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MAX3086ECSD+中文资料

Selector Guide

*Pin compatible with 75180, with additional features implemented using pins 1, 6, 8, and 13.

MAX3080E–MAX3089E

±15kV ESD-Protected,Fail-Safe,High-Speed (10Mbps),

Slew-Rate-Limited RS-485/RS-422 T ransceivers

________________________________________________________________Maxim Integrated Products

1

19-1800; Rev 1; 5/06

Ordering Information continued at end of data sheet.

General Description

The MAX3080E–MAX3089E are ±15kV electrostatic dis-charge (ESD)-protected, high-speed transceivers for RS-485/RS-422 communication that contain one driver and one receiver. These devices feature fail-safe circuitry,which guarantees a logic-high receiver output when the receiver inputs are open or shorted. This means that the receiver output will be a logic high if all transmitters on a terminated bus are disabled (high impedance). The MAX3080E/MAX3081E/MAX3082E feature reduced slew-rate drivers that minimize EMI and reduce reflec-tions caused by improperly terminated cables, allowing error-free data transmission up to 115kbps. The MAX3083E/MAX3084E/MAX3085E offer higher driver output slew-rate limits, allowing transmit speeds up to 500kbps. The MAX3086E/MAX3087E/ MAX3088Es’ dri-ver slew rates are not limited, making transmit speeds up to 10Mbps possible. The MAX3089E’s slew rate is selectable between 115kbps, 500kbps, and 10Mbps by driving a selector pin with a single three-state driver. All devices feature enhanced ESD protection. All transmitter outputs and receiver inputs are protected to ±15kV using the Human Body Model.

These transceivers typically draw 375μA of supply current when unloaded, or when fully loaded with the dri-vers disabled.

All devices have a 1/8-unit-load receiver input impedance that allows up to 256 transceivers on the bus. The MAX3082E/MAX3085E/MAX3088E are intended for half-duplex communications, while the MAX3080E/MAX3081E/MAX3083E/MAX3084E/MAX3086E/MAX3087E are intended for full-duplex communications. The MAX3089E is selectable between half-duplex and full-duplex opera-tion. It also features independently programmable receiver and transmitter output phase via separate pins.

Features

o ESD Protection for RS-485 I/O Pins

±15kV, Human Body Model

o True Fail-Safe Receiver While Maintaining EIA/TIA-485 Compatibility

o Enhanced Slew-Rate Limiting Facilitates Error-Free Data Transmission

(MAX3080E–MAX3085E/MAX3089E)

o 1nA Low-Current Shutdown Mode (Except MAX3081E/MAX3084E/MAX3087E)

o Pin-Selectable Full/Half-Duplex Operation (MAX3089E)

o Phase Controls to Correct for Twisted-Pair Reversal (MAX3089E)

o Allow Up to 256 Transceivers on the Bus

Applications

RS-422/RS-485 Communications Level Translators

Transceivers for EMI-Sensitive Applications Industrial-Control Local Area Networks

For free samples and the latest literature, visit https://www.sodocs.net/doc/3613358025.html, or phone 1-800-998-8800.For small orders, phone 1-800-835-8769.

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

(V CC = +5V ±5%, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +5V and T A = +25°C.) (Note 1)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Supply Voltage (V CC ) ............................................................+7V Control Input Voltage (RE , DE)...................-0.3V to (V CC + 0.3V)Special Input Voltage

(H/F , SRL, TXP, RXP)..............................-0.3V to (V CC + 0.3V)Driver Input Voltage (DI).............................-0.3V to (V CC + 0.3V)Driver Output Voltage (A, B, Y, Z)........................................±13V Receiver Input Voltage (A, B)..............................................±13V Receiver Input Voltage, Full Duplex (A, B)..........................±25V Receiver Output Voltage (RO)....................-0.3V to (V CC + 0.3V)

Continuous Power Dissipation

8-Pin Plastic DIP (derate 9.09mW/°C above +70°C)...727mW 8-Pin SO (derate 5.88mW/°C above +70°C)................471mW 14-Pin Plastic DIP (derate 10.0mW/°C above +70°C)....800mW 14-Pin SO (derate 8.33mW/°C above +70°C)..............667mW Operating Temperature Ranges

MAX308_EC_ _...................................................0°C to +70°C MAX308_EE_ _................................................-40°C to +85°C Storage Temperature Range.............................-65°C to +150°C Lead Temperature (soldering, 10s).................................+300°C

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

_______________________________________________________________________________________3

DC ELECTRICAL CHARACTERISTICS (continued)

(V CC = +5V ±5%, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +5V and T A = +25°C.) (Note 1)

Note 1:All currents into the device are positive; all currents out of the device are negative. All voltages are referred to device

ground unless otherwise noted.

