiver Full-Duplex in SO-8 LTC1480 3V, Ultralow Power RS485 Transceiver 1μA Shutdown Mode LTC1481 3V, Ultralow Power RS485 Transceiver Lowest Power on 5V Supply LTC1483 Ultralow Power RS485 Low EMI Transceiver Low EMI/Low Power with Shutdown LTC1485 Fast RS485 Transceiver 10Mbps Operation LTC1487 Ultralow Power RS485 with Low EMI and High Input Impedance Up to 256 Nodes on a Bus LTC1685 High Speed RS485 Transceiver 52Mbps, Pin Compatible with LTC485 LTC1686/LTC1687 High Speed RS485 Full-Duplex Transceiver 52Mbps, Pin Compatible LTC490/LTC491 4889fb 12 Linear Technology Corporation LT 0309 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 1992