MAX13487EESA+T - Maxim Integrated Products, Inc.

General Description

The MAX13487E/MAX13488E +5V, half-duplex, ±15kV

ESD-protected RS-485/RS-422-compatible transceivers

feature one driver and one receiver. The MAX13487E/

MAX13488E include a hot-swap capability to eliminate

false transitions on the bus during power-up or live

insertion.

The MAX13487E/MAX13488E feature Maxim’s propri-

etary AutoDirection control. This architecture makes the

devices ideal for applications, such as isolated RS-485

ports, where the driver input is used in conjunction with

the driver-enable signal to drive the differential bus.

The MAX13487E features reduced slew-rate drivers

that minimize EMI and reduce reflections caused by

improperly terminated cables, allowing error-free trans-

mission up to 500kbps. The MAX13488E driver slew

rate is not limited, allowing transmit speeds up to

16Mbps.

The MAX13487E/MAX13488E feature a 1/4-unit load

receiver input impedance, allowing up to 128 trans-

ceivers on the bus. These devices are intended for half-

duplex communications. All driver outputs are

protected to ±15kV ESD using the Human Body Model.

The MAX13487E/MAX13488E are available in an 8-pin

SO package. The devices operate over the extended

-40°C to +85°C temperature range.

Applications

Isolated RS-485 Interfaces

Utility Meters

Industrial Controls

Industrial Motor Drives

Automated HVAC Systems

Features

♦+5V Operation

♦AutoDirection Enables Driver Automatically on

Transmission

♦Hot-Swappable for Telecom Applications

♦Enhanced Slew-Rate Limiting Facilitates Error-

Free Data Transmission (MAX13487E)

♦High-Speed Version (MAX13488E) Allows for

Transmission Speeds Up to 16Mbps

♦Extended ESD Protection for RS-485 I/O Pins

±15kV Human Body Model

♦1/4-Unit Load, Allowing Up to 128 Transceivers on

the Bus

♦8-Pin SO Package

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

________________________________________________________________

Maxim Integrated Products

19-0740; Rev 0; 1/07

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.

EVALUATION KIT

AVAILABLE

Ordering Information/

Selector Guide

PART PIN-

PACKAGE

SLEW-RATE

LIMITED

PKG

CODE

MAX13487EESA+ 8 SO Yes S8-2

MAX13488EESA+ 8 SO No S8-2

Denotes a lead-free package

Note: All devices operate over the -40°C to +85°C temperature

range.

Pin Configuration/Typical Application Circuit appear at end

of data sheet.

VCC 8

STATE

MACHINE

COM

GND

SHDN

VDT

MAX13487E

MAX13488E

Functional Diagram

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.

(All voltages referenced to GND.)

Supply Voltage VCC ...............................................................+6V

SHDN, RE, DI..............................................................-0.3V to +6

A, B........................................................................... -8V to +13V

Short-Circuit Duration (RO, A, B) to GND ..................Continuous

Continuous Power Dissipation (TA= +70°C)

8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW

Operating Temperature Range ...........................-40°C to +85°C

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

Storage Temperature Range .............................-65°C to +150°C

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

ELECTRICAL CHARACTERISTICS

(VCC = +5V ±5%, 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

DRIVER

RDIFF = 100Ω, Figure 1 2.0 VCC

RDIFF = 54Ω, Figure 1 1.5Differential Driver Output VOD

No load VCC

Driver Common-Mode Output

Voltage VOC RL = 100Ω or 54Ω, Figure 1 VCC / 2 3 V

Driver Disable Threshold VDT Figure 2 (Note 2) +0.6 +1 V

Input-High Voltage VIH DI, SHDN, RE 2.0 V

Input-Low Voltage VIL DI, SHDN, RE 0.8 V

Input Current IIN DI, SHDN, RE ±1 µA

0V ≤ VOUT ≤ +12V +50 +250

Driver Short-Circuit Output

Current

(Note 3)