Note 2:?V OD and ?V OC are the changes in V OD and V OC , respectively, when the DI input changes state.

Note 3:The SRL pin is internally biased to V CC / 2 by a 100k ?/100k ?resistor-divider. It is guaranteed to be V CC / 2 if left

unconnected.

Note 4:Maximum current level applies to peak current just prior to foldback-current limiting; minimum current level applies during

current limiting.

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers 4_______________________________________________________________________________________

SWITCHING CHARACTERISTICS—MAX3080E/MAX3081E/MAX3082E, and MAX3089E with SRL = Unconnected

(V CC = +5V ±5%, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +5V and T A = +25°C.)

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

_______________________________________________________________________________________5

SWITCHING CHARACTERISTICS—MAX3083E/MAX3084E/MAX3085E, and MAX3089E with SRL = V CC

(V CC = +5V ±5%, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +5V and T A = +25°C.)

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers 6_______________________________________________________________________________________

SWITCHING CHARACTERISTICS—MAX3086E/MAX3087E/MAX3088E, and MAX3089E with SRL = GND

(V CC = +5V ±5%, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +5V and T A = +25°C.)

Note 5:The device is put into shutdown by bringing RE high and DE low. If the enable inputs are in this state for less than 50ns, the

device is guaranteed not to enter shutdown. If the enable inputs are in this state for at least 600ns, the device is guaranteed to have entered shutdown.

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

_______________________________________________________________________________________7

300

-60100

NO-LOAD SUPPLY CURRENT

vs. TEMPERATURE

350325525

TEMPERATURE (°C)

N O -L O A D S U P P L Y C U R R E N T (μA )

40

4504253754000

60

500475-40-20

20

80

100

5OUTPUT CURRENT

vs. RECEIVER OUTPUT LOW VOLTAGE

2060M A X 3080/3089 T O C -2

OUTPUT LOW VOLTAGE (V)O U T P U T C U R R E N T (m A )

34030250140

505

OUTPUT CURRENT

vs. RECEIVER OUTPUT HIGH VOLTAGE

1030M A X 3080/3089 T O C -3

OUTPUT HIGH VOLTAGE (V)

O U T P U T C U R R E N T (m A )

32015225140

2-60100

SHUTDOWN CURRENT vs. TEMPERATURE

4620M A X 3080/3089 T O C -1

TEMPERATURE (°C)S H U T D O W N C U R R E

N T (n A )

40

12141080

60

1618-40-20

20

80

0.10

0.15

-6080

100

RECEIVER OUTPUT LOW VOLTAGE

vs. TEMPERATURE

0.200.50TEMPERATURE (°C)

O U T P U T L O W

V O L T A G E (V )

20

0.400.350.300.250

40

0.45-40

-20

60

3.8

3.9-6080100

RECEIVER OUTPUT HIGH VOLTAGE

vs. TEMPERATURE

4.04.5TEMPERATURE (°C)

O U T P U T V

O L T A G E (V )

204.34.24.10404.4-40-2060115

-60100

RECEIVER PROPAGATION DELAY (500kbps MODE) vs. TEMPERATURE

120

140

TEMPERATURE (°C)

P R O P A G A T I O N D E L A Y (

n s )

40

130

1250

60

135-40-20

20

80

94

-60100

RECEIVER PROPAGATION DELAY (10Mbps MODE) vs. TEMPERATURE

9896

112TEMPERATURE (°C)

P R O P A G A T I O N D E L A Y (

n s )

40

1061041001020

60

110108-40-20

20

80

1.90

-60100

DRIVER PROPAGATION DELAY (115kbps MODE) vs. TEMPERATURE

1.95

2.20

TEMPERATURE (°C)

P R O P A G A T I O N D E L A Y (μs )

40

2.102.002.050

60

2.15-40-20

20

80

Typical Operating Characteristics

(V CC = +5V, T A = +25°C, unless otherwise noted.)

