LTC485 Low Power RS485 Interface Transceiver Features

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Low Power S485 Interface Transceiver Features n Low Power: I CC = 3μ Typ n Designed for S485 Interface pplications n Single 5V supply n 7V to 12V us Common Mode ange Permits ±7V Ground Difference

1 Low Power S485 Interface Transceiver Features n Low Power: I CC = 3μ Typ n Designed for S485 Interface pplications n Single 5V supply n 7V to 12V us Common Mode ange Permits ±7V Ground Difference etween Devices on the us n Thermal Shutdown Protection n Power-Up/Down Glitch-Free Driver Outputs Permit Live Insertion or emoval of Transceiver n Driver Maintains High Impedance in Three-State or with the Power Off n Combined Impedance of a Driver Output and eceiver llows Up to 32 Transceivers on the us n 7mV Typical Input Hysteresis n 3ns Typical Driver Propagation Delays with 5ns Skew for Up to 2.5M Operation n Pin Compatible with ±6V Protected LT1785 and 52Mbps LTC1685 pplications n Low Power S485/S422 Transceiver n Level Translator Description The LTC 485 is a low power differential bus/line transceiver designed for multipoint data transmission standard S485 applications with extended common mode range (12V to 7V). It also meets the requirements of S422. The CMOS design offers significant power savings over its bipolar counterpart without sacrificing ruggedness against overload of ESD damage. The driver and receiver feature three-state outputs, with the driver outputs maintaining high impedance over the entire common mode range. Excessive power dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit which forces the driver outputs into a high impedance state. The receiver has a fail-safe feature which guarantees a high output state when the inputs are left open. The LTC485 is fully specified over the commercial and extended industrial temperature range. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. ll other trademarks are the property of their respective owners. Typical pplication Driver Outputs O1 E1 DE1 1 D V CC1 GND1 t O2 E2 V CC2 t DE2 2 D GND2 485 T1a 485 T1b 1

2 bsolute Maximum atings (Note 1) Supply Voltage...12V Control Input Voltages....5V to V CC +.5V Driver Input Voltage....5V to V CC +.5V Driver Output Voltage...±14V eceiver Input Voltage...±14V eceiver Output Voltages....5V to V CC +.5V Operating Temperature ange LTC485I... 4 C T 85 C LTC485C... C T 7 C LTC485M C T 125 C Lead Temperature (Soldering, 1 sec)... 3 C Pin Configuration O E DE N8 PCKGE 8-LED PLSTIC P TOP VIEW D V CC GND S8 PCKGE 8-LED PLSTIC SOIC J8 PCKGE 8-LED CEMIC P T JMX = 125 C, θ J = 1 C/W (N) T JMX = 15 C, θ J = 15 C/W (S) T JMX = 155 C, θ J = 1 C/W (J) Order Information LED FEE FINISH TPE ND EEL PT MKING* PCKGE DESCIPTION TEMPETUE NGE LTC485CN8#PF LTC485CN8#TPF LTC485CN8 8-Lead Plastic P C to 7 C LTC485CS8#PF LTC485CS8#TPF Lead Plastic SOIC C to 7 C LTC485IN8#PF LTC485IN8#TPF LTC485IN8 8-Lead Plastic P 4 C to 85 C LTC485IS8#PF LTC485IS8#TPF 485I 8-Lead Plastic SOIC 4 C to 85 C LED SED FINISH TPE ND EEL PT MKING* PCKGE DESCIPTION TEMPETUE NGE LTC485CN8 LTC485CN8#T LTC485CN8 8-Lead Plastic P C to 7 C LTC485CS8 LTC485CS8#T Lead Plastic SOIC C to 7 C LTC485IN8 LTC485IN8#T LTC485IN8 8-Lead Plastic P 4 C to 85 C LTC485IS8 LTC485IS8#T 485I 8-Lead Plastic SOIC 4 C to 85 C LTC485MJ8 LTC485MJ8#T LTC485MJ8 8-Lead Ceramic P 55 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: For more information on tape and reel specifications, go to: Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V CC = 5V ±5%, unless otherwise noted. (Notes 2 and 3) SYMOL PMETE CONTIONS MIN TYP MX UNITS V OD1 Differential Driver Output Voltage (Unloaded) I O = l 5 V V OD2 Differential Driver Output Voltage (with Load) = 5Ω (S422) = 27Ω (S485), Figure 1 ΔV OD Change in Magnitude of Driver Differential Output Voltage for Complementary States l l = 27Ω or = 5Ω, Figure 1 l.2 V V OC Driver Common Mode Output Voltage = 27Ω or = 5Ω, Figure 1 l 3 V Δ V OC Change in Magnitude of Driver Common Mode = 27Ω or = 5Ω, Figure 1 l.2 V Output Voltage for Complementary States V V 2

