LTM2885
6500VRMS Isolated
RS485/RS422 µModule
Transceiver + PowerDESCRIPTIONFEATURES
RS485/RS422 Transceiver: 6500VRMS for 1 Minute
nn Reinforced Insulation
nn Isolated DC Power: 5V at 200mA
nn No External Components Required
nn 20Mbps or Low EMI 250kbps Data Rate
nn High ESD: ±15kV HBM on Transceiver Interface
nn High Common Mode Transient Immunity: 50kV/μs
nn Integrated Selectable 120Ω Termination
nn Extended Creepage and Clearance ~14.6mm
nn 1.62V to 5.5V Logic Supply Pin for Flexible
Digital Interface
nn Maximum Continuous Working Voltage: 690V
RMS
nn High Input Impedance Failsafe RS485 Receivernn Current Limited Drivers and Thermal Shutdown
nn Compatible with TIA/EIA-485-A and PROFIBUS
nn High Impedance Output During Internal Fault Condition
nn Low Current Shutdown Mode (< 10µA)
nn General Purpose CMOS Isolated Channel
nn 22mm × 9mm × 5.16mm Surface Mount BGA Packagenn

APPLICATIONSThe LTM®2885 is a complete galvanically isolated
full-duplex RS485/RS422 µModule® (micromodule)transceiver. No external components are required. A
single supply powers both sides of the interface throughan integrated, isolated, low noise, efficient 5V output
DC/DC converter.
Coupled inductors and an isolation power transformer
provide 6500VRMS of isolation between the line transceiverand the logic interface. This device is ideal for systems
where the ground loop is broken allowing for large common
mode voltage variation. Uninterrupted communication is
guaranteed for common mode transients up to 50kV/μs.
Maximum data rates are 20Mbps or 250kbps in slew
limited mode. Transmit data, DI, and receive data, RO, areimplemented 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 interfacingwith different logic levels from 1.62V to 5.5V, independentof the main supply.
Enhanced ESD protection allows this part to withstand up
to ±15kV (human body model) on the transceiver interface
pins to isolated supplies and ±25kV through the isolation
barrier to logic supplies without latch-up or damage.

Isolated RS485/RS422 Interface
Industrial Networks
nn Breaking RS485 Ground Loops
nn Isolated PROFIBUS-DP Networksnn
nn

L, LT, LTC, LTM, Linear Technology, the Linear logo and µModule are registered trademarks of
Analog Devices, Inc. All other trademarks are the property of their respective owners.

TYPICAL APPLICATION
Isolated Half-Duplex RS485 μModule Transceiver

LTM2885 Operating Through 100kV/μs CM Transients

5V
VCC

PWR
ISOLATION BARRIER

VL
RO
RE
TE
DE
DI

LTM2885

VCC2
A

5V/DIVDI
RO

5V/DIV

B
TWISTED-PAIRCABLE

MULTIPLE SWEEPSOF COMMON MODE
TRANSIENTS

Y
Z

GND

5V
OUT

300V/DIV
20ns/DIVGND22885 TA01b

2885 TA01a

2885faFor more information www.linear.com/LTM2885

1

LTM2885
ABSOLUTE MAXIMUM RATINGS(Note 1)Signal Voltages SLO,
DIN to GND2.....................................–0.3V to VCC2 +0.3V
Operating Temperature Range (Note 4)
LTM2885C................................................ 0°C to 70°C
LTM2885I.............................................–40°C to 85°C
LTM2885H.......................................... –40°C to 105°C
Maximum Internal Operating Temperature............. 125°C
Storage Temperature Range................... –55°C to 125°C
Peak Body Reflow Temperature............................. 245°C

VCC to GND................................................... –0.3V to 6V
VCC2 to GND2................................................ –0.3V to 6V
VL to GND..................................................... –0.3V to 6V
Interface Voltages(A, B, Y, Z) to GND2......................... VCC2 –15V to 15V(A-B) with Terminator Enabled...............................±6V
Signal Voltages ON, RO, DI, DE,
RE, TE, DOUT to GND.......................... –0.3V to VL +0.3V

PIN CONFIGURATIONTOP VIEW
7
ON
6
VL

VCC

VCC2

5
RO

A

RE

B

DE

Z

4

3

2
DI

GND

TE

DOUT

NC

A

B

C

GND2

Y

NC

DIN

SLO

R

S

T

1

D

E

F

G

H

J

K

L

M

N

P

BGA PACKAGE
42-PIN (22mm × 9mm × 5.2mm)
TJMAX = 125°C, θJA = 35°C/W, θJC(BOTTOM) = 23.9°C/W, θJC(TOP) = 29.6°C/W, θJBOARD = 22.7°C/W
θ VALUES DETERMINED PER JESD51-9, WEIGHT = 1.9g

ORDER INFORMATION http://www.linear.com/product/LTM2885#orderinfo
PART MARKINGPART NUMBERPAD OR BALL FINISH

DEVICEFINISH CODE

PACKAGETYPE

MSL
RATING

LTM2885CY#PBF
LTM2885IY#PBF

TEMPERATURE RANGE
0°C to 70°C

SAC305 (RoHS)

LTM2885Y

e1

42-BGALTM2885HY#PBF

3–40°C to 85°C
–40°C to 105°C• Device temperature grade is indicated by a label on the shipping
container.

• Recommended BGA PCB Assembly and Manufacturing Procedures:www.linear.com/BGA-assy• Pad or ball finish code is per IPC/JEDEC J-STD-609.

