RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance

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RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance

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19-1405; 4/99
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication
MAX3291/MAX3292 high-speed RS-485/RS-422 transceivers feature driver preemphasis circuitry, which extends distance increases data rate reliable communication reducing intersymbol interference (ISI) caused long cables. MAX3291 programmable data rates 5Mbps 10Mbps, while MAX3292 programmable data rates 10Mbps using single external resistor. MAX3291/MAX3292 full-duplex devices that operate from single supply offer low-current shutdown mode that reduces supply current 100nA. They feature driver output short-circuit current limiting fail-safe receiver input that guarantees logic-high output input open circuit. 1/4-unitload receiver input impedance allows transceivers bus.
_Features
Preemphasis Increases Distance Data Rate Reliable RS-485/RS-422 Communication Data Rate Optimized 5Mbps 10Mbps (MAX3291) Programmable 10Mbps (MAX3292) 100nA Low-Current Shutdown Mode Allow Transceivers +12V Common-Mode Input Voltage Range Pin-Compatible with '75180, MAX489, MAX491 MAX3080, MAX3083, MAX3086, MAX1482
MAX3291/MAX3292
_Ordering Information
PART MAX3291CSD TEMP. RANGE +70°C +70°C -40°C +85°C -40°C +85°C +70°C +70°C -40°C +85°C -40°C +85°C PIN-PACKAGE Plastic Plastic Plastic Plastic
_Applications
Long-Distance, High-Speed RS-485/RS-422 Communications Telecommunications Industrial-Control Local Area Networks
MAX3291CPD MAX3291ESD MAX3291EPD MAX3292CSD MAX3292CPD MAX3292ESD MAX3292EPD
Typical Operating Circuit Functional Diagram
RPSET* RPSET*
(PSET) CPSET* (VCCD) (PSET) CPSET* (VCCD)
MAX3292 MAX3292 ONLY CHARACTERISTIC IMPEDANCE CABLE
MAX3291 MAX3292
7(6)
MAX3291 MAX3292
7(6)
Configuration appears data sheet.
Maxim Integrated Products
free samples latest literature: http://www.maxim-ic.com, phone 1-800-998-8800. small orders, phone 1-800-835-8769.
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC, VCCD) .+6V Control Input Voltage (RE, PEE, PSET, .-0.3V (VCC 0.3V) Driver Output Voltage .-7.5V +12.5V Receiver Input Voltage B).-7.5V +12.5V Receiver Output Voltage (RO).-0.3V (VCC 0.3V) Continuous Power Dissipation +70°C) 14-Pin (derate 8.7mW/°C above +70°C).695mW 14-Pin Plastic (derate 10.0mW/°C above +70°C) .800mW Operating Temperature Ranges MAX329_C_ D.0°C +70°C MAX329_E_ .-40°C +85°C Storage Temperature Range .-65°C +160°C Lead Temperature (soldering, 10sec) .+300°C
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, ±5%, RPSET (MAX3292), VCCD (MAX3292), TMIN TMAX, unless otherwise noted. Typical values +25°C.) (Note PARAMETER DRIVER Differential Driver Output Differential Driver Output with Preemphasis Differential Driver Preemphasis Ratio Change Magnitude Differential Output Voltage (Normal Preemphasis) Driver Common-Mode Output Voltage (Normal Preemphasis) Change Magnitude Common-Mode Voltage (Normal Preemphasis) Change Magnitude Common-Mode Output Voltage (Normal Preemphasis) Input High Voltage Input Voltage Input Current Input Current (MAX3291) PSET Input Current (MAX3292) Output Leakage Driver Short-Circuit Output Current VODP DPER VOD, VODP Figure Figure (Note load (Note 1.65 2.35 5.25 SYMBOL CONDITIONS UNITS
Figure (Note
Figure
Figure (Note
Figure VPSET GND, 5.25V +12V
IPEE IPSET IOSD
3.75 ±250
VOUT +12V (Note
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, ±5%, RPSET (MAX3292), VCCD (MAX3292), TMIN TMAX, unless otherwise noted. Typical values +25°C.) (Note PARAMETER RECEIVER Input Current Receiver Differential Threshold Voltage Receiver Input Hysteresis Receiver Output High Voltage Receiver Output Voltage Three-State Output Current Receiver Receiver Input Resistance Receiver Output Short-Circuit Current SUPPLY CURRENT No-Load Supply Current Supply Current Shutdown Mode ICCD GND, ISHDN VCC, GND, floating IOZR IOSR GND, 5.25V +12V -4mA, 4mA, -VTH +12V +12V -200 -150 SYMBOL CONDITIONS UNITS
