Linear Technology DC1794A Quick setup guide

dc1794afa

DEMO MANUAL DC1794A

Description

LTM2885

Isolated RS485/RS422

µModule Transceiver + Power

Demonstration circuit 1794A is an isolated RS485/RS422

μModule

transceiver+powerfeaturingtheLTM

2885.The

demo circuit is a 6500VRMS galvanically isolated RS485/

RS422 transceiver interface. The demo circuit features

an EMI optimized circuit conﬁguration and printed circuit

board layout. The demo circuit operates from a single

external supply on VCC. The part generates the output L, LT, LTC, LTM, µModule, Linear Technology and the Linear logo are registered trademarks of

Linear Technology Corporation. All other trademarks are the property of their respective owners.

perForMAnce sUMMArY

operAting principles

voltage VCC2 and communicates all necessary signaling

across the isolation barrier using LTC’s isolator µModule

technology.

Design ﬁles for this circuit board are available at

http://www.linear.com/demo

(TA= 25°C)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VCC Input Supply Range LTM2885 4.5 5 5.5 V

VCC2 Output Voltage ILOAD = 0mA to 100mA, DE = 0V 4.75 5 V

fMAX Maximum Data rate SLO = VCC2 20 Mbps

VIORM Maximum Working Insulation Voltage GND to GND2 890

600 VDC

VRMS

Common Mode Transient Immunity 50 kV/µs

The LTM2885 contains an isolated DC/DC converter, de-

livering power to VCC2 at 5V from the input supply, VCC.

IsolationismaintainedbytheseparationofGNDandGND2,

which signiﬁcant operating voltages and transients can

exist without affecting the operation of the LTM2885. The

logic side ON pin enables or shuts down the LTM2885.

RS485/RS422 signaling is controlled by the logic inputs

DE, DI, TE and RE. Connection to the transceiver pins (A,

B, Y and Z) allows full- or half-duplex operation on the

isolatedsideofthedemocircuit.Afull-/half-duplexjumper

is included on the demo circuit to ease setting the system

conﬁguration. The SLO pin conﬁgures the slew rate of the

driver output pins Y and Z.

Data is transmitted out the driver pins Y and Z from the

input DI with DE set on. Data is received through the dif-

ference in A and B to the output RO with RE set on.

TheLTM2885µModuleanddemocircuithasbeendesigned

and optimized for low RF emissions. To this end some

features of the LTM2885 are not available for evaluation

on the demo circuit, primarily to minimize the size of the

demo board and to limit the number of I/O connections.

The logic supply voltage, VL, is tied to VCC on the demo

circuit. All control signals are selectable by jumper pro-

gramming only, including ON, RE, DE, TE and SLO. The

spare logic channel DIN to DOUT is not available.

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DEMO MANUAL DC1794A

operAting principles

EMI mitigation techniques used include the following:

1. Board/ground plane size has been minimized. This

reduces the dipole antenna formed between the logic

side and isolated side ground planes.

2. Top signal routing and ground ﬂoods have been opti-

mized to reduce signal loops, minimizing differential

mode radiation.

3. A high ESR tantalum capacitor is included to minimize

board resonances and prevent voltage spikes due to

hot plugging of the input supply voltage.

4. Optional discrete bridge capacitors (C3, C4) can be

mounted between GND2 and GND. The discrete ca-

pacitors provide additional attenuation at frequencies

below 300MHz as shown in Figure 1. Capacitors are

safety rated type Y1, manufactured by Vishay, part #

VY115K31Y5SQ63V0.

EMI performance is shown in Figure 1, measured using

a Gigahertz Transverse Electromagnetic (GTEM) cell and

method detailed in IEC 61000-4-20, “Testing and Mea-

surement Techniques—Emission and Immunity Testing

in Transverse Electromagnetic Waveguides”.

CISPR 22 CLASS B LIMIT

DETECTOR = QuasiPeak

RBW = 120kHz

VBW = 300kHz

SWEEP TIME = 17s

# OF POINTS = 501

FREQUENCY (MHz)

100

200

300

400

500

600

700

800

900

1000

–30

–20

–10

AMPLITUDE (dBµV/m)

DC1794A F01

Figure 1. DC1794A Radiated Emissions

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DEMO MANUAL DC1794A

qUick stArt proceDUre

Figure 2. Demo Board Setup

Demonstration circuit 1794A is easy to set up and evalu-

ate the performance of the LTM2885. Refer to Figure 2

for proper measurement equipment setup and follow the

procedure below.

NOTE: When measuring the input or output voltage ripple

or high speed signals, care must be taken to avoid a long

ground lead on the oscilloscope probe.

1. Install jumpers in following positions: (all are default

except JP5 and JP6)

JP1 (TE pin) place in ON position

JP2 (DE pin) place in ON position

JP3 (RE pin) place in ON position

JP4 (ON pin) place in ON position

JP5 (SLO pin) place in OFF position

JP6 (Duplex header) place in HALF DUPLEX position

2. With power off, connect the input power supply to VCC

and GND turrets.

3. Turn on the power at the input.

NOTE: Make sure that the input voltage does not exceed

6V.

4. Check for the proper output voltage. VCC2 = 5V, this can

be measured between probe points VCC2 and GND2.

5. Oncetheproperoutputvoltageisestablished,connecta

function generator to TXD turret and set to square wave

with a low of 0V, high = VCC. Set frequency to 10MHz

(20Mbps). Enable output of function generator.

6. ConnectoscilloscopetoRXDturretand observe10MHz

waveform. This demonstration shows data that is

transmitted from TXD, loops back through half-duplex

connection, and out of RXD.

VIN

OSCOPE

FUNCTION

GENERATOR

–

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DEMO MANUAL DC1794A

pcB lAYoUt

pArts list

Layer 1. Top Layer Layer 2. Bottom Layer

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 U1 I.C., LTM2885IY LINEAR LTM2885IY#PBF

Hardware/Components (For Demo Board Only)

2 1 C1 CAP., TANT 10μF 16V 10% 3216 AVX TAJA106K016RNJ

3 4 E1-4 TURRET MILL-MAX 2501-2-00-80-00-00-07-0

4 2 J1 TERMINAL BLOCK, 2 POSITION, 3.5mm, HEADER WÜRTH 691214110002

5 5 JP1-5 HEADER, 1×3 0.1" WÜRTH 61300311121

6 1 JP6 HEADER, 2×3 0.1” WÜRTH 61300621121

7 5 JP1-5 SHUNT, 1×2 0.1", BLACK WÜRTH 60900213421

8 1 JP6 SHUNT, 2×2 0.1”, BLACK WÜRTH 60910213421

9 2 L1-2 COMMON MODE CHOKE WÜRTH 744232222

10 0 C2-3 OPTIONAL, CAP., X1Y1, 150pF 10% 760VAC VISHAY VY1151K31Y5SQ63V0

11 0 C4-5 OPTIONAL

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DEMO MANUAL DC1794A

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However,noresponsibilityisassumed foritsuse.LinearTechnologyCorporationmakesnorepresentation

that the interconnection of its circuits as described herein will not infringe on existing patent rights.

scheMAtic DiAgrAM

10uF

3216

JP3

JP4

OPT

JP2

JP1

JP5

SLO

HGFEDCBA

TITLE: SCHEMATIC

SIZE IC NO. REV.

DATE:SHEET OF

APPROVALS

SCALE = NONE

CUSTOMER NOTICE

Thursday, February12, 2015

REINFORCED RS485 ISOLATOR

KEITH B.

1 1

LTM2885IY

DEMO CIRCUIT 1794A

ETADDEVORPPAVEROCE

REVISION HISTORY

DESCRIPTION

1630 McCarthy Blvd.

Milpitas, CA 95035

Phone: (408) 432-1900

Fax: (408) 434-0507

www.linear.com

LTC CONFIDENTIAL

FOR CUSTOMER

USE ONLY

THIS CIRCUIT IS PROPRIETARY TO

LINEAR TECHNOLOGY AND SUPPLIED FOR

USE WITH LINEAR TECHNOLOGY PARTS.

LINEAR TECHNOLOGY HAS MADE A BEST EFFORT

TO DESIGN A CIRCUIT THAT MEETS CUSTOMER -

SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS

THE CUSTOMERS RESPONSIBILITY TO VERIFY

PROPER AND RELIABLE OPERATION IN THE ACTUAL

APPLICATION. COMPONENT SUBSTITUTION AND

PRINTED CIRCUIT LAYOUT MAY SIGNIFICANTLY

AFFECT CIRCUIT PERFORMANCE OR RELIABILITY.

CONTACT LINEAR TECHNOLOGY APPLICATIONS

ENGINEERING FOR ASSISTANCE.

TECHNOLOGY

PCB DES.

APP ENG. KEITH B.

-3 3RD PROTOTYPE KEITH B. 10-13-14

OFF

HALF

FULL

N/A

VCC

TXD

RXD

GND

4.5V - 5.5V

VCC2 T7

VCC2 T6

A5 ON

A7 VL

A6 VCC

ZT3

BT4

AT5

DOUT

GND

YT2

SLO T1

DIN S1

GND2 S2

VCC

GND

GND2 S3

GND2 S4

GND2 S5

GND2 S6

GND2 S7

LTM2885IY

DUPLEX

VCC2

GND2

1 2

3 4

JP6

OPT

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dc1794afa

DEMO MANUAL DC1794A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ●FAX: (408) 434-0507 ●www.linear.com

 LINEAR TECHNOLOGY CORPORATION 2011

LT 0715 REV A • PRINTED IN USA

DEMONSTRATION BOARD IMPORTANT NOTICE

Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:

Thisdemonstrationboard(DEMOBOARD)kitbeingsoldorprovidedbyLinearTechnologyisintendedforuseforENGINEERING DEVELOPMENT

OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete

in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety

measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union direc-

tive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.

If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date

of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU

OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS

FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR

ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.

The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims

arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all

appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or

agency certified (FCC, UL, CE, etc.).

No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,

customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.

LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.

Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and

observe good laboratory practice standards. Common sense is encouraged.

This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC applica-

tion engineer.

Mailing Address:

Linear Technology

1630 McCarthy Blvd.

Milpitas, CA 95035

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