MAX3535EEVKIT+ - Maxim Integrated Products, Inc.

General Description

The MAX3535E evaluation kit (EV kit) is a fully assem-

bled and tested PCB that contains a 2500VRMS isolated

RS-485/RS-422 transceiver with ESD protection. The EV

kit circuit features a differential driver and one receiver.

The circuit’s receiver is a 1/8 unit load for the RS-485

bus and communicates up to 1000kbps. The MAX3535E

fail-safe circuitry and driver slew-rate features are demon-

strated and easily reconfigured.

Additionally, the EV kit features an H-bridge DC-DC

converter to power the isolated section of the MAX3535E

RS-485/RS-422 circuit. Input power to the circuit is

supplied by a +3V to +5.5VDC source. This circuit uses a

full-wave rectifier on the unregulated output and provides

unregulated voltage to the MAX3535E internal, linear

low-dropout (LDO) regulator. Using an H-bridge design

minimizes input ripple current and radiated noise.

Undervoltage lockout (UVLO) and thermal shutdown

provide for a robust, isolated RS-485/RS-422 transceiver

circuit and power supply. The surface-mount transformer

provides up to 2500VRMS galvanic isolation and the out-

put is powered from a center-tapped, full-wave rectifier

circuit to reduce output voltage ripple.

The isolated H-bridge DC-DC converter operation at

420kHz allows the use of ceramic-only output capaci-

tors and a small transformer.

Features

Designed for 2500VRMS Isolation

1/8 RS-485 Unit Load

1000kbps Full-Duplex RS-485/RS-422

Communication (Configurable for Half Duplex)

+3.0V to +5.5VDC Input Range

Isolated VCC2 Output

Center-Tapped, Full-Wave Rectifier Output

420kHz Switching Frequency

Undervoltage Lockout (UVLO) and Thermal

Shutdown

Low-Cost Integrated-FET H-Bridge Design

Fully Assembled and Tested

Evaluates: MAX3535E

MAX3535E Evaluation Kit

________________________________________________________________

Maxim Integrated Products

19-0716; Rev 0; 12/06

Component List

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.

Ordering Information

PART TEMP RANGE IC PACKAGE

MAX3535EEVKIT+ 0°C to +70°C* 28 Wide SO

DESIGNATION QTY DESCRIPTION

C1, C3 2

10µF ±10%, 10V X7R ceramic

capacitors (1206)

Murata GRM31CR71A106K

C2, C4 2

0.1µF ±10%, 25V X7R ceramic

capacitors (0805)

Murata GRM21BR71E104K

D1 1 30V , 200m A S chottky d i od e ( S O T- 23)

C entr al S em i cond uctor C BAT54C

JU1 1 3-pin header

JU2, JU3, JU4 3 2-pin headers

R1, R2 0 Not installed, resistors (0805)

10kΩ ±1% resistor recommended

R3, R4 2 100kΩ ±5% resistors (0805)

T1 1

500µH, 3kVRMS 1CT:1:33CT turns

transformer (6 pin)

HALO Electronics TGMR-340NA5RL

U1 1 MAX3535EEWI+ (28-pin Wide SO)

— 4 Shunts (JU1–JU4)

— 4 Rubber bumpers

— 1 PCB: MAX3535EEVKIT+

Denotes a lead-free and RoHS-compliant EV Kit.

This limited temperature range applies to the EV kit PCB only.

The MAX3535E IC temperature range is -40°C to +85°C.

Component Suppliers

SUPPLIER PHONE WEBSITE

C entr al

S emi cond uctor 631-435-1110 www.centralsemi.com

HALO Electronics 650-903-3800 w w w.haloel ectr oni cs.com

M urata M fg . C o., Ltd. 770-436-1300 www.murata.com

Note: Indicate that you are using the MAX3535E when contact-

ing these component suppliers.

Evaluates: MAX3535E

MAX3535E Evaluation Kit

2 _______________________________________________________________________________________

Quick Start

Required Equipment

• One 5V, 1A current-limited power supply with built-in

current meter

• One voltmeter

• One logic signal generator

• One oscilloscope

Procedure

The MAX3535E EV kit is fully assembled and tested.

Follow the steps below to verify board operation.

Caution: Do not turn on the power supply until all con-

nections are completed.

1) Connect a voltmeter to the VCC2 and SGND PC

pads.

2) Verify that a shunt is installed across pins 2-3 of

jumper JU1 (receiver enabled).

3) Verify that a shunt is not installed across the pins of

jumper JU2 (fast slew rate).

4) Verify that a shunt is installed across the pins of

jumpers JU3 and JU4 (half duplex).

5) Connect the +5V power supply to the VCC1 pad.

Connect the power supply’s ground to the GND

pad.