SWITCHING CHARACTERISTICS
(Typical Operating Circuit, ±5%, RPSET (MAX3292), VCCD (MAX3292), +25°C, unless otherwise noted. Typical values +25°C.) PARAMETER Driver Propagation Delay Driver Differential Output Rise Fall Time SYMBOL tDPLH tDPHL CONDITIONS Figures RDIFF 50pF Figures RDIFF 50pF Figures RDIFF 50pF MAX3291/MAX3292, RPSET MAX3292, RPSET 523k 0.75 1.25 UNITS Mbps
Driver Preemphasis Interval
tPRE
Preemphasis Voltage Level Normal Voltage Level Delay Differential Driver Output Skew tDPLH tDPHL Maximum Data Rate
tPTND tDSKEW fMAX
Figures RDIFF 50pF Figures RDIFF 50pF
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
SWITCHING CHARACTERISTICS (continued)
(Typical Operating Circuit, ±5%, RPSET (MAX3292), VCCD (MAX3292), +25°C, unless otherwise noted. Typical values +25°C.) PARAMETER Driver Enable Output High Driver Enable Output Driver Disable Time from Driver Disable Time from High Receiver Propagation Delay Receiver Output Skew tRPLH tRPHL Receiver Enable Output Receiver Enable Output High Receiver Disable Time from Receiver Disable Time from High Time Shutdown Driver Enable from Shutdown Output High Driver Enable from Shutdown Output Receiver Enable from Shutdown Output High Receiver Enable from Shutdown Output SYMBOL tDZH tDZL tDLZ tDHZ tRPLH tRPHL tRSKEW tRZL tRZH tRLZ tRHZ tSHDN tDZH(SHDN) tDZL(SHDN) tRZH(SHDN) tRZL(SHDN) CONDITIONS Figures closed, 500, 100pF Figures closed, 500, 100pF Figures closed, 500, 15pF Figures closed, 500, 15pF Figures 50pF, Figures 100pF Figures 100pF, closed Figures 100pF, closed Figures 15pF, closed Figures 15pF, closed Figures (Note Figures 500, 100pF, closed Figures 500, 100pF, closed Figures 100pF, closed Figures 100pF, closed 6000 6000 8750 8750 1500 1500 UNITS
Note currents into device positive; currents device negative. voltages referenced device ground unless otherwise noted. Note Guaranteed design. Note DPER defined (VODP VOD). Note VODP changes VOC, respectively, when input changes. This specification reflects constant operating conditions. When operating conditions shift, maximum value momentarily exceeded. Note VODP changes VOC, respectively, when input changes state. Note Maximum current level applies peak current just prior foldback-current limiting; minimum current level applies during current limiting. Note Shutdown enabled bringing high low. enable inputs this state less than 50ns, device guaranteed enter shutdown. enable inputs this state least 500ns, device guaranteed have entered shutdown. Time shutdown device (tSHDN) measured monitoring Figure
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication
_Typical Operating Characteristics
(VCC +5V, +25°C, unless otherwise noted.)
TYPICAL PREEMPHASIS WAVEFORM
MAX3291/2-01
MAX3291/MAX3292
PREEMPHASIS INTERVAL RPSET (CPSET 0.1µF)
MAX3291/2-02
RPRE tPRE tBAUD
MAX3291/92
2500 2250 PREEMPHASIS INTERVAL (ns) 2000 1750
1200 1000 RPRE NOTE
1500 1250 1000 NOTE
100ns/div
1000 RPSET
1000 tBAUD (ns)
1500
2000
DRIVER DIFFERENTIAL OUTPUT VOLTAGE RDIFF
MAX3291/2-04
DRIVER DIFFERENTIAL OUTPUT VOLTAGE TEMPERATURE
MAX3291/2-05
RECEIVER PROPAGATION DELAY TEMPERATURE
50pF 57.5 PROPAGATION DELAY (ns) 55.0 52.5 50.0 47.5 45.0 42.5
MAX3291/2-06
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
NORMAL STRONG
4.25 DIFFERENTIAL OUTPUT VOLTAGE 4.00 3.75 3.50 3.25 3.00 2.75 2.50 2.25 2.00 RDIFF NORMAL (VOD) STRONG (VODP)
60.0
40.0 TEMPERATURE (°C) TEMPERATURE (°C)
RDIFF
DRIVER PROPAGATION DELAY TEMPERATURE
MAX3291/2-07
RECEIVER PROPAGATION DELAY
MAX3291/2-08
50.0 47.5 PROPAGATION DELAY (ns) 45.0 42.5 40.0 37.5 35.0 32.5 30.0 50pF
2.5V/
20ns/div
TEMPERATURE (°C)
Note Dotted line represents region which preemphasis work systems with excessive power-supply noise. Preemphasis Data Rates.