3 Electrical Characteristics LTC485 The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V CC = 5V ±5%, unless otherwise noted. (Notes 2 and 3) SYMOL PMETE CONTIONS MIN TYP MX UNITS V IH Input High Voltage DE,, E l 2 V V IL Input Low Voltage DE,, E l.8 V I IN1 Input Current DE,, E l ±2 μ I IN2 Input Current (, ) DE =, V CC = V or 5.25V V IN = 12V V IN = 7V V TH Differential Input Threshold Voltage for eceiver 7V V CM 12V l.2.2 V ΔV TH eceiver Input Hysteresis V CM = V l 7 mv V OH eceiver Output High Voltage I O = 4m, V ID = 2mV l 3.5 V V OL eceiver Output Low Voltage I O = 4m, V ID = 2mV l.4 V I OZ Three-State (High Impedance) Output Current at eceiver V CC = Max,.4V V O 2.4V l ±1 μ IN eceiver Input esistance 7V V CM 12V l 12 kω l l ±1.8 m m Switching Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V CC = 5V ±5%, unless otherwise noted. (Notes 2 and 3) SYMOL PMETE CONTIONS MIN TYP MX UNITS I CC Supply Current No Load, Pins 2, 3, 4 = V or 5V Outputs Enabled Outputs Disabled I OSD1 Driver Short-Circuit Current, V OUT = HIGH V O = 7V l m I OSD2 Driver Short-Circuit Current, V OUT = LOW V O = 1V l m I OS eceiver Short-Circuit Current V V O V CC l 7 85 m t PLH Driver Input to Output FF = 54Ω, C L1 = C L2 = 1pF, l ns t PHL Driver Input to Output (Figures 3 and 5) l ns t SKEW Driver Output to Output l 5 1 ns t r, t f Driver ise or Fall Time l ns t ZH Driver Enable to Output High C L = 1pF (Figures 4 and 6) S2 Closed l 4 7 ns t ZL Driver Enable to Output Low C L = 1pF (Figures 4 and 6) S1 Closed l 4 7 ns t LZ Driver Disable Time from Low C L = 15pF (Figures 4 and 6) S1 Closed l 4 7 ns t HZ Driver Disable Time from High C L = 15pF (Figures 4 and 6) S2 Closed l 4 7 ns t PLH eceiver Input to Output FF = 54Ω, CL1 = CL2 = 1pF, l ns t PHL (Figures 3 and 7) l ns t SKD t PLH t PHL Differential eceiver Skew l 13 ns t ZL eceiver Enable to Output Low C L = 15pF (Figures 2 and 8) S1 Closed l 2 5 ns t ZH eceiver Enable to Output High C L = 15pF (Figures 2 and 8) S2 Closed l 2 5 ns t LZ eceiver Disable from Low C L = 15pF (Figures 2 and 8) S1 Closed l 2 5 ns t HZ eceiver Disable from High C L = 15pF (Figures 2 and 8) S2 Closed l 2 5 ns l l μ μ Note 1: Stresses beyond those listed under bsolute Maximum atings may cause permanent damage to the device. Exposure to any bsolute Maximum ating condition for extended periods may affect device reliability and lifetime. Note 2: ll currents into device pins are positive; all currents out ot device pins are negative. ll voltages are referenced to device ground unless otherwise specified. Note 3: ll typicals are given for V CC = 5V and T = 25 C. Note 4: The LTC485 is guaranteed by design to be functional over a supply voltage range of 5V ±1%. Data sheet parameters are guaranteed over the tested supply voltage range of 5V ±5%. 3