IOSD

-7V ≤ VOUT ≤ 0V -250 -50

(VCC - 1V) ≤ VOUT ≤ +12V 20 mA

Driver Short-Circuit Foldback

Output Current (Note 3) IOSDF -7V ≤ VOUT ≤ 0V -20

RECEIVER

VIN = +12V 250

Input Current

(A and B) IA, B DI = VCC, VCC

= GND or +5V VIN = -7V -200 µA

Receiver Differential Threshold

Voltage VTH -7V ≤ VCM ≤ +12V -200 +200 mV

Receiver Input Hysteresis ΔVTH VA + VB = 0V 25 mV

Output-High Voltage VOH IO = -1.6mA, VA - VB > VTH VCC -

1.5 V

Output-Low Voltage VOL IO = 1mA, VA - VB < -VTH 0.4 V

Tri-State Output Current at

Receiver IOZR 0V ≤ VO ≤ VCC ±1 µA

Receiver Input Resistance RIN -7V ≤ VCM ≤ +12V 48 kΩ

Receiver Output Short-Circuit

Current IOSR 0V ≤ VRO ≤ VCC ±7 ±95 mA

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +5V ±5%, 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

POWER SUPPLY

Supply Voltage VCC 4.75 5.25 V

Supply Current ICC SHDN = 1, RE = 0, no load 4.5 mA

Shutdown Supply Current ISHDN SHDN = 0 10 µA

ESD PROTECTION

Air Gap Discharge IEC 61000-4-2

(MAX13487E) ±15

ESD Protection (A, B)

Human Body Model ±15

ESD Protection (All Other Pins) Human Body Model ±2 kV

SWITCHING CHARACTERISTICS—MAX13487E

(VCC = +5V ±5%, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DRIVER

tDPLH 200 1000

Driver Propagation Delay tDPHL

RL = 110Ω, CL = 50pF, Figures 2 and 3 200 1000 ns

tHL 200 900

Driver Differential Output Rise or

Fall Time tLH

RL = 110Ω, CL = 50pF, Figures 2 and 3 200 900 ns

Maximum Data Rate 500 kbps

Driver Disable Delay tDDD Figure 3 2500 ns

Driver Enable from Shutdown to

Output High tDZH

(

SHDN

)

Figure 4 5.5 µs

Driver Enable from Shutdown to

Output Low tDZL

(

SHDN

)

Figure 4 5.5 µs

Time to Shutdown tSHDN 50 340 700 ns

RECEIVER

tRPLH 80

Receiver Propagation Delay tRPHL

CL = 15pF, Figures 5 and 6 80 ns

Receiver Output Skew tRSKEW CL = 15pF, Figure 6 13 ns

Maximum Data Rate 500 kbps

Receiver Enable to Output High tRZH Figure 7 50 ns

Receiver Enable to Output Low tRZL Figure 7 50 ns

Receiver Disable Time from High tRHZ Figure 7 50 ns

Receiver Disable Time from Low tRLZ Figure 7 50 ns

Receiver Enable from Shutdown

to Output High

tRZH

(SHDN) Figure 8 2200 ns

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

4 _______________________________________________________________________________________

SWITCHING CHARACTERISTICS—MAX13487E (continued)

(VCC = +5V ±5%, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Receiver Enable from Shutdown

to Output Low

tRZL

(SHDN) Figure 8 2200 ns

Receiver Enable Delay tRED Figure 3 70 ns

Time to Shutdown tSHDN 50 340 700 ns

SWITCHING CHARACTERISTICS—MAX13488E

(VCC = +5V ±5%, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DRIVER

tDPLH 50

Driver Propagation Delay tDPHL

RL = 110Ω, CL = 50pF, Figures 2 and 3 50 ns

tHL 15

Driver Differential Output Rise or

Fall Time tLH

RL = 110Ω, CL = 50pF, Figures 2 and 3 15 ns

Maximum Data Rate 16 Mbps

Driver Disable Delay tDDD Figure 3 70 ns

Driver Enable from Shutdown to

Output High tDZH

(

SHDN

)