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
_Typical Operating Characteristics (continued)
(VCC +5V, +25°C, unless otherwise noted.)
DRIVER PROPAGATION DELAY
MAX3291/2-09
RECEIVER OUTPUT VOLTAGE TEMPERATURE
MAX3291/2-10
RECEIVER OUTPUT HIGH VOLTAGE TEMPERATURE
4.55 OUTPUT HIGH VOLTAGE 4.50 4.45 4.40 4.35 4.30 4.25 4.20 4.15
MAX3291/2-11
0.30 0.25 OUTPUT VOLTAGE 0.20 0.15 0.10 0.05
4.60
2.5V/
4.10 TEMPERATURE (°C) TEMPERATURE (°C)
20ns/div
NO-LOAD SUPPLY CURRENT TEMPERATURE
2.75 2.50 2.25 2.00 1.75 1.50 1.25 1.00 0.75 0.50 0.25 TEMPERATURE (°C)
MAX3291/2-12
OUTPUT SINK CURRENT RECEIVER OUTPUT VOLTAGE
MAX3291/2-13
OUTPUT SOURCE CURRENT RECEIVER OUTPUT HIGH VOLTAGE
MAX3291/2-14
3.00 NO-LOAD SUPPLY CURRENT (mA)
OUTPUT SINK CURRENT (mA)
OUTPUT SOURCE CURRENT (mA)
OUTPUT VOLTAGE
OUTPUT HIGH VOLTAGE
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication
Description
NAME MAX3291 MAX3292 Preemphasis Enable Input. enable preemphasis, leave unconnected, connect VCC, drive high. enable strong-level-drive only mode, connect drive low. Preemphasis Input. Sets preemphasis interval. Connect resistor (RPSET) parallel with capacitor (CPSET) from PSET preemphasis interval. Typical Operating Circuit. Receiver Output. When 200mV, high; -200mV, low. Receiver Output Enable. Drive enable high impedance when high. Drive high enter low-power shutdown mode. Driver Output Enable. Drive high enable driver outputs. These outputs high impedance when low. Drive high enter low-power shutdown mode. Driver Input. With high, forces noninverting output inverting output high. Similarly, high forces noninverting output high inverting output low. Connection. internally connected. Ground Noninverting Driver Output Inverting Driver Output Inverting Receiver Input Noninverting Receiver Input Connect Positive Supply: +4.75V +5.25V FUNCTION
MAX3291/MAX3292
PSET
N.C. VCCD
VODP OUTPUT UNDER TEST
Figure Driver Test Load
Figure Driver Receiver Enable/Disable Timing Test Load
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
VODP RDIFF tSHDN tRZH(SHDN) tSHDN
Figure Driver Timing Test Circuit
Figure Shutdown Timing Diagram
DIFFERENTIAL VDIFF VDIFF DIFFERENTIAL 1.5V tDPLH tDPHL 1.5V
1.5V tDZL(SHDN), tDZL 2.3V OUTPUT NORMALLY VOL* 0.5V tDLZ 1.5V
2.3V
OUTPUT NORMALLY HIGH VOH* 0.5V tDHZ
tSKEW tPLH tPHL VODP
tDZH(SHDN), tDZH
*NOTE: OUTPUT LEVELS FIGURE WITH CLOSED, RESPECTIVELY.
Figure Driver Propagation Delays
Figure Driver Enable Disable Times
1.5V tRPHL tRPLH 1.5V tRZL(SHDN), tRZL tRLZ 0.5V 1.5V 1.5V
1.5V OUTPUT NORMALLY OUTPUT NORMALLY HIGH
DIFFERENTIAL tRSKEW tRPLH tRPHL tRZH(SHDN), tRZH tRHZ 1.5V 0.5V
Figure Receiver Propagation Delays
Figure Receiver Enable Disable Times
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
tPTND DIFFERENTIAL tPRE
Figure Receiver Propagation Delay Test Circuit
Figure Preemphasis Timing
MAX3291 MAX3292
Figure Time-to-Shutdown Test Circuit
Function Tables
TRANSMITTING INPUTS High-Z OUTPUTS High-Z High-Z SHUTDOWN RECEIVING INPUTS INPUTS 0.2V -0.2V Open OUTPUT High-Z High-Z SHUTDOWN
Don't care High impedance SHUTDOWN Low-power shutdown; driver receiver outputs high impedance.