• BGA Package and Tray Drawings: www.linear.com/packaging• Terminal Finish Part Marking: www.linear.com/leadfree• This product is moisture sensitive. For more information, go to:www.linear.com/BGA-assy• This product is not recommended for second side reflow. For more
information, go to: www.linear.com/BGA-assy

2

For more information www.linear.com/LTM2885

2885faLTM2885
ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5.0V, VL = 3.3V,
GND = GND2 = 0V, ON = VL unless otherwise noted.
SYMBOLPARAMETERCONDITIONS

MIN

TYP

MAX

UNITS

5.0

5.5

V

5.5

V

Power Supply
VCC

VCC Supply Voltage

l

4.5

VL

VL Supply Voltage

l

1.62

ICCPOFFVCC Supply Current in Off Mode

ON = 0V

l

0

10

µA

ICCS

VCC Supply Current in On Mode

DE = 0V, RE = VL , No Load

l

38

50

mA

VCC2

Regulated VCC2 Output Voltage,
LoadedDE = 0V, RE = VL , ILOAD = 150mAl

VCC2NOLOAD Regulated VCC2 Output Voltage,
No LoadDE = 0V, RE = VL , No Load

4.75

5.0

4.8

5.0

V
5.35

V

Efficiency

ICC2 = 100mA (Note 2)

50%

VCC2 Short-Circuit Current

DE = 0V, RE = VL , VCC2 = 0V

200

mA

|VOD|

Differential Driver Output Voltage

R = ∞ (Figure 1)
R = 27Ω (RS485) (Figure 1)
R = 50Ω (RS422) (Figure 1)∆|VOD|

Difference in Magnitude of Driver R = 27Ω or R = 50Ω (Figure 1)
Differential Output Voltage forComplementary Output States

VOC

Driver Common Mode Output
Voltage

ICC2S
Driver

VCC2
VCC2
VCC2

V
V
V

l

0.2

V

R = 27Ω or R = 50Ω (Figure 1)

l

3

V

∆|VOC|

Difference in Magnitude of Driver R = 27Ω or R = 50Ω (Figure 1)
Common Mode Output Voltage
for Complementary Output States

l

0.2

V

IOZD

Driver Three-State (High
Impedance) Output Current on
Y and Z

DE = 0V, (Y or Z) = –7V, +12V
DE = 0V, (Y or Z) = –7V, +12V, H-Grade

l
l

±10
±50

µA
µA

IOSD

Maximum Driver Short-Circuit
Current– 7V ≤ (Y or Z) ≤ 12V (Figure 2)

l

– 250

250

mA

RIN

Receiver Input ResistanceRE = 0V or VL , VIN = –7V, –3V, 3V, 7V, 12V (Figure 3)
RE = 0V or VL , VIN = –7V, –3V, 3V, 7V, 12V (Figure 3),
H-Grade

l
l

96
48

125
125

RTE

Receiver Termination Resistance
EnabledTE = VL , VAB = 2V, VB = – 7V, 0V, 10V (Figure 8)

l

105

120

IIN

Receiver Input Current (A, B)

ON = 0V VCC2 = 0V or 5V, VIN = 12V (Figure 3)
ON = 0V VCC2 = 0V or 5V, VIN = 12V (Figure 3), H-Gradell

ON = 0V VCC2 = 0V or 5V, VIN = –7V (Figure 3)
ON = 0V VCC2 = 0V or 5V, VIN = –7V (Figure 3), H-Grade

l
l

–100
–145

–7V ≤ B ≤ 12V

l

–0.2

l
l
l

2.1
2.1

Receiver

VTH

Receiver Differential Input
Threshold Voltage (A-B)∆VTH

Receiver Input Failsafe Hysteresis B = 0V
Receiver Input Failsafe Threshold B = 0V

kΩ
kΩ
156

Ω

125
250

µA
µA
µA
µA

0.2
25

–0.2

–0.05

V
mV

0

V

2885faFor more information www.linear.com/LTM2885

3

LTM2885
ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5.0V, VL = 3.3V, GND = GND2 = 0V, ON = VL unless otherwise
noted.
SYMBOLPARAMETERCONDITIONS

MIN

TYP

MAX

UNITS

VIL

Logic Input Low Voltage

1.62V ≤ VL ≤ 5.5Vl

VIH

Logic Input High Voltage

DIN
SLO
DI, TE, DE, ON, RE:
VL ≥ 2.35V
1.62V ≤ VL < 2.35V

l 0.67•VCC2
l
2

V
V

0.67•VL
0.75•VL

V
V

Logic

l
l

0.4

V

IINL

Logic Input Current

VHYS

Logic Input Hysteresis(Note 2)

VOH

Output High Voltage

Output High, ILOAD = –4mA
(Sourcing), 5.5V ≥ VL ≥ 3V
Output High, ILOAD = –1mA
(Sourcing), 1.62V ≤ VL < 3Vl

VL –0.4

Vl

VL –0.4

V

Output Low, ILOAD = 4mA(Sinking), 5.5V ≥ VL ≥ 3V
Output High, ILOAD = 1mA(Sinking), 1.62V ≤ VL < 3V

l

0.4

V

l

0.4

V

VOL

Output Low Voltage

0

l

±1

150

µA
mV

IOZR

Three-State (High Impedance)
Output Current on RO

RE = VL , 0V ≤ RO ≤ VL

l

±1

µA

IOSR

Short-Circuit Current

0V ≤ (RO or DOUT) ≤ VL

l

±85

mA

ESD (HBM) (Note 2)

4

RS485 Driver and Receiver
Protection(Y, Z, A, B) to (GND, GND2)

±15

kV

Isolation Boundary(VCC2, GND2) to (VCC, VL, GND)

±25

kV

2885faFor more information www.linear.com/LTM2885

LTM2885
SWITCHING CHARACTERISTICS

The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5.0V, VL = 3.3V, GND = GND2 = 0V, ON = VL unless otherwise
noted.
SYMBOLPARAMETERCONDITIONS

MIN
20

TYP

MAX

UNITS

Driver SLO = VCC2
fMAX

Maximum Data Rate

(Note 3)