6) Turn on the power supply and verify that the volt-

meter at VCC2 reads over +5V.

7) Apply a logic signal to the DI PCB pad and GND.

Using an oscilloscope, verify the signal at the A-B,

RO2, and RO1 output pads.

The +5V supply powering the MAX3535E EV kit must

be current limited at 1A.

Detailed Description

The EV kit features a MAX3535E IC in a 28-pin wide SO

surface-mount package and demonstrates the

MAX3535E 2500VRMS isolated RS-485/RS-422 trans-

ceiver with ESD protection. The circuit’s differential dri-

ver and receiver are configurable for full- or half-duplex

operation and can communicate up to 1000kbps. The

circuit is a 1/8 unit load on the receiver’s bus.

The EV kit features PCB pads to ease interfacing with

logic signals for the driver and receiver signals. On the

nonisolated side, the DI pad is the driver input pad and

the RO1 pad is the receiver-signal output pad. Resistor

R3 pulls the DI pad up to VCC1, and resistor R4 pulls

the DE pad up to VCC1. On the isolated side, the RO2

pad is the receiver output.

The MAX3535E fail-safe circuitry signals are also provid-

ed on the RO1 (receiver output) and RO2 (isolated receiv-

er output) PC pads. Either pad gives a logic-high if A-B is

> -10mV, or if A-B floats or shorts. A logic-low is given if

A-B is < -200mV. Refer to the

Fail Safe

section and

Table

in the MAX3535E IC data sheet for additional informa-

tion on the fail-safe circuitry and operation.

The circuit’s input power is typically a +5VDC source,

or is operated from a +3V to +5.5VDC source with a

corresponding reduction in the output voltage on the

isolated side. The EV kit circuit’s DC source must pro-

vide at least 350mA of current, but can also be operat-

ed at lower voltages consistent with the UVLO limit.

The MAX3535E integrates a primary-side controller and

H-bridge drivers. The device contains an on-board

oscillator, protection circuitry, and internal FET drivers

to provide up to 500mW of power to the primary of

transformer T1.

The MAX3535E driver slew rate is reconfigured using

jumper JU2 on the EV kit. The slew rate can be config-

ured for 400kbps (slow) operation to minimize EMI radi-

ation or 1000kbps (fast). See the

Slew-Rate Selection

section for configuring the slew rate.

The circuit’s H-bridge DC-DC converter powers the

MAX3535E isolated section of the circuit. One of the

benefits of the easy-to-use H-bridge DC-DC converter

topology is minimized input ripple current, and radiated

noise by the inherent balanced nature of the design,

with no interruption in the input current. UVLO and ther-

mal shutdown provide for a robust isolated supply.

Thermal-shutdown circuitry provides additional protec-

tion against damage due to overtemperature condi-

tions. The MAX3535E IC’s UVLO provides controlled

turn-on while powering up and during brownouts.

The surface-mount transformer provides up to

2500VRMS galvanic isolation and the output is powered

from a center-tapped, full-wave rectifier circuit to

reduce output voltage ripple. The isolated H-bridge

DC-DC converter operation at 420kHz allows the use of

ceramic-only output capacitors and a small trans-

former. The switching-frequency duty cycle is fixed at

50% to control energy transfer to the isolated output

and to prevent DC current flow in the transformer.

The PCB is designed for 2500V isolation with 300 mils

spacing between the GND and SGND planes. Test

points TP1 (GND) and TP2 (SGND) are provided on the

PCB for probing the respective ground plane, or to con-

nect the GND to SGND planes for nonisolated evalua-

tion of the circuit.

Jumper Selection

The MAX3535E EV kit features several jumpers to

reconfigure the circuit’s receiver/driver enable circuits,

slew-rate control, and full- or half-duplex operation.

Additionally, PCB pads are provided for connecting an

external load to the isolated output at VCC2 and SGND.

Driver and Receiver Enable Selection

The MAX3535E EV kit features a 3-pin jumper (JU1) to

set the MAX3535E driver and receiver output-enable

modes. Table 1 lists the jumper options for the various

modes of operation. Refer to the MAX3535E IC data

sheet for more information on the MAX3535E DE and

RE pin’s driver/receiver modes of operation. See Table 3

for configuring the MAX3535E communication mode.

Slew-Rate Selection

The MAX3535E EV kit features a 2-pin jumper (JU2) to

set the MAX3535E communication slew rate. Table 2

lists jumper options for configuring the slew rate that

will affect the maximum data rate. Refer to the

MAX3535E IC data sheet for more information on the

slew-rate configuration.