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers 8_______________________________________________________________________________________

Typical Operating Characteristics (continued)

(V CC = +5V, T A = +25°C, unless otherwise noted.)

520

560-60100DRIVER PROPAGATION DELAY (500kbps MODE) vs. TEMPERATURE

600640920

TEMPERATURE (°C)P R O P A G A T I O N D E L A Y (n s )

40

7608007206800

60

840880-40-20

20

80

20

25-60100DRIVER PROPAGATION DELAY (10Mbps MODE) vs. TEMPERATURE

30

60TEMPERATURE (°C)P R O P A G A T I O N D E L A Y (n s )

404550403506055-40-202080 1.83

1.84

-60100

DRIVER DIFFERENTIAL OUTPUT VOLTAGE

vs. TEMPERATURE

1.851.90

TEMPERATURE (°C)

O U T P U T V O L T A G E (V )

401.881.871.860601.89-40-2020800

-10-20-30-40-50-60-70-80-90-100

-8-2OUTPUT CURRENT vs.DRIVER OUTPUT HIGH VOLTAGE

OUTPUT HIGH VOLTAGE (V)

O U T P U T C U R R E N T (m A )

6

42-6-40100

0.01

1

DRIVER OUTPUT CURRENT

vs. DIFFERENTIAL OUTPUT VOLTAGE

0.1

10

1

M A X 3080 T O C -12

DIFFERENTIAL OUTPUT VOLTAGE (V)

O U T P U T C U R R E N T (m A

)

2

3

4

5

020

406080100120140OUTPUT CURRENT vs.DRIVER OUTPUT LOW VOLTAGE

OUTPUT LOW VOLTAGE (V)

O U T P U T C U R R E N T (m A )

2

4

6

8

10

12

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

_______________________________________________________________________________________9

2μs/div

DRIVER PROPAGATION DELAY

MAX3080E/MAX3081E/MAX3082E AND MAX3089E

WITH SRL = OPEN

DI V Y - V Z 5V/div

2.5V/div

MAX3080/3089 TYP-20

500ns/div

DRIVER PROPAGATION DELAY

MAX3083E/MAX3084E/MAX3085E AND MAX3089E

WITH SRL = V

CC

DI V Y - V Z 5V/div

2.5V/div

MAX3080/3089 TYP-21

50ns/div

DRIVER PROPAGATION DELAY

MAX3086E/MAX3087E/MAX3088E AND MAX3089E

WITH SRL = GND

DI V Y - V Z 5V/div

2.5V/div

MAX3080/3089 TYP-22

Typical Operating Characteristics (continued)

(V CC = +5V, T A = +25°C, unless otherwise noted.)

50ns/div

V A - V B RO 2V/div

5V/div

MAX3080/3089 TYP-18

RECEIVER PROPAGATION DELAY

MAX3086E/MAX3087E/MAX3088E AND MAX3089E

WITH SRL = GND

50ns/div

V A - V B RO 2V/div

5V/div

MAX3080/3089 TYP-17

RECEIVER PROPAGATION DELAY MAX3080E–MAX3085E AND MAX3089E

WITH SRL = OPEN OR V CC

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers 10______________________________________________________________________________________

Pin Description

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

______________________________________________________________________________________11

Pin Description (continued)

X = Don’t care

Shutdown mode, driver and receiver outputs high impedance

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers 12______________________________________________________________________________________

Function Tables (continued)

TRANSMITTING

INPUTS

OUTPUTS RE DE DI B/Z

A/Y X 1101X 101000X High-Z

High-Z

1

X

Shutdown RECEIVING INPUTS

OUTPUT RE DE A-B RO 0X ≥-0.05V 10X ≤-0.2V 00X Open/shorted

111X High-Z 1

X

Shutdown

MAX3089E

INPUTS

OUTPUT H/F RXP RE DE A-B Y-Z RO 000X ≥-0.05V X 1000X ≤-0.2V X 0010X ≥-0.05V X 0010X ≤-0.2V X 11000X ≥-0.05V 11000X ≤-0.2V 01100X ≥-0.05V 01100X ≤-0.2V 1000X Open/shorted X 11000X Open/shorted 1010X Open/shorted X 01100X Open/shorted 0X X 11X X High-Z X