Mbps

tPLHD
tPHLD

Driver Input to Output

RDIFF = 54Ω, CL = 100pF(Figure 4)

l

60

85

ns

∆tPD

Driver Input to Output Difference|tPLHD – tPHLD|RDIFF = 54Ω, CL = 100pF(Figure 4)

l

1

8

ns

tSKEWD

Driver Output Y to Output Z

RDIFF = 54Ω, CL = 100pF(Figure 4)

l

1

±8

ns

tRD
tFD

Driver Rise or Fall Time

RDIFF = 54Ω, CL = 100pF(Figure 4)

l

4

12.5

ns

tZLD , tZHD ,tLZD , tHZD

Driver Output Enable or Disable
Time

RL = 500Ω, CL = 50pF
(Figure 5)

l

170

ns

Driver SLO = GND2
fMAX

Maximum Data Rate

(Note 3)

250

kbps

tPLHD
tPHLD

Driver Input to Output

RDIFF = 54Ω, CL = 100pF(Figure 4)

1

1.55

µs

∆tPD

Driver Input to Output Difference|tPLHD – tPHLD|RDIFF = 54Ω, CL = 100pF(Figure 4)

50

500

ns

tSKEWD

Driver Output Y to Output Z

RDIFF = 54Ω, CL = 100pF(Figure 4)

±200

±750

ns

tRD
tFD

Driver Rise or Fall Time

RDIFF = 54Ω, CL = 100pF(Figure 4)

l

0.9

1.5

µs

tZLD , tZHD ,tLZD , tHZD

Driver Output Enable or Disable
Time

RL = 500Ω, CL = 50pF
(Figure 5)

l

400

ns

tPLHR
tPHLR

Receiver Input to Output

CL = 15pF, VCM = 2.5V, |VAB| = 1.4V,
tR and tF < 4ns, (Figure 6)

l

100

140

ns

tSKEWR

Differential Receiver Skew|tPLHR – tPHLR|

CL = 15pF(Figure 6)

l

1

8

ns

tRR
tFR

Receiver Output Rise or Fall Time CL = 15pF
(Figure 6)

l

3

12.5

ns

tZLR , tZHR ,tLZR , tHZR

Receiver Output Enable or
Disable TimeRL =1kΩ, CL = 15pF
(Figure 7)

l

50

ns

tRTEN , tRTZ

Termination Enable or Disable
TimeRE = 0V, DE = 0V, VAB = 2V, VB = 0V (Figure 8)

l

100

µs

CL = 15pF,
tR and tF < 4ns

l

60

100

ns

ON

l

200

500

µs

Receiver

Generic Logic Input
tPLHL1
tPHLL1

DIN to DOUT Input to Output

Power Supply Generator
VCC2 – GND2 Supply Start-UpTime(0V to 4.5V)

VL, No Load

2885faFor more information www.linear.com/LTM2885

5

LTM2885
ISOLATION CHARACTERISTICS TA = 25°C
SYMBOLPARAMETERCONDITIONS

MIN

VISO

Rated Dielectric Insulation Voltage

1 Minute (Derived from 1 Second Test)

6500

1 Second (Notes 5, 6, 7)

7800

VRMS

Common Mode Transient Immunity

VCC = 5V, VL = ON = 3.3V,∆VCM = 1kV, ∆T = 20ns (Note 2)

50

kV/µs

Maximum Working Insulation Voltage(Note 2)

1000
690

VPEAK, VDC
VRMS

VIORM

TYP

MAX

UNITS
VRMS

Partial Discharge

VPR = 1300VRMS (Notes 2, 5)

CTI

Comparative Tracking Index

IEC 60112 (Note 2)

Depth of Erosion

IEC 60112 (Note 2)

0.017

mm

DTI

Distance Through Insulation(Note 2)0.2mm

Input to Output Resistance(Notes 2, 5)

5TΩ

Input to Output Capacitance(Notes 2, 5)

6

pF

Creepage Distance(Notes 2, 5)

14.6

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 2: Guaranteed by design and not subject to production test.
Note 3: Maximum Data rate is guaranteed by other measured parameters
and is not tested directly.
Note 4: This µModule transceiver includes over temperature protectionthat 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.

6

5
600

1

pC
VRMS

Note 5: Device considered a 2-terminal device. Pin group A1 through C7
shorted together and pin group R1 through T7 shorted together.
Note 6: The rated dielectric insulation voltage should not be interpreted asa continuous voltage rating.
Note 7: In accordance with UL1577, each device is proof tested for the
1 minute RMS rating by applying the equivalent RMS voltage multiplied byan acceleration factor of 1.2 for one second.

2885faFor more information www.linear.com/LTM2885

LTM2885
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, VCC = 5.0V, VL = 3.3V unlessotherwise noted.

2.0

80

1.5

1.5

75

1.0
0.5
0

DRIVER PROP DELAY (ns)

2.0

–0.5

1.0
0.5
0

–25

0
25
50
75
TEMPERATURE (°C)

100

–1.0
–50

125

–25

0
25
50
75
TEMPERATURE (°C)

1002885 G01

4.5

126

4.0

124

3.5

122
120
118
116

1.5

0.5
0

125

OUTPUT LOW

0

10

20
30
40
50
OUTPUT CURRENT (mA)

60

R = 100Ω

3

R = 54Ω

2

0
–50

70

–25

0
25
50
75
TEMPERATURE (°C)

100

125

2885 G06

Receiver Propagation Delayvs Temperature

Supply Current vs Data Rate
150

120

4

140

3

2

1

115

130
SUPPLY CURRENT (mA)RECEIVER PROP DELAY (ns)

SOURCE

110
105
100

120

R = 54Ω

110
100
90
80

R = 100Ω

70

95

60

SINK
2
3
4
OUTPUT CURRENT (mA)R=∞
42885 G05

Receiver Output Voltage vs
Output Current (Source and Sink)

