Linear Technology DC1794A Quick setup guide

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DEMO MANUAL DC1794A
Description
LTM2885
Isolated RS485/RS422
µModule Transceiver + Power
Demonstration circuit 1794A is an isolated RS485/RS422
μModule
®
transceiver+powerfeaturingtheLTM
®
2885.The
demo circuit is a 6500VRMS galvanically isolated RS485/
RS422 transceiver interface. The demo circuit features
an EMI optimized circuit configuration and printed circuit
board layout. The demo circuit operates from a single
external supply on VCC. The part generates the output 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
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 LTM2885 4.5 5 5.5 V
VCC2 Output Voltage ILOAD = 0mA to 100mA, DE = 0V 4.75 5 V
fMAX Maximum Data rate SLO = VCC2 20 Mbps
VIORM Maximum Working Insulation Voltage GND to GND2 890
600 VDC VRMS
Common Mode Transient Immunity 50 kV/µs
The LTM2885 contains an isolated DC/DC converter, de-
livering power to VCC2 at 5V from the input supply, VCC.
IsolationismaintainedbytheseparationofGNDandGND2,
which significant operating voltages and transients can
exist without affecting the operation of the LTM2885. The
logic side ON pin enables or shuts down the LTM2885.
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
isolatedsideofthedemocircuit.Afull-/half-duplexjumper
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.
TheLTM2885µModuleanddemocircuithasbeendesigned
and optimized for low RF emissions. To this end some
features of the LTM2885 are not available for evaluation
on the demo circuit, primarily to minimize the size of the
demo board and to limit the number of I/O connections.
The logic supply voltage, VL, is tied to VCC on the demo
circuit. All control signals are selectable by jumper pro-
gramming only, including ON, RE, DE, TE and SLO. The
spare logic channel DIN to DOUT is not available.
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DEMO MANUAL DC1794A
operAting principles
EMI mitigation techniques used include the following:
1. Board/ground plane size has been minimized. This
reduces the dipole antenna formed between the logic
side and isolated side ground planes.
2. Top signal routing and ground floods have been opti-
mized to reduce signal loops, minimizing differential
mode radiation.
3. A high ESR tantalum capacitor is included to minimize
board resonances and prevent voltage spikes due to
hot plugging of the input supply voltage.
4. Optional discrete bridge capacitors (C3, C4) can be
mounted between GND2 and GND. The discrete ca-
pacitors provide additional attenuation at frequencies
below 300MHz as shown in Figure 1. Capacitors are
safety rated type Y1, manufactured by Vishay, part #
VY115K31Y5SQ63V0.
EMI performance is shown in Figure 1, measured using
a Gigahertz Transverse Electromagnetic (GTEM) cell and
method detailed in IEC 61000-4-20, “Testing and Mea-
surement Techniques—Emission and Immunity Testing
in Transverse Electromagnetic Waveguides”.
CISPR 22 CLASS B LIMIT
DETECTOR = QuasiPeak
RBW = 120kHz
VBW = 300kHz
SWEEP TIME = 17s
# OF POINTS = 501
FREQUENCY (MHz)
0
100
200
300
400
500
600
700
800
900
1000
–30
–20
–10
0
10
20
30
40
50
60
AMPLITUDE (dBµV/m)
DC1794A F01
Figure 1. DC1794A Radiated Emissions
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DEMO MANUAL DC1794A
qUick stArt proceDUre
Figure 2. Demo Board Setup
Demonstration circuit 1794A is easy to set up and evalu-
ate the performance of the LTM2885. Refer to Figure 2
for proper measurement equipment setup and follow the
procedure below.
NOTE: When measuring the input or output voltage ripple
or high speed signals, care must be taken to avoid a long
ground lead on the oscilloscope probe.
1. Install jumpers in following positions: (all are default
except JP5 and JP6)
JP1 (TE pin) place in ON position
JP2 (DE pin) place in ON position
JP3 (RE pin) place in ON position
JP4 (ON pin) place in ON position
JP5 (SLO pin) place in OFF position
JP6 (Duplex header) place in HALF DUPLEX position
2. With power off, connect the input power supply to VCC
and GND turrets.
3. Turn on the power at the input.
NOTE: Make sure that the input voltage does not exceed
6V.
4. Check for the proper output voltage. VCC2 = 5V, this can
be measured between probe points VCC2 and GND2.