X

1

X

X

Shutdown

RECEIVING X = Don’t care

Shutdown mode, driver and receiver outputs high impedance

MAX3082E/MAX3085E/MAX3088E

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

______________________________________________________________________________________

13

Figure 1. MAX3080E/MAX3083E/MAX3086E Pin Configuration and Typical Full-Duplex Operating Circuit

M A X 3080E –M A X 3089E

Detailed Description

The MAX3080E–MAX3089E high-speed transceivers for RS-485/RS-422 communication contain one driver and one receiver. These devices feature fail-safe circuitry,which guarantees a logic-high receiver output when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled (see the Fail-Safe section). The MAX3080E/MAX3081E/MAX3082E feature reduced slew-rate drivers that minimize EMI and reduce reflec-tions caused by improperly terminated cables, allowing error-free data transmission up to 115kbps (see the Reduced EMI and Reflections section). The MAX3083E/MAX3084E/MAX3085E offer higher driver output slew-rate limits, allowing transmit speeds up to 500kbps. The MAX3086E/MAX3087E/MAX3088E’s dri-ver slew rates are not limited, making transmit speeds up to 10Mbps possible. The MAX3089E’s slew rate is selectable between 115kbps, 500kbps, and 10Mbps by driving a selector pin with a three-state driver.

The MAX3082E/MAX3085E/MAX3088E are half-duplex transceivers, while the MAX3080E/MAX3081E/MAX3083E/MAX3084E/MAX3086E/MAX3087E are full-duplex transceivers. The MAX3089E is selectable between half- and full-duplex communication by driving a selector pin high or low, respectively.

All of these parts operate from a single +5V supply.Drivers are output short-circuit current limited. Thermal shutdown circuitry protects drivers against excessive power dissipation. When activated, the thermal shut-down circuitry places the driver outputs into a high-impedance state.

Receiver Input Filtering

The receivers of the MAX3080E–MAX3085E, and the MAX3089E when operating in 115kbps or 500kbps mode, incorporate input filtering in addition to input hysteresis. This filtering enhances noise immunity with differential signals that have very slow rise and fall times. Receiver propagation delay increases by 20%due to this filtering.

Fail-Safe

The MAX3080E family guarantees a logic-high receiver output when the receiver inputs are shorted or open, or when they are connected to a terminated transmission line with all drivers disabled. This is done by setting the receiver threshold between -50mV and -200mV. If the differential receiver input voltage (A-B) is greater than or equal to -50mV, RO is logic high. If A-B is less than or equal to -200mV, RO is logic low. In the case of a terminated bus with all transmitters disabled, the receiver’s differential input voltage is pulled to 0V by

the termination. With the receiver thresholds of the MAX3080E family, this results in a logic high with a 50mV minimum noise margin. Unlike previous fail-safe devices, the -50mV to -200mV threshold complies with the ±200mV EIA/TIA-485 standard.

MAX3089E Programming

The MAX3089E has several programmable operating modes. Transmitter rise and fall times are programma-ble between 2500ns, 750ns, and 25ns, resulting in maximum data rates of 115kbps, 500kbps, and 10Mbps, respectively. To select the desired data rate,drive SRL to one of three possible states by using a three-state driver, by connecting it to V CC or GND, or by leaving it unconnected. For 115kbps operation, set the three-state device in high-impedance mode or leave SRL unconnected. For 500kbps operation, drive SRL high or connect it to V CC . For 10Mbps operation,drive SRL low or connect it to GND. SRL can be changed during operation without interrupting data communications.

Occasionally, twisted-pair lines are connected back-ward from normal orientation. The MAX3089E has two pins that invert the phase of the driver and the receiver to correct for this problem. For normal operation, drive TXP and RXP low, connect them to ground, or leave them unconnected (internal pulldown). To invert the dri-ver phase, drive TXP high or connect it to V CC . To invert the receiver phase, drive RXP high or connect it to V CC . Note that the receiver threshold is positive when RXP is high.

The MAX3089E can operate in full- or half-duplex mode. Drive the H /F pin low, leave it unconnected (internal pulldown), or connect it to GND for full-duplex operation, and drive it high for half-duplex operation. In full-duplex mode, the pin configuration of the driver and receiver is the same as that of a MAX3080E (Figure 4).In half-duplex mode, the receiver inputs are switched to the driver outputs, connecting outputs Y and Z to inputs A and B, respectively. In half-duplex mode, the internal full-duplex receiver input resistors are still connected to pins 11 and 12.

