MAX3158CPI+ - Maxim Integrated Products, Inc.

General Description

The MAX3158 is a high CMRR RS-485/RS-422 data-com-

munications interface providing ±60V isolation in a

hybrid microcircuit. A single +5V supply on the logic side

powers both sides of the interface, with external 100V

capacitors transferring power from the logic side to the

isolated side. Each MAX3158 contains one transmitter

and one receiver and is guaranteed to operate at data

rates up to 250kbps. Drivers are short-circuit current lim-

ited and protected against excessive power dissipation

by thermal shutdown circuitry that places the driver out-

puts into a high-impedance state. The receiver input has

a fail-safe feature that guarantees a logic-high receiver

output if the inputs are open, shorted, or connected to a

terminated transmission line with all drivers disabled.

The MAX3158 typically draws 25mA of supply current

when unloaded or when fully loaded with the driver dis-

abled. Supply current drops to 25µA when the device is

placed in shutdown mode. The device is pin selectable

between half- and full-duplex mode and also features

an independently programmable receiver and transmit-

ter output phase through separate pins. The MAX3158

is a low-cost replacement for opto-isolated trans-

ceivers. For fully isolated RS-485/RS-422 transceivers,

refer to the MAX1480 family data sheet.

________________________Applications

Industrial Controls Telecommunications

Level Translators Local Area Networks

Features

♦±60V Isolated Data Interface

♦+5V Single Supply

♦Low-Cost Replacement for Opto-Isolated

Transceivers

♦True Fail-Safe Receiver While Maintaining

EIA/TIA-485 Compliance

♦Pin-Selectable Full/Half-Duplex Operation

♦Phase Controls to Correct for Twisted-Pair

Reversal

♦25µA Low-Power Shutdown Mode

♦Thermal Shutdown for Driver Overload Protection

♦28-Pin SSOP Package

♦Slew-Rate-Limited Reduced EMI

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

________________________________________________________________ Maxim Integrated Products 1

MAX3158

C1HI C2LO C2HIC1LO

TXP

RXP

GND

MICRO RT = 100Ω

VCC

0.1µF

1µF

10nF

0.047µF

±60V

GND OFFSET

ISOCOM

REMOTE GND

REMOTE MICRO

RS-485

NODE

VCC

H/F

ISOVCC

Typical Operating Circuit

19-2778; Rev 0; 2/03

Ordering Information

Pin Configurations appear at end of data sheet.

PART TEMP RANGE

PIN-PACKAGE

MAX3158CAI 0°C to +70°C 28 SSOP

MAX3158CPI 0°C to +70°C 28 PDIP

MAX3158EAI -40°C to +85°C 28 SSOP

MAX3158EPI -40°C to +85°C 28 PDIP

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

(All voltages referenced to GND, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS

(VCC = +5V ±5%, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047µF, C3 = C4 = 1µF, TA= TMIN to TMAX, unless otherwise noted.

Typical values are at VCC = +5V and TA= +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 (VCC).............................................................+7V

Cable Ground (ISOCOM) ....................................................±75V

Isolated Supply ISOVCC Relative to Cable Ground

(ISOCOM) ...........................................................................+7V

Digital Input, Output Voltage

(DI, DE, RE, TXP, RXP, RO).....................-0.3V to (VCC + 0.3V)

Digital Inputs (H/F) Relative to Cable Ground

(ISOCOM) .........................................-0.3V to (ISOVCC + 0.3V)

Driver Output Voltage (Y, Z) Relative to Cable Ground

(ISOCOM)............................................................-8V to +12.5V

Receiver Input Voltage (A, B) Relative to Cable Ground

(ISOCOM)............................................................-8V to +12.5V

Termination Connections (YR, ZR, AR, BR) Relative to Cable

Ground (ISOCOM)...............................................-8V to +12.5V

Charge-Pump Capacitance Low

(C1LO, C2LO) .........................................-0.3V to (VCC + 0.3V)

Charge-Pump Capacitance High (C1HI, C2HI) Relative

to Cable Ground (ISOCOM) .............-0.3V to (ISOVCC + 0.3V)