1252885 G03

12885 G04

1100

5
OUTPUT HIGH

2.0

112

0

0
25
50
75
TEMPERATURE (°C)

6

2.5

1.0

100

–25

Driver Differential Output Voltage
vs Temperature

3.0

114

0

50
–50

125

OUTPUT VOLTAGE (V)128

OUTPUT VOLTAGE (V)RESISTANCE (Ω)

5.0

0
25
50
75
TEMPERATURE (°C)

60

Driver Output Low/High Voltage
vs Output Current

130

–25

65

2885 G02

RTERM vs Temperature

110
–50

70

55

–0.5

–1.0
–50

OUTPUT VOLTAGE (V)

Driver Propagation Delayvs Temperature

Driver Skew vs Temperature

DRIVER SKEW (ns)

RECEIVER SKEW (ns)Receiver Skew vs Temperature

52885 G07

90
–50

–25

0
25
50
75
TEMPERATURE (°C)

100

125

2885 G08

50
0.1

1DATA RATE (Mbps)

10202885 G09

2885faFor more information www.linear.com/LTM2885

7

LTM2885
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, VCC = 5.0V, VL = 3.3V unlessotherwise noted.

VCC Supply Current vs Temperature
at ILOAD = 100mA on VCC2

Available VCC2 Current
vs Temperaturevs Temperature

300

100

70
60
50
NO LOAD

30

10
0
–50

–25

4.9

225

4.8

175
150
125
100

VCC = 4.5V
VCC = 5.0V
VCC = 5.5V

20

250

200

75

0
25
50
75
TEMPERATURE (°C)

100

50
–50

125

0
25
50
75
TEMPERATURE (°C)

4.7
4.6
4.4
4.3

R485 = OPEN, C485 = 0pF,
0Mbps, VCM = 0V
R485 = 54Ω, C485 = 500pF,
10Mbps, VCM = –7V–25

VCC2 vs Load Current

5.0

VOLTAGE (V)

ICC2 CURRENT (mA)

ICC CURRENT (mA)

80

40

VCC = 5.0V, VCC2 ≥ 4.75V

275

RS485 ENABLED AND TERMINATED

90

5.1

VCC = 4.5V
VCC = 5.0V
VCC = 5.5V

4.2
4.1
100

125

4.0

0

2885 G11

50

100
150
200
LOAD CURRENT (mA)

2885 G122885 G10

VCC2 Efficiency and Power Loss

vs Load Current

VCC2 Noise

VCC2 Load Step (100mA)

2.4

60

250

EFFICIENCY
2.0

40

1.6

VCC = 4.5V
VCC = 5.0V
VCC = 5.5V

30

1.2
0.8

20
10
0

0.4

POWER LOSS
0

50

100
150
200
LOAD CURRENT (mA)

0.0
250

POWER LOSS (W)EFFICIENCY (%)

50

VCC2
200mV/DIV

10mV/DIV

ILOAD
50mA/DIV

100µs/DIV

2885 G138200µs/DIV
2885 G14

2885 G15

2885faFor more information www.linear.com/LTM2885

LTM2885
PIN FUNCTIONSLOGIC SIDEGND (Pins B2-B5): Circuit Ground.

TE (Pin A1): Terminator Enable. A logic high enables atermination resistor (typically 120Ω) between pins A
and B. Do not float.

VCC (Pins B6-B7): Supply Voltage. Recommended operating voltage is 4.5V to 5.5V. Internally bypassed to GND
with 2.2µF.

DI (Pin A2): Driver Input. If the driver outputs are enabled(DE high), then a low on DI forces the driver noninverting
output (Y) low and the inverting output (Z) high. A highon DI, with the driver outputs enabled, forces the drivernoninverting output (Y) high and inverting output (Z) low.
Do not float.

NC (Pins C1-C7): No Connect. Pins with no internal
connection.
ISOLATED SIDE
NC (Pins R1-R7): No Connect. Pins with no internal connection.

DE (Pin A3): 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. Do not float.

DIN (Pin S1): General Purpose Isolated Logic Input. Logic
input on the isolated side relative to VCC2 and GND2. A
logic high on DIN will generate a logic high on DOUT. A logic
low on DIN will generate a logic low on DOUT. Do not float.

RE (Pin A4): Receiver Enable. A logic low enables thereceiver output. A logic high disables RO to a high impedance state. Do not float.

GND2 (Pins S2-S7): Isolated Side Circuit Ground. The
pads should be connected to the isolated ground and/or
cable shield.

RO (Pin A5): Receiver Output. If the receiver output isena­bled (RE low) 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 for more than approximately 3μs, RO is a logic
high. Under the condition of an isolation communication
failure RO is in a high impedance state.

SLO (Pin T1): Driver Slew Rate Control. A low input, relative 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. Do not float.

VL (Pin A6): Logic Supply. Interface supply voltage forpins RO, RE, TE, DI, DE, DOUT, and ON. Recommended
operating voltage is 1.62V to 5.5V. Internally bypassed
to GND with 2.2µF.

Z (Pin T3): Inverting Driver Output. High impedance when
the driver is disabled.

ON (Pin A7): Enable. Enables power and data communication through the isolation barrier. If ON is high the part isenabled and power and communications are functional tothe isolated side. If ON is low the logic side is held in reset
and the isolated side is unpowered. Do not float.
DOUT (Pin B1): General Purpose Logic Output. Logic
output connected through isolation path to DIN . Under
the condition of an isolation communication failure DOUT
is in a high impedance state.

Y (Pin T2): Noninverting Driver Output. High impedance
when the driver is disabled.

B (Pin T4): Inverting Receiver Input. Impedance is > 96kΩin all modes, powered and unpowered.
A (Pin T5): Noninverting Receiver Input. Impedance is> 96kΩ in all modes, powered and unpowered.
VCC2 (Pins T6-T7): Isolated Supply Voltage. Internallygenerated from VCC by an isolated DC/DC converter andregulated to 5V. Internally bypassed to GND2 with 2.2µF.

