Linear Technology 1791A User manual

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DEMO MANUAL DC1791A
Description
LTM2887
SPI/Digital or I2C µModule Isolator
with Dual Adjustable 5V Regulators
Demonstration circuit 1791A is a serialperipheral interface
bus (SPI) or inter-IC bus (I2C) µModule isolator with dual
adjustable5V regulatorsfeaturing theLT M
®
2887. The demo
circuit features an EMI optimized circuit configuration and
printed circuit board layout. All components are integrated
into the µModule isolator. The demo circuit operates
from a single external supply on VCC. The part generates L, LT, LTC, LTM, µModule, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
perForMAnce sUMMArY
operAting principles
output voltages on VCC2 and VL2 which may be adjusted
by external programming resistors. It communicates all
necessary signaling across the isolation barrier through
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 LTM2887-3 3.0 3.3 3.6 V
LTM2887-5 4.5 5.0 5.5 V
VCC2 Regulated Output Voltage 4.75 5 5.25 V
Adjustable Output Voltage Range 0.6 5.5 V
Internal Current Limit ∆VCC2 = –5% 110 mA
VL2 Regulated Output Voltage 4.75 5 5.25 V
Adjustable Output Voltage Range 1.62 5.5 V
Internal Current Limit ∆VL2 = –5% 110 mA
fMAX Maximum Data Rate DI1 →O1, Ix →DOx, CL = 15pF 20 MHz
LTM2887-S, Bidirectional Communication
LTM2887-S, Unidirectional Communication
4
8
MHz
MHz
LTM2883-I 400 kHz
VIORM Maximum Working Insulation Voltage GND to GND2 560 VDC
400 VRMS
Common Mode Transient Immunity 30 kV/µs
The LTM2887 contains an isolated DC/DC conversion
system with multiple LDOs to deliver power to the two
output voltage rails from VCC. Isolation is maintained by
the separation of GND and GND2 where significant operat-
ing voltages and transients can exist without affecting the
operation of the LTM2887. The logic side ON pin enables
or shuts down the LTM2887. All logic side signals are
referenced to the logic supply pin VL. The LTM2887 is
available in two data bus configurations, SPI (–S) or I2C
(–I), and with two input voltage ranges, 3.0 to 3.6 volts
(–3) or 4.5 to 5.5 volts (–5).

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DEMO MANUAL DC1791A
operAting principles
SPI signaling is controlled by the logic inputs CS, SDI,
and SCK. SDOE controls the SDO output and is normally
connected to CS. The corresponding isolated side output
signals are CS2, SDI2, and SCK2. SDO2 is the isolated
side SPI data input. All of the SPI communication channels
may be used as generic digital I/O.
I2C signaling is controlled by the logic inputs SDA and
SCL, corresponding to SDA2 and SCL2 on the isolated
side. The SCL channel is unidirectional supporting master
mode only I2C communication. SCL2 output is standard
CMOS push-pull drive. SDA signaling is bidirectional,
and includes an internal current source pull-up on SDA2
supporting up to 200pF of load capacitance.
Demo circuit 1791A is available in four configurations
supporting all versions of the LTM2887. Table 1 details
the demo circuit configurations.
Table 1.
DEMO CIRCUIT INPUT VOLTAGE COMMUNICATION
DC1791A-A 3.0V to 3.6V SPI/Digital
DC1791A-B 4.5V to 5.5V SPI/Digital
DC1791A-C 3.0V to 3.6V I2C
DC1791A-D 4.5V to 5.5V I2C
The demo circuit has been designed and optimized for low
RF emissions. To this end some features of the LTM2887
are not available for evaluation on the demo circuit. The
logic supply voltage VLis tied to VCC on the demo circuit,
and the ON pin is not available on the input pin header,
but may be controlled by jumper JP1. EMI mitigation
techniques used include the following.
1. Four layer PCB, allowing for isolated side to logic side
“bridge” capacitor. The bridge capacitor is formed be-
tween an inner layer of floating copper which overlaps
the logic side and isolated side ground planes. This
structure creates two series capacitors, each with
approximately .008” of insulation, supporting the full
dielectric withstand rating of 2500VRMS. The bridge
capacitor provides a low impedance return path for
injected currents due to parasitic capacitances of the
LTM2887’s signal and power isolating elements.
2. Discrete bridge capacitors (C3, C4) mounted between
GND2 and GND. The discrete capacitors provide ad-
ditional attenuation at frequencies below 400MHz.
Capacitors are safety rated type Y2, manufactured by
Murata, part # GA342QR7GF471KW01L.
3. Board/ground plane size has been minimized. This
reduces the dipole antenna formed between the logic
side and isolated side ground planes.
4. Top signal routing and ground floods have been opti-
mized to reduce signal loops, minimizing differential
mode radiation.
5. Common mode filtering is integrated into the input and
output pin headers. Filtering helps to reduce emissions
caused by conducted noise and minimizes the effects
of cabling to common mode emissions.
6. A combination of low ESL and high ESR decoupling is
used. A low ESL ceramic capacitor is located close to
the moduleminimizing highfrequency noiseconduction.
A high ESR tantalum capacitor is included to minimize
board resonances and prevent voltage spikes due to
hot plugging of the supply voltage.
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”.

