Datasheet

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General Description

The MAX3157 is a high CMRR RS-485/RS-422 data-com-

munications interface providing ±50V isolation in a

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

powers both sides of the interface, with external ±50V

capacitors transferring power from the logic side to the

isolated side. Each MAX3157 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 MAX3157 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

independently programmable receiver and transmitter

output phase through separate pins. The MAX3157 is a

low-cost replacement for opto-isolated transceivers. For

fully isolated RS-485/RS-422 transceivers, refer to the

MAX1480 family data sheet.

________________________Applications

Industrial Controls

Level Translators

Telecommunications

Local Area Networks

Features

♦ ±50V 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

MAX3157

High CMRR RS-485 Transceiver

with ±50V Isolation

________________________________________________________________ Maxim Integrated Products 1

MAX3157

C1HI C2LO C2HIC1LO

TXP

RXP

GND

MICRO

RT = 100Ω

0.1µF

1µF

10nF

0.047µF

±50V

GND OFFSET

ISOCOM

REMOTE GND

REMOTE MICRO

RS-485

NODE

H/F

ISOV

Typical Operating Circuit

19-1778; Rev 3; 11/01

Ordering Information

Pin Configurations appear at end of data sheet.

PART TEMP. RANGE

PIN-PACKAGE

MAX3157CAI 0°C to +70°C 28 SSOP

MAX3157EAI -40°C to +85°C 28 SSOP

MAX3157CPI 0°C to +70°C 28 PDIP

MAX3157EPI -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.

Summary of content (13 pages)

PAGE 1
9-1778; Rev 3; 11/01 High CMRR RS-485 Transceiver with ±50V Isolation Features ♦ ±50V 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 Ordering Information ___
PAGE 2
MAX3157 High CMRR RS-485 Transceiver with ±50V Isolation ABSOLUTE MAXIMUM RATINGS All voltages referenced to GND unless otherwise noted. 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).................
PAGE 3
High CMRR RS-485 Transceiver with ±50V Isolation (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 Output Leakage (Y and Z) Full Duplex Driver Short-Circuit Output Current (Note 3) SYMBOL CONDITIONS MIN DE = GND, VCC = GND or 5.25V, -7V ≤ (VIN VISOCOM) ≤ 12V, YR = ZR = ISOCOM -5.0 8.0 DE = GND, VCC = GND or 5.25V, -7V ≤ (VIN VISOCOM) ≤ 12V, YR open, ZR open -0.
PAGE 4
MAX3157 High CMRR RS-485 Transceiver with ±50V Isolation SWITCHING CHARACTERISTICS (continued) (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.
PAGE 5
High CMRR RS-485 Transceiver with ±50V Isolation SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE 100 80 60 40 100 0 VISOCOM = 0 -100 VISOCOM = +50V NO LOAD 30 25 20 15 5 -300 0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 TEMPERATURE (°C) TEMPERATURE (°C) RECEIVER OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE 14 12 10 8 6 IRO = 8mA 0.40 0.30 0.25 0.20 0.15 4.25 4.20 4.15 4.10 0.10 4.05 2 0.05 4.00 0 3.
PAGE 6
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.) RECEIVER PROPAGATION DELAY vs. TEMPERATURE 1.92 1.90 1.88 1.86 470 460 450 440 1.84 430 1.82 420 1.80 410 RL = 54Ω 1.50 PROPAGATION DELAY (µs) 480 PROPAGATION DELAY (ns) OUTPUT VOLTAGE (V) 1.94 1.52 MAX3157toc11 RL = 54Ω 1.96 490 MAX3157toc10 1.98 DRIVER PROPAGATION DELAY vs.
PAGE 7
High CMRR RS-485 Transceiver with ±50V Isolation MAX3157 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.) POWER-UP DELAY (VISOCOM = +50V) DE 5V/div 0 +50V VY 10V/div 60 MAXIMUM COMMON PEAK VOLTAGE TO ISOCOM 50 40 COMMON-MODE VOLTAGE TO ISOCOM = 7V PEAK 30 20 10 0 0.
PAGE 8
High CMRR RS-485 Transceiver with ±50V Isolation MAX3157 Test Circuits and Timing Diagrams (continued) 3V 3V DI 1.5V RE 1.5V 0 1.5V 1/2 VO tRZL(SHDN), tRZL Z VO 1/2 VO 10% 1.5V OUTPUT NORMALLY LOW RO 1.5V tDR VOL + 0.5V OUTPUT NORMALLY HIGH VDIFF = V (Y) - V (Z) 90% 90% tRLZ VCC RO Y VO VDIFF 0 -VO 1.5V 0 tDPHL tDPLH 10% VOH - 0.5V 0 tRZH(SHDN), tRZH tDF tDSKEW = | tDPLH - tDPHL | Figure 5. Driver Propagation Delays tRHZ Figure 8. Receiver Enable and Disable Times 3V DE 1.
PAGE 9
High CMRR RS-485 Transceiver with ±50V Isolation PIN NAME FUNCTION SSOP PDIP 1 2 RO Receiver Output. When RE is low and A - B > -50mV, RO will be high; if A - B ≤ -200mV, RO will be low. 2 3 RE Receiver Output Enable. Drive RE low to enable RO. 3 4 DE Driver Output Enable. Drive DE high to enable driver outputs. 4 5 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.
PAGE 10
MAX3157 High CMRR RS-485 Transceiver with ±50V Isolation Detailed Description The MAX3157 is a high CMRR RS-485/RS-422 datacommunications interface providing ±50V isolation in a hybrid microcircuit. A single +5V supply on the logic side powers both sides of the interface, with external ±50V capacitors transferring power from the logic side to the isolated side (see Block Diagram). The MAX3157 typically draws 25mA of supply current when unloaded or when fully loaded with the driver disabled.
PAGE 11
High CMRR RS-485 Transceiver with ±50V Isolation Y DI Z TXP YR DE ZR RO A B RE RXP AR BR H/F VCC ISCOVCC POWER OSC GND C1L C2L 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.
PAGE 12
High CMRR RS-485 Transceiver with ±50V Isolation MAX3157 Pin Configurations TOP VIEW TOP VIEW RO 1 28 VCC N.C. 1 28 N.C. RE 2 27 RXP RO 2 27 VCC DE 3 26 TXP RE 3 26 RXP DI 4 25 GND DE 4 25 TXP 24 C2LO DI 5 C1LO 5 N.C. 6 MAX3157 23 N.C. C1LO 6 N.C. 7 22 N.C. C1HI 7 C1HI 8 21 C2HI 23 C2LO 22 C2HI ISOVCC 8 21 AR ISOVCC 9 20 AR H/F 9 20 BR H/F 10 19 BR ZR 10 19 A ZR 11 18 A YR 11 18 B N.C. 12 17 B N.C. 12 17 Y YR 13 16 Y ISOCOM 13 16 Z ISOCOM 14 15 Z N.C.
PAGE 13
High CMRR RS-485 Transceiver with ±50V Isolation SSOP.EPS PDIPN.EPS 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.