2885faFor more information www.linear.com/LTM2885

9

LTM2885
BLOCK DIAGRAM
VCC
2.2µF

VCC2

5V
REG

ISOLATED
DC/DC
CONVERTER

2.2µF

VL
2.2µF
A

RO
RX

B

RE
ISOLATEDCOMMINTERFACEDE

ISOLATEDCOMMINTERFACE

120Ω

DI

Y
DX

ON

Z
SLO

TE

DIN

DOUT

GND

GND2
2885 BD= LOGIC SIDE COMMON= ISOLATED SIDE COMMONTEST CIRCUITS
Y
GND
OR
VL

DI

Y

+

DRIVER

VOD

–

Z

R
R

GND
OR
VL

+
–

DI

IOSD
DRIVER

VOC

Z

2885 F01+––7V TO 12V

2885 F02

Figure 1. Driver DC Characteristics

Figure 2. Driver Output Short-Circuit Current
IIN

VIN

+
–

A OR BB OR ARECEIVER

2885 F03

V
RIN = IN
IIN

Figure 3. Receiver Input Current and Input Resistance102885faFor more information www.linear.com/LTM2885

LTM2885
TEST CIRCUITS
DI

Y
DI

VL

tPLHD

0V

tPHLD
tSKEWD

CL
DRIVER

RDIFF

Y, Z VOD

1/2 VOD

CL
Z

90%2885 F04a

(Y-Z)

10%

0

0

90%
10%

tRD

tFD

2885 F04b

Figure 4. Driver Timing Measurement

RL

Y
VL
OR
GND

DI

CL

GND
OR
VCC2

RL
Z

VL

1/2 VL

0V

tZLD

VCC2
Y OR ZDRIVER
DE

DE

CL

VCC2
OR
GND
2885 F05atLZD
1/2 VCC2

0.5V
0.5V

1/2 VCC2

Z OR Y
0V
tZHD

2885 F05btHZD

Figure 5. Driver Enable and Disable Timing MeasurementstR
VAB±VAB/2VCM±VAB/2

A-B
–VAB

A

B

RECEIVER

RO
CL
2885 F06a

RO

VL
0

90%
10%

tF
90%

0

10%
tPLHR

90%
1/2 VL
10%
tRR

tPHLR
1/2 VL

90%
10%
tFR

2885 F06b

Figure 6. Receiver Propagation Delay Measurements

2885faFor more information www.linear.com/LTM2885

11

LTM2885
TEST CIRCUITSREB

VCC2 OR 0V

1/2 VL

0V

A

0V OR VCC2

VL

RL

RO

RECEIVER

VL
OR
GND

CL

RE

RO

tZLR

VL

1/2 VL

VOL
RO

VOH

0.5V
0.5V

1/2 VL0V

2885 F07a

tLZR

2885 F07b

tZHR

tHZR

Figure 7. Receiver Enable/Disable Time Measurements

IA
A

RO

RTE =

+
–

RECEIVER

VAB
IA
TE

VAB

VL
1/2 VL
0V

IA

B

+
–

TE

tRTEN

tRTZ

90%

10%
2885 F08

VB

Figure 8. Termination Resistance and Timing Measurements

FUNCTIONAL TABLELOGIC INPUTS
ON

RE

TE

DE

MODE

1

0

0

0

Receive

1

0

0

1

Transceive

1

0

1

0

Receive + Term On

1

0

1

1

Transceive + Term On

1

1

0

0

Power On

1

1

0

1

Transmit

1

1

1

0

Term On

1

1

1

1

Transmit + Term On

0

X

X

X

Off

12

A, B
RIN
RTE
RIN
RTE
RIN

Y, Z

RO

DC/DC
CONVERTER

Hi-Z
DrivenHi-Z

OffEnabledOn

Driven

On

Hi-Z

Off

Driven
Hi-Z

Hi-Z

On

DrivenHi-ZTERMINATOR

Off

Off

2885faFor more information www.linear.com/LTM2885

LTM2885
APPLICATIONS INFORMATION
Overview
The LTM2885 µModule transceiver provides a galvanicallyisolated robust RS485/RS422 interface, powered by an
integrated, regulated DC/DC converter, complete withdecoupling capacitors. A switchable termination resistor
is integrated at the receiver input to provide proper termination to the RS485 bus. The LTM2885 is ideal for use in
networks where grounds can take on different voltages.
Isolation in the LTM2885 blocks high voltage differencesand eliminates ground loops and is extremely tolerant ofcommon mode transients between ground potentials. Error
free operation is maintained through common mode events
greater than 50kV/μs providing excellent noise isolation.
µModule Technology
The LTM2885 utilizes isolator µModule technology totranslate 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 bidirectionalsignal isolation. The µModule technology provides themeans to combine the isolated signaling with our RS485
transceiver and powerful isolated DC/DC converter in one
small package.
DC/DC Converter
The LTM2885 contains a fully integrated isolated DC/DC
converter, including the transformer, so that no external
components are necessary. The logic side contains a fullbridge driver, running about 2MHz, and is AC-coupled to asingle transformer primary. A series DC blocking capacitor
prevents transformer saturation due to driver duty cycle
imbalance. The transformer scales the primary voltage,
which is then rectified by a voltage doubler. This topology
eliminates transformer saturation caused by secondary
imbalances.
The DC/DC converter is connected to a low dropout reg­ulator (LDO) to provide a regulated low noise 5V output.
The internal power solution is sufficient to support thetransceiver interface at its maximum specified load anddata rate. The logic supplies, VCC and VL have a 2.2µF
decoupling capacitance to GND and the isolated supply
VCC2 has a 2.2µF decoupling capacitance to GND2 within
the µModule package.
VCC2 Output
The on-board DC/DC converter provides isolated 5V power
to output VCC2. VCC2 is capable of suppling up to 1W ofpower at 5V. This surplus current is available to external
applications. The amount of surplus current is dependent
upon the implementation and current delivered to theRS485 driver and line load. An example of available surplus
current is shown in the Typical Performance Characteristics
graph, VCC2 Surplus Current vs Temperature. Figure 21
demonstrates a method of using the VCC2 output directly
and with a switched power path that is controlled with theisolated RS485 data channel.
Driver
The driver provides full RS485 and RS422 compatibility.
When enabled, if DI is high, Y–Z is positive. When thedriver is disabled, both outputs are high impedance withless than 10µA of leakage current over the entire common
mode range of –7V to 12V, with respect to GND2.
Driver Overvoltage and Overcurrent Protection
The driver outputs are protected from short circuits toany voltage within the absolute maximum range of (VCC2–15V) to (GND2 +15V) levels. The maximum VCC2 current in this condition is 250mA. If the pin voltage exceeds
about ±10V, current limit folds back to about half of thepeak value to reduce overall power dissipation and avoid
damaging the part.
The device also features thermal shutdown protectionthat disables the driver and receiver output in case ofexcessive power dissipation (see Note 4 in the Electrical
Characteristics section).
SLO Mode
The LTM2885 features a logic-selectable reduced slew
rate mode (SLO mode) that softens the driver output
edges to reduce EMI emissions from equipment anddata cables. The reduced slew rate mode is entered by