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
Detailed Description
MAX3291/MAX3292 high-speed RS-485/RS-422 transceivers feature driver preemphasis circuitry, which extends distance increases data rate reliable communication reducing intersymbol interference (ISI) caused long cables. MAX3291 programmable data rates 5Mbps 10Mbps, while MAX3292 programmable data rates 10Mbps using single external resistor. MAX3291/MAX3292 full-duplex devices that operate from single supply offer low-current shutdown mode that reduces supply current 100nA. They feature driver output short-circuit current limiting fail-safe receiver input that guarantees logic-high output input open circuit. 1/4-unitload receiver input impedance allows transceivers bus. Inter-symbol interference (ISI) causes significant problems UARTs total RS-485/RS-422 signal jitter becomes more baud period. caused effect cable's time constant different patterns. series ones transmitted, followed zero, transmission-line voltage rises high value string ones (signal Figure 12). signal moves towards zero state, takes longer reach zero-crossing, because starting voltage farther from zero crossing. other hand, data pattern string zeros followed then another zero, one-to-zero transition starts from voltage that much closer zero-crossing takes much less time signal reach zerocrossing (signal Figure 12). other words, propagation delay depends upon previous pattern. This inter-symbol interference (ISI). Preemphasis reduces increasing signal amplitude every transition edge about baud period, counteracting effects cable (see section Setting Preemphasis Interval). Figure shows typical preemphasis waveform optimized data rates between 5Mbps 10Mbps. When changes from logic logic high, differential output switches strong high. preemphasis interval, strong high returns normal high level. Both levels meet RS-485/RS-422 specifications, strong levels typically times larger than normal levels. switches back logic before preemphasis interval, differential output switches directly from strong high strong low. Similarly, this explanation applies when transitions from high low.
SIGNAL
BAUD PERIOD
tISI SIGNAL
Figure Inter-Symbol Interference among Data Patterns: Signal 11111110, Signal 00000010
2.5V/div
5V/div
100ns
Figure Typical Preemphasis Waveform with 100ns Preemphasis Interval
Applications Information
Data Rate Cable Length
general, preemphasis allows either double distance fixed data rate double data rate fixed existing cable distance over existing RS-485 transceivers that feature preemphasis. Figure shows that MAX3291/MAX3292 transmits approximately twice same data rate twice fast same cable length conventional RS-485 transceiver without preemphasis jitter.
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication
Setting Preemphasis Interval
MAX3291 internal fixed preemphasis interval 100ns. MAX3291 existing designs requiring industry-standard '75180 pin-compatibility data rates 5Mbps 10Mbps. MAX3292 resistor-programmable preemphasis interval more flexibility. data rates less than 1Mbps, following equation calculate RPSET (the preemphasis setting resistor): RPSET (tBAUD 100) where tBAUD baud period example, baud rate 500kbps produces baud period (2µs 2000ns). RPSET (tBAUD 100) RPSET (2000 100) 1.1M data rates 1Mbps 10Mbps, following equation calculate RPSET: RPSET (tBAUD 100)(tBAUD 1000) where tBAUD baud period example, baud rate 1Mbps produces baud period (1µs 1000ns). RPSET (1000 100)(1000 1000) 522k (closest standard value 523k) preemphasis interval connecting RPSET resistor from PSET VCC. 0.1µF bypass capacitor (CPSET) from PSET VCC. PSET connected directly (RPSET preemphasis interval reverts nominal 100ns value.
10,000 24-GAUGE TWISTED PAIR CABLE LENGTH (FEET) JITTER PREEMPHASIS DRIVER LIMIT 1000 CONVENTIONAL DRIVER LIMIT PREEMPHASIS REQUIRED ERROR-FREE TRANSMISSION DATA RATE (Mbps)
Diagrams
simple method quickly determine your circuit configuration view diagram. diagram scope photo (voltage time) showing transitions pseudo-random string displaying least interval. diagram quickly calculate total jitter circuit configuration. Jitter total time variation zero-volt differential crossing, percent jitter expressed percentage baud period, tBAUD. Figures show typical diagrams non-preemphasis device MAX3291/MAX3292. jitter often used interchangeably; however, they exactly same thing. usually makes majority jitter, asymmetrical high driver output voltage levels time skews non-ideal transceivers (driver receiver) also contribute jitter.