Continuous Power Dissipation (TA= +70°C)

28-Pin SSOP (derate 10.8mW/°C above +70°C) ..........860mW

28-Pin PDIP (derate 14.3mW/°C above +70°C)..........1143mW

Operating Temperature Ranges

MAX3158C_I .......................................................0°C to +70°C

MAX3158E_I ....................................................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range ............................-65°C to +160°C

Lead Temperature (soldering, 10s) ................................+300°C

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DRIVER

Differential Driver Output,

No Load VOD1 Figure 1, R = 10MΩ6V

Figure 1, R = 50Ω (RS-422) 2.0

Differential Driver Output,

Loaded VOD2 Figure 1, R = 27Ω (RS-485) 1.5 V

Change in Magnitude of

Differential Output Voltage

(Note 2)

∆VOD Figure 1, R = 50Ω or R = 27Ω0.2 V

Driver Common-Mode Voltage VOC Figure 1, R = 50Ω or R = 27Ω,

VOC relative to ISOCOM 3.5 V

Change in Magnitude of

Common-Mode Voltage

(Note 2)

∆VOC Figure 1, R = 50Ω or R = 27Ω0.2 V

Input High Voltage VIH DE, DI, RE, TXP, RXP, relative to GND,

H/F relative to ISOCOM 2.0 V

Input Low Voltage VIL DE, DI, RE, TXP, RXP, relative to GND,

H/F relative to ISOCOM 0.8 V

DI Input Hysteresis VHYS 100 mV

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +5V ±5%, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047µF, C3 = C4 = 1µF, TA= TMIN to TMAX, unless otherwise noted.

Typical values are at VCC = +5V and TA= +25°C.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

IIN1 DE, DI, RE ±2

Input Current IIN2 H/F, TXP, RXP internal pulldown 10 40 µA

DE = GND, VCC = GND or 5.25V, -7V ≤ (VIN -

VISOCOM) ≤ +12V, AR = BR = ISOCOM -5.0 +8.0

Input Current (A and B) IIN3 DE = GND, VCC = GND or 5.25V, -7V ≤ (VIN -

VISOCOM) ≤ +12V, AR open, BR open -0.58 +1.0

DE = GND, VCC = GND or 5.25V, -7V ≤ (VIN -

VISOCOM) ≤ +12V, YR = ZR = ISOCOM -5.0 +8.0

Output Leakage (Y and Z)

Full Duplex IODE = GND, VCC = GND or 5.25V, -7V ≤ (VIN -

VISOCOM) ≤ +12V, YR open, ZR open -0.58 +1.0

IOSD1 VISOCOM - 7V ≤ VOUT ≤ VISOVCC -250

Driver Short-Circuit Output

Current (Note 3) IOSD2 VISOCOM - 7V ≤ VOUT ≤ VISOCOM + 12V 250 mA

RECEIVER

Receiver Differential Threshold

Voltage VTH -7V ≤ VCM - VISOCOM ≤ +12V -200 -125 -50 m V

Receiver Input Hysteresis ∆VTH 25 mV

Receiver Output High Voltage VOH IO = -4mA, VID = -50mV V CC - 1.5 V

Receiver Output Low Voltage VOL IO = 4mA, VID = -200mV 0.4 V

Three-State Output Current at

Receiver IOZR 0.4V ≤ VO ≤ 2.4V ±1µA

-7V ≤ VCM - VISOCOM ≤ +12V, AR = BR =

ISOCOM 1.5

Receiver Input Resistance RIN -7V ≤ VCM - VISOCOM ≤ +12V, AR open,

BR open 12

kΩ

Receiver Output Short-Circuit

Current IOSR 0V ≤ VRO ≤ VCC ±7±100 mA

SUPPLY CURRENT

Supply Current ICC No load, RE = DE = DI = GND or VCC 25 85 mA

DE = GND, RE = VCC, VISOCOM = GND 25 60

Supply Current in Shutdown

Mode ISHDN DE = GND, RE = VCC, VISOCOM = ±60V ±650 µA

Maximum Ground Differential ∆VGND DE = GND, RE = VCC,

| ISOCOM leakage | ≤ 650µA ±60 V

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

4 _______________________________________________________________________________________