4 Typical Performance Characteristics eceiver Output Low Voltage vs Output Current T = 25 C eceiver Output High Voltage vs Output Current T = 25 C eceiver Output High Voltage vs Temperature I = 8m OUTPUT CUENT (m) OUTPUT CUENT (m) OUTPUT VOLTGE (V) OUTPUT VOLTGE (V) OUTPUT VOLTGE (V) TEMPETUE ( C) 485 G1 485 G2 485 G3.9.8 eceiver Output Low Voltage vs Temperature I = 8m Driver Differential Output Voltage vs Output Current T = 25 C Driver Differential Output Voltage vs Temperature I = 54Ω OUTPUT VOLTGE (V) OUTPUT CUENT (m) FFEENTIL VOLTGE (V) TEMPETUE ( C) OUTPUT VOLTGE (V) TEMPETUE ( C) 485 G4 485 G5 485 G6 9 8 Driver Output Low Voltage vs Output Current T = 25 C Driver Output High Voltage vs Output Current T = 25 C TTL Input Threshold vs Temperature OUTPUT CUENT (m) OUTPUT CUENT (m) INPUT THESHOLD VOLTGE (V) OUTPUT VOLTGE (V) OUTPUT VOLTGE (V) TEMPETUE ( C) 485 G7 485 G8 485 G9 4

5 Typical Performance Characteristics eceiver t PLH t PHL vs Temperature Driver Skew vs Temperature Supply Current vs Temperature TIME (ns) TIME (ns) SUPPLY CUENT (µ) VE ENLED VE SLED TEMPETUE ( C) TEMPETUE ( C) TEMPETUE ( C) 485 G1 485 G G12 Pin Functions O (Pin 1): eceiver Output. If the receiver output is enabled (E low), then if > by 2mV, O will be high. If < by 2mV, then O will be low. E (Pin 2): eceiver Output Enable. low enables the receiver output, O. high input forces the receiver output into a high impedance state. DE (Pin 3): Driver Outputs Enable. high on DE enables the driver output. and, and the chip will function as a line driver. low input will force the driver outputs into a high impedance state and the chip will function as a line receiver. (Pin 4): Driver Input. If the driver outputs are enabled (DE high), then a low on forces the outputs low and high. high on with the driver outputs enabled will force high and low. GND (Pin 5): Ground Connection. (Pin 6): Driver Output/eceiver Input. (Pin 7): Driver Output/eceiver Input. V CC (Pin 8): Positive Supply; 4.75 < V CC <

6 Test Circuits V OD V OC ECEIVE OUTPUT TEST POINT C L 15pF 1k S1 S2 1k V CC 485 F1 485 F2 Figure 1. Driver DC Test Load Figure 2. eceiver Timing Test Load 3V DE FF C L1 C L2 E O OUTPUT UNDE TEST 5Ω S1 S2 V CC 15pF C L 485 F3 485 F4 Figure 3. Driver/eceiver Timing Test Circuit Figure 4. Driver Timing Test Load #2 Switching Time Waveforms 3V V f = 1MHz, t r 1ns, t f 1ns t PLH t PLH 1/2 V O V O V V O V O 1/2 VO 1% t r t SKEW 8% V FF = V() V() t f t SKEW 9% 2% 485 F5 Figure 5. Driver Propagation Delays 6

