PDF Circuit Note

Circuit Note
CN-0373
Devices Connected/Referenced
2.5 kV, Signal and Power Isolated, Dual
ADM3252E
Channel, RS-232 Line Driver/Receiver
Circuits from the Lab® reference designs are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0373.
ADM2587E
2.5 kV, Signal and Power Isolated, ±15 kV
ESD Protected, Full/Half-Duplex, RS-485
Transceiver
ADuM3160
Full/Low Speed, 2.5 kV, USB Digital Isolator
ADuM3070
2.5 kV, Isolated Switch Regulator With
Integrated Feedback
ADP190
Logic Controlled, High-Side Power Switch
ADP7102
20 V, 300 mA, Low Noise, CMOS LDO
Isolated USB to Isolated RS-485/Isolated RS-232 Interface
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
CN-0373 Circuit Evaluation Board (EVAL-CN0373-EB1Z)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
The circuit shown in Figure 1 provides a completely isolated
connection between the popular USB bus and an RS-485 or
RS-232 bus. Both signal and power isolation ensures a safe USB
device interface to an industrial bus or debug port, allowing
TIA/EIA-485/232 bus traffic monitoring and the convenience of
sending and receiving commands to and from a PC that is not
equipped with an RS-485 or RS-232 port.
Isolation in this circuit increases system safety and robustness
by providing protection against electrical line surges and breaks
the ground connection between bus and digital pins, thereby
removing possible ground loops within the system.
The TIA/EIA RS-485 bus standard is one of the most widely used
physical layer bus designs in industrial and instrumentation
applications. RS-485 offers differential data transmission
between multiple systems, often over very long distances.
RS-485 communication offers additional robustness through
differential communication when compared to the RS-232
standard.
TIA/EIA RS-232 devices are widely used in industrial machines,
networking equipment, and scientific instruments. In modern
personal computers, which are often used for debugging network
problems, USB has displaced RS-232 from most of its peripheral
interface roles, and many computers do not come equipped
with RS-232 ports. The circuit in Figure 1 offers a robust and
compact solution for both RS-232 and RS-485 interfaces.
Rev. 0
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Devices engineers. Standard engineering practices have been employed in the design and
construction of each circuit, and their function and performance have been tested and verified in a lab
environment at room temperature. However, you are solely responsible for testing the circuit and
determining its suitability and applicability for your use and application. Accordingly, in no event shall
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©2015 Analog Devices, Inc. All rights reserved.
CN-0373
Circuit Note
T2
64µH
D5
VISO
+3.3V
L3
47µH
VISO = +3.3V
VIN VOUT
C2
47µF
C15
47µF
D8
ADP190
C12
0.1µF
R19
16.5kΩ
J1
GND2
VIN = 6V
VOUT = 5V
VOUT
X1
ADP7102
ADuM3070
C11
1µF
SENSE
R18
549Ω
EN/
UVLO
10nF
VDDA
GND
GND1
0.1µF
GND1
GND1
GND1
R16
10kΩ
R20
100kΩ
OC
100nF
GND2
VFB
FB
D6
LED
PG
C16
0.1µF
VDD2
X2
NC
EP
VREG
GND2
12MHz
OSC
FERRITE
600Ω
FT2232H
VISO = +3.3V
DD–
R7
UD+
DD+
VCCIO(20)
VCCIO(31)
VCCIO(42)
SPD
VCCIO(56)
VREGIN
VDD2
UD–
VOUT
BCBUS0
ADP190
ADBUS3
USB
MINI
D–
0.1µF
VISO
ADM3252E V+
C1+
ADBUS2
GND2
C1–
GND2
J3/J5
RS-232
BUS
RIN1
C2–
GND
GND2
GND1
10µF
RIN2
GND2
C2+
GND2
0.1µF
GND232
+ C1
0.1µF
16V
TOUT2
0.1µF
