IsoLoop
Isolated PROFIBUS
Evaluation Board
®
Board No.: IL3685-3-01
NVE Corporation
(952) 829-9217
iso-apps@nve.com
YouTube.com/NveCorporation
www.nve.com
About This Evaluation Board
Isolation reduces noise, eliminates ground loops, and improves safety.
This Evaluation Board provides a complete isolated PROFIBUS node using the ultraminiature
IL3685-3E narrow-body isolated transceiver.
The evaluation board provides screw terminal and DB9 connections, and demonstrates best
layout practices including separate ground planes. Termination, pull-up, and pull-down
resistors can be changed to accommodate different configurations.
The IL3685 is a galvanically isolated transceiver using NVE’s patented IsoLoop spintronic
Giant Magnetoresistance (GMR) technology.
Full PROFIBUS compliance includes the rigorous PROFIBUS differential output voltage
specifications. Current limiting and thermal shutdown features protect against output short
circuits and bus contention that may cause excessive power dissipation. Receiver inputs feature
a “fail-safe if open” design, ensuring a logic high R-output if A/B are floating.
IL3685 Specification Highlights
• 40 Mbps data rate
• 3 V to 5.5 V power supplies
• 20 ns propagation delay
• 5 ns pulse skew
• 100 ps jitter
• Low quiescent supply current
• 2.5 kV
RMS
and 6 kV
RMS
isolation versions
• Low EMC footprint
• Thermal shutdown protection
•
−40°C
to +85°C temperature range
• Meets or exceeds ANSI RS-485 and ISO 8482:1987(E)
• PROFIBUS compliant
• VDE V 0884 certified and UL 1577 recognized
• Availalble in 16-pin wide-body, narrow-body and QSOP packages
Visit
www.IsoLoop.com
for datasheets and illustrative applications.
NVE Corporation
(952) 829-9217
iso-apps@nve.com
YouTube.com/NveCorporation
www.nve.com
Evaluation Board Layout
47 nF decoupling
capacitors close to
VDD1 and VDD2 pins
Power
connections
Bus
connections
Input
connections
DB9
PROFIBUS
connector
IL3685-3E isolated narrow-body
PROFIBUS transceiver
Termination resistor
minimizes reflections
Test points
(15 places)
Fail-safe resistors ensure
known bus state with no
active drivers
Quick Start
• Connect V
DD1
to a 3.3 V power supply and V
DD2
to a 5 V supply.
• Tie “DE” high and “RE” low to enable the input and output data.
• Connect a square-wave signal to the “D” input with an amplitude of 2.4 to 3.3 V.
• Look for the complementary “A” and “B” outputs on an oscilloscope.
NVE Corporation
(952) 829-9217
iso-apps@nve.com
YouTube.com/NveCorporation
www.nve.com
Circuit Diagram
VDD1
VDD2
C
DD1
47nF
1
IL3685-3E
C
DD2
47
nF
13 16
14
ISODE
15
GND2I
10
XDE
6
DE
D 5
R
RE
3
4
2
R
FSH
390R
P5V
1
6
3
8
11
12
A
B
R
T
220R
CNTR-P
DGND
4
5
9
GND1
Isolation
Boundary
9
GND2X
R
FSL
390R
GND2
Device
pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Symbol
VDD1
GND1
R
RE
D
DE
NC
NC
GND2X
XDE
A
B
VDD2X
ISODE
GND2I
VDD2I
Description
Input power supply
Input power supply ground return
Output data from bus
Read data enable (R=high impedance if RE is high)
Data input to bus
Drive enable
No internal connection
No internal connection
Output transceiver ground return (normally connected to pin 15)
Transceiver Device Enable (normally connected to pin 14)
Non-inverting bus line
Inverting bus line
Output transceiver power supply (normally connected to pin 16)
Isolated DE output (normally connected to pin 10)
Output isolation power supply ground return (normally connected to pin 9)
Output power supply (normally connected to pin 13)
NVE Corporation
(952) 829-9217
iso-apps@nve.com
YouTube.com/NveCorporation
www.nve.com
Board Layout and Cabling
Board Layout Best Practices
Although not always necessary, the following connector layout precautions are best practices:
• The connector, termination resistor, and transceiver should be as close together as possible.
• Use 47 nF decoupling capacitors as close as possible to the transceiver V
DD
pins
.
• Provide ground planes for both power supplies.
Cable Specifications
PROFIBUS Type A bus cable is recommended for high transmission speeds (more than
500 Kbps). Type B should only be used at low baud rates and low requirements on the network
distances.
Cable Length
IL3685 transceivers are intended for networks up to 4,000 feet (1,200 m) with Type A bus
cable and proper termination. The maximum data rate decreases as cable length increases.
Differential Bus Output Voltage
Unlike many other PROFIBUS transceivers, the IL3685 meets stringent PROFIBUS standards
for transceiver differential output voltage. Some transceivers manufacturers erroneously
believe maximizing differential output voltage is a good thing.
The PROFIBUS specification requires:
“The differential voltage between A- and B-line shall be a minimum of 4 V
and a maximum of 7 V.”
Unfortunately, most RS-485 transceiver don’t specify bus voltages that way. They specify a
maximum and a minimum differential voltage between A and B. Differential maximum and
minimum is almost always quoted with a single output state under low and high loads
respectively.
The PROFIBUS specification is with respect to terminal A of the bus, however. When A is
greater than B, a negative voltage is measured with respect to A.
With no load, the voltage measured will be approximately
−3.2
V for compatible transceivers.
When the opposite logic state is driven from TxD, the B node will become positive with
respect to A.
NVE Corporation
(952) 829-9217
iso-apps@nve.com
YouTube.com/NveCorporation
www.nve.com
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