1
dc1746af
DEMO MANUAL DC1746A
DESCRIPTION
LTM2881:
Isolated RS485/RS422
µModule Transceiver + Power
Demonstration circuit 1746A is an isolated RS485/RS422
Module
®
transceiver + power featuring the LTM
®
2881.
The demo circuit is a 2500VRMS galvanically isolated
RS485/RS422 transceiver interface. The demo circuit
featuresanEMIoptimizedcircuitconfigurationandprinted
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.