Figure 4 2.2 µs

Driver Enable from Shutdown to

Output Low tDZL

(

SHDN

)

Figure 4 2.2 µs

Time to Shutdown tSHDN 50 340 700 ns

RECEIVER

tRPLH 80

Receiver Propagation Delay tRPHL

CL = 15pF, Figures 5 and 6 80 ns

Receiver Output Skew tRSKEW CL = 15pF, Figure 6 13 ns

Maximum Data Rate 16 Mbps

Receiver Enable to Output High tRZH Figure 7 50 ns

Receiver Enable to Output Low tRZL Figure 7 50 ns

Receiver Disable Time from High tRHZ Figure 7 50 ns

Receiver Disable Time from Low tRLZ Figure 7 50 ns

Receiver Enable from Shutdown

to Output High

tRZH

(SHDN) Figure 8 2200 ns

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

_______________________________________________________________________________________ 5

SWITCHING CHARACTERISTICS—MAX13488E (continued)

(VCC = +5V ±5%, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Receiver Enable from Shutdown

to Output Low

tRZL

(SHDN) Figure 8 2200 ns

Receiver Enable Delay tRED Figure 3 70 ns

Time to Shutdown tSHDN 50 340 700 ns

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

unless otherwise noted.

Note 2: This is a differential voltage from A to B that the driving device must see on the bus to disable its driver.

Note 3: The short-circuit output current applied to peak current just prior to foldback current limiting. The short-circuit foldback out-

put current applies during current limiting to allow a recovery from bus contention.

Typical Operating Characteristics

(VCC = +5.0V, TA= +25°C, unless otherwise noted.)

SUPPLY CURRENT vs. TEMPERATURE

MAX13487Etoc01

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

603510-15

3.2

3.4

3.6

3.8

4.0

3.0

-40 85

NO LOAD

OUTPUT CURRENT

vs. RECEIVER OUTPUT-HIGH VOLTAGE

MAX13487Etoc02

OUTPUT-HIGH VOLTAGE (V)

OUTPUT CURRENT (mA)

4321

OUTPUT CURRENT

vs. RECEIVER OUTPUT-LOW VOLTAGE

MAX13487Etoc03

OUTPUT-LOW VOLTAGE (V)

OUTPUT CURRENT (mA)

4321

RECEIVER OUTPUT-HIGH VOLTAGE

vs. TEMPERATURE

MAX13487Etoc04

TEMPERATURE (°C)

OUTPUT-HIGH VOLTAGE (V)

603510-15

4.2

4.6

4.4

4.8

5.0

5.2

5.4

4.0

-40 85

IO = 1mA

RECEIVER OUTPUT-LOW

VOLTAGE vs. TEMPERATURE

MAX13487Etoc05

TEMPERATURE (°C)

OUTPUT-LOW VOLTAGE (V)

603510-15

0.1

0.2

0.3

0.4

0.5

-40 85

IO = 1mA

DIFFERENTIAL OUTPUT CURRENT

vs. DIFFERENTIAL OUTPUT VOLTAGE

MAX13487Etoc06

OUTPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

4321

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

6 _______________________________________________________________________________________

DRIVER DIFFERENTIAL OUTPUT VOLTAGE

vs. TEMPERATURE

MAX13487Etoc07

TEMPERATURE (°C)

DIFFERENTIAL OUTPUT VOLTAGE (V)

603510-15

0.5

1.0

1.5

2.0

2.5

3.0

-40 85

RDIFF = 54Ω

OUTPUT CURRENT

vs. TRANSMITTER OUTPUT-HIGH VOLTAGE

MAX13487Etoc08

OUTPUT-HIGH VOLTAGE (V)

OUTPUT CURRENT (mA)