SWITCHING CHARACTERISTICS

(VCC = +5V ±5%, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047µF, C3 = C4 = 1µF. Typical values are at VCC = +5V and TA= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

tDPLH Figures 3 and 5, RDIFF = 54Ω,

CL1 = CL2 = 100pF 400 1400 2000

Driver Input to Output

tDPHL Figures 3 and 5, RDIFF = 54Ω,

CL1 = CL2 = 100pF 400 1400 2000

Driver Output Skew

| tDPLH - tDPHL |tDSKEW Figures 3 and 5, RDIFF = 54Ω,

CL1 = CL2 = 100pF 250 ns

Driver Rise or Fall Time tDR, tDF Figures 3 and 5, RDIFF = 54Ω,

CL1 = CL2 =100pF 200 1200 2200 ns

Maximum Data Rate fMAX 250 kbps

Driver Enable to Output High tDZH Figures 4 and 6, CL = 100pF, S2 closed 3500 ns

Driver Enable to Output Low tDZL Figures 4 and 6, CL = 100pF, S1 closed 3500 ns

Driver Disable Time from Low tDLZ Figures 4 and 6, CL = 15pF, S1 closed 300 ns

Driver Disable Time from High tDHZ Figures 4 and 6, CL = 15pF, S2 closed 300 ns

Receiver Input to Output tRPLH,

tRPHL Figures 7 and 9; | VID | ≥ 2.0V 440 600 ns

Differential Receiver Skew

| tRPLH - tRPHL |tRSKEW Figures 7 and 9; | VID | ≥ 2.0V 20 ns

Receiver Enable to Output Low tRZL Figures 2 and 8, CL = 100pF, S1 closed 20 50 ns

Receiver Enable to Output High tRZH Figures 2 and 8, CL = 100pF, S2 closed 20 50 ns

Receiver Disable Time from Low tRLZ Figures 2 and 8, CL = 100pF, S1 closed 200 500 ns

Receiver Disable Time from High tRHZ Figures 2 and 8, CL = 100pF, S2 closed 200 500 ns

Time to Shutdown tSHDN (Note 4) 50 200 700 ns

Driver Enable from Shutdown to

Output High

tDZH

(SHDN) Figures 4 and 6, CL = 15pF, S2 closed 0.2 1 ms

Driver Enable from Shutdown to

Output Low

tDZL

(SHDN) Figures 4 and 6, CL = 15pF, S1 closed 0.2 1 ms

Receiver Enable from Shutdown

to Output High

tRZH

(SHDN) Figures 2 and 8, CL = 100pF, S2 closed 0.2 1 m s

Receiver Enable from Shutdown

to Output Low

tRZL

(SHDN) Figures 2 and 8, CL = 100pF, S1 closed 0.2 1 ms

Charge-Pump Oscillating

Frequency fOSC 1.3 MHz

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: ∆VOD and ∆VOC are the changes in VOD and VOC, respectively, when the DI input changes state.

Note 3: Current level applies to peak current just prior to foldback-current limiting.

Note 4: 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 700ns, the device is guaran-

teed to have entered shutdown.

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

_______________________________________________________________________________________ 5

120

140

100

160

-40 -20 -10 0 10 20 30-30 40 50 60 70 80 90

SUPPLY CURRENT vs. TEMPERATURE

MAX3158 toc01

TEMPERATURE (°C)

SUPPY CURRENT (mA)

RL = 54Ω

NO LOAD

-300

-100

-200

200

100

300

-40 -20 -10 0 10 20 30-30 40 50 60 70 80 90

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

MAX3158 toc02

TEMPERATURE (°C)

SUPPY CURRENT (µA)

VISOCOM = -50V

VISOCOM = 0V

VISOCOM = +50V

021 3456

RECEIVER OUTPUT CURRENT

vs. RECEIVER OUTPUT LOW VOLTAGE

MAX3158 toc03

OUTPUT LOW VOLTAGE (V)