MAX3291/MAX3292
Figure Diagram Typical RS-485 Transceiver Without Preemphasis, while Driving 1000 feet Cable 5Mbps
Figure Preemphasis Driver Performance Compared Conventional Driver Without Preemphasis Jitter
Figure Diagram MAX3292 with Preemphasis Interval 175ns, while Driving 1000 feet Cable 5Mbps
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
Jitter (total jitter tBAUD) When total amount time skew becomes more baud period, data error rate increase sharply.
Line Repeater
line lengths greater than what MAX3291/ MAX3292 drive, repeater application shown Figure Figure shows system differential voltage MAX3292 driving 4000 feet 26AWG twisted-pair wire into termination loads.
Transceivers
standard RS-485 receiver input impedance (one unit load), standard driver drive unit loads. MAX3291/MAX3292 transceivers have 1/4-unit-load receiver input impedance (48k), allowing transceivers connected parallel communication line. combination these devices and/or other RS-485 transceivers with total unit-loads less connected line.
Line Termination
MAX3291/MAX3292 targeted applications requiring best combination long cable length lowest bit-error rate. order achieve this combination, cable system must with care. There three basic steps: cable should only have ends tree configuration with long branches), which terminated with simple resistor termination whose value cable's characteristic impedance (ZO). Avoid terminations anywhere else along cable. This ensures that there reflections cable, that transmitters (whether they located ends cable somewhere along length) same impedance, equal Make branches stubs short enough that twice propagation delay along stub (down back) significantly less than baud period (around less). This ensures that reflections from stub (which unavoidable, since stubs terminated) settle much less than baud period. application requires branch much longer than this, repeater (see Line Repeater section).
Low-Power Shutdown Mode
Initiate low-power shutdown mode bringing high low. shutdown MAX3291/MAX3292 typically draw only supply current. Simultaneously driving allowed; parts guaranteed enter shutdown high less than 80ns. inputs this state least 300ns, parts guaranteed enter shutdown. Enable times Switching Characteristics tables correspond when part lowpower shutdown state. Enable times ZH(SHDN) tZL(SHDN) assume parts shut down. takes drivers receivers longer activate from lowpower shutdown mode (tZH(SHDN), tZL(SHDN)) than from driver/receiver disable mode (tZH, tZL).
MAX3291 MAX3292
RECEIVER INPUT
5V/div
DATA
1V/div
5V/div
DATA
2µs/div TYPICAL OPERATING CIRCUIT, RPSET
Figure Line-Repeater Application
Figure MAX3292 System Differential Voltage Driving 4000 Feet, Using Termination Resistors
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
Don't overload cable with many receivers. Even though MAX3291/MAX3292 receives present only 1/4-unit load, placing receivers cable will attenuate signal spaced along cable and, addition, cause reflections clumped spot. MAX3291/MAX3292 successfully drive cables correct RS-485/RS-422 levels with receivers, preemphasis effect significantly diminished. MAX3291/ MAX3292 centered load impedance which corresponds parallel combination cable impedance termination resistors. your cable impedance deviates somewhat from this value, still preemphasis effect (although ideal preemphasis time, PRE, need adjustment). However, your cable impedance significantly different, preemphasis ratio DPER changes, resulting significantly less preemphasis. Determine preemphasis ratio versus load referring Driver Differential Output Voltage RDIFF graph Typical Operating Characteristics. Read strong normal levels from graph (remember that horizontal units half your cable impedance) divide numbers DPER (DPER VSTRONG VNORMAL VODP VOD). Figures show typical network application circuits with proper termination.
Preemphasis Data Rates (MAX3292)
data rates (<1Msps), preemphasis operation guaranteed because highly dependent system power-supply noise. Minimize this noise increasing bypass capacitance using power supply with fast transient response.
MAX3291 MAX3292 Figure Typical Half-Duplex RS-485 Network
NOTE:
MAX3291 MAX3292
Figure Typical Full-Duplex RS-485 Network
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
Configuration
VIEW
Chip Information
TRANSISTOR COUNT: 2280 SUBSTRATE CONNECTED
MAX3291 MAX3292
(PSET) N.C. (PVCC) N.C.
N.C. (GND)
SO/DIP
MAX3292 ONLY.
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication
_Package Information
SOICN.EPS
MAX3291/MAX3292
RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance Communication MAX3291/MAX3292
_Package Information (continued)
PDIPN.EPS
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
_Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 1999 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.

RS-485/RS-422 Transceivers with Preemphasis High-Speed, Long-Distance

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