0.1µF
C3
+ 0.1µF
10V
TOUT1
0.1µF
GND1
FERRITE
600Ω
VCC
10µF
ROUT1
ROUT2
TIN1
TIN2
0.1µF
GND
GND485
GND2
ADBUS0
VBUS
D+
GND485
VIN
ADBUS1
DP
J4
USB
CABLE
TO PC
GND2
10µF
0.1µF
BDBUS1
PWREN#
BDBUS0
DM
VBUS2
R5
OSCO
OSCI
VPHY
0.1µF
GND2
PIN
GND2
VISO = +3.3V
GND2
VPLL
SPU
GND1
0.1µF
4.7µF
GND1
Z
Y
GND485
GND2
VISO = +3.3V
0.1µF PDEN
B
18pF
GND2
4.7µF
ADuM3160
A
J2
RS-485
BUS
VISOOUT
18pF
FERRITE
600Ω
VDD1
RXD
RE
TXD
VISO = +3.3V
0.1µF
VISOIN
DE
GND2
VBUS1
ADM2587E
VCC
V–
GNDISO
GND232
+ C2
0.1µF
16V
GND232
C4
+ 0.1µF
16V
GND2
GND1
ISOLATION
BARRIER
ISOLATION
BARRIER
Figure 1. Isolated USB to FTDI Isolated RS-232/Isolated RS-485 Circuit (Simplified Schematic, All Connections Not Shown)
CIRCUIT DESCRIPTION
The circuit in Figure 1 provides highly integrated and robust
isolation of fully TIA/EIA-485/232 compliant transceivers. The
ADM3252E 2.5 kV rms isolated RS-232 and the ADM2587E
2.5 kV rms isolated RS-485 solutions are the smallest available
in the industry. The ADuM3160 provides market-leading USB
port 2.5 kV rms isolation, and is easily integrated with low and
full speed USB-compatible peripheral devices. The FTDI
FT2232H (USB to UART converter) facilitates transmission via
UART to RS-485 or RS-232 bus ports. TIA/EIA RS-232 devices
are widely used in industrial machines, networking equipment,
and scientific instruments. Applications for RS-485 include
process control networks; industrial automation; remote
terminals; building automation, such as heating, ventilation,
air conditioning (HVAC) and security systems; motor control;
and motion control.
In these real-world systems, lightning strikes and power source
fluctuations can cause damage to communications ports by
generating large transient voltages. Isolation in the Figure 1
circuit increases system safety by providing protection against
these electrical line surges.
Rev. 0 | Page 2 of 6
12925-001
VIN
Circuit Note
CN-0373
12925-002
EVAL-CN0373-EB1Z
Figure 2. EVAL-CN0373-EB1Z Board
Figure 2 shows a photo of the isolated USB to FTDI isolated
RS-232/isolated RS-485 circuit. It is possible to transmit from
the USB port to both RS-485 and RS-232 ports simultaneously,
if required, or to just one port.
The ADuM3160 provides 2.5 kV rms digital isolation of the
data signals on the D+ and D− USB bus input to the FTDI
FT2232H (USB to UART converter). The isolated USB output
DD− and DD+ signals are connected to the DM and DP pins of
the FTDI, respectively. The FTDI FT2232H can transmit data
via UART to RS-232/RS-485 depending on which PC virtual
COM port (VCP) is chosen. The ADuM3160 VBUS1 power is
supplied via the USB cable connection. The ADuM3070
provides a regulated isolated power source. Power (+6 V) and
ground for the ADuM3070 are connected via the J1 barrel
socket connector. The ADuM3160 VBUS2 pin is supplied with
3.3 V isolated power by the ADuM3070. The ADuM3070 3.3 V
output also supplies the primary power for the ADM3252E
2.5 kV rms isolated RS-232 and the ADM2587E 2.5 kV rms
isolated RS-485 transceiver.
The ADM2587E 2.5 kV rms isolated RS-485 transceiver is the
industry-leading signal and power isolated solution. This
transceiver is capable of operating at 3.3 V or 5 V. Data transmits
on the TxD pin, and it is received on the RxD pin. Both the
driver and receiver outputs can be enabled or disabled, that is,
put into a high impedance state, by changing the logic levels
on the DE and RE pins, respectively.