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DEMO MANUAL DC1791A
operAting principles
Figure 1. DC1791A Radiated Emissions
LTM2887 Low EMI Demo Board Radiated Emissions
The demo circuit includes provisions for programming the
two output voltagerails. Resistors R6, R7 andR5, R10 allow
the VL2 and VCC2 power rails, respectively, to be reduced
from their nominal operating voltages. The value of R6 or
R5 should be no greater than 6.04k to minimize errors in
the output voltage caused by the internal voltage dividers.
The formulas presented in Table 2 allow selection of the
appropriate resistor values. In addition the current limit
of each output voltage rail may also be programmed. The
current limit threshold is set by resistors R8 and R9 for
IVL2 and IVCC2 respectively. The current limit is nominally
100mA. The current limit may be reduced for either output
by the following equation:
RIMAX(R8, R9) = [119.22–(0.894) • (VL2, VCC2)]/ILIMIT
Table 2.
VOLTAGE RAIL RESISTOR TO REDUCE OUTPUT
VCC2 = 0.6V(1 + R7/R6)
VL2 = 0.6V(1 + R10/R5)
DETECTOR = QPEAK
RBW = 120kHz
VBW = 300kHz
SWEEP TIME = 17s
# OF POINTS = 501
CISPR 22 CLASS B LIMIT
DC1791A–A
DC1791A–B
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)
DC1791A

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DEMO MANUAL DC1791A
qUick stArt proceDUre
Demonstration circuit 1791A is easy to set up and evalu-
ate the performance of the LTM2887. 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 JP1 in the ON (default) position.
2. With power off, connect the input power supply to VCC
and GND on pin header J1.
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 voltages. VCC2 = 5V and
VL2 = 5V on pin header J2.
5. Once the proper output voltages are established, con-
nect signals to J1 and J2 pin headers as appropriate.
The header pin names and locations are detailed on the
demo board silkscreen below the pin headers.
TECHNOLOGY
µ
TECHNOLOGY
VIN
– +
Figure 2. Demo Board Setup

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DEMO MANUAL DC1791A
pcB lAYoUt
Layer 1. Top Layer
Layer 2. Ground Plane
Layer 3. Signal Layer
Layer 4. Bottom Layer