OUTPUT CURRENT (mA)

0 2.0 2.51.51.00.5 3.0 3.5 4.0 4.5 5.0 5.5

RECEIVER OUTPUT CURRENT

vs. RECEIVER OUTPUT HIGH VOLTAGE

MAX3158 toc04

OUTPUT HIGH VOLTAGE (V)

OUTPUT CURRENT (mA)

0.15

0.10

0.05

0.25

0.20

0.45

0.40

0.35

0.30

0.50

-40 -20 0 20 40 60 80 100

RECEIVER OUTPUT LOW VOLTAGE

vs. TEMPERATURE

MAX3158 toc05

TEMPERATURE (°C)

OUTPUT LOW VOLTAGE (V)

IRO = 8mA

3.95

4.05

4.00

4.15

4.10

4.35

4.30

4.25

4.20

4.40

-40 -20 0 20 40 60 80 100

RECEIVER OUTPUT HIGH VOLTAGE

vs. TEMPERATURE

MAX3158 toc06

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

IRO = -8mA

140

120

100

160

042 6 8 101214

DRIVER OUTPUT CURRENT

vs. DRIVER OUTPUT LOW VOLTAGE

MAX3158 toc07

OUTPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

-120

-90

-110

-100

-60

-80

-70

-10

-30

-20

-40

-50

-8 -4-6 -20246

DRIVER OUTPUT CURRENT

vs. DRIVER OUTPUT HIGH VOLTAGE

MAX3158 toc08

OUTPUT HIGH VOLTAGE (V)

OUTPUT CURRENT (mA)

100

0.01

01 32546

DRIVER OUTPUT CURRENT

vs. DIFFERENTIAL OUTPUT VOLTAGE

0.1

MAX3158 toc09

DIFFERENTIAL OUTPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

Typical Operating Characteristics

(VCC = +5V, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047µF, C3 = 1µF, C4 = 10nF, TA= +25°C, unless otherwise noted.)

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

6 _______________________________________________________________________________________

1.80

1.84

1.82

1.90

1.88

1.86

1.92

1.94

1.96

1.98

-40 0-20 20 40 60 80

DRIVER DIFFERENTIAL OUTPUT

VOLTAGE vs. TEMPERATURE

MAX3158 toc10

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

RL = 54Ω

410

420

450

440

430

460

470

480

490

-40 0-20 20 40 60 80

RECEIVER PROPAGATION DELAY

vs. TEMPERATURE

MAX3158 toc11

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

1.32

1.34

1.36

1.42

1.44

1.40

1.38

1.46

1.48

1.50

1.52

-40 0-20 20 40 60 80

DRIVER PROPAGATION DELAY

vs. TEMPERATURE

MAX3158 toc12

TEMPERATURE (°C)

PROPAGATION DELAY (µs)

RL = 54Ω

1.300

1.350

1.325

1.400

1.375

1.475

1.450

1.425

1.500

-40 0-20 20 40 60 80 100

DRIVER ENABLE TIME

vs. TEMPERATURE

MAX3158 toc13

TEMPERATURE (°C)

DRIVER ENABLE TIME (µs)

100

200

150

250

-40 0-20 20 40 60 80 100

DRIVER DISABLE TIME

vs. TEMPERATURE

MAX3158 toc14

TEMPERATURE (°C)

DRIVER DISABLE TIME (ns)

VA - VB

5V/div

RECEIVER PROPAGATION DELAY

MAX3158 toc15

2µs/div

2V/div

VY - VZ

DRIVER PROPAGATION DELAY

MAX3158 toc16

2µs/div

RDIFF = 54Ω

CL1 = CL2 = 100pF

POWER-UP DELAY

(VISOCOM = 0V)

MAX3158 toc17

40µs/div

10V/div

5V/div

10V/div

100µs/div

-50V

POWER-UP DELAY

(VISOCOM = -50V)

MAX3158 toc18

Typical Operating Characteristics (continued)

(VCC = +5V, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047µF, C3 = 1µF, C4 = 10nF, TA= +25°C, unless otherwise noted.)

