LTM2881_12 [Linear]
Complete Isolated RS485/RS422 μModule; 完整的隔离型RS485 / RS422微型模块
| 型号： | LTM2881_12 |
| 厂家： | 
Linear |
| 描述： | Complete Isolated RS485/RS422 μModule |
| 文件： | 总24页 (文件大小：390K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTM2881
Complete Isolated
RS485/RS422 µModule
Transceiver + Power
FEATURES
DESCRIPTION
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UL Rated RS485/RS422 Transceiver: 2500V
The LTM®2881 is a complete galvanically isolated full-
duplex RS485/RS422 μModule® transceiver. No external
components are required. A single supply powers both
sides of the interface through an integrated, isolated, low
noise, efficient 5V output DC/DC converter.
RMS
UL Recognized
File #E151738
®
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Isolated DC Power: 5V at Up to 200mA
No External Components Required
20Mbps or Low EMI 250kbps Data Rate
High ESD: 15kV HꢀM on Transceiver Interface
High Common Mode Transient Immunity: 30kV/μs
Integrated Selectable 120Ω Termination
3.3V ꢁLTM2881-3ꢂ or 5.0V ꢁLTM2881-5ꢂ Operation
1.62V to 5.5V Logic Supply Pin for Flexible Digital Interface
Common Mode Working Voltage: 560V
High Input Impedance Failsafe RS485 Receiver
Current Limited Drivers and Thermal Shutdown
Compatible with TIA/EIA-485-A and PROFIBUS
High Impedance Output During Internal Fault Condition
Low Current Shutdown Mode ꢁ< 10μAꢂ
General Purpose CMOS Isolated Channel
Small, Low Profile ꢁ15mm × 11.25mmꢂ
Coupled inductors and an isolation power transformer
provide2500V
ofisolationbetweenthelinetransceiver
RMS
and the logic interface. This device is ideal for systems
where the ground loop is broken allowing for large com-
mon mode voltage variation. Uninterrupted communica-
tion is guaranteed for common mode transients greater
than 30kV/ꢀs.
PEAK
Maximum data rates are 20Mbps or 250kbps in slew
limited mode. Transmit data, DI and receive data, RO, are
implemented with event driven low jitter processing. The
receiver has a one-eighth unit load supporting up to 256
nodes per bus. A logic supply pin allows easy interfacing
with different logic levels from 1.62V to 5.5V, independent
of the main supply.
Surface Mount BGA and LGA Packages
APPLICATIONS
Enhanced ESD protection allows this part to withstand up
to 15kVꢁhumanbodymodelꢂonthetransceiverinterface
pins to isolated supplies and 10kV through the isolation
barrier to logic supplies without latch-up or damage.
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Isolated RS485/RS422 Interface
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Industrial Networks
Breaking RS485 Ground Loops
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L, LT, LTC, LTM, Linear Technology, the Linear logo and μModule are registered trademarks of
Isolated PROFIBUS-DP Networks
Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Isolated Half-Duplex RS485 μModule Transceiver
LTM2881 Operating Through 35kV/μs CM Transients
3.3V ꢁLTM2881-3ꢂ
5V ꢁLTM2881-5ꢂ
MULTIPLE SWEEPS
OF COMMON MODE
TRANSIENTS
V
CC
LTM2881
AVAILABLE CURRENT:
150mA ꢁLTM2881-5ꢂ
100mA ꢁLTM2881-3ꢂ
V
5V
500V/DIV
CC2
A
PWR
V
L
RO
DI
B
RE
RO
TWISTED-PAIR
CABLE
1V/DIV
1V/DIV
TE
DE
Y
Z
DI
2881 TA01a
50ns/DIV
GND
GND2
2881 TA01
2881fe
1
LTM2881
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V
V
to GND ..................................................–0.3V to 6V
CC2
V to GND ....................................................–0.3V to 6V
CC
1
2
3
4
5
6
7
8
to GND2...............................................–0.3V to 6V
D
TE DI DE RE RO
V
ON
OUT
L
L
A
B
C
D
E
F
Interface Voltages
ꢁA, B, Y, Zꢂ to GND2........................ V
–15V to 15V
V
CC2
GND
CC
ꢁA-Bꢂ with Terminator Enabled.............................. 6V
Signal Voltages ON, RO, DI, DE,
RE, TE, D
to GND......................... –0.3V to V +0.3V
L
OUT
Signal Voltages SLO,
G
H
J
D to GND2....................................–0.3V to V
+0.3V
IN
CC2
Operating Temperature Range
GND2
K
L
LTM2881C ............................................... 0°C to 70°C
LTM2881I.............................................–40°C to 85°C
LTM2881H ......................................... –40°C to 105°C
LTM2881MP ...................................... –55°C to 105°C
Maximum Internal Operating Temperature ....... 125°C
Storage Temperature Range ..................–55°C to 125°C
Peak Package Body Reflow Temperature.............. 245°C
D
IN
SLO
Y
Z
B
A
V
CC2
BGA PACKAGE
LGA PACKAGE
32-PIN ꢁ15mm s 11.25mm s 3.42mmꢂ
32-PIN ꢁ15mm s 11.25mm s 2.8mmꢂ
T
JA
JCTOP
JCBOTTOM
Q
= 125°C,
T
= 125°C,
JMAX
JMAX
= 31.1°C/W,
Q
= 32.2°C/W,
Q
JA
Q
= 27.2°C/W,
Q
= 27.3°C/W,
JCTOP
Q
= 20.9°C/W,
Q
= 19.5°C/W,
JCBOTTOM
= 26.4°C/W,
Q
= 25.1°C/W,
JB
WEIGHT = 1g
JB
WEIGHT = 1g
ORDER INFORMATION
LEAD FREE FINISH
LTM2881CY-3#PBF
LTM2881IY-3#PBF
LTM2881HY-3#PBF
LTM2881MPY-3#PBF
LTM2881CY-5#PBF
LTM2881IY-5#PBF
LTM2881HY-5#PBF
LTM2881MPY-5#PBF
LTM2881CV-3#PBF
LTM2881IV-3#PBF
LTM2881HV-3#PBF
LTM2881CV-5#PBF
LTM2881IV-5#PBF
LTM2881HV-5#PBF
TRAY
PART MARKING*
LTM2881Y-3
LTM2881Y-3
LTM2881Y-3
LTM2881Y-3
LTM2881Y-5
LTM2881Y-5
LTM2881Y-5
LTM2881Y-5
LTM2881V-3
LTM2881V-3
LTM2881V-3
LTM2881V-5
LTM2881V-5
LTM2881V-5
PACKAGE DESCRIPTION
TEMPERATURE RANGE
0°C to 70°C
LTM2881CY-3#PBF
LTM2881IY-3#PBF
LTM2881HY-3#PBF
LTM2881MPY-3#PBF
LTM2881CY-5#PBF
LTM2881IY-5#PBF
LTM2881HY-5#PBF
LTM2881MPY-5#PBF
LTM2881CV-3#PBF
LTM2881IV-3#PBF
LTM2881HV-3#PBF
LTM2881CV-5#PBF
LTM2881IV-5#PBF
LTM2881HV-5#PBF
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 3.42mmꢂ BGA
32-Pin ꢁ15mm × 11.25mm × 2.8mmꢂ LGA
32-Pin ꢁ15mm × 11.25mm × 2.8mmꢂ LGA
32-Pin ꢁ15mm × 11.25mm × 2.8mmꢂ LGA
32-Pin ꢁ15mm × 11.25mm × 2.8mmꢂ LGA
32-Pin ꢁ15mm × 11.25mm × 2.8mmꢂ LGA
32-Pin ꢁ15mm × 11.25mm × 2.8mmꢂ LGA
–40°C to 85°C
–40°C to 105°C
–55°C to 105°C
0°C to 70°C
–40°C to 85°C
–40°C to 105°C
–55°C to 105°C
0°C to 70°C
–40°C to 85°C
–40°C to 105°C
0°C to 70°C
–40°C to 85°C
–40°C to 105°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
This product is only offered in trays. For more information go to: http://www.linear.com/packaging/
2881fe
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LTM2881
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V, GND = GND2 =
0V, ON = VL unless otherwise noted.