For more information www.linear.com/LTM2885

2885fa13

LTM2885

Y-Z 10dB/DIV

Y-Z 10dB/DIVAPPLICATIONS INFORMATION

06.25
FREQUENCY (MHz)

12.5

0

6.25
FREQUENCY (MHz)12.5
2885 F09b

2885 F09a

Figure 9a. Frequency Spectrum SLO Mode 125kHz Input

Figure 9b. Normal Mode Frequency Spectrum 125kHz Input

taking the SLO pin low to GND2, where the data rate islimited to about 250kbps. Slew limiting also mitigates theadverse effects of imperfect transmission line termination
caused by stubs or mismatched cables.

the input failsafe threshold for longer than about 3µs witha hysteresis of 25mV. This failsafe feature is guaranteed
to work for inputs spanning the entire common mode
range of –7V to 12V.

Figures 9a and 9b show the frequency spectrums of the
LTM2885 driver outputs in normal and SLO mode operating at 250kbps. SLO mode significantly reduces the highfrequency harmonics.

The receiver output is internally driven high (to VL) or
low (to GND) with no external pull-up needed. When thereceiver is disabled the RO pin becomes Hi-Z with leakageof less than ±1µA for voltages within the supply range.

Receiver and Failsafe

Receiver Input ResistanceWith the receiver enabled, when the absolute value of thedifferential voltage between the A and B pins is greaterthan 200mV, the state of RO will reflect the polarity of(A‑B). During data communication the receiver detects thestate of the input with symmetric thresholds around 0V.
The symmetric thresholds preserve duty cycle for attenuated signals with slow transition rates on high capacitive
busses, or long cable lengths. The receiver incorporates
a failsafe feature that guarantees the receiver output tobe a logic-high during an idle bus, when the inputs areshorted, left open or terminated, but not driven for morethan approximately 3μs. The failsafe feature eliminates theneed for system level integration of network pre-biasing by
guaranteeing a logic-high on RO under the conditions of anidle bus. Further network biasing constructed to conditiontransient noise during an idle state is unnecessary due tothe common mode transient rejection of the LTM2885.
The failsafe detector monitors A and B in parallel with thereceiver and detects the state of the bus when A-B is above

The receiver input resistance from A or B to GND2 isgreater than 96k permitting up to a total of 256 receivers
per system without exceeding the RS485 receiver loading
specification. High temperature H-grade operation reduces
the input resistance to 48k permitting 128 receivers on thebus. The input resistance of the receiver is unaffected byenabling/disabling the receiver or by powering/unpowering the part. The equivalent input resistance looking into
A and B is shown in Figure 10.

14

>96k

A
60Ω
TE
60Ω

>96k

B
2885 F10

Figure 10. Equivalent Input Resistance into A and B
2885faFor more information www.linear.com/LTM2885

LTM2885
APPLICATIONS INFORMATION
Switchable Termination
Proper cable termination is very important for signal fidelity. If the cable is not terminated with its characteristic
impedance, reflections will distort the signal waveforms.
The integrated switchable termination resistor provides
logic control of the line termination for optimal perfor­
mance when configuring transceiver networks.

Supply Current
The static supply current is dominated by power delivered tothe termination resistance. Power supply current increases
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
current from VCC2.
10

150

140

PHASE

0

–10

130
120

MAGNITUDE

–20

–30

110
100
0.1

PHASE (DEGREES)MAGNITUDE (Ω)

When the TE pin is high, the termination resistor is enabled 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
response which does not limit performance at the maximum specified data rate. Figure 13 shows the magnitude

and phase of the termination impedance versus frequency.
The termination resistor cannot be enabled by TE if thedevice is unpowered, ON is low or the LTM2885 is inthermal shutdown.