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

_______________________________________________________________________________________ 7

5V/div

10V/div

100µs/div

+50V

POWER-UP DELAY

(VISOCOM = +50V)

MAX3158 toc19

0.1 1 10

MAXIMUM COMMON-MODE VOLTAGE TO

GROUND vs. COMMON-MODE FREQUENCY

MAX3158 toc20

COMMON-MODE FREQUENCY (kHz)

COMMON-MODE VOLTAGE TO GROUND (V)

MAXIMUM COMMON-MODE

VOLTAGE TO ISOCOM

COMMON-MODE VOLTAGE TO

ISOCOM = 7V PEAK

Test Circuits and Timing Diagrams

VOD

VOC

Figure 1. Driver DC Test Load

CL1

CL2

RDIFF

VID

Figure 3. Driver Timing Test Circuit

RECEIVER

OUTPUT

TEST POINT

1kΩ

VCC

100pF OUTPUT

UNDER TEST

500ΩS1

VCC

Figure 2. Receiver Enable/Disable Timing Test Load Figure 4. Driver Enable/Disable Timing Test Load

Typical Operating Characteristics (continued)

(VCC = +5V, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047µF, C3 = 1µF, C4 = 10nF, TA= +25°C, unless otherwise noted.)

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

8 _______________________________________________________________________________________

-VO

1.5V

tDPLH

1/2 VO

10%

tDR

90% 90%

tDPHL

1.5V

1/2 VO

10%

tDF

VDIFF = V (Y) - V (Z)

VDIFF

tDSKEW = | tDPLH - tDPHL |

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

Y, Z

VOL

Y, Z

1.5V 1.5V

VOL + 0.5V

VOH - 0.5V

2.3V

tDZL(SHDN), tDZL tDLZ

tDZH(SHDN), tDZH tDHZ

Figure 5. Driver Propagation Delays

Figure 6. Driver Enable and Disable Times

VOH

VOL

-1V

1.5V 1.5V

OUTPUT

INPUT

tRPLH

tRPHL

tRSKEW = | tRPLH - tRPHL |

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

VCC

1.5V 1.5V

VOL + 0.5V

VOH - 0.5V

1.5V

tRZL(SHDN), tRZL tRLZ

tRZH(SHDN), tRZH tRHZ

Figure 7. Receiver Propagation Delays

Figure 8. Receiver Enable and Disable Times

RECEIVER

OUTPUT

ATE

VID R

Figure 9. Receiver Propagation Delay Test Circuit

Test Circuits and Timing Diagrams (continued)

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

_______________________________________________________________________________________ 9

Pin Description

SSOP

PDIP NAME FUNCTION

12 RO

Receiver Output. When RE is low and A - B > -50mV, RO will be high; if A - B ≤ -200mV,

RO will be low.

23 RE Receiver Output Enable. Drive RE low to enable RO.

3 4 DE Driver Output Enable. Drive DE high to enable driver outputs.

45 DI

Driver Input. With DE high, a low on DI forces the noninverting output low and the inverting

output high; with DI high, outputs reverse.

5 6 C1LO Connect to the negative terminal of C1 (0.047µF, 100V).

6, 7,

12, 22,

1, 12,

14, 15,

N.C. No Connection. Not internally connected.

8 7 C1HI Connect to the positive terminal of C1 (0.047µF, 100V).

9 8 ISOVCC Internally generated power-supply voltage, referenced to the cable ground (ISOCOM).

Connect a 1µF capacitor to ISOCOM.

10 9 H/FHalf/Full-Duplex Selector Pin. Leave open, or connect to ISOCOM to select Full Duplex,

or connect to ISOVCC to select Half Duplex.

11 10 ZR Connect to ISOCOM for a 1.5kΩ input impedance on Z. Leave open for a 12kΩ input

impedance on Z.