3-1-3-5 1 402-2-4-6

100

120

-7 5

OUTPUT CURRENT

vs. TRANSMITTER OUTPUT-LOW VOLTAGE

MAX13487Etoc09

OUTPUT-LOW VOLTAGE (V)

OUTPUT CURRENT (mA)

108624

100

120

012

SHUTDOWN CURRENT vs. TEMPERATURE

MAX13487Etoc10

TEMPERATURE (°C)

SHUTDOWN CURRENT (μA)

603510-15

-40 85

DRIVER PROPAGATION vs. TEMPERATURE

(MAX13487E)

MAX13487Etoc12

TEMPERATURE (°C)

DRIVER PROPAGATION DELAY (ns)

603510-15

200

100

300

400

500

600

-40 85

tDPLH

tDPHL

RL = 110Ω

DRIVER PROPAGATION vs. TEMPERATURE

(MAX13487E)

MAX13487Etoc11

TEMPERATURE (°C)

DRIVER PROPAGATION DELAY (ns)

603510-15

200

400

600

800

1000

-40 85

tDPLH

tDPHL

RL = 10kΩ

RECEIVER PROPAGATION vs. TEMPERATURE

(MAX13487E)

MAX13487Etoc15

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

603510-15

-40 85

tRPHL

tRPLH

DRIVER PROPAGATION vs. TEMPERATURE

(MAX13488E)

MAX13487Etoc13

TEMPERATURE (°C)

DRIVER PROPAGATION DELAY (ns)

603510-15

-40 85

tDPLH

tDPHL

RL = 10kΩ

DRIVER PROPAGATION vs. TEMPERATURE

(MAX13488E)

MAX13487Etoc14

TEMPERATURE (°C)

DRIVER PROPAGATION DELAY (ns)

603510-15

-40 85

tDPLH

tDPHL

RL = 110Ω

Typical Operating Characteristics (continued)

(VCC = +5.0V, TA= +25°C, unless otherwise noted.)

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

_______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VCC = +5.0V, TA= +25°C, unless otherwise noted.)

RECEIVER PROPAGATION vs. TEMPERATURE

(MAX13488E)

MAX13487Etoc16

TEMPERATURE (°C)

RECEIVER PROPAGATION (ns)

603510-15

-40 85

tRPLH

tRPHL

DRIVER PROPAGATION (500kbps)

(MAX13487E)

MAX13487Etoc17

2V/div

A-B

5V/div

400ns/div

DRIVER PROPAGATION (16Mbps)

(MAX13488E)

MAX13487Etoc18

2V/div

A-B

5V/div

10ns/div

WAVEFORM INTENSITY: 68%

RECEIVER PROPAGATION (16Mbps)

(MAX13488E)

MAX13487Etoc19

2V/div

10ns/div

DRIVING 16nF (19.2kbps)

(MAX13487E)

MAX13487Etoc20

2V/div

A-B

5V/div

10μs/div

DRIVING 16nF (19.2kbps)

(MAX13488E)

MAX13487Etoc21

2V/div

A-B

5V/div

10μs/div

DRIVING 16nF (750kbps)

(MAX13488E)

MAX13487Etoc22

2V/div

A-B

5V/div

400ns/div

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

8 _______________________________________________________________________________________

VOD CL

RDIFF 2

RDIFF 2VOC

Figure 1. Driver DC Test Load

VID

VCC

GND CL

Figure 2. Driver-Timing Test Circuit

1.5V 1.5V

tDPLH tDPHL

1/2 VO

tDDD, tRED

(RO PULLED LOW)

10%

90%

10%

90%

-VO

VDIFF

VDIFF = V(A) - V(B)

tHL

tLH

f = 1MHz, tLH ≤ 3ns, tHL ≤ 3ns

VCC

RE = VCC

Figure 3. Driver Propagation Delays

Test Circuits and Waveforms

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

_______________________________________________________________________________________ 9

tDZH(SHDN)

tDZL(SHDN)