1
FREQUENCY (MHz)

10

–40

2885 F13

Figure 13. Termination Magnitude and Phase vs Frequency

130

200

128

190

126

180
SUPPLY CURRENT (mA)RESISTANCE (Ω)

Figure 11. Curve Trace Between A and B with Termination
Enabled and Disabled

124
122
120
118
116

170
160
150
140
130

114

120

112

110

110
–10

–5
0
5
10
COMMON MODE VOLTAGE (V)

15

100
0.1

1
DATA RATE (Mbps)

10202885 F14

2885 F12

Figure 12. Termination Resistance vs Common Mode Voltage

R = 54Ω C L = 0
R = 54Ω C L =100p
R = 54Ω C L = 1000p

Figure 14. Supply Current vs Data Rate
2885faFor more information www.linear.com/LTM2885

15

LTM2885
APPLICATIONS INFORMATIONPROFIBUS Applications
The LTM2885 can be used in PROFIBUS-DP networks
where isolation is required. The standard PROFIBUS
termination differs from RS485 termination and is shownin Figure 15. If used in this way, the internal termination
should remain disabled (TE low). The 390Ω resistors in
Figure 15 pre-bias the bus so that when the line is not
driven, the receiver’s output is high.
VCC2, provides an isolated source for the external termination resistor as shown in the Figure 15. When using the
LTM2885 in PROFIBUS applications, it is recommended
that no additional loads are connected to VCC2 in order tomaintain the specified driver output swing.
5V
VCC
PWR

VL
ISOLATION BARRIER

RO
DE
DI
TE
GND

VCC2
A
B
Y

Z
GND2

390Ω

PROFIBUS CABLE
TYPE A220Ω
390Ω

SHIELD

LTM28852885 F15

Figure 15. PROFIBUS-DP Connections with Termination

PCB Layout
The high integration of the LTM2885 makes PCB layout
very simple. However, to optimize its electrical isolation
characteristics, EMI, and thermal performance, somelayout considerations are necessary.
• Under heavily loaded conditions VCC and GND current
can exceed 300mA. Sufficient copper must be usedon the PCB to insure resistive losses do not cause thesupply voltage to drop below the minimum allowed
level. Similarly, the VCC2 and GND2 conductors mustbe sized to support any external load current. These
heavy copper traces will also help to reduce thermal
stress and improve the thermal conductivity.

16• Input and output decoupling is not required, since thesecomponents are integrated within the package. An additional bulk capacitor with a value of 6.8µF to 22µF is
recommended. The high ESR of this capacitor reduces
board resonances and minimizes voltage spikes causedby hot plugging of the supply voltage. For EMI sensitive
applications, an additional low ESL ceramic capacitor of
1µF to 4.7µF, placed as close to the power and groundterminals as possible, is recommended. Alternatively, anumber of smaller value parallel capacitors may be used
to reduce ESL and achieve the same net capacitance.
• Do not place copper on the PCB between the inner columns of pads. This area must remain open to withstandthe rated isolation voltage.
• The use of solid ground planes for GND and GND2
is recommended for non-EMI critical applications to
optimize signal fidelity, thermal performance, and tominimize 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
antenna structure which can radiate differential voltages
formed between GND and GND2. If ground planes areused it is recommended to minimize their area, anduse contiguous planes as any openings or splits canexacerbate RF emissions.
• For large ground planes a small capacitance (≤330pF)
from GND to GND2, either discrete or embedded within
the substrate, provides a low impedance current return
path for the module parasitic capacitance, minimizing
any high frequency differential voltages and substantiallyreducing radiated emissions. Discrete capacitance will
not be as effective due to parasitic ESL. In addition, voltage rating, leakage, and clearance must be considered
for component selection. Embedding the capacitancewithin the PCB substrate provides a near ideal capacitor
and eliminates component selection issues; however,the PCB must be 4 layers. Care must be exercised inapplying either technique to insure the voltage ratingof the barrier is not compromised.

2885faFor more information www.linear.com/LTM2885

LTM2885
APPLICATIONS INFORMATIONThe PCB layout in Figures 16a and 16b shows the demoboard for the LTM2885. The demo board includes provisions for adding two series discrete capacitors across theisolation boundary (C3 and C4). Safety rated Class X1 or
Y1 capacitors are recommended, Vishay’s VY1 or WKP
series are appropriate.

Figure 16a. LTM2885 Demo Board Layout

Top Layer

Bottom Layer

Figure 16b. LTM2885 Demo Board Layout (DC1794A)

2885faFor more information www.linear.com/LTM2885

17

LTM2885
APPLICATIONS INFORMATION
EMI performance is shown in Figure 17, measured using a Gigahertz Transverse Electromagnetic (GTEM) celland method detailed in IEC 61000-4-20, “Testing and
Measurement Techniques – Emission and Immunity Testingin Transverse Electromagnetic Waveguides”.
50
40

CABLE LENGTH (FT)

60

10k

CISPR 22 CLASS B LIMITNO BRIDGE CAPS
2x100pF BRIDGE CAPS

(dBµV/m)

100

10
10k

20
10

–10
–20
–30

NORMAL
MODE MAXDATA RATE
RS485 MAXDATA RATE

30

0

LOW-EMI MODE
MAX DATA RATE

1k

100k

1M
10M
DATA RATE (bps)100M2885 F18

Figure 18. Cable Length vs Data Rate
DETECTOR = QPEAK
RBW = 120kHz
VBW = 300kHzSWEEP TIME = 17s# OF POINTS = 501
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (MHz)2885 F17

Figure 17. LTM2885 Demo Circuit 1794A Emissions

Cable Length versus Data Rate
For a given data rate, the maximum transmission distanceis bounded by the cable properties. A typical curve ofcable length versus data rate compliant with the RS485
standard is shown in Figure 18. Three regions of thiscurve reflect different performance limiting factors in datatransmission. In the flat region of the curve, maximum
distance is determined by resistive loss in the cable. The
downward sloping region represents limits in distance andrate due to the AC losses in the cable. The solid verticalline 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.