SYMꢀOL
PARAMETER
CONDITIONS
MIN
TYP MAX UNITS
Power Supply
l
l
V
V
Supply Voltage
CC
LTM2881-3
LTM2881-5
3.0
4.5
3.3
5.0
3.6
5.5
V
V
CC
l
l
V
V Supply Voltage
1.62
5.5
10
V
L
L
I
I
V
V
Supply Current in Off Mode
Supply Current in On Mode
ON = 0V
0
μA
CCPOFF
CC
CC
l
l
l
LTM2881-3 DE = 0V, RE = V , No Load
20
15
25
19
20
mA
mA
mA
CCS
L
L
LTM2881-5 DE = 0V, RE = V , No Load
LTM2881-5, H/MP-Grade
l
l
l
V
V
Regulated V
Loaded
Output Voltage,
Output Voltage,
LTM2881-3 DE = 0V, RE = V , I
= 100mA
= 150mA
4.75
4.75
4.75
5.0
5.0
V
V
V
CC2
CC2
L
LOAD
LOAD
LTM2881-5 DE = 0V, RE = V , I
L
LTM2881-3, H/MP-Grade, I
= 90mA
LOAD
Regulated V
No Load
DE = 0V, RE = V , No Load
4.8
5.0
62
5.35
250
V
CC2NOLOAD
CC2
L
Efficiency
I
= 100mA, LTM2881-5 ꢁNote 2ꢂ
%
CC2
l
I
V
Short-Circuit Current
DE = 0V, RE = V , V = 0V
CC2
mA
CC2S
CC2
L
Driver
l
l
l
|V
|
OD
Differential Driver Output Voltage R = ∞ ꢁFigure 1ꢂ
V
V
V
V
V
V
CC2
CC2
CC2
R = 27Ω ꢁRS485ꢂ ꢁFigure 1ꢂ
R = 50Ω ꢁRS422ꢂ ꢁFigure 1ꢂ
2.1
2.1
l
Δ|V
|
OD
Difference in Magnitude of Driver R = 27Ω or R = 50Ω ꢁFigure 1ꢂ
Differential Output Voltage for
Complementary Output States
0.2
V
l
l
V
Driver Common Mode Output
Voltage
R = 27Ω or R = 50Ω ꢁFigure 1ꢂ
3
V
V
OC
Δ|V
|
Difference in Magnitude of Driver R = 27Ω or R = 50Ω ꢁFigure 1ꢂ
Common Mode Output Voltage
for Complementary Output States
0.2
OC
l
l
I
Driver Three-State ꢁHigh
Impedanceꢂ Output Current on
Y and Z
DE = 0V, ꢁY or Zꢂ = –7V, +12V
DE = 0V, ꢁY or Zꢂ = –7V, +12V, H/MP-Grade
10
50
μA
μA
OZD
l
I
Maximum Driver Short-Circuit
Current
–7V ≤ ꢁY or Zꢂ ≤ 12V ꢁFigure 2ꢂ
–250
250
mA
OSD
Receiver
l
l
R
Receiver Input Resistance
RE = 0V or V , V = –7V, –3V, 3V, 7V, 12V ꢁFigure 3ꢂ
96
48
125
125
kΩ
kΩ
IN
L
IN
RE = 0V or V , V = –7V, –3V, 3V, 7V, 12V ꢁFigure 3ꢂ,
L
IN
H/MP-Grade
l
R
Receiver Termination Resistance TE = V , V = 2V, V = –7V, 0V, 10V ꢁFigure 8ꢂ
108
120
156
Ω
μA
μA
V
TE
L
AB
B
Enabled
l
l
I
Receiver Input Current ꢁA, Bꢂ
ON = 0V V = 0V or 5V, V = 12V ꢁFigure 3ꢂ
125
250
IN
CC2
IN
ON = 0V V = 0V or 5V, V = 12V ꢁFigure 3ꢂ, H/MP-Grade
CC2
IN
l
l
ON = 0V V = 0V or 5V, V = –7V ꢁFigure 3ꢂ
–100
–145
CC2
IN
ON = 0V V = 0V or 5V, V = –7V ꢁFigure 3ꢂ, H/MP-Grade
CC2
IN
l
V
TH
Receiver Differential Input
Threshold Voltage ꢁA-Bꢂ
–7V ≤ B ≤ 12V
–0.2
0.2
0
ΔV
Receiver Input Failsafe Hysteresis B = 0V
Receiver Input Failsafe Threshold B = 0V
25
mV
V
TH
–0.2
–0.05
2881fe
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LTM2881
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V, GND = GND2 =
0V, ON = VL unless otherwise noted.