±15kV ESD Protection

As with all Maxim devices, ESD-protection structures are incorporated on all pins to protect against electro-static discharges encountered during handling and assembly. The driver outputs and receiver inputs of the MAX3080E–MAX3089E family have extra protection against static electricity. Maxim’s engineers have developed state-of-the-art structures to protect these pins against ESD of ±15kV without damage.

Slew-Rate-Limited RS-485/RS-422 T ransceivers 14

______________________________________________________________________________________

The ESD-protected pins are tested with reference to the ground pin in a powered-down condition. They are test-ed to ±15kV using the Human Body Model.

ESD Test Conditions

ESD performance depends on a variety of conditions.Contact Maxim for a reliability report that documents test setup, test methodology, and test results.

Human Body Model

Figure 14a shows the Human Body Model, and Figure 14b shows the current waveform it generates when dis-

charged into a low impedance. This model consists of a 100pF capacitor charged to the ESD voltage of inter-est, which is then discharged into the test device through a 1.5k ?resistor.

Machine Model

The Machine Model for ESD tests all pins using a 200pF storage capacitor and zero discharge resis-tance. The objective is to emulate the stress caused when I/O pins are contacted by handling equipment during test and assembly. All pins require this protec-

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

______________________________________________________________________________________15

Figure 5. Driver DC Test Load Figure 6. Receiver Enable/Disable Timing Test Load

Figure 4. MAX3089E Pin Configuration and Functional Diagram

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers 16______________________________________________________________________________________

Figure 7. Driver Timing Test Circuit Figure 8. Driver Enable and Disable Timing Test Load

Figure 9. Driver Propagation Delays

Figure 10. Driver Enable and Disable Times (Except MAX3081E/MAX3084E/MAX3087E)

Figure 11. Receiver Propagation Delays

Figure 12. Receiver Enable and Disable Times (Except MAX3081E/MAX3084E/MAX3087E)

MAX3080E–MAX3089E

ransceivers

______________________________________________________________________________________

17

M A X 3080/3089 F I G -14

Figure 15. Driver Output Waveform and FFT Plot of

MAX3086E/MAX3087E/MAX3088E, and MAX3089E with SRL = GND, Transmitting a 20kHz Signal

Figure 14a. Human Body ESD Test Model

Figure 14b. Human Body Current Waveform

M A X 3080/3089 F I G -15

Figure 16. Driver Output Waveform and FFT Plot of MAX3083E/MAX3084E/MAX3085E, and MAX3089E with SRL = V CC,Transmitting a 20kHz Signal 100kHz/div 0Hz 1MHz

B

A

20dB/div

M A X 3080/3089 F I G -16

Figure 17. Driver Output Waveform and FFT Plot of MAX3080E/MAX3081E/MAX3082E, and MAX3089E with SRL = Unconnected, Transmitting a 20kHz Signal

M A X 3080E –M A X 3089E

during test and assembly. All pins require this protec-tion, not just RS-485 inputs and outputs.

Applications Information

256 Transceivers on the Bus

The standard RS-485 receiver input impedance is 12k ?(one-unit load), and the standard driver can drive up to 32 unit loads. The MAX3080E family of transceivers have a 1/8-unit-load receiver input impedance (96k ?),allowing up to 256 transceivers to be connected in par-allel on one communication line. Any combination of these devices and/or other RS-485 transceivers with a total of 32 unit loads or less can be connected to the line.

Reduced EMI and Reflections

The MAX3080E–MAX3085E, and MAX3089E with SRL =V CC or unconnected, are slew-rate limited, minimizing EMI and reducing reflections caused by improperly ter-minated cables. Figure 15 shows the driver output waveform and its Fourier analysis of a 20kH z signal transmitted by a MAX3086E/MAX3087E/MAX3088E,and MAX3089E with SRL = GND. High-frequency har-monic components with large amplitudes are evident.Figure 16 shows the same signal displayed for a MAX3083E/MAX3084E/MAX3085E, and MAX3089E with SRL = V CC ), transmitting under the same conditions.Figure 16’s high-frequency harmonic components are much lower in amplitude, compared with Figure 15’s,and the potential for EMI is significantly reduced. Figure 17 shows the same signal displayed for a MAX3080E/MAX3081E/MAX3082E, and MAX3089E with SRL =unconnected, transmitting under the same conditions.

