il3422 NVE Corp., il3422 Datasheet - Page 7

• Manufacturer Part Number: il3422
• Description: High Speed Rs-485 And Rs-422 Isolated Transceivers
• Manufacturer: NVE Corp.

Power Supply Decoupling
Both V
proper operation. Additionally, V
Operation
The IL3422 and IL3485 are current-mode devices. Changes in input coil current switch internal spintronic GMR sensors, which
then change the logic state of the outputs. The GMR bridge is designed so the output of the isolator is logic high when no field
signal is present.
A single resistor is required to limit the input coil current to the recommended 5 mA. The absolute maximum current through any
coil is 25 mA DC. Although logic threshold currents are typically less than the worst-case 5 mA, NVE recommends designing for
5 mA logic threshold current in all applications.
Figure 1 shows the input response of the IL3422 and IL3485.
the low state with approximately 3.5 mA of coil current, and back to the high state when the input current falls below
approximately 1.5 mA. This allows glitch-free interface with low slew-rate signals.
IsoLoop Isolators use Wheatstone Bridge structures that are only sensitive to differential magnetic fields. There are several ways to
further enhanced the magnetic field immunity of IL3000 Transceivers. Providing a larger internal field will reduce the effect of an
external field on the GMR sensor. Immunity to external magnetic fields can also be enhanced by proper orientation of the device
with respect to the field direction and field boosting capacitors.
Orientation of the device with respect to the field direction
An applied field in the “H1” direction is the worst case for magnetic immunity. In this case the external field is in the same
Coil Current
Figure 1. IL3000 Series Input Transfer Function
Figure 2. Orientation of External Magnetic Field
Logic State
NVE Corporation
GND
V
GND
V
COIL1
RE
DE
DD1
R
D
1
1
High
Low
DD1
mA
3.5
1.5
5
and V
H2
11409 Valley View Road, Eden Prairie, MN 55344-3617
DD2
V
GND
NC
B
A
V
NC
GND
COIL2
DD2
2
2
must be bypassed with 47 nF ceramic capacitors. These should be placed as close as possible to V
DD2
should be bypassed with a 10 µF tantalum capacitor.
H1
t
t
direction as the applied internal field. In one direction it will tend to help
switching; in the other it will hinder switching. This can cause
unpredictable operation.
An applied field in the direction of “H2” has considerably less effect on
the sensor and will result in significantly higher immunity levels as
shown in Table 1.
The greatest magnetic immunity is achieved by adding the current boost
capacitor across the input resistor. Very high immunity can be achieved
with this method.
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Magnetic Field Booster Capacitor
A small capacitor (200 pF to 1 nF) in parallel the current limiting
resistor boosts the instantaneous current through the coil at the point of
signal transition. The resultant magnetic field boost pushes the GMR
bridge output through the comparator threshold voltage with less
propagation delay and pulse width distortion. The booster capacitor
gives a great deal of design headroom and can usually eliminate design
concerns related to temperature and power supply fluctuations.
Magnetic Field Immunity
IsoLoop devices operate by imposing a magnetic field on a GMR
sensor, which translates the change in field into a change in logic state.
The devices are manufactured with a magnetic shield above the sensor.
The shield acts as a flux concentrator to boost the magnetic signal from
the internal coil, and as a shield against external magnetic fields. The
shield absorbs surrounding stray flux until it becomes saturated. At
saturation the shield is transparent to external applied fields, and the
GMR sensor may react to the field. To compensate for this effect,
Output logic high is the zero input current state.
7
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www.IsoLoop.com
IL3485/IL3422
The output switches to
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DD
pins for