SYMꢀOL
Logic
PARAMETER
CONDITIONS
MIN
TYP MAX UNITS
l
V
V
Logic Input Low Voltage
1.62V ≤ V ≤ 5.5V
0.4
V
IL
L
l
l
D
0.67•V
2
V
V
IH
IN
CC2
SLO
Logic Input High Voltage
DI, TE, DE, ON, RE:
l
l
V ≥ 2.35V
0.67•V
0.75•V
V
V
L
L
L
1.62V ≤ V < 2.35V
L
l
I
Logic Input Current
Logic Input Hysteresis
Output High Voltage
0
1
μA
mV
V
INL
V
V
ꢁNote 2ꢂ
Output High, I
150
HYS
l
l
= –4mA
V –0.4
L
OH
LOAD
ꢁSourcingꢂ, 5.5V ≥ V ≥ 3V
L
Output High, I
= –1mA
V –0.4
L
V
LOAD
ꢁSourcingꢂ, 1.62V ≤ V < 3V
L
l
l
V
Output Low Voltage
Output Low, I
= 4mA
0.4
0.4
V
V
OL
LO AD
ꢁSinkingꢂ, 5.5V ≥ V ≥ 3V
L
Output High, I
ꢁSinkingꢂ, 1.62V ≤ V < 3V
= 1mA
LOAD
L
l
l
I
I
Three-State ꢁHigh Impedanceꢂ
Output Current on RO
RE = V , 0V ≤ RO ≤ V
L
1
μA
OZR
L
Short-Circuit Current
0V ≤ ꢁRO or D ꢂ ≤ V
85
mA
OSR
OUT
L
SWITCHING CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V, GND = GND2 =
0V, ON = VL unless otherwise noted.
SYMꢀOL
PARAMETER
CONDITIONS
MIN
TYP MAX UNITS
Driver SLO = V
CC2
f
Maximum Data Rate
Driver Input to Output
ꢁNote 3ꢂ
20
Mbps
MAX
l
l
l
l
l
t
t
R
= 54Ω, C = 100pF
60
1
85
8
ns
ns
ns
ns
ns
PLHD
PHLD
DIFF
L
ꢁFigure 4ꢂ
R = 54Ω, C = 100pF
DIFF
Δt
Driver Input to Output Difference
PD
L
|t
– t
|
PHLD
ꢁFigure 4ꢂ
PLHD
t
Driver Output Y to Output Z
R
= 54Ω, C = 100pF
1
8
SKEWD
DIFF
L
ꢁFigure 4ꢂ
t
t
Driver Rise or Fall Time
R
= 54Ω, C = 100pF
4
12.5
170
RD
FD
DIFF
L
ꢁFigure 4ꢂ
t
t
, t
,
Driver Output Enable or Disable
Time
R = 500Ω, C = 50pF
ZLD ZHD
L
L
, t
ꢁFigure 5ꢂ
LZD HZD
Driver SLO = GND2
f
Maximum Data Rate
Driver Input to Output
ꢁNote 3ꢂ
250
kbps
μs
MAX
t
t
R
= 54Ω, C = 100pF
1
1.55
500
500
PLHD
PHLD
DIFF
L
ꢁFigure 4ꢂ
Δt
Driver Input to Output Difference
R
= 54Ω, C = 100pF
50
200
ns
ns
PD
DIFF
L
|t
– t
|
PHLD
ꢁFigure 4ꢂ
PLHD
t
Driver Output Y to Output Z
R
DIFF
= 54Ω, C = 100pF
SKEWD
L
ꢁFigure 4ꢂ
2881fe
4
LTM2881
SWITCHING CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V, GND = GND2 =
0V, ON = VL unless otherwise noted.
SYMꢀOL
PARAMETER
CONDITIONS
= 54Ω, C = 100pF
MIN
TYP MAX UNITS
l
l
t
t
Driver Rise or Fall Time
R
0.9
1.5
μs
RD
FD
DIFF
L
ꢁFigure 4ꢂ
t
t
, t
,
Driver Output Enable or Disable
Time
R = 500Ω, C = 50pF
400
ns
ZLD ZHD
L
L
, t
ꢁFigure 5ꢂ
LZD HZD
Receiver
l
l
l
l
l
t
t
Receiver Input to Output
Differential Receiver Skew
C = 15pF, V = 2.5V, |V | = 1.4V,
100
1
140
8
ns
ns
ns
ns
μs
PLHR
PHLR
L
CM
AB
t and t < 4ns, ꢁFigure 6ꢂ
R
F
t
C = 15pF
SKEWR
L
|t
- t
|
ꢁFigure 6ꢂ
PLHR PHLR
t
t
Receiver Output Rise or Fall Time C = 15pF
3
12.5
50
RR
FR
L
ꢁFigure 6ꢂ
t
t
, t
,
Receiver Output Enable Time
R =1kΩ, C = 15pF
ZLR ZHR
L
L
, t
ꢁFigure 7ꢂ
LZR HZR
t
, t
Termination Enable or Disable
Time
RE = 0V, DE = 0V, V = 2V, V = 0V ꢁFigure 8ꢂ
100
RTEN RTZ
AB
B
Generic Logic Input
l
l
t
t
D
to D
Input to Output
C = 15pF,
60
100
800
ns
μs
PLHL1
PHLL1
IN
OUT
L
t and t < 4ns
R
F
Power Supply Generator
–GND2 Supply Start-Up
V
CC2
325
ON
V , No Load
L
Time
ꢁ0V to 4.5Vꢂ
ISOLATION CHARACTERISTICS TA = 25°C, LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V unless
otherwise noted.
SYMꢀOL
PARAMETER
CONDITIONS
MIN
2500
4400
30
TYP
MAX
UNITS
V
Rated Dielectric Insulation Voltage
1 Minute ꢁDerived from 1 Second Testꢂ
1 Second ꢁNote 5ꢂ
V
RMS
ISO
V
DC
Common Mode Transient Immunity
Maximum Working Insulation Voltage
LTM2881-3 V = 3.3V, LTM2881-5 V = 5V,
kV/μs
CC
CC
V = ON = 3.3V, V = 1kV, Δt = 33ns ꢁNote 2ꢂ
L
CM
V
ꢁNotes 2, 5ꢂ
560
400
V
PEAK
IORM
V
RMS
Partial Discharge
V
= 1050 V
ꢁNote 2ꢂ
PEAK
5
pC
PR
9
Input to Output Resistance
Input to Output Capacitance
Creepage Distance
ꢁNotes 2, 5ꢂ
ꢁNotes 2, 5ꢂ
ꢁNotes 2, 5ꢂ
10
Ω
pF
6
9.48
mm
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 4: This μModule transceiver includes overtemperature protection that
is intended to protect the device during momentary overload conditions.
Junction temperature will exceed 125°C when overtemperature protection
is active. Continuous operation above specified maximum operating
junction temperature may result in device degradation or failure.
Note 2: Guaranteed by design and not subject to production test.
Note 5: Device considered a 2-terminal device. Pin group A1 through B8
shorted together and pin group K1 through L8 shorted together.