1.5V

2.3V

OUTPUT NORMALLY HIGH

OUTPUT NORMALLY LOW

VCC

A, B

VOL

SHDN

500Ω

OUTPUT

UNDER TEST

Figure 4. Driver Enable and Disable Times

VID

RRECEIVER

OUTPUT

ATE

Figure 5. Receiver-Propagation-Delay Test Circuit

1.5V 1.5V

-1V

f = 1MHz, tLH ≤ 3ns, tHL ≤ 3ns

tRPHL

tRSKEW = | tRPHL - tRPLH |

tRPLH

VOH

VOL

Figure 6. Receiver Propagation Delays

Test Circuits and Waveforms (continued)

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

10 ______________________________________________________________________________________

1.5V 1.5V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

tRZH(SHDN), tRZH t

RHZ

tRHZ

2.3V

2.3V VOH + 0.5V

VOH + 0.5V

DI = 0V

VCC

tRZL(SHDN), tRZL

Figure 7. Receiver Enable and Disable Times

tRZH(SHDN)

tRZL(SHDN)

1.5V

2.3V

OUTPUT NORMALLY HIGH

OUTPUT NORMALLY LOW

VCC

SHDN

500Ω

DI = 1

Figure 8. Receiver Enable Time from Shutdown

Test Circuits and Waveforms (continued)

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

______________________________________________________________________________________ 11

Pin Description

PIN NAME FUNCTION

1RO

Receiver Output. When receiver is enabled and V(A) - V(B) > +200mV, RO is high. If V(A) - V(B)

< -200mV, RO is low.

2RE Receiver Output Enable. Drive RE low to enable the RO. Drive RE high to let the AutoDirection circuit

control the receiver. RE is a hot-swap input (see the Hot-Swap Capability section for more details).

3SHDN Shutdown. Drive SHDN high to let the device operate in normal operation. Drive SHDN low to put the part

in shutdown.

4DI

Driver Input. Drive DI low to force noninverting output low and inverting output high. Drive DI high to force

noninverting output high and inverting output low. DI is an input to the internal state machine that

automatically enables and disables the driver. See the Function Tables and General Description for more

information. DI is a hot-swap input (see the Hot-Swap Capability section for more details).

5 GND Ground

6 A Noninverting Receiver Input and Noninverting Driver Output

7 B Inverting Receiver Input and Inverting Driver Output

CC Positive Supply, VCC = +5V ±5%. Bypass VCC to GND with a 0.1µF capacitor.

TRANSMITTING

INPUTS OUTPUTS

SHDN DI A-B > VDT ACTION A B

1 0 X Turn driver ON 0 1

1 1 False If driver was OFF, keep it OFF HIGH IMPEDANCE HIGH IMPEDANCE

1 1 False If driver was ON, keep it ON 1 0

1 1 True Turn driver OFF HIGH IMPEDANCE HIGH IMPEDANCE

0 X X X SHUTDOWN

RECEIVING

INPUTS OUTPUT

SHDN RE A-B DRIVER STATE RECEIVER STATE RO

10≥+200mV X ON 1

10≤-200mV X ON 0

1 1 X ON OFF HIGH IMPEDANCE

11≥+200mV OFF ON 1

11≤-200mV OFF ON 0

0 X X X X SHUTDOWN

Function Tables

X = Don’t care, shutdown mode, driver, and receiver outputs are in high impedance.

MAX13487E/MAX13488E

Detailed Description

The MAX13487E/MAX13488E half-duplex, high-speed

transceivers for RS-485/RS-422 communication contain

one driver and one receiver. The MAX13487E/

MAX13488E feature a hot-swap capability allowing line

insertion without erroneous data transfer (see the

Hot-

Swap Capability

section). The MAX13487E features

reduced slew-rate drivers that minimize EMI and

reduce reflections caused by improperly terminated

cables, allowing error-free transmission up to 500kbps.