7 Switching Time Waveforms 3V V f = 1MHz, t r 1ns, t f 1ns 5V, V OL t ZL 2.3V OUTPUT NOMLLY LOW t LZ.5V V OH, V t ZH 2.3V OUTPUT NOMLLY HIGH t HZ.5V 485 F6 Figure 6. Driver Enable and Disable Times V OH V OL t PHL OUTPUT f = 1MHz, t r 1ns, t f 1ns t PLH V OD2, V V OD2 INPUT 485 F7 Figure 7. eceiver Propagation Delays E 3V V f = 1MHz, t r 1ns, t f 1ns 5V t ZL OUTPUT NOMLLY LOW t LZ.5V V t ZH OUTPUT NOMLLY HIGH t HZ.5V 485 F8 Figure 8. eceiver Enable and Disable Times Function Tables LTC485 Transmitting INPUTS LINE OUTPUTS E DE CONTION X 1 1 No Fault 1 X 1 No Fault 1 X X X Z Z X 1 X Fault Z Z LTC485 eceiving INPUTS OUTPUTS E DE.2V 1.2V Inputs Open 1 1 X Z 7

8 pplications Information asic Theory of Operation Previous S485 transceivers have been designed using bipolar technology because the common mode range of the device must extend beyond the supplies and the device must be immune to ESD damage and latchup. Unfortunately, the bipolar devices draw a large amount of supply current, which is unacceptable for the numerous applications that require low power consumption. The LTC485 is the first CMOS S485/S422 transceiver which features ultralow power consumption without sacrificing ESD and latchup immunity. The LTC485 uses a proprietary driver output stage, which allows a common-mode range that extends beyond the power supplies while virtually eliminating latchup and providing excellent ESD protection. Figure 9 shows the LTC485 output stage while Figure 1 shows a conventional CMOS output stage. When the conventional CMOS output stage of Figure 1 enters a high impedance state, both the P-channel (P1) and the N-channel (N1) are turned off. If the output is then driven above V CC or below ground, the P + /N-well diode (D1) or the N + /P-substrate diode (D2) respectively will turn on and clamp the output to the supply. Thus, the output stage is no longer in a high impedance state and is not able to meet the S485 common mode range requirement. In addition, the large amount of current flowing through either diode will induce the well known CMOS latchup condition, which could destroy the device. The LTC485 output stage of Figure 9 eliminates these problems by adding two Schottky diodes, SD3 and SD4. The Schottky diodes are fabricated by a proprietary modification to the standard N-well CMOS process. When the output stage is operating normally, the Schottky diodes are forward biased and have a small voltage drop across them. When the output is in the high impedance state and is driven above V CC or below ground, the parasitic diodes D1 or D2 still turn on, but SD3 or SD4 will reverse bias and prevent current from flowing into the N-well or the substrate. Thus, the high impedance state is maintained even with the output voltage beyond the supplies. With no minority carrier current flowing into the N-well or substrate, latchup is virtually eliminated under power-up or power-down conditions. V CC P1 SD3 P1 V CC D1 D1 LOGIC SD4 OUTPUT LOGIC OUTPUT N1 D2 N1 D2 485 F9 485 F1 Figure 9. LTC485 Output Stage Figure 1. Conventional CMOS Output Stage 8

pplications Information The LTC485 output stage will maintain a high impedance state until the breakdown of the N-channel or P-channel is reached when going positive or negative respectively.

This clamp protects the MOS gates from ESD voltages well over 2V.