Note 3: Maximum Data rate is guaranteed by other measured parameters
and is not tested directly.
2881fe
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LTM2881
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, LTM2881-3 VCC = 3.3V, LTM2881-5
V
CC = 5.0V, VL = 3.3V unless otherwise noted.
Driver Propagation Delay
vs Temperature
Receiver Skew vs Temperature
Driver Skew vs Temperature
2.0
1.5
80
75
70
65
60
55
50
2.0
1.5
1.0
1.0
0.5
0.5
0
0
–0.5
–1.0
–0.5
–1.0
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
TEMPERATURE ꢁ°Cꢂ
TEMPERATURE ꢁ°Cꢂ
TEMPERATURE ꢁ°Cꢂ
2881 G02
2881 G03
2881 G01
Driver Output Low/High Voltage
vs Output Current
Driver Differential Output Voltage
vs Temperature
RTERM vs Temperature
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
130
128
126
124
122
120
118
116
114
112
110
6
5
4
OUTPUT HIGH
R = ∞
R = 100Ω
R = 54Ω
3
2
OUTPUT LOW
1
0
0
10
20
30
40
50
60
70
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
OUTPUT CURRENT ꢁmAꢂ
TEMPERATURE ꢁ°Cꢂ
TEMPERATURE ꢁ°Cꢂ
2881 G05
2881 G04
2881 G06
Receiver Output Voltage vs
Output Current (Source and Sink)
Receiver Propagation Delay
vs Temperature
Supply Current vs Data Rate
4
3
2
1
0
120
115
110
105
100
95
200
180
160
140
120
100
80
SOURCE
R = 54ꢃ ꢁLTM2881-3ꢂ
R = 100ꢃ ꢁLTM2881-3ꢂ
R = 54ꢃ ꢁLTM2881-5ꢂ
R = 100ꢃ ꢁLTM2881-5ꢂ
60
40
R = ∞ ꢁLTM2881-3ꢂ
R = ∞ ꢁLTM2881-5ꢂ
20
SINK
90
0
0.1
0
1
2
3
4
5
–50 –25
0
25
50
75 100 125
1
10
OUTPUT CURRENT ꢁmAꢂ
TEMPERATURE ꢁ°Cꢂ
DATA RATE ꢁMbpsꢂ
2881 G07
2881 G08
2881 G09
2881fe
6
LTM2881
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, LTM2881-3 VCC = 3.3V, LTM2881-5
V
CC = 5.0V, VL = 3.3V unless otherwise noted.
VCC2 Surplus Current
vs Temperature
VCC Supply Current vs Temperature
VCC2 vs Load Current
at ILOAD = 100mA on VCC2
350
250
200
150
100
50
6
LTM2881-3, V = 3.3V
CC
300
250
200
150
100
50
LTM2881-5
LTM2881-5 ꢁRS485 60mAꢂ
5
4
LTM2881-3
LTM2881-5, V = 5V
CC
LTM2881-5 ꢁRS485 90mAꢂ
LTM2881-3 ꢁRS485 60mAꢂ
3
2
LTM2881-3 ꢁRS485 90mAꢂ
0
0
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
10 20 40 60 80 100 120 140 160 180
LOAD CURRENT ꢁmAꢂ
TEMPERATURE ꢁ°Cꢂ
TEMPERATURE ꢁ°Cꢂ
V
CC2
2881 G10
2881 G11
2881 G12
VCC2 Power Efficiency
VCC2 Load Step (100mA)
VCC2 Noise
70
60
50
40
30
20
10
LTM2881-5
V
CC2
100mV/DIV
LTM2881-3
10mV/DIV
I
LOAD
50mA/DIV
2881 G14
2881 G15
100μs/DIV
200μs/DIV
0
50
100
150
200
I
OUTPUT CURRENT ꢁmAꢂ
CC2
2881 G13
2881fe
7
LTM2881
PIN FUNCTIONS
LOGIC SIDE (V , V , GND)
ISOLATED SIDE (V , GND2)
CC2
CC
L
D
(Pin A1): General Purpose Logic Output. Logic
D (Pin L1): General Purpose Isolated Logic Input. Logic
IN
OUT
output connected through isolation path to D . Under
input on the isolated side relative to V
and GND2. A
IN
CC2
the condition of an isolation communication failure D
is in a high impedance state.
logic high on D will generate a logic high on D . A
OUT
IN OUT
logic low on D will generate a logic low on D
.
IN
OUT
TE (Pin A2): Terminator Enable. A logic high enables a
SLO (Pin L2): Driver Slew Rate Control. A low input, rela-
tive to GND2, will force the driver into a reduced slew rate
mode for reduced EMI. A high input, relative to GND2,
puts the driver into full speed mode to support maximum
data rates.
terminationresistorꢁtypically120ΩꢂbetweenpinsAandB.
DI (Pin A3): Driver Input. If the driver outputs are enabled
ꢁDE highꢂ, then a low on DI forces the driver noninverting
output ꢁYꢂ low and the inverting output ꢁZꢂ high. A high
on DI, with the driver outputs enabled, forces the driver
noninverting output ꢁYꢂ high and inverting output ꢁZꢂ low.
Y (Pin L3): Non Inverting Driver Output. High impedance
when the driver is disabled.
DE (Pin A4): Driver Enable. A logic low disables the driver
leaving the outputs Y and Z in a high impedance state. A
logic high enables the driver.
Z (Pin L4): Inverting Driver Output. High impedance when
the driver is disabled.
ꢀ (Pin L5): Inverting Receiver Input. Impedance is > 96kΩ
in receive mode with TE low or unpowered.
RE (Pin A5): Receiver Enable. A logic low enables the
receiver output. A logic high disables RO to a high imped-
ance state.
A (Pin L6): Non Inverting Receiver Input. Impedance is
> 96kΩ in receive mode with TE low or unpowered.
RO (Pin A6): Receiver Output. If the receiver output is
enabled ꢁRE lowꢂ and if A – B is > 200mV, RO is a logic
high, if A – B is < –200mV RO is a logic low. If the receiver
inputs are open, shorted, or terminated without a valid
signal, RO will be high. Under the condition of an isolation
communication failure RO is in a high impedance state.
V
(Pins L7-L8): Isolated Supply Voltage. Internally
CC2
generated from V by an isolated DC/DC converter and
CC
regulated to 5V. Internally bypassed to GND2 with 2.2μF.
GND2 (Pins K1-K8): Isolated Side Circuit Ground. The
pads should be connected to the isolated ground and/or
cable shield.