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DEMO MANUAL DC1791A
pArts list
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 U1 –A
–B
–C
–D
I.C., LTM2887CY-3S
I.C., LTM2887CY-5S
I.C., LTM2887CY-3I
I.C., LTM2887CY-5I
LINEAR LTM2887CY-3S#PBF
LINEAR LTM2887CY-5S#PBF
LINEAR LTM2887CY-3I#PBF
LINEAR LTM2887CY-5I#PBF
Hardware/Components (For Demo Board Only)
2 1 C1 CAP., TANT 10μF 10V 20% 1206 AVX TAJA106M016RNJ
3 1 C2 CAP., CER 1μF 10V 20% 0508 MURATA LLL219R71A105MA01L
4 2 C3, C4 CAP., CER 470pF 250Vac 10% 1808 MURATA GA342QR7GF471KW01L
5 2 J1, J2 0.1” DOUBLE ROW HEADER, 5 ×2 PIN SAMTEC TSW-105-22-G-D
6 2 J1, J2 0.1” FERRITE PLATE, 5 ×2 HOLE FAIR RITE 2644247101
7 1 JP1 Header, 1 ×3 2mm WURTH 62000311121
8 1 JP1 SHUNT, 1 ×2 2mm WURTH 60800213421
9 1 R1 –C
–D
RES., CHIP 10kΩ 1% 0805
RES., CHIP 10kΩ 1% 0805
YAGEO RC0805FR-0710KL
YAGEO RC0805FR-0710KL
10 1 R2 –C
–D
RES., CHIP 10kΩ 1% 0805
RES., CHIP 10kΩ 1% 0805
YAGEO RC0805FR-0710KL
YAGEO RC0805FR-0710KL
11 1 R3 –C
–D
RES., CHIP 0 0805
RES., CHIP 0 0805
YAGEO RC0805FR-070RL
YAGEO RC0805FR-070RL
12 1 R4 –A
–B
RES., CHIP 0 0805
RES., CHIP 0 0805
YAGEO RC0805FR-070RL
YAGEO RC0805FR-070RL
13 2 R6, R7 RES., CHIP 1.15kΩ 1% 0805 YAGEO RC0805FR-071K15L

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DEMO MANUAL DC1791A
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.
scheMAtic DiAgrAM
GND2
AVCC2
K8
SCL
A3
DI1
A5
VCC2
L8
SDA
A4
IVCC2
L7
IVL2
K7
DNC
A2
GND1
A6
ON
A7
VL
A8
VCC
B8
SDA2
L4
O1
L5
AVL2
K6
VL2
L6
DO2
A1
DO1
B1
GND
B3
SCL2
L3
DNC
L2
I2
L1
I1
K1
GND2
K2
U1
LTM2887CY-*
C3
470pF
1808
C4
470pF
1808
PCB SUBSTRATE 'BRIDGE' CAPACITOR, 20pF TOTAL
TOP COPPER
TOP COPPER
INNER LAYER 1
R7
OPEN
R8
1.15k
R10
OPEN
C2
1uF
0508
JP1
ON
C1
10uF
3216
1
2
3
4
5
6
7
8
9
10
J1
R1
*
R2
*
1
2
3
4
5
6
7
8
9
10
J2
VCC
VCC
DI1
DNC
DO1
GND
GND
SDA
SCL
DO2
LTM2887-I
VCC
VCC
CSB
DO2
DO1
GND
GND
SDI
SCK
SDO
LTM2887-S
VL2
GND2
SDA2
SCL2
I2
VCC2
GND2
O1
DNC
I1
LTM2887-I
VL2
GND2
SDI2
SCK2
SDO2
VCC2
GND2
CS2B
I2
I1
LTM2887-S
R3
*
R4
*
OFF
-
2
2ND PROTOTYPE
KEITH B.
3-4-15
A
B
C
D
E
F
G
H
A
B
C
D
E
F
G
H
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
Wednesday, March 04, 2015
2
SPI/DIGITAL OR I2C uMODULE ISOLATOR, LOW EMI
KEITH B.
1
1
LTM2887CY-3S/-5S/-3I/-5I
DEMO CIRCUIT 1791A
ECO
REV
APPROVED
DATE
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.
INPUT CONNECTOR
OUTPUT CONNECTOR
N/A
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL RESISTORS ARE IN OHMS, 0805.
ALL CAPACITORS ARE IN MICROFARADS, 0805.
ASSY
U1
VCC
R1
R2
R3
R4
LTM2887CY-3S
-A
3.0V - 3.6V
OPT
OPT
OPT
0
LTM2887CY-5S
-B
4.5V - 5.5V
OPT
OPT
OPT
0
LTM2887CY-3I
-C
3.0V - 3.6V
10K
10K
0
OPT
LTM2887CY-5I
-D
4.5V - 5.5V
10K
10K
0
OPT
*
VCC
R9
1.15k
R6
OPEN
R5
OPEN

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DEMO MANUAL DC1791A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2014
LT 1015 REV A • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING 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
directive 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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