IL3285 IL3222
6
NVE Corporation
11409 Valley View Road
Eden Prairie, MN 55344-3617 USA
Telephone: (952) 829-9217
Fax (952) 829-9189
Internet: www.isoloop.com
Introduction
The IL3000 family of isolated RS485 and RS422
transceivers are based on the revolutionary IL600 family of
digital isolators. A single external resistor is used to set each
input channel’s maximum current for input voltages above
0.5 V. For additional information, view the IL600 Series
data sheet.
Operation
The IL3000 series are current mode devices and utilize
NVE’s IL600 Series of digital isolators configured for non-
inverting outputs. The default state of each isolator output is
the logic high state for zero coil current. Therefore, to switch
the digital isolator output low, a logic low input signal
voltage is applied to the input coil via a current limiting
resistor. The resulting coil current switches the isolator
output low which in turn is sent to the transceiver. See
Figure 1 and Figure 2 below for typical coil connections.
Figure 1. Typical coil Connections for IL3285
Figure 2. Typical coil Connections for IL3222
Only a single resistor is required to limit the input coil to the
recommended 10 mA. This allows a wide range of input
voltages to be used since there is no semiconductor structure
on the input.
The absolute maximum current through the coil of the
IL3000 series is 25 mA DC. However, it is important to limit
input current to levels well below this in all applications.
The worst case logic threshold current is 10 mA. While
typical threshold currents are substantially less than this,
NVE recommends designing a 10 mA logic threshold
current in each application.
Figure 3 shows the response of the IL3000 Series. The GMR
bridge structure is designed such that the output of the
isolator is logic high when no field signal is present. The
output will switch to the low state with 10 mA of coil
current and the output will switch back to the high state
when the input current falls below 2 mA. This allows glitch-
free interface with low slew rate signals.
Figure 3. IL3000 Series Transfer Function
To calculate the value of the protection resistor (R1)
required, use Ohm’s law as shown in the examples below. It
should be noted that we are concerned only with the
magnitude of the voltage across the coil. The absolute values
of Vin High and Vin Low are arbitrary.
Figure 4. Series Resistor Calculation Equivalent Circuit.
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