V (Pin A7): Logic Supply. Interface supply voltage for
L
pins RO, RE, TE, DI, DE, D , and ON. Recommended
OUT
operating voltage is 1.62V to 5.5V. Internally bypassed
to GND with 2.2μF.
ON(PinA8):Enable. Enablespoweranddatacommunica-
tion through the isolation barrier. If ON is high the part is
enabled and power and communications are functional
to the isolated side. If ON is low the logic side is held in
reset and the isolated side is unpowered.
GND (Pins ꢀ1-ꢀ5): Circuit Ground.
V
(Pinsꢀ6-ꢀ8):SupplyVoltage. Recommendedoperat-
CC
ing voltage is 3V to 3.6V for LTM2881-3 and 4.5V to 5.5V
for LTM2881-5. Internally bypassed to GND with 2.2μF.
2881fe
8
LTM2881
BLOCK DIAGRAM
V
2.2μF
CC
V
CC2
5V
REG
ISOLATED
DC/DC
CONVERTER
2.2μF
V
L
2.2μF
A
B
RO
RX
RE
DE
DI
ISOLATED
ISOLATED
COMM
INTERFACE
120Ω
COMM
INTERFACE
Y
Z
DX
ON
TE
SLO
D
IN
D
OUT
GND
GND2
2881 BD
= LOGIC SIDE COMMON
= ISOLATED SIDE COMMON
TEST CIRCUITS
Y
Z
Y
Z
R
I
OSD
GND
DI
GND
DI
+
OR
DRIVER
OR
DRIVER
V
OD
V
V
L
L
–
R
+
–
+
–7V TO 12V
V
OC
–
2881 F01
2881 F02
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
I
IN
A OR B
B OR A
RECEIVER
+
V
IN
–
2881 F03
V
I
IN
IN
R
=
IN
Figure 3. Receiver Input Current and Input Resistance
2881fe
9
LTM2881
TEST CIRCUITS
V
L
t
t
DI
Y, Z
PLHD
PHLD
Y
Z
0V
t
C
C
SKEWD
L
L
DI
DRIVER
R
DIFF
V
1/2 V
OD
OD
2881 F04a
90%
90%
0
0
ꢁY-Zꢂ
10%
10%
2881 F04b
t
t
FD
RD
Figure 4. Driver Timing Measurement
V
L
GND
OR
CC2
R
R
L
DE
Y OR Z
Z OR Y
1/2 V
L
Y
Z
0V
V
C
C
t
L
L
ZLD
t
V
LZD
L
DI
V
CC2
OR
DRIVER
DE
1/2 V
1/2 V
GND
CC2
0.5V
V
CC2
L
OR
GND
0.5V
2881 F05a
CC2
0V
2881 F05b
t
t
HZD
ZHD
Figure 5. Driver Enable and Disable Timing Measurements
t
t
F
R
V
90%
10%
AB
90%
A-B
0
A
B
10%
V
/2
/2
AB
–V
AB
RO
t
t
PHLR
PLHR
V
RECEIVER
CM
V
L
90%
10%
C
90%
10%
L
V
AB
1/2 V
1/2 V
RO
L
L
2881 F06a
0
2881 F06b
t
t
RR
FR
Figure 6. Receiver Propagation Delay Measurements
2881fe
10
LTM2881
TEST CIRCUITS
V
L
RE
RO
RO
1/2 V
L
0V
A
0V OR V
CC2
t
t
t
ZLR
LZR
R
V
L
L
RO
V
L
OR
RECEIVER
RE
1/2 V
1/2 V
L
L
GND
B
0.5V
0.5V
C
V
OR 0V
L
V
CC2
OL
V
OH
2881 F07a
0V
2881 F07b
t
ZHR
HZR
Figure 7. Receiver Enable/Disable Time Measurements
V
AB
I
R
=
A
TE
I
A
V
L
A
B
TE
1/2 V
L
RO
+
–
RECEIVER
V
V
0V
AB
t
RTEN
t
RTZ
90%
I
A
10%
+
–
TE
B
2881 F08
Figure 8. Termination Resistance and Timing Measurements
FUNCTIONAL TABLE
DC/DC
CONVERTER
LOGIC INPUTS
MODE
A, ꢀ
Y, Z
RO
TERMINATOR
ON
1
RE
0
TE
0
DE
0
Receive
Transceiver
Transmit
R
R
R
Hi-Z
Driven
Driven
Hi-Z
Enabled
Enabled
Hi-Z
On
On
On
On
Off
Off
Off
Off
On
Off
IN
IN
IN
TE
1
0
0
1
1
1
0
1
1
0
1
0
Receive + Term On
Off
R
Enabled
Hi-Z
0
X
X
X
R
Hi-Z
IN
2881fe
11
LTM2881
APPLICATIONS INFORMATION
Overview
rate, and external pins are supplied for extra decoupling
ꢁoptionalꢂandheatdissipation.Thelogicsupplies,V and
L
CC
TheLTM2881μModuletransceiverprovidesagalvanically-
isolated robust RS485/RS422 interface, powered by an
integrated, regulated DC/DC converter, complete with
decoupling capacitors. A switchable termination resistor
is integrated at the receiver input to provide proper termi-
nation to the RS485 bus. The LTM2881 is ideal for use in
networks where grounds can take on different voltages.
Isolation in the LTM2881 blocks high voltage differences
and eliminates ground loops and is extremely tolerant of
commonmodetransientsbetweengroundpotentials.Error
freeoperationismaintainedthroughcommonmodeevents
greater than 30kV/ꢀs providing excellent noise isolation.
V have a 2.2μF decoupling capacitance to GND and the
isolated supply V has a 2.2μF decoupling capacitance
CC2
to GND2 within the μModule package.
V
CC2
Output
Theon-boardDC/DCconverterprovidesisolated5Vpower
to output V . V is capable of suppling up to 1W of
CC2 CC2
power at 5V in the LTM2881-5 option and up to 600mW
of power in the LTM2881-3 option. This surplus current is
available to external applications. The amount of surplus
currentisdependentupontheimplementationandcurrent
delivered to the RS485 driver and line load. An example
of available surplus current is shown in the Typical Per-
ꢁModule Technology
formance Characteristics graph, V
Surplus Current vs
CC2
The LTM2881 utilizes isolator μModule technology to
translate signals and power across an isolation barrier.
Signals on either side of the barrier are encoded into
pulses and translated across the isolation boundary using
coreless transformers formed in the μModule substrate.
This system, complete with data refresh, error checking,
safe shutdown on fail, and extremely high common mode
immunity, provides a robust solution for bidirectional
signal isolation. The μModule technology provides the
means to combine the isolated signaling with our RS485
transceiver and powerful isolated DC/DC converter in one
small package.
