IL710

8

NVE Corporation

11409 Valley View Road, Eden Prairie, MN 55344-3617

(952) 829-9217

www.nve.com

YouTube.com/NveCorporation

iso-apps@nve.com

80 ns

Application Information

Isolator Operation

An equivalent circuit is shown below:

Data

In

Data

Out

Field

Isolator Signal Path

The GMR isolator signal path starts with a buffered input signal that is

driven through an ultraminiature coil. This generates a small magnetic

field that changes the electron spin polarization of GMR resistors,

which are configured as a Wheatstone bridge. The change in spin

polarization of the resistors creates a bridge voltage which drives an

output comparator to construct an isolated version of the input signal.

Small Size, High Speed, and Low EMI

The coil, GMR, and circuitry are integrated to allow small

packages. GMR is inherently high speed and low distortion, and

unlike transformers, does not rely on energy transfer, so power is

low and EMI emissions are minimal.

High Magnetic Immunity

GMR provides large signals which improve magnetic immunity,

and the Wheatstone bridge configuration cancels ambient common-

mode magnetic fields, further enhancing immunity to external

magnetic fields.

Electrostatic Discharge Sensitivity

This product has been tested for electrostatic sensitivity to the

limits stated in the specifications. However, NVE recommends that

all integrated circuits be handled with appropriate care to avoid

damage. Damage caused by inappropriate handling or storage could

range from performance degradation to complete failure.

Electromagnetic Compatibility

IsoLoop Isolators have the lowest EMC footprint of any isolation

technology. IsoLoop Isolators’ Wheatstone bridge configuration

and differential magnetic field signaling ensure excellent EMC

performance against all relevant standards. These isolators are fully

compliant with IEC 61000-6-1 and IEC 61000-6-2 standards for

immunity, and IEC 61000-6-3, IEC 61000-6-4, CISPR, and FCC

Class A standards for emissions.

Immunity to external magnetic fields is even higher if the field

direction is “end-to-end” rather than to “pin-to-pin” as shown in the

diagram below:

Cross-axis Field Direction

Dynamic Power Consumption

IsoLoop Isolators achieve their low power consumption from the

way they transmit data across the isolation barrier. By detecting the

edge transitions of the input logic signal and converting these to

narrow current pulses, a magnetic field is created around the GMR

Wheatstone bridge. Depending on the direction of the magnetic

field, the bridge causes the output comparator to switch following

the input logic signal. Since the current pulses are narrow, about

2.5 ns, the power consumption is independent of mark-to-space

ratio and solely dependent on frequency. This has obvious

advantages over optocouplers, which have power consumption

heavily dependent on mark-to-space ratio.

Power Supply Decoupling

Both power supplies should be decoupled with 0.1 µF typical

(0.047 µF minimum) capacitors as close as possible to the VDD

pins. Ground planes for both GND1 and GND2 are highly

recommended for data rates above 10 Mbps.

Signal Status on Start-Up and Shut Down

To minimize power dissipation, input signals are differentiated and

then latched on the output side of the isolation barrier to reconstruct

the signal. This could result in an ambiguous output state

depending on power up, shutdown and power loss sequencing.

Therefore, the designer should consider including an initialization

signal in the start-up circuit. Initialization consists of toggling the

input either high then low, or low then high.

Data Transmission Rates

The reliability of a transmission system is directly related to the

accuracy and quality of the transmitted digital information. For a digital

system, those parameters which determine the limits of the data

transmission are pulse width distortion and propagation delay skew.

Propagation delay is the time taken for the signal to travel through

the device. This is usually different when sending a low-to-high

than when sending a high-to-low signal. This difference, or error, is

called pulse width distortion (PWD) and is usually in nanoseconds.

It may also be expressed as a percentage:

PWD% = Maximum Pulse Width Distortion (ns)

x 100%

Signal Pulse Width (ns)

For example, with data rates of 12.5 Mbps:

PWD% = 3 ns

x 100% = 3.75%

This figure is almost three times better than any available

optocoupler with the same temperature range, and two times better

than any optocoupler regardless of published temperature range.

IsoLoop isolators exceed the 10% maximum PWD recommended

by PROFIBUS, and will run to nearly 35 Mb within the 10% limit.

Propagation delay skew is the signal propagation difference

between two or more channels. This becomes significant in clocked

systems because it is undesirable for the clock pulse to arrive

before the data has settled. Short propagation delay skew is

therefore especially critical in high data rate parallel systems for

establishing and maintaining accuracy and repeatability. Worst-

case channel-to-channel skew in an IL700 Isolator is only 3 ns,

which is ten times better than any optocoupler. IL700 Isolators

have a maximum propagation delay skew of 6 ns, which is five

times better than any optocoupler.