Isolated RS485 + 1W Power
3.3V or 5V
Isolated
Power
REG
5V
RO
RS485/RS422
Bus
DI
ON
LTM2881
Galvanic Isolation
Complete 20Mbps µModule® Transceiver Includes 2500VRMS Isolated Power—
No External Components Required
The LTM®2881 is an isolated RS485 transceiver that guards against large ground-to-ground differentials. The LTM2881’s internal
inductive isolation barrier breaks ground loops by isolating the logic level interface and line transceiver. An onboard DC/DC
converter provides power to the transceiver with an isolated 5V supply output for powering additional system circuitry.
With 2500VRMS galvanic isolation, onboard secondary power and a fully compliant RS485 transmitter and receiver, the LTM2881
requires no external components and provides a small, complete µModule solution for isolated serial data communications.
LTM2881 Demo Board
Features
Isolator µModule Technology
Isolated RS485/RS422 Transceiver: 2500VRMS
UL Recognized
File #E151738
Integrated Isolated, 1W DC/DC Converter
Good Efficiency (up to 62%)
Low EMI
3.3V or 5V Input Supply Voltage
(LTM2881-3/LTM2881-5)
20Mbps or Low EMI 250kbps Data Rate
High ESD: ±15kV HBM
Common Mode Transient Immunity: >30kV/µs
Integrated Selectable 120Ω Termination
Small Footprint, Low Profile
(11.25mm × 15mm × 2.8mm) in
Surface Mount LGA & BGA Packages
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L, LT, LTC, LTM, Linear Technology, the Linear logo and µModule are
registered trademarks and Isolator logo is a trademark of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
Isolated µModule Technology
TOP VIEW
1
To achieve greater than 2500VRMS isolation,
the LTM2881 utilizes Isolator µModule
Technology, which uses coupled signal
inductors embedded in the µModule
substrate. This technique ensures consistent
ruggedness and reliability, and will be
certified by UL, CSA and IEC to guarantee
the isolation barrier’s effectiveness. The
μModule package integrates several
technologies to deliver a cost-effective,
advanced solution that minimizes board space and improves
electrical and thermal performance.
A
2
DOUT TE
3
4
5
6
7
8
DI DE RE RO VL ON
B
VCC
GND
C
D
E
F
G
H
J
GND2
K
L
DIN SLO Y
Z
B
A
VCC2
BGA/LGA PACKAGE
32-PIN (15mm × 11.25mm)
Common Mode Transient Immunity
MULTIPLE SWEEPS
OF COMMON MODE
TRANSIENTS
Unlike other isolated solutions, the LTM2881 allows communication
through common mode transient events, greater than 30kV/µs,
unaffected by the transient and without introducing any priority data
jitter or data corruption.
500V/DIV
DI
RO
1V/DIV
1V/DIV
50ns/DIV
Isolated Supply Voltage Output
The LTM2881 is not only self-powered, but also provides a well regulated 5V, up to
1W, isolated supply for powering any supporting components on the isolated bus
side. This regulated power is continuously available over the operating temperature
range, even while driving full RS485 compliant signal levels.
SURPLUS CURRENT (mA)
250
200
3.3V
LTM2881-5 (RS485 60mA)
VCC
150
LTM2881-5 (RS485 90mA)
LTM2881-3 (RS485 60mA)
100
50
LTM2881-3 (RS485 90mA)
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
VL
RO
RE
TE
DE
DI
GND
Integrated Selectable 120Ω Termination
RE
TE
A
GALVANIC
ISOLATION
RO
B
A pin-selectable 120Ω termination is available for minimizing reflections that
may be present on an unterminated transmission line. RS485 networks require
120Ω termination resistors to be installed by the end-user based on the physical
layout of the twisted-pair wires and the placement of the nodes. The LTM2881’s
pin-selectable termination allows the proper nodes to be terminated by switching
the integrated termination on or off, under software control, without the need for
physical intervention by the user.
3.3V
VCC
VL
RO
RE
www.linear.com/2881 n 1-800-4-LINEAR
TE
DE
DI
0211B