4
Dynamic Power Consumption
Isoloop£devices achieve their low power consumption from the
manner by which 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 2.5ns wide, the power
consumption is independent of mark-to-space ratio and solely
dependent on frequency. This has obvious advantages over
optocouplers whose power consumption is heavily dependent on
its on-state and frequency.
The approximate power supply current per channel for
Power Supply Decoupling
Both power supplies to these devices should be decoupled with
low ESR 47 nF ceramic capacitors. For data rates in excess of
10MBd, use of ground planes for both GND1 and GND2 is highly
recommended. Capacitors should be located as close as possible to
the device.
Signal Status on Start-up and Shut Down
To minimize power dissipation, the 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 the inclusion
of an initialization signal in his start-up circuit. Initialization
consists of toggling each channel either high then low or low then
high, depending on the desired state.
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.
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 ns. It may
also be expressed as a percentage:
This figure is almost three times better than for any available
optocoupler with the same temperature range, and two times better
than any optocoupler regardless of published temperature range.
The IsoLoop®range of isolators surpasses the 10% maximum
PWD recommended by PROFIBUS, and will run at almost 35 Mb
before reaching the 10% limit.
Propagation delay skew is the difference in time taken for two or
more channels to propagate their signals. This becomes significant
when clocking is involved since it is undesirable for the clock
pulse to arrive before the data has settled. A short propagation
delay skew is therefore critical, especially in high data rate parallel
systems, to establish and maintain accuracy and repeatability. The
IsoLoop®range of isolators all have a maximum propagation delay
skew of 6 ns, which is five times better than any optocoupler. The
maximum channel to channel skew in the IsoLoop®coupler is only
3 ns which is ten times better than any optocoupler.
Application Notes:
PWD% = Maximum Pulse Width Distortion (ns) x 100%
Signal Pulse Width (ns)
For example: For data rates of 12.5 Mb
PWD% = 3 ns x 100% = 3.75%
80 ns
NVE Corporation 11409 Valley View Road Eden Prairie, MN 55344-3617 USA Telephone: (952) 829-9217 Fax: (952) 829-9189 Internet: www.isoloop.com
IL715/6/7ISOLOOP®