The FTDI output pin BDBUS0 is connected to the TxD data
input pin of the ADM2587E. The FTDI output pins BCBUS0,
PWREN#, and BDBUS1 are connected to the DE, RE, and RxD
input pins of the ADM2587E, respectively. The DE and RE pin
state can also be configured via the LK1 and LK2 jumpers. For
each link, Position A connects the logic pin to 3.3 V, Position B
connects the logic pin to GND, and Position C connects the
logic pin to the FTDI output pins.
The ADM2587E can transmit and receive bus data via the A, B,
Y, and Z RS-485 inputs/outputs. An RS-485 bus cable can be
connected via the J2 five-way connector. Disconnecting the
LK5 and LK6 jumpers places the ADM2587E in a full duplex
configuration, where data can be transmitted via the Y and Z pins,
and received via the A and B pins. Connecting the LK5 and LK6
jumpers places the ADM2587E inputs/outputs in a half duplex
configuration, which is where bus data can only be transmitted
or received, but not simultaneously.
The ADM3252E is a high speed, 2.5 kV, fully isolated, dual channel
RS-232/V.28 transceiver device that is operational from a single
3.3 V or 5 V power supply. The RS-232 interface supports fullduplex communication and provides CTS and RTS for hardware
handshaking via the J5 five-way connector or the J3 connector.
J3 provides an RS-232 cable connector for connecting to
industrial equipment.
The ADM3252E transmitter inputs (TINx) accept TTL/CMOS
input levels from the ADBUS0 and ADBUS2 output pins of
the FTDI. The TINx inputs are inverted and coupled across the
isolation barrier, where they are transmitted as EIA/TIA-232E
bus signals via the J3 or J5 connector. The ADM3252E receiver
inputs (RINx) accept EIA/TIA-232E signal levels from the J3 or
J5 connector. The RINx inputs are inverted and coupled across
the isolation barrier to appear at the ROUTx pins. The ROUTx pins
are connected to the ADBUS1 and ADBUS3 inputs to the FTDI.
Two separate ADP190 circuits are used as soft start circuitry
to power the ADM2587E and ADM3252E after the FTDI
FT2232H has fully powered up. Jumper LK7 links the FTDI
FT2232H PWREN# pin to the EN pin of the ADP190 circuits
via the 74AHC1G14W5-7 inverter. The ADP190 EN pin must
be high to turn on the power switch; drive EN low to turn off
the power switch. Connecting LK7 in Position A (Position B
disconnected) means that the ADP190 EN pin is always high/
enabled. Connecting LK7 in Position B (Position A disconnected)
means that the ADP190 EN pin is triggered via the inverted
PWREN# signal.
The FTDI FT2232H data sheet provides a comprehensive listing
of the pin functions for RS-232 communications. The LK3 and
LK4 jumpers allow handshaking options for RS-232. When LK3
is connected, ADBUS4 (DTR#) is connected to ADBUS5 (DSR#).
When LK4 is connected, ADBUS4 (DTR#) is connected to
ADBUS6 (DCD#).
Rev. 0 | Page 3 of 6
CN-0373
Circuit Note
CIRCUIT EVALUATION AND TEST
Apply 6 V to the J1 barrel socket connector to power the EVALCN0373-EB1Z board. The voltage can be checked on the
VCC_REG test point at the output of the ADP7102 regulator.
The ADP7102 output voltage should measure 5 V. The 5 V is
routed to the ADuM3070 and T2 transformer, which supply the
3.3 V outputs to power the RS-485, RS-232, and FTDI circuits.
Check that the ISO_VCC test point measures 3.3 V.
12925-004
A complete transmit and receive path can be tested by connecting
the RS-232 and RS-485 outputs to an Analog Devices ezLINX™
iCoupler® Isolated Interface Development Environment board.
Alternatively, a USB to RS-232/RS-485 transmit test can be
performed by using the Tera Term open source terminal emulator
program. It is possible to transmit from the USB port to both
RS-485/RS-232 ports simultaneously, if required, or to just
one port.