9 pplications Information The LTC485 output stage will maintain a high impedance state until the breakdown of the N-channel or P-channel is reached when going positive or negative respectively. The output will be clamped to either V CC or ground by a Zener voltage plus a Schottky diode drop, but this voltage is way beyond the S485 operating range. This clamp protects the MOS gates from ESD voltages well over 2V. ecause the ESD injected current in the N-well or substrate consists of majority carriers, latchup is prevented by careful layout techniques. Propagation Delay Many digital encoding schemes are dependent upon the difference in the propagation delay times of the driver and the receiver. Using the test circuit of Figure 13, Figures 11 and 12 show the typical LTC485 receiver propagation delay. The receiver delay times are: t PLH t PHL = 9ns Typ, V CC = 5V The driver skew times are: Skew = 5ns Typ, V CC = 5V 1ns Max, V CC = 5V, T = 4 C to 85 C VE OUTPUTS ECEIVE OUTPUTS O VE OUTPUTS ECEIVE OUTPUTS O 485 F F12 Figure 11. eceiver t PHL Figure 12. eceiver t PLH TTL IN t r, t f < 6ns D 1pF 1Ω ECEIVE OUT 1pF 485 F13 Figure 13. eceiver Propagation Delay Test Circuit 9

pplications Information LTC485 Line Length vs Data ate The maximum line length allowable for the S422/S485 standard is 4 feet.

1Ω O TTL IN LTC485 NOISE GENETO C D 4 FT 26WG TWISTED PI LTC485 TTL OUT COMMON MODE VOLTGE ( + )/2 485 F14 Figure 14.

the line, The LTC485 is able to reconstruct the data stream at the end of 4 feet of twisted pair wire. 485 F17 Figure 17.

System Differential Voltage at 11kHz 485 F15 When specifying line length vs maximum data rate the curve in Figure 19 should be used.

10 pplications Information LTC485 Line Length vs Data ate The maximum line length allowable for the S422/S485 standard is 4 feet. Figures 17 and 18 show that the LTC485 is able to comfortably drive 4 feet of wire at 11kHz. 1Ω O TTL IN LTC485 NOISE GENETO C D 4 FT 26WG TWISTED PI LTC485 TTL OUT COMMON MODE VOLTGE ( + )/2 485 F14 Figure 14. Line Length Test Circuit Using the test circuit in Figure 14, Figures 15 and 16 show that with ~2V P-P common mode noise injected on the line, The LTC485 is able to reconstruct the data stream at the end of 4 feet of twisted pair wire. 485 F17 Figure 17. System Common Mode Voltage at 11kHz COMMON MODE VOLTGE ( ) O COMMON MODE VOLTGE ( + )/2 O 485 F18 Figure 18. System Differential Voltage at 11kHz 485 F15 When specifying line length vs maximum data rate the curve in Figure 19 should be used. Figure 15. System Common Mode Voltage at 19.2kHz 1k FFEENTIL VOLTGE O CLE LENGTH (FT) 1k 1 1 1k 1k 1M 2.5M 1M MXIMUM DT TE 485 F F19 Figure 16. System Differential Voltage at 19.2kHz Figure 19. Cable Length vs Maximum Data ate 1

11 Typical pplication Typical S485 Network t t 485 T2 Package Description J8 Package 8-Lead CEP (Narrow.3 Inch, Hermetic) (eference LTC DWG # ) ( ) FULL LED OPTION.3 SC (7.62 SC) CONE LEDS OPTION (4 PLCS) ( ) HLF LED OPTION.5 (.127) MIN.25 (.635) D TYP.45 (1.287) MX ( ).2 (5.8) MX.15.6 ( ).8.18 ( ) 15 NOTE: LED MENSIONS PPLY TO SOLDE P/PLTE O TIN PLTE LEDS ( ) (.36.66).1 (2.54) SC MIN J

12 Package Description N8 Package 8-Lead PP (Narrow.3 Inch) (eference LTC DWG # ).4* (1.16) MX ( ) ( ).13.5 ( ) * ( ) ( ) ( ).65 (1.651) TYP.1 (2.54) SC.12 (3.48) MIN.18.3 ( ).2 (.58) MIN N8 12 NOTE: INCHES 1. MENSIONS E MILLIMETES *THESE MENSIONS DO NOT INCLUDE MOLD FLSH O POTUSIONS. MOLD FLSH O POTUSIONS SHLL NOT EXCEED.1 INCH (.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow.15 Inch) (eference LTC DWG # ).5 SC.45 ± ( ) NOTE MIN.16 ± ( ) ( ) NOTE 3.3 ±.5 TYP ECOMMENDED SOLDE PD LYOUT ( ).1.2 ( ) 45 8 TYP ( ).4.1 ( ).16.5 ( ) NOTE: INCHES 1. MENSIONS IN (MILLIMETES) ( ) TYP 2. DWING NOT TO SCLE 3. THESE MENSIONS DO NOT INCLUDE MOLD FLSH O POTUSIONS. MOLD FLSH O POTUSIONS SHLL NOT EXCEED.6" (.15mm).5 (1.27) SC SO