Temperature. Figure 19 demonstrates a method of using
the V
output directly and with a switched power path
CC2
that is controlled with the isolated RS485 data channel.
Driver
The driver provides full RS485 and RS422 compatibility.
When enabled, if DI is high, Y–Z is positive. When the
driver is disabled, both outputs are high impedance with
less than 10μA of leakage current over the entire common
mode range of –7V to 12V, with respect to GND2.
Driver Overvoltage and Overcurrent Protection
DC/DC Converter
The driver outputs are protected from short circuits to
any voltage within the absolute maximum range of ꢁV
The LTM2881 contains a fully integrated isolated DC/DC
converter, including the transformer, so that no external
components are necessary. The logic side contains a full-
bridge driver, running about 2MHz, and is AC-coupled
to a single transformer primary. A series DC blocking
capacitor prevents transformer saturation due to driver
duty cycle imbalance. The transformer scales the primary
voltage, and is rectified by a full-wave voltage doubler.
This topology eliminates transformer saturation caused
by secondary imbalances.
CC2
cur-
–15Vꢂ to ꢁGND2 +15Vꢂ levels. The maximum V
CC2
rent in this condition is 250mA. If the pin voltage exceeds
about 10V, current limit folds back to about half of the
peak value to reduce overall power dissipation and avoid
damaging the part.
The device also features thermal shutdown protection
that disables the driver and receiver output in case of
excessive power dissipation ꢁSee Note 4 in the Electrical
Characteristics sectionꢂ.
The DC/DC converter is connected to a low dropout reg-
ulator ꢁLDOꢂ to provide a regulated low noise 5V output.
SLO Mode
TheLTM2881featuresalogic-selectablereducedslewrate
mode ꢁSLO modeꢂ that softens the driver output edges to
2881fe
The internal power solution is sufficient to support the
transceiverinterfaceatitsmaximumspecifiedloadanddata
12
LTM2881
APPLICATIONS INFORMATION
0
6.25
12.5
0
6.25
12.5
FREQUENCY ꢁMHzꢂ
FREQUENCY ꢁMHzꢂ
2881 F09b
2881 F09a
Figure 9a. Frequency Spectrum SLO Mode 125kHz Input
Figure 9b. Normal Mode Frequency Spectrum 125kHz Input
reduce EMI emissions from equipment and data cables.
The reduced slew rate mode is entered by taking the SLO
pin low to GND2, where the data rate is limited to about
250kbps. Slew limiting also mitigates the adverse effects
ofimperfecttransmissionlineterminationcausedbystubs
or mismatched cables.
of the bus when A-B is above the input failsafe threshold
for longer than about 3μs with a hysteresis of 25mV. This
failsafe feature is guaranteed to work for inputs spanning
the entire common mode range of –7V to 12V.
The receiver output is internally driven high ꢁto V ꢂ or
L
low ꢁto GNDꢂ with no external pull-up needed. When the
receiver is disabled the RO pin becomes Hi-Z with leakage
of less than 1μA for voltages within the supply range.
Figures 9a and 9b show the frequency spectrums of the
LTM2881 driver outputs in normal and SLO mode operat-
ing at 250kbps. SLO mode significantly reduces the high
frequency harmonics.
Receiver Input Resistance
The receiver input resistance from A or B to GND2 is
greater than 96k permitting up to a total of 256 receivers
per system without exceeding the RS485 receiver loading
specification. High temperature H-/MP-Grade operation
reduces the input resistance to 48k permitting 128 re-
ceivers on the bus. The input resistance of the receiver is
unaffected by enabling/disabling the receiver or by power-
ing/unpowering the part. The equivalent input resistance
looking into A and B is shown in Figure 10.
Receiver and Failsafe
With the receiver enabled, when the absolute value of the
differentialvoltagebetweentheAandBpinsisgreaterthan
200mV, the state of RO will reflect the polarity of ꢁA-Bꢂ.
During data communication the receiver detects the state
of the input with symmetric thresholds around 0V. The
symmetric thresholds preserve duty cycle for attenu-
ated signals with slow transition rates on high capacitive
busses, or long cable lengths. The receiver incorporates
a failsafe feature that guarantees the receiver output to
be a logic-high during an idle bus, when the inputs are
shorted,leftopenorterminated,butnotdriven.Thefailsafe
feature eliminates the need for system level integration of
network pre-biasing by guaranteeing a logic-high on RO
under the conditions of an idle bus. Further network bias-
ing constructed to condition transient noise during an idle
state is unnecessary due to the common mode transient
rejection of the LTM2881. The failsafe detector monitors
A and B in parallel with the receiver and detects the state
A
>96k
60ꢃ
TE
60ꢃ
B
2881 F10
>96k
Figure 10. Equivalent Input Resistance into A and ꢀ
2881fe
13
LTM2881
APPLICATIONS INFORMATION
Switchable Termination
phase of the termination impedance versus frequency.
The termination resistor cannot be enabled by TE if the
device is unpowered, ON is low or the LTM2881 is in
thermal shutdown.
Proper cable termination is very important for signal fi-
delity. If the cable is not terminated with its characteristic
impedance, reflections will distort the signal waveforms.
Supply Current
The integrated switchable termination resistor provides
logic control of the line termination for optimal perfor-
mance when configuring transceiver networks.
Thestaticsupplycurrentisdominatedbypowerdeliveredto
theterminationresistance.Powersupplycurrentincreases
with data rate due to capacitive loading. Figure 14 shows
supply current versus data rate for three different loads
for the circuit configuration of Figure 4. Supply current
increases with additional external applications drawing
WhentheTEpinishigh,theterminationresistorisenabled
and the differential resistance from A to B is 120Ω. Figure
11 shows the I/V characteristics between pins A and B
with the termination resistor enabled and disabled. The
resistance is maintained over the entire RS485 common
mode range of –7V to 12V as shown in Figure 12. The
integrated termination resistor has a high frequency re-
sponsewhichdoesnotlimitperformanceatthemaximum
specified data rate. Figure 13 shows the magnitude and
current from V
.