Full-/Half-Duplex Communication Configuration

The MAX3535E EV kit features two jumpers that set the

communication mode of operation (full duplex or half

duplex). Jumpers JU3 and JU4 configure the circuit for

the mode (see Table 3 for configuration options). See

Table 2 for reconfiguring the communication slew rate,

which also impacts the maximum communication

speed; see Table 1 for configuring the MAX3535E

receiver and driver modes of operation.

Resistors R1 and R2 Configuration

Pads are provided for pullup and pulldown resistors for

the A-B lines, although the use of these resistors is

purely optional. Pullup and pulldown resistors are used

on the receiver inputs to guarantee a known state in the

event that all nodes on the bus are in receive mode, or

the cable becomes disconnected. The exact value for

these resistors varies with the application. For example,

a cable that is doubly terminated with 120Ωresistors

may use 750Ω, while an unterminated cable may use

10kΩ. These resistors are not required because the

MAX3535E has a fail-safe receiver designed to guaran-

tee a high output in the event a cable disconnects or

shorts between A-B. Use surface-mount 0805 case-size

resistors for R1 and R2.

Evaluating Other Transformer

Configurations/Designs

Evaluating the HALO TGM-350NA Transformer

Use the layout of the MAX3535E EV kit to evaluate other

pin-for-pin transformer replacements for the TGM-340,

provided with the EV kit. For example, the TGM-350,

which has a 1:1 turns ratio and lowers the primary cur-

rent consumption, can be used in place of the default

transformer that has a 3:4 turns ratio. The lower turns

ratio causes the circuit to have a lower output voltage,

while being able to supply slightly more current. This

lower output voltage implies an increase of the lower

bound for the input-supply voltage. When used with the

TGM-350 transformer, the input-supply voltage range is

Evaluates: MAX3535E

MAX3535E Evaluation Kit

_______________________________________________________________________________________ 3

SHUNT

LOCATION DE PIN RE PIN

MAX3535E

DRIVER/

RECEIVER

MODE

1-2

Connected

to RE and R4

pulled up to

VCC1

Connected to

DE and

pulled up to

VCC1 by R4

Driver is enabled,

receiver is

disabled and vice

versa.

2-3*

(default)

Connected

to DE PC

pad and R4

pulled up to

VCC1

Connected to

GND

Receiver is

always on and

driver is enabled

with the DE

signal.

None*

Connected

to DE PC

pad and R4

pulled up to

VCC1

Connected to

RE PC pad

only

Independent

control of driver-

and receiver-

enable states.

Table 1. Driver and Receiver Functions

(JU1)

SHUNT

LOCATION SLO PIN SLEW-RATE

(DATA RATE)

None Not connected Fast (up to 1000kbps)

Installed Connected to

SGND Slow (up to 400kbps)

Table 2. Slew-Rate Functions (JU2)

To avoid bus contention, ensure that only one driver has con-

trol of the bus.

JU3 SHUNT

LOCATION

JU4 SHUNT

LOCATION

COMMUNICATION

MODE

Installed Installed Half duplex

None None Full duplex

Table 3. Communication Mode Functions

(JU3 and JU4)

Evaluates: MAX3535E

reduced to +3.6V to +5.5V. Other changes to the trans-

former turns ratio may be possible to suit the exact

needs of the application. Refer to the MAX3535E IC

data sheet for more information. Contact HALO

Electronics to obtain a TGM-350NA transformer.

Smaller Transformer and 2kV Isolation Design

The transformer (T1) is an integral part of the dielectric-

withstand voltage of the EV kit circuit. The MAX3535E

IC is guaranteed to withstand 2500VRMS for one minute

(min). However, the circuit uses an isolated transformer

to transfer power from the primary side to the sec-

ondary side. The withstand voltage of the transformer,

as well as the MAX3535E, must be considered when

designing and testing the EV kit circuit. For example, if

less than 3kV isolation is needed, a smaller 2kV trans-

former can be used to save board area, but the entire

circuit will have only 2kV of isolation.

MAX3535E Evaluation Kit

4 _______________________________________________________________________________________

Figure 1. MAX3535E EV Kit Schematic

VCC2

ST2ST1

VCC2

0.1µF

10µF

OPEN

R02

SGND

VCC2

R02

SLO

JU3

JU4

JU2

TP2

SGND

TP1

GND

GND2

GND1

411

10µF

0.1µF

1VCC1

25 DI

VCC1

GND

VCC1

100kΩ

JU1

28 RO1

RO1

MAX3535E

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 _____________________

Evaluates: MAX3535E

MAX3535E Evaluation Kit

Boblet

Figure 2. MAX3535E EV Kit Component Placement Guide—

Component Side

Figure 3. MAX3535E EV Kit PCB Layout—Component Side

Figure 4. MAX3535E EV Kit PCB Layout—Solder Side