The MAX13488E driver slew rate is not limited, making

data throughput of up to 16Mbps possible.

AutoDirection Circuitry

Internal circuitry in the MAX13487E/MAX13488E, in

conjunction with an external pullup resistor on A and

pulldown resistor on B (see

Typical Application Circuit

act to automatically disable or enable the driver and

receiver to keep the bus in the correct state. This

AutoDirection circuitry consists of a state machine and

an additional receive comparator that determines

whether this device is trying to drive the bus, or another

node on the network is driving the bus.

The internal state machine has two inputs:

•DI

• The current state of A-B (determined by a dedicated

differential comparator)

The state machine also has two outputs:

• DRIVER_ENABLE—Internal signal that enables and

disables the driver

• RECEIVER_ENABLE—Internal signal that is the

inverse of the DRIVER_ENABLE signal, but it can be

overridden by an external pin

When DI is low, the device always drives the bus low.

When DI is high, the device drives the bus for a short

time, then disables the driver and allows the external

pullup/pulldown resistors to hold the bus in the high

state (A-B > 200mV). During each low-to-high transition

of DI, the driver stays enabled until (A-B) > VDT, and

then disables the driver, letting the pullup/pulldown

resistors hold the A and B lines in the correct state.

Pullup and Pulldown Resistors

The pullup and pulldown resistors on the A and B lines

are required for proper operation of the device

although their exact value is not critical. They function

to hold the bus in the high state (A-B > 200mV) follow-

ing a low-to-high transition. Sizing of these resistors is

determined in the same way as when using any other

RS-485 driver and depends on how the line is terminat-

ed and how many nodes are on the bus. The most

important factor when sizing these resistors is to guar-

antee that the idle voltage on the bus (A-B) is greater

than 200mV in order to remain compatible with stan-

dard RS-485 receiver thresholds.

Idle State

When not transmitting data, the MAX13487E/

MAX13488E require the DI input be driven high to

remain in the idle state. A conventional RS-485 trans-

ceiver has DE and RE inputs that are used to enable

and disable the driver and receiver. However, the

MAX13487E/MAX13488E does not have a DE input,

and instead uses an internal state machine to enable

and disable the drivers. DI must be driven high in order

to go to the idle state.

Hot-Swap Capability

Hot-Swap Inputs

When circuit boards are inserted into a hot or powered

back plane, differential disturbances to the data bus

can lead to data errors. Upon initial circuit-board inser-

tion, the data communication processor undergoes its

own power-up sequence. During this period, the

processor’s logic-output drivers are high impedance

and are unable to drive the DI and RE inputs of these

devices to a defined logic level. Leakage currents up to

±10µA from the high-impedance state of the proces-

sor’s logic drivers could cause standard CMOS enable

inputs of a transceiver to drift to an incorrect logic level.

Additionally, parasitic circuit-board capacitance could

cause coupling of VCC or GND to the enable inputs.

Without the hot-swap capability, these factors could

improperly enable the transceiver’s driver.

To overcome both these problems, two different pullup

switches (strong and weak) are turned on during the

power-up. When VCC rises, an internal power-up signal

enables a strong pullup circuit. It holds DI and RE high

with 1mA for 15µs. Once the timeout is expired, this

strong pullup is switched off. A weak pullup (100µA)

remains active to overcome leakage on the pin. This

second weak pullup disappears as soon as the micro-

controller forces a low state on these pins. Therefore, in

normal operation (after the first activation), these pins

can be considered as high-impedance pins (CMOS

inputs) without any pullup circuitry.

The AutoDirection state machine is initialized, forcing the

driver disabled. The receiver is enabled in AutoDirection

mode.

Hot-Swap Input Circuitry

The enable inputs feature hot-swap capability. At the

input there are two pMOS devices, M1 and M2 (Figure 9).

When VCC ramps from zero, an internal 15µs timer turns

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

12 ______________________________________________________________________________________

on M2 and sets the SR latch, which also turns on M1.