13 11 YR Connect to ISOCOM for a 1.5kΩ input impedance on Y. Leave open for a 12kΩ input

impedance on Y.

14 13

ISOCOM

Cable Ground

15 16 Z Inverting Driver Output (and Inverting Receiver Input in Half-Duplex Mode)

16 17 Y Noninverting Driver Output (and Noninverting Receiver Input in Half-Duplex Mode)

17 18 B Inverting Receiver Input in Full-Duplex Mode

18 19 A Noninverting Receiver Input in Full-Duplex Mode

19 20 BR Connect to ISOCOM for a 1.5kΩ input impedance on B. Leave open for a 12kΩ input

impedance on B.

20 21 AR Connect to ISOCOM for a 1.5kΩ input impedance on A. Leave open for a 12kΩ input

impedance on A.

21 22 C2HI Connect to the positive terminal of C2 (0.047µF, 100V).

24 23 C2LO Connect to the negative terminal of C2 (0.047µF, 100V).

25 24 GND Ground

26 25 TXP Transmitter Phase. Leave open, or connect to GND for normal transmitter polarity, or connect

to VCC to invert the transmitter polarity.

27 26 RXP Receiver Phase. Leave open, or connect to GND for normal receiver polarity, or connect to

VCC to invert the receiver polarity.

28 27 VCC +4.75V to +5.25V Positive Supply. Connect a 0.1µF capacitor to GND.

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

10 ______________________________________________________________________________________

Detailed Description

The MAX3158 is a high CMRR RS-485/RS-422 data-

communications interface providing ±60V isolation in a

hybrid microcircuit. A single +5V supply on the logic

side powers both sides of the interface, with external

100V capacitors transferring power from the logic side

to the isolated side (see Block Diagram). The MAX3158

typically draws 25mA of supply current when unloaded

or when fully loaded with the driver disabled. Supply

current drops to 25µA when the device is placed in

shutdown mode (see Low-Power Shutdown Mode sec-

tion). The MAX3158 transceiver for RS-485/RS-422

communication contains one driver and one receiver.

This device features fail-safe circuitry, which guaran-

tees 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 dis-

abled (see Fail-Safe section). The MAX3158 is selec-

table between half- and full-duplex communication by

connecting a selector pin to ISOVCC or ISOCOM,

respectively. Drivers are output short-circuit current lim-

ited. Thermal shutdown circuitry protects drivers

against excessive power dissipation. When activated,

the thermal shutdown circuitry places the driver outputs

into a high-impedance state. The device also features

independently programmable receiver and transmitter

output phase through separate pins. The MAX3158 is a

low-cost replacement for opto-isolated transceivers.

Fail-Safe

The MAX3158 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. The receiver threshold is fixed

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 volt-

age is pulled to 0V by the termination. With the receiver

thresholds of the MAX3158, this results in a logic high

with a 50mV minimum noise margin. Unlike competitor’s

fail-safe devices, the -50mV to -200mV threshold com-

plies with the ±200mV EIA/TIA-485 standard.

MAX3158 Programming

The MAX3158 has several programmable operating

modes. Occasionally, twisted-pair lines are reversed.

The MAX3158 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 driver phase, drive TXP high or

connect it to VCC. To invert the receiver phase, drive

RXP high or connect it to VCC. Note that the receiver

threshold is positive when RXP is high.

The MAX3158 can operate in full- or half-duplex mode.

Connect H/Fto ISOCOM for full-duplex mode, and con-

nect it to ISOVCC for half-duplex operation. 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 A and B.

Low-Power Shutdown Mode

The low-power shutdown mode is initiated by bringing

both RE high and DE low. In shutdown, this device typi-

cally draws only 25µA of supply current, and no power

is transferred across the isolation capacitors in this

mode. 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 700ns, the parts are guaranteed

to enter shutdown. Enable times t_ZH and t_ZL in the

Switching Characteristics table 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_ZL(SHDN) than from driver/receiver-disable mode

(t_ZH, t_ZL).

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—typically around +150°C.