13 evision History (evision history begins at ev I) EV DTE DESCIPTION PGE NUME I 4/11 emoved lead free version of LTC485MJ8 from Order Information section. 2 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. 13

14 elated Parts PT NUME DESCIPTION COMMENTS LTC486/LTC487 Low Power Quad S485 Drivers 11μ Supply Current LTC488/LTC489 Low Power Quad S485 eceivers 7m Supply Current LTC49/LTC491 Low Power Full-Duplex S485 Transceivers 3μ Supply Current LTC V Supply S485 Transceiver Lower Supply Voltage LTC1481 Low Power S485 Transceiver with Shutdown Lowest Power LTC1482 S485 Transceiver with Carrier Detect ±15kV ESD, Fail-Safe LTC1483 Low Power, Low EMI S485 Transceiver Slew ate Limited Driver Outputs, Lowest Power LTC1484 S485 Transceiver with Fail-Safe ±15kV ESD, MSOP Package LTC1485 1Mbps S485 Transceiver High Speed LTC1518/LTC Mbps Quad S485 eceivers Higher Speed, LTC488/LTC489 Pin-Compatible LTC152 LVDS-Compatible Quad eceiver 1mV Threshold, Low Channel-to-Channel Skew LTC V Isolated S485 Transceiver Full-Duplex, Self-Powered Using External Transformer LTC Mbps S485 Transceiver Industry-Standard Pinout, 5ps Propagation Delay Skew LTC1686/LTC Mbps Full-Duplex S485 Transceivers LTC49/LTC491 Pin Compatible LTC1688/LTC1689 1Mbps Quad S485 Drivers Highest Speed, LTC486/LTC487 Pin Compatible LTC169 Full-Duplex S485 Transceiver with Fail-Safe ±15kV ESD, LTC49 Pin Compatible LT1785/LTC1785 ±6V Protected S485 Transceivers ±15kV ESD, Fail-Safe (LT1785) LT1791/LTC1791 ±6V Protected Full-Duplex S485 Transceivers ±15kV ESD, Fail-Safe (LT1791) LTC285/LTC2851/ 3.3V Supply S485 Transceivers ±15kV ESD, 2Mbps, 9µ Supply Current, Fail-Safe LTC2852 LTC2854/LTC V Supply S485 Transceivers ±15kV ESD, 2Mbps, 9µ Supply Current, Integrated Switchable Termination LTC2856/LTC2857/ 2Mbps S485 Transceivers ±15kV ESD, 9µ Supply Current, Fail-Safe LTC2858 LTC2859/LTC2861 2Mbps S485 Transceivers ±15kV ESD, 9µ Supply Current, Integrated Switchable Termination 14 LT 411 EV I PINTED IN US Linear Technology Corporation 163 McCarthy lvd., Milpitas, C (48) l FX: (48) l LINE TECHNOLOGY COPOTION 1994

APPLICATIO S. LTC485 Low Power RS485 Interface Transceiver FEATURES DESCRIPTIO TYPICAL APPLICATIO

APPLICATIO S. LTC485 Low Power RS485 Interface Transceiver FEATURES DESCRIPTIO TYPICAL APPLICATIO Low Power S85 Interface Transceiver FETES Low Power: I CC = 3µ Typ Designed for S85 Interface pplications Single 5V supply 7V to 12V us Common Mode ange Permits ±7V Ground Difference etween Devices on