Transistors M2, a 1.5mA current source, and M1, a 500µA

current source, pull RE to VCC through a 5kΩresistor. M2

is designed to pull RE to the disabled state against an

external parasitic capacitance up to 100pF that can drive

RE high. After 15µs, the timer deactivates M2 while M1

remains on, holding DI high against three-state leakages

that can drive RE low. M1 remains on until an external

source overcomes the required input current. At this time,

the SR latch resets and M1 turns off. When M1 turns off,

RE reverts to a standard, high-impedance CMOS input.

Whenever VCC drops below 1V, the hot-swap input is

reset. DI has similar hot-swap circuitry.

±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

MAX13487E/MAX13488E 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. The ESD structures

withstand high ESD in all states: normal operation, shut-

down, and powered down. After an ESD event, the

MAX13487E/MAX13488E keep working without latchup

or damage.

ESD protection can be tested in various ways. The

transmitter outputs and receiver inputs of the

MAX13487E/MAX13488E are characterized for protec-

tion to the following limits:

• ±15kV using the Human Body Model

• ±15kV using the Air Gap Discharge Method speci-

fied in IEC 61000-4-2 (MAX13487E only)

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 10a shows the Human Body Model, and Figure

10b 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 1.5kΩresistor.

IEC 61000-4-2

The IEC 61000-4-2 standard covers ESD testing and

performance of finished equipment. However, it does

not specifically refer to integrated circuits. The

MAX13487E/MAX13488E help you design equipment to

meet IEC 61000-4-2 without the need for additional

ESD-protection components.

The major difference between tests done using the

Human Body Model and IEC 61000-4-2 is higher peak

current in IEC 61000-4-2 because series resistance is

lower in the IEC 61000-4-2 model. Hence, the ESD

withstand voltage measured to IEC 61000-4-2 is gener-

ally lower than that measured using the Human Body

Model. Figure 10c shows the IEC 61000-4-2 model,

and Figure 10d shows the current waveform for IEC

61000-4-2 ESD Contact Discharge test.

Machine Model

The machine model for ESD tests all pins using a 200pF

storage capacitor and zero discharge resistance.

The objective is to emulate the stress caused when I/O

pins are contacted by handling equipment during test

and assembly. Of course, all pins require this protec-

tion, not just RS-485 inputs and outputs.

The Air-Gap test involves approaching the device with a

charged probe. The Contact-Discharge method connects

the probe to the device before the probe is energized.

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

______________________________________________________________________________________ 13

VCC

M1 M2

100μA

500μA

5kΩ

SR LATCH

15μs

VCC

TIMER

(HOT SWAP)

Figure 9. Simplified Structure of the Receiver Enable Pin (RE)

MAX13487E/MAX13488E

Applications Information

128 Transceivers on the Bus

The standard RS-485 receiver input impedance is 12kΩ

(1-unit load), and the standard driver can drive up to

32-unit loads. The MAX13487E/MAX13488E have a 1/4-

unit load receiver input impedance (48kΩ), allowing up

to 128 transceivers to be connected in parallel on one

communication line. Any combination of these devices,

as well as other RS-485 transceivers with a total of 32-

unit loads or fewer, can be connected to the line.

Reduced EMI and Reflections

The MAX13487E features reduced slew-rate drivers

that minimize EMI and reduce reflections caused by

improperly terminated cables, allowing error-free data

transmission up to 500kbps.

Low-Power Shutdown Mode

Low-power shutdown mode is initiated by bringing

SHDN low. In shutdown, the devices draw a maximum

of 10µA of supply current.

The devices are guaranteed not to enter shutdown if

SHDN is low for less than 50ns. If the inputs are in this

state for at least 700ns, the devices are guaranteed to

enter shutdown.