Figure 17’s high-frequency harmonic components are even lower.

In general, a transmitter’s rise time relates directly to the length of an unterminated stub, which can be driven with only minor waveform reflections. The following equation expresses this relationship conservatively:

Length = t RISE / (10 x 1.5ns/ft)

where t RISE is the transmitter’s rise time.

For example, the MAX3080E’s rise time is typically 1320ns, which results in excellent waveforms with a stub length up to 90 feet. A system can work well with longer unterminated stubs, even with severe reflections, if the waveform settles out before the UART samples them.

Low-Power Shutdown Mode

(Except MAX3082E/MAX3085E/MAX3088E)

Low-power shutdown mode is initiated by bringing both RE high and DE low. In shutdown, the devices typically draw only 1nA of supply current.

RE and DE may be driven simultaneously; the parts are guaranteed not to enter shutdown if RE is high and DE is low for less than 50ns. If the inputs are in this state for at least 600ns, the parts are guaranteed to enter shutdown.

Enable times t ZH and t ZL in the Switching Char-acteristics tables assume the part was not in a low-power shutdown state. Enable times t ZH(SHDN)and t ZL(SHDN)assume the parts were shut down. It takes drivers and receivers longer to become enabled from low-power shutdown mode (t ZH(SHDN), t ZH(SHDN)) than from driver/receiver-disable mode (t ZH , t ZL ).

Slew-Rate-Limited RS-485/RS-422 T ransceivers 18

______________________________________________________________________________________

Figure 18. Line Repeater for MAX3080E/MAX3081E/MAX3083E/MAX3084E/MAX3086E/MAX3087E, and MAX3089E in Full-Duplex Mode

5μs/div

V A - V B

DI RO

1V/div

5V/div

5V/div

MAX3080/3089 FIG-18

Figure 19. MAX3080E/MAX3081E/MAX3082E, and MAX3089E with SRL = Unconnected, System Differential Voltage at 50kHz Driving 4000ft of Cable

Driver Output Protection

Two mechanisms prevent excessive output current and power dissipation caused by faults or by bus con-tention. The first, a foldback current limit on the output stage, provides immediate protection against short cir-cuits over the whole common-mode voltage range (see Typical Operating Characteristics ). The second, a ther-mal shutdown circuit, forces the driver outputs into a high-impedance state if the die temperature becomes excessive.

Line Length vs. Data Rate

The RS-485/RS-422 standard covers line lengths up to 4000 feet. For line lengths greater than 4000 feet, use the repeater application shown in Figure 18.

Figures 19, 20, and 21 show the system differential volt-age for the parts driving 4000 feet of 26AWG twisted-pair wire at 110kHz into 120?loads.

Typical Applications

The MAX3082E/MAX3085E/MAX3088E/MAX3089E transceivers are designed for bidirectional data com-munications on multipoint bus transmission lines.Figures 22 and 23 show typical network applications circuits. These parts can also be used as line repeaters,with cable lengths longer than 4000 feet, as shown in Figure 18.

To minimize reflections, the line should be terminated at both ends in its characteristic impedance, and stub lengths off the main line should be kept as short as possible. The slew-rate-limited MAX3082E/MAX3085E,and the two modes of the MAX3089E, are more tolerant of imperfect termination.

MAX3080E–MAX3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers

______________________________________________________________________________________19

2μs/div V A - V B DI

RO 1V/div 5V/div 5V/div MAX3080/3089 FIG-19

Figure 20. MAX3083E/MAX3084E/MAX3085E, and MAX3089E with SRL = V CC,System Differential Voltage at 50kHz Driving 4000ft of Cable

1μs/div

V A - V B DI RO 1V/div

5V/div

5V/div

MAX3080/3089 FIG-20

Figure 21. MAX3086E/MAX3087E/MAX3088E, and MAX3089E with SRL = GND, System Differential Voltage at 200kHz Driving 4000ft of Cable

Figure 22. Typical Half-Duplex RS-485 Network

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

20__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600?2006 Maxim Integrated Products

is a registered trademark of Maxim Integrated Products, Inc.

M A X 3080E –M A X 3089E

Slew-Rate-Limited RS-485/RS-422 T ransceivers Figure 23. Typical Full-Duplex RS-485 Network

Ordering Information (continued)

Revision History

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