Connect a USB cable from the laptop/PC to the J4 connector.
Attach an oscilloscope probe to the ISOTxD test point next to
the ADM3252E transceiver, as shown in Figure 3. Open the PC
application software and select COM5, then click OK, as shown
in Figure 4.
Figure 4. Tera Term COM5 for USB Transmission to the RS-232 Port on the
EVAL-CN0373-EB1Z Board
12925-005
Load the RS-232 data to be transmitted by clicking Send under
the File menu. Choose any large data size file for continuous
test transmission and click Send, as shown in Figure 5.
OSCILLOSCOPE
J1
Observe the isolated RS-232 signal on an oscilloscope by
probing the ISOTxD test point on the EVAL-CN0373-EB1Z
board (see Figure 6).
ADM2587E
Y
PC/LAPTOP
Z
FT2232H
TERA TERM
COM5 RS-232
TERA TERM
COM6 RS-485
J2
RS-485
ISOTxD
ADM3252E
J4 USB
J5
RS-232
J3
RS-232
12925-003
6.0V
POWER
SUPPLY
Figure 5. Tera Term COM5 Data for USB Transmission to the RS-232 Port on
the EVAL-CN0373-EB1Z Board
12925-006
Figure 3. Test Setup for the EVAL-CN0373-EB1Z Board
Figure 6. ISOTxD Signal for the RS-232 Port on the EVAL-CN0373-EB1Z Board
Rev. 0 | Page 4 of 6
Circuit Note
CN-0373
12925-008
A similar test can be performed for the ADM2587E transceiver.
Connect a USB cable from the laptop/PC to the J4 connector.
Attach an oscilloscope probe to the Y and Z test points next to
the ADM2587E transceiver as shown in Figure 3. Open a
second Tera Term emulator window, and select COM6 for
RS-485 transmission, as shown in Figure 7.
Figure 8. Tera Term COM6 Data for USB Transmission to the RS-485 Port on
the EVAL-CN0373-EB1Z Board
12925-007
Observe the isolated RS-485 signals on an oscilloscope by
probing the Y and Z test points, or the differential bus signal
by using the oscilloscope Y − Z Math function, as shown in
Figure 9.
Figure 7. Tera Term COM6 for USB Transmission to the RS-485 Port on the
EVAL-CN0373-EB1Z Board
12925-009
Load the RS-485 data to be transmitted by clicking Send under
the File menu. Choose any large data size file for continuous
test transmission and click Send, as shown in Figure 8.
Figure 9. Math Y – Z Waveform for the RS-485 Port on the
EVAL-CN0373-EB1Z Board
Rev. 0 | Page 5 of 6
CN-0373
Circuit Note
LEARN MORE
Data Sheets and Evaluation Boards
CN-0373 Design Support Package:
www.analog.com/CN0373-DesignSupport
ADM2587E Data Sheet
ezLINX™ iCoupler® Isolated Interface Development
Environment, ezLINX Board Quick Start Guide.
ADuM3160 Data Sheet
Marais, Hein. AN-960 Application Note. RS-485/RS-422
Circuit Implementation Guide. Analog Devices, Inc.
ADP190 Data Sheet
Clark, Sean and Ronn Kliger. AN-740 Application Note.
iCoupler® Isolation in RS-232 Applications.
Analog Devices, Inc.
UG-400 User Guide. ezLINX™ iCoupler® Isolated Interface
Development Environment. Analog Devices, Inc.
ADM3252E Data Sheet
ADuM3070 Data Sheet
ADP7102 Data Sheet
ezLINX™ iCoupler® Isolated Interface Development
Environment (EZLINX-IIIDE-EBZ)
REVISION HISTORY
4/15—Revision 0: Initial Version
(Continued from first page) Circuits from the Lab reference designs are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors.
While you may use the Circuits from the Lab reference designs in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual
property by application or use of the Circuits from the Lab reference designs. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the
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noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties
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©2015 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
CN12925-0-4/15(0)
Rev. 0 | Page 6 of 6