Applications Information

Capacitor and Grounding Resistor

Selection

The value for the charge-pump capacitors C1 and C2

should be between 47nF and 100nF. Smaller values will

result in insufficient supply voltage on the isolated side.

Larger values are allowed but will not result in better

charge-pump capacity. The values for C1 and C2, as

well as that of C4, determine the maximum frequency

and amplitude of the voltage difference (under operat-

ing conditions) between the local and isolated ground.

Besides the capacitor values, this maximum frequency

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

______________________________________________________________________________________ 11

TXP

RXP

VCC

OSC POWER

GND C1L C2L C1H C2H ISOCOM

H/F

ISOVCC

H/F

MAX3158

and amplitude are also determined by the resistance

between the remote ground and the ISOCOM pin. The

receiver input resistors will cause the isolated common

voltage to go to the mean voltage of the receiver inputs,

which will be a direct function of the remote ground

potential. The receiver input resistance and the capaci-

tors C1, C2, and C4 set up a time constant that limits

how fast the ISOCOM pin can follow variations in the

remote ground voltage. Connecting YR and ZR in half-

duplex operation, or AR and BR in full-duplex operation,

to ISOCOM results in a relatively low input impedance of

the MAX3158 receiver inputs (2kΩ). This allows for a

60Hz sine wave with a 60V maximum amplitude (see

Typical Operating Characteristics). If YR, ZR, AR, and

BR are left open, the receiver input impedance is 12kΩ

allowing up to 32 transceivers on the bus. To guarantee

the same low time constant under those conditions, use

a shielded cable with a 1kΩresistor connected between

the shield and ISOCOM. Using a lower value for this

resistor is not recommended because this could trigger

a holding current in the internal ESD protection device if

the ±75V isolation limit is exceeded.

A single point hard-ground connection for the shield is

recommended.

Communication Between

Two MAX3158s

If two MAX3158 devices are used to communicate with

each other, one of the devices must have ISOCOM

connected to local ground. Failure to do so will result in

floating ISOCOM pins, with both devices trying to adapt

to the isolated ground of the other.

Chip Information

TRANSISTOR COUNT: 1309

Block Diagram

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

12 ______________________________________________________________________________________

VCC

RXP

TXP

GND

C2LO

N.C.

C2HI

ISOCOM

N.C.

H/F

ISOVCC

C1HI

N.C.

C1LO

28 SSOP

TOP VIEW

MAX3158

VCC

N.C.

RXP

TXP

GND

C2LO

N.C.

C2HI

ISOCOM

N.C.

H/F

ISOVCC

C1HI

C1LO

N.C.

28 PDIP

MAX3157MAX3158

Pin Configurations

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

______________________________________________________________________________________ 13

SSOP.EPS

PACKAGE OUTLINE, SSOP, 5.3 MM

21-0056 C

REV.DOCUMENT CONTROL NO.APPROVAL

PROPRIETARY INFORMATION

TITLE:

NOTES:

1. D&E DO NOT INCLUDE MOLD FLASH.

2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006").

3. CONTROLLING DIMENSION: MILLIMETERS.

4. MEETS JEDEC MO150.

5. LEADS TO BE COPLANAR WITHIN 0.10 MM.

7.90

0∞

0.301

0.025

8∞

0.311

0.037

0∞

7.65

0.63

8∞

0.95

MAX

5.38

MILLIMETERS

DIM

SEE VARIATIONS

0.0256 BSC

0.010

0.004

0.205

0.002

0.015

0.008

0.212

0.008

INCHES

MIN MAX

0.078

0.65 BSC

0.25

0.09

5.20

0.05

0.38

0.20

0.21

MIN

1.73 1.99

MILLIMETERS

6.07

10.07

8.07

7.07

INCHES

0.239

0.397

0.317

0.278

MIN

0.249

0.407

0.328

0.289

MAX MIN

6.33

10.33

8.33

7.33

14L

16L

28L

24L

20L

MAX N

eA1 L

0.068

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

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.

14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

MAX3158

High CMRR RS-485 Transceiver

with ±60V Isolation

PDIPN.EPS

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)