5. Oncetheproperoutputvoltageisestablished,connecta
function generator to TXD turret and set to square wave
with a low of 0V, high = VCC. Set frequency to 10MHz
(20Mbps). Enable output of function generator.
6. ConnectoscilloscopetoRXDturretand observe10MHz
waveform. This demonstration shows data that is
transmitted from TXD, loops back through half-duplex
connection, and out of RXD.
VIN
OSCOPE
FUNCTION
GENERATOR
+
–
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DEMO MANUAL DC1794A
pcB lAYoUt
pArts list
Layer 1. Top Layer Layer 2. Bottom Layer
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 U1 I.C., LTM2885IY LINEAR LTM2885IY#PBF
Hardware/Components (For Demo Board Only)
2 1 C1 CAP., TANT 10μF 16V 10% 3216 AVX TAJA106K016RNJ
3 4 E1-4 TURRET MILL-MAX 2501-2-00-80-00-00-07-0
4 2 J1 TERMINAL BLOCK, 2 POSITION, 3.5mm, HEADER WÜRTH 691214110002
5 5 JP1-5 HEADER, 1×3 0.1" WÜRTH 61300311121
6 1 JP6 HEADER, 2×3 0.1” WÜRTH 61300621121
7 5 JP1-5 SHUNT, 1×2 0.1", BLACK WÜRTH 60900213421
8 1 JP6 SHUNT, 2×2 0.1”, BLACK WÜRTH 60910213421
9 2 L1-2 COMMON MODE CHOKE WÜRTH 744232222
10 0 C2-3 OPTIONAL, CAP., X1Y1, 150pF 10% 760VAC VISHAY VY1151K31Y5SQ63V0
11 0 C4-5 OPTIONAL
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DEMO MANUAL DC1794A
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However,noresponsibilityisassumed foritsuse.LinearTechnologyCorporationmakesnorepresentation
that the interconnection of its circuits as described herein will not infringe on existing patent rights.
scheMAtic DiAgrAM
C1 10uF 3216
JP3
RE
JP4
ON
C2
OPT
C3
OPT
JP2
DE
JP1
TE
JP5
SLO
HGFEDCBA
HGFEDCBA
1 2 3 4 5 6 7
1 2 3 4 5 6 7
TITLE: SCHEMATIC
SIZE IC NO. REV.
DATE:SHEET OF
APPROVALS
SCALE = NONE
CUSTOMER NOTICE
Thursday, February12, 2015
3
REINFORCED RS485 ISOLATOR
KEITH B.
1 1
LTM2885IY
DEMO CIRCUIT 1794A
ETADDEVORPPAVEROCE
REVISION HISTORY
DESCRIPTION
1630 McCarthy Blvd.
Milpitas, CA 95035 Phone: [phone]
Fax: [phone] www.linear.com
LTC CONFIDENTIAL
FOR CUSTOMER
USE ONLY
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER -
SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS
THE CUSTOMERS RESPONSIBILITY TO VERIFY
PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND
PRINTED CIRCUIT LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY.
CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
TECHNOLOGY
PCB DES. APP ENG. KEITH B.
-3 3RD PROTOTYPE KEITH B. 10-13-14
ON
OFF
ON
ON
ON
OFF
OFF
OFF
OFF ON
HALF
FULL
N/A
E3
VCC
E2
TXD
E1
RXD
E4
GND
4.5V - 5.5V
A B Z Y
VCC2 T7
DI
A2
RE
A4
VCC2 T6
DE
A3
TE
A1
RO
A5 ON
A7 VL
A6 VCC
B6
ZT3
BT4
AT5
DOUT
B1
GND
B2
YT2
SLO T1
DIN S1
GND2 S2
VCC
B7
GND
B3
GND
B4
GND
B5
GND2 S3 GND2 S4
GND2 S5
GND2 S6
GND2 S7
U1 LTM2885IY
DUPLEX
VCC2
GND2
1 2 3 4
56
JP6
1
2
3 4
J1
L1
C4 OPT C5 OPT
L2
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DEMO MANUAL DC1794A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2011
LT 0715 REV A • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
Thisdemonstrationboard(DEMOBOARD)kitbeingsoldorprovidedbyLinearTechnologyisintendedforuseforENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union direc-
tive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims
arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.
Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC applica-
tion engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
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