CC2
130
128
126
124
122
120
118
116
114
112
110
–10
–5
0
5
10
15
COMMON MODE VOLTAGE ꢁVꢂ
2881 G11
2881 F11
Figure 11. Curve Trace ꢀetween A and ꢀ with Termination
Enabled and Disabled
Figure 12. Termination Resistance vs Common Mode Voltage
250
230
150
140
130
120
10
PHASE
210
0
LTM2881-3
190
170
150
130
110
90
R=54 CL=1000p
R=54 CL=100p
R=54 CL=0
–10
–20
MAGNITUDE
LTM2881-5
R=54 CL=1000p
R=54 CL=100p
R=54 CL=0
110
100
–30
–40
70
50
0.1
1
10
0.1
1
10
FREQUENCY ꢁMHzꢂ
DATA RATE ꢁMbpsꢂ
2881 F13
2881 F14
Figure 13. Termination Magnitude and Phase vs Frequency
Figure 14. Supply Current vs Data Rate
2881fe
14
LTM2881
APPLICATIONS INFORMATION
PROFIꢀUS Applications
• InputandOutputdecouplingisnotrequired,sincethese
components are integrated within the package. An ad-
ditional bulk capacitor with a value of 6.8μF to 22μF is
recommended. The high ESR of this capacitor reduces
boardresonancesandminimizesvoltagespikescaused
by hot plugging of the supply voltage. For EMI sensitive
applications,anadditionallowESLceramiccapacitorof
1μF to 4.7μF, placed as close to the power and ground
terminals as possible, is recommended. Alternatively, a
numberofsmallervalueparallelcapacitorsmaybeused
to reduce ESL and achieve the same net capacitance.
The LTM2881 can be used in PROFIBUS-DP networks
where isolation is required. The standard PROFIBUS
termination differs from RS485 termination and is shown
in Figure 15. If used in this way, the internal termination
should remain disabled ꢁTE lowꢂ. The 390Ω resistors in
Figure 15 pre-bias the bus so that when the line is not
driven, the receiver delivers a high output. Since the
LTM2881usesafail-safereceiver,thepre-biasingresistors
are not necessary and standard RS485 termination can
be used with control from TE.
• Do not place copper on the PCB between the inner col-
umnsofpads. Thisareamustremainopentowithstand
the rated isolation voltage.
V
, provides an isolated source for the external termina-
CC2
tion resistor as shown in the Figure 15. When using the
LTM2881 in PROFIBUS applications, it is recommended
that no additional loads are connected to V
maintain the specified driver output swing.
in order to
• The use of solid ground planes for GND and GND2
is recommended for non-EMI critical applications to
optimize signal fidelity, thermal performance, and to
minimize RF emissions due to uncoupled PCB trace
conduction. The drawback of using ground planes,
where EMI is of concern, is the creation of a dipole
antennastructurewhichcanradiatedifferentialvoltages
formed between GND and GND2. If ground planes are
used it is recommended to minimize their area, and
use contiguous planes as any openings or splits can
exacerbate RF emissions.
CC2
3.3V ꢁLTM2881-3ꢂ
5V ꢁLTM2881-5ꢂ
V
CC
V
390Ω
CC2
A
PWR
V
L
PROFIBUS CABLE
TYPE A
RO
B
Y
DE
220Ω
390Ω
DI
SHIELD
Z
TE
LTM2881
GND
GND2
• For large ground planes a small capacitance ꢁ≤ 330pFꢂ
from GND to GND2, either discrete or embedded within
the substrate, provides a low impedance current return
path for the module parasitic capacitance, minimizing
anyhighfrequencydifferentialvoltagesandsubstantially
reducing radiated emissions. Discrete capacitance will
notbeaseffectiveduetoparasiticESL.Inaddition,volt-
age rating, leakage, and clearance must be considered
for component selection. Embedding the capacitance
withinthePCBsubstrateprovidesanearidealcapacitor
and eliminates component selection issues; however,
the PCB must be 4 layers. Care must be exercised in
applying either technique to insure the voltage rating
of the barrier is not compromised.
2881 F15
Figure 15. PROFIꢀUS-DP Connections with Termination
PCꢀ Layout Considerations
The high integration of the LTM2881 makes PCB layout
very simple. However, to optimize its electrical isolation
characteristics, EMI, and thermal performance, some
layout considerations are necessary.
• Under heavily loaded conditions V and GND current
CC
can exceed 300mA. Sufficient copper must be used
on the PCB to insure resistive losses do not cause the
supply voltage to drop below the minimum allowed
level. Similarly, the V
and GND2 conductors must
CC2
be sized to support any external load current. These
heavy copper traces will also help to reduce thermal
stress and improve the thermal conductivity.
2881fe
15
LTM2881
APPLICATIONS INFORMATION
TECHNOLOGY
Figure 16a. Low EMI Demo ꢀoard Layout
Figure 16b. Low EMI Demo ꢀoard Layout (DC1746A), Top Layer
Figure 16c. Low EMI Demo ꢀoard Layout (DC1746A), Inner Layer 1
2881fe
16
LTM2881
APPLICATIONS INFORMATION
Figure 16d. Low EMI Demo ꢀoard Layout (DC1746A), Inner Layer 2
Figure 16e. Low EMI Demo ꢀoard Layout (DC1746A), ꢀottom Layer
60
DETECTOR = QuasiPeak
R
= 120kHz, V = 300kHz
BW
BW
50
40
SWEEP TIME = 17sec
# OF POINTS = 501
30
20
10
0
–10
–20
–30
DC1746A-B
CISPR 22 CLASS 8 LIMIT
0
100 200 300 400 500 600 700 800 9001000
FREQUENCY ꢁMHzꢂ
2881 F17
Figure 17. Low EMI Demo ꢀoard Emissions
2881fe
17
LTM2881
APPLICATIONS INFORMATION
The PCB layout in Figures 16a to 16e show the low EMI
demo board for the LTM2881. The demo board uses a
combination of EMI mitigation techniques, including both
embedded PCB bridge capacitance and discrete GND to
GND2 capacitors. Two safety rated type Y2 capacitors
are used in series, manufactured by Murata, part number
GA342QR7GF471KW01L. The embedded capacitor ef-
fectively suppresses emissions above 400MHz, whereas
the discrete capacitors are more effective below 400MHz.
RF, Magnetic Field Immunity
The LTM2881 has been independently evaluated and has
successfully passed the RF and magnetic field immunity
testing requirements per European Standard EN 55024,
in accordance with the following test standards:
EN 61000-4-3 Radiated, Radio-Frequency,
Electromagnetic Field Immunity
EN 61000-4-8 Power Frequency Magnetic Field
Immunity
EMI performance is shown in Figure 17, measured using
a Gigahertz Transverse Electromagnetic ꢁGTEMꢂ cell and
method detailed in IEC 61000-4-20, “Testing and Mea-
surement Techniques – Emission and Immunity Testing
in Transverse Electromagnetic Waveguides.”
EN 61000-4-9 Pulsed Magnetic Field Immunity
Tests were performed using an unshielded test card de-
signed per the data sheet PCB layout recommendations.
Specific limits per test are detailed in Table 1.
