1
dc1746af
DEMO MANUAL DC1746A
DESCRIPTION
LTM2881:
Isolated RS485/RS422
µModule Trans Power
Demonstration circuit 1746A is an isolated RS485/RS422
μModule
®
trans power featuring the LTM
®
2881.
The demo circuit is a 2500V
RMS
galvanically isolated
RS485/RS422 transceiver interface. The demo circuit
features an EMI optimized circuit confi guration and printed
circuit board layout. All components are integrated into
the μModule transceiver. The demo circuit operates from
a single external supply on V
CC
. 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 V
CC2
and communicates all necessary
signaling across the isolation barrier using LTC’s isolator
μModule technology.
Design fi les for this circuit board are available at
http://www.linear.com/demo
(T
A
= 25°C)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
CC
Input Supply Range
LTM2881-5
LTM2881-3
4.5
3.0
5
3
5.5
3.6
V
V
V
CC2
Output Voltage
I
LOAD
= 0mA to 100mA, DE = 0V
4.7
5
V
f
MAX
Maximum Data rate
SLO
= V
CC2
20
Mbps
V
IORM
Maximum Working Insulation Voltage
GND to GND2
560
400
V
DC
V
RMS
Common Mode Transient Immunity
30
kV/μs
The LTM2881 contains an isolated DC/DC converter, de-
livering power to V
CC2
at 5V from the input supply, V
CC
.
Isolation is maintained by the separation of GND and GND2
where signifi cant 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
confi guration. The
SLO
pin confi gures 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, V
L
, is tied to V
CC
on the demo circuit.
All control signals are selectable by jumper programming
only, including ON,
RE
, DE, TE and
SLO
. The spare logic
channel D
IN
to D
OUT
is not available.