RF, Magnetic Field Immunity
The LTM2885 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
EN 61000-4-9 Pulsed Magnetic Field Immunity
Tests were performed using an unshielded test card designed per the data sheet PCB layout recommendations.
Specific limits per test are detailed in Table 1.
Table 1TESTFREQUENCY

FIELD STRENGTH

EN 61000-4-3, Annex D

80MHz to 1GHz

10V/m

1.4MHz to 2GHz

3V/m

2GHz to 2.7GHz

1V/m

50Hz and 60Hz

30A/m

EN61000-4-8, Level 5

60Hz

100A/m*

EN61000-4-9, Level 5

Pulse

1000A/m

EN61000-4-8, Level 4*Non IEC Method182885faFor more information www.linear.com/LTM2885

LTM2885
TYPICAL APPLICATIONS
VCC

VCC

PWR
ISOLATION BARRIER

RO
RE
TE
DE
DI
330k

A

VL

B

RO

Y

DE

Z

DI

DIN

GND

LTM2885
PWR

RE
TE

DOUT

FAULT

VCC

LTM2885

GND2

A

ISOLATION BARRIER

VL

VCC

B

Y
Z

GND

GND2

2885 F19

2885 F20

Figure 20. Full-Duplex RS485 Connection

Figure 19. Isolated System Fault Detection

VCC
1.8V

VCC

PWR
ISOLATION BARRIER

VL
RO
RE
TE
DE
OFF ONDIAGND

IRLML6402

B
LTM2885

330k

Z
DIN

DOUT
CMOS OUTPUT

REGULATED 5V
SWITCHED 5V

VCC2

GND2

CMOS INPUT
2885 F21

Figure 21. Switched 5V Power with Isolated CMOS Logic Connection with Low Voltage Interface

VCC

VCCB

ISOLATION BARRIER

RO
RE

DE
DI

LTM2885

LTM2885
PWR

A
B

Y

Y

51Ω
10nF

Z
51Ω

A

51Ω

Z
GND

GND2

VCC

PWR
ISOLATION BARRIER

VCC
VL

VL
DE
DI

RE
RO

B
51Ω

10nF

GND2
BUS INHERITED

GND
2885 F22

B

Figure 22. 4-Wire Full-Duplex Self Biasing for Unshielded CAT5 Connection
2885faFor more information www.linear.com/LTM2885

19

LTM2885
PACKAGE DESCRIPTION

Please refer to http://www.linear.com/product/LTM2885#packaging for the most recent package drawings.
BGA Package
42-Lead (22mm × 9mm × 5.16mm)(Reference LTC DWG# 05-08-1960 Rev A)
Z

A

aaa Z

E

Y

SEE NOTESDETAIL A

A2

X

SEE NOTES

7

6

5

4

3

2

7

1

PIN 1

3
A
PIN “A1”CORNER

A1

4

b

B

ccc Z

C
D
E

b1

MOLD
CAP

F
SUBSTRATE

H

Z// bbb Z

D

G

H1

H2

DETAIL B

J

F

K
L

Øb (42 PLACES)
ddd M Z X Y
eee M Z

M
N
P
RS

DETAIL A

e
T

aaa Z
e
G

PACKAGE BOTTOM VIEW

3.81

2.54

0.00

DETAIL B
PACKAGE SIDE VIEW
1.27

1.27

3.49
2.54

3.81

4.13

PACKAGE TOP VIEWNOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994

10.16

2. ALL DIMENSIONS ARE IN MILLIMETERS

8.89

0.63 ±0.025 Ø 42xb

DIMENSIONS

7.62

SYMBOL
A
A1
A2
b
b1
D
E
e
F
G
H1
H2
aaa
bbb
ccc
ddd
eee

0.00

7.62

MIN
4.91
0.50
4.41
0.60
0.60

0.46
3.95

NOM
5.16
0.60
4.56
0.75
0.63
22.0
9.0
1.27
20.32
7.62
0.56
4.00

MAX
5.41
0.70
4.71
0.90
0.66

0.66
4.05
0.15
0.10
0.15
0.15
0.08
TOTAL NUMBER OF BALLS: 42

NOTES

3

BALL DESIGNATION PER JESD MS-028 AND JEP95

4

DETAILS OF PIN #1 IDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE ZONE INDICATED.
THE PIN #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE

5. PRIMARY DATUM -Z- IS SEATING PLANE
6. SOLDER BALL COMPOSITION IS 96.5% Sn/3.0% Ag/0.5% Cu
7COMPONENTPIN “A1”!

PACKAGE ROW AND COLUMN LABELING MAY VARY
AMONG µModule PRODUCTS. REVIEW EACH PACKAGELAYOUT CAREFULLYLTMXXXXXXµModule

8.89
10.16

9.84

TRAY PIN 1
BEVEL

10.48

20

PACKAGE IN TRAY LOADING ORIENTATIONBGA 42 0314 REV A

SUGGESTED PCB LAYOUTTOP VIEW

2885faFor more information www.linear.com/LTM2885

LTM2885
REVISION HISTORY
REV

DATE

DESCRIPTION

A

04/17

Added Receiver Output Disable Time

PAGE NUMBER
52885faInformation 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 representaFor more
www.linear.com/LTM2885
tion that the interconnectionof itsinformation
circuits as describedherein will not infringe on existing patent rights.

21

LTM2885
TYPICAL APPLICATION
Multi-Node Network with End Termination and Single Ground Connection on Isolation Bus
VCCC
VCCA
VCC

LTM2885PWR
ISOLATION BARRIER

GND

B
CABLE SHIELDOR GROUND RETURN

Y

Y

Z

Z

GND2
A

A

RE
TE

VCC2

DE
DI
GND

GND2

C

Z

DI

B

VL
RO

PWR

GND2

DE

A

Y

VCC1

RE
TE

A

PWR
ISOLATION BARRIER

RO

VCC

LTM2885

B

VL

ISOLATION BARRIER

GND
DI

DE

TE

RE

RO

VL

VCC

VCCB

LTM28852885 TA02

B

B

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2885faLT 0417 REV A • PRINTED IN USA

For more information www.linear.com/LTM2885

www.linear.com/LTM2885

 LINEAR TECHNOLOGY CORPORATION 2016