Cable Length versus Data Rate
Table 1
TEST
FREQUENCY
80MHz to 1GHz
1.4MHz to 2GHz
2GHz to 2.7GHz
50Hz and 60Hz
60Hz
FIELD STRENGTH
10V/m
For a given data rate, the maximum transmission distance
is bounded by the cable properties. A typical curve of
cable length versus data rate compliant with the RS485
standard is shown in Figure 18. Three regions of this
curve reflect different performance limiting factors in data
transmission. In the flat region of the curve, maximum
distance is determined by resistive loss in the cable. The
downwardslopingregionrepresentslimitsindistanceand
rate due to the AC losses in the cable. The solid vertical
line represents the specified maximum data rate in the
RS485 standard. The dashed line at 250kbps shows the
maximum data rate when SLO is low. The dashed line at
20Mbps shows the maximum data rate when SLO is high.
EN 61000-4-3, Annex D
3V/m
1V/m
EN 61000-4-8, Level 4
EN 61000-4-8, Level 5
EN 61000-4-9, Level 5
*Non IEC Method
30A/m
100A/m*
1000A/m
Pulse
10k
LOW-EMI MODE
MAX DATA RATE
1k
100
10
NORMAL
MODE MAX
DATA RATE
RS485 MAX
DATA RATE
10k
100k
1M
10M
100M
DATA RATE ꢁbpsꢂ
2881 F18
Figure 18. Cable Length vs Data Rate
2881fe
18
LTM2881
TYPICAL APPLICATIONS
V
V
CC
CC
LTM2881
V
L
A
B
RO
RE
TE
DE
Y
DI
Z
330k
D
D
OUT
IN
GND
GND2
FAULT
2881 F19
Figure 19. Isolated System Fault Detection
V
V
CC
CC
LTM2881
PWR
V
L
A
B
RO
RE
TE
DE
DI
Y
Z
GND
GND2
2881 F20
Figure 20. Full-Duplex RS485 Connection
2881fe
19
LTM2881
TYPICAL APPLICATIONS
V
V
CC
REGULATED 5V
SWITCHED 5V
1.8V
V
CC
CC2
A
PWR
V
L
RO
IRLML6402
B
RE
LTM2881
TE
DE
330k
DI
D
OFF ON
Z
D
OUT
IN
GND
GND2
CMOS OUTPUT
CMOS INPUT
2881 F21
Figure 21. Switched 5V Power with Isolated CMOS Logic Connection with Low Voltage Interface
V
V
V
CCB
CC
V
CC
CC
LTM2881
LTM2881
V
DE
L
PWR
PWR
V
L
A
B
Y
51Ω
51Ω
RO
DI
Z
RE
10nF
DE
DI
RE
Y
Z
A
B
51Ω
51Ω
RO
10nF
GND
GND2
GND2
GND
2881 F22
BUS INHERITED
B
Figure 22. 4-Wire Full Duplex Self ꢀiasing for Unshielded CAT5 Connection
2881fe
20
LTM2881
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
/ / b b b
Z
4 . 4 4 5
3 . 1 7 5
1 . 9 0 5
0 . 6 3 5
0 . 6 3 5
0 . 0 0 0
1 . 9 0 5
3 . 1 7 5
4 . 4 4 5
a a a
Z
2881fe
21
LTM2881
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
Z
b b b
Z
4 . 4 4 5
3 . 1 7 5
1 . 9 0 5
0 . 6 3 5
0 . 6 3 5
1 . 9 0 5
3 . 1 7 5
4 . 4 4 5
a a a
Z
2881fe
22
LTM2881
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMꢀER
A
3/10
Changes to Features, Description and Typical Application
Add BGA Package to Pin Configuration, Order Information and Package Description Sections
Changes to LGA Package in Pin Configuration Section
Changes to Electrical Characteristics Section
Changes to Graphs G09, G13, G14
1
2, 19
2
3
6, 7
8
Update to Pin Functions
Update to Applications Information
12
13
14
15
16
22
1-22
Change to X-Axis on Figures 9a and 9b
Update to Supply Current Section
“PCB Layout Isolation Considerations” Section Replaced
RF, Magnetic Field Immunity Section Added
Changes to Related Parts
B
C
8/10
5/11
H-Grade parts added. Reflected throughout the data sheet.
HV-Grade parts removed. Reflected throughout the data sheet.
Updated the PCB Layout section.
1-24
15, 16, 17
24
Updated the Related Parts.
D
E
1/12
4/12
HV and MPY parts added. Reflected throughout the data sheet.
1-24
Added H/MP-Grade condition for I
Corrected Figure 15
3
OZD
15
2881fe
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
23
LTM2881
TYPICAL APPLICATION
V
CCC
V
CCA
V
CC
V
CC
LTM2881
LTM2881
PWR
PWR
V
V
L
L
A
A
RO
RO
B
B
RE
RE
TE
TE
V
CC2
V
CC1
CABLE SHIELD
OR GROUND RETURN
DE
DI
DE
DI
Y
Z
Y
Z
GND
GND2
GND2
GND
A
C
ISOLATION BARRIER
LTM2881
B
2881 F23
B
Figure 23. Multi-Node Network with End Termination
and Single Ground Connection on Isolation ꢀus
RELATED PARTS
PART NUMꢀER
LTM2882
DESCRIPTION
COMMENTS
1Mbps, 10kV HBM ESD, 2500V
Dual Isolated RS232 μModule Transceiver + Power
Isolated RS485 Transceiver
RMS
LTC1535
2500V
Isolation in Surface Mount Package
RMS
LT1785
60V Fault-Protected Transceiver
Half Duplex
Full Duplex
LT1791
60V Fault-Protected Transceiver
LTC2861
20Mbps RS485 Transceivers with Integrated Switchable Termination
RS232/RS485 Multiprotocol Transceivers with Integrated Termination
Full Duplex 15kV ESD
LTC2870/LTC2871
20Mbps RS485 and 500kbps RS232,
26kV ESD, 3V to 5V Operation
LTC2862/LTC2863/
LTC2864/LTC2865
60V Fault Protected 3V to 5.5V RS485/RS422 Transceivers
20Mbps or 250kbps, 15kV HBM ESD,
25V Common Mode Range
2881fe
LT 0412 REV E • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
24
●
●
© LINEAR TECHNOLOGY CORPORATION 2009
ꢁ408ꢂ 432-1900 FAX: ꢁ408ꢂ 434-0507 www.linear.com
相关型号：
LTM2882CV-3#PBF
LTM2882 - Dual Isolated RS232 uModule Transceiver + Power; Package: LGA; Pins: 32; Temperature Range: 0°C to 70°C
Linear
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