Enable times tZH and tZL (see the

Switching Character-

istics

section) assume the devices were not in a low-

power shutdown state. Enable times tZH(SHDN) and

tZL(SHDN) assume the devices were in shutdown state. It

takes drivers and receivers longer to become enabled

from low-power shutdown mode (tZH(SHDN), tZL(SHDN))

than from driver/receiver-disable mode (tZH, tZL).

Line Length

The RS-485/RS-422 standard covers line lengths up to

4000ft.

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

14 ______________________________________________________________________________________

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

100pF

1MΩ

1500Ω

HIGH-

VOLTAGE

SOURCE

DEVICE

UNDER

TEST

Figure 10a. Human Body ESD Test Model

IP 100%

90%

36.8%

tRL TIME

tDL

CURRENT WAVEFORM

PEAK-TO-PEAK RINGING

(NOT DRAWN TO SCALE)

10%

AMPS

Figure 10b. Human Body Current Waveform

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

150pF

50MΩ TO 100MΩ

330Ω

HIGH-

VOLTAGE

SOURCE

DEVICE

UNDER

TEST

Figure 10c. IEC 61000-4-2 ESD Test Model

tr = 0.7ns TO 1ns 30ns

60ns

100%

90%

10%

PEAK

Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform

Typical Applications

The MAX13487E/MAX13488E transceivers are

designed for half-duplex, bidirectional data communi-

cations on multipoint bus transmission lines. Figure 11

shows a typical network application. To minimize reflec-

tions, terminate the line at both ends in its characteristic

impedance, and keep stub lengths off the main line as

short as possible. The slew-rate-limited MAX13487E is

more tolerant of imperfect termination.

Isolated RS-485 Interface

An isolated RS-485 interface electrically isolates differ-

ent nodes on the bus to protect the bus from problems

due to high common-mode voltages that exceed the

RS-485 common-mode voltage range, conductive

noise, and ground loops. The

Typical Application

Circuit

shows an isolated RS-485 interface using the

MAX13487E/MAX13488E. The transceiver is powered

separately from the controlling circuitry. The

AutoDirection feature of the MAX13487E/MAX13488E

(see the

AutoDirection Circuitry

section), replaces an

external relay allowing faster switching speeds, no con-

tact bounce, better reliability, and better electrical isola-

tion. The MAX13487E/MAX13488E only require two

optocouplers to electrically isolate the transceiver.

Chip Information

PROCESS: BiCMOS

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

______________________________________________________________________________________ 15

DI DI

RO RO

RtRt

DI RO RE DI RO RE

SHDN SHDN

MAX13487E

MAX13488E

VCC

SHDN SHDN

Figure 11. Typical Half-Duplex RS-485 Network

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

16 ______________________________________________________________________________________

GND

VCC

VISO

VCC

SHDN

0.1μF

VISO

VSYS

RXD

TXD

Pin Configuration/Typical Application Circuit

MAX13487E/MAX13488E

Half-Duplex RS-485-/RS-422-Compatible

Transceiver with AutoDirection Control

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.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________

Boblet

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.)

SOICN .EPS

PACKAGE OUTLINE, .150" SOIC

21-0041 B

REV.DOCUMENT CONTROL NO.APPROVAL

PROPRIETARY INFORMATION

TITLE:

TOP VIEW

FRONT VIEW

MAX

0.010

0.069

0.019

0.157

0.010

INCHES

0.150

0.007

DIM

0.014

0.004

MIN

0.053A

0.19

3.80 4.00

0.25

MILLIMETERS

0.10

0.35

1.35

MIN

0.49

0.25

MAX

1.75

0.050

0.016L0.40 1.27

0.3940.386D

MINDIM

INCHES

MAX

9.80 10.00

MILLIMETERS

MIN MAX

16 AC

0.337 0.344 AB8.758.55 14

0.189 0.197 AA5.004.80 8

N MS012

SIDE VIEW

H 0.2440.228 5.80 6.20

e 0.050 BSC 1.27 BSC

eBA1

0∞-8∞

VARIATIONS: