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dc1746af

DEMO MANUAL DC1746A

DESCRIPTION

LTM2881:

Isolated RS485/RS422

µModule Transceiver + Power

Demonstration circuit 1746A is an isolated RS485/RS422

μModule® transceiver + power featuring the LTM®2881.

The demo circuit is a 2500VRMS galvanically isolated

RS485/RS422 transceiver interface. The demo circuit

features an EMI optimized circuit configuration and printed

circuit board layout. All components are integrated into

the μModule transceiver. The demo circuit operates from

a single external supply on VCC. The part generates the

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

output 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

LTM2881-5

LTM2881-3

4.5

3.0

5

3

5.5

3.6

V

V

VCC2

Output Voltage

ILOAD = 0mA to 100mA, DE = 0V

4.7

5

V

fMAX

Maximum Data rate

SLO = VCC2

20

Mbps

VIORM

Maximum Working Insulation Voltage

GND to GND2

560

400

VDC

VRMS

Common Mode Transient Immunity

30

kV/μs

The LTM2881 contains an isolated DC/DC converter, de-

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

Isolation is maintained by the separation of GND and GND2

where significant operating voltages and transients can

exist without affecting the operation of the LTM2881. The

logic side ON pin enables or shuts down the LTM2881.

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

isolated side of the demo circuit. A full-/half-duplex switch

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.

The demo circuit has been designed and optimized for low

RF emissions. To this end some features of the LTM2881

are not available for evaluation on the demo circuit. The

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

All control signals are selectable by jumper programming

only, including ON, RE, DE, TE and SLO. The spare logic

channel DIN to DOUT is not available.