ADM2490EBRWZ Analog Devices Inc, ADM2490EBRWZ Datasheet - Page 13

• Manufacturer Part Number: ADM2490EBRWZ
• Description: IC TXRX RS-485 ISOLATED 16-SOIC
• Manufacturer: Analog Devices Inc
• Series: iCoupler®r

Specifications of ADM2490EBRWZ

• Inputs - Side 1/side 2: RS-485
• Number Of Channels: 1
• Isolation Rating: 5000Vrms
• Voltage - Supply: 4.75 V ~ 5.25 V
• Data Rate: 16Mbps
• Propagation Delay: 45ns
• Output Type: Logic
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Operating Temperature: -40°C ~ 105°C
• Device Type: Transceiver
• Ic Interface Type: RS485
• No. Of Drivers: 1
• Supply Voltage Range: 2.7V To 5.5V
• Driver Case Style: SOIC
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +105°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

THERMAL SHUTDOWN
The ADM2490E contains thermal-shutdown circuitry that protects
the part from excessive power dissipation during fault conditions.
Shorting the driver outputs to a low impedance source can result in
high driver currents. The thermal sensing circuitry detects the
increase in die temperature under this condition and disables
the driver outputs. This circuitry is designed to disable the driver
outputs when a die temperature of 150°C is reached. As the device
cools, the drivers are re-enabled at a temperature of 140°C.
FAIL-SAFE RECEIVER INPUTS
The receiver inputs include a fail-safe feature that guarantees a
logic high on the RxD pin when the A and B inputs are floating
or open-circuited.
MAGNETIC FIELD IMMUNITY
The limitation on the magnetic field immunity of the iCoupler
is set by the condition in which an induced voltage in the receiv-
ing coil of the transformer is large enough to either falsely set or
reset the decoder. The following analysis defines the conditions
under which this may occur. The 3 V operating condition of
the ADM2490E is examined because it represents the most
susceptible mode of operation.
The pulses at the transformer output have an amplitude greater
than 1 V. The decoder has a sensing threshold of about 0.5 V,
thus establishing a 0.5 V margin in which induced voltages can
be tolerated.
The voltage induced across the receiving coil is given by
where:
β is the magnetic flux density (gauss).
N is the number of turns in the receiving coil.
r
Given the geometry of the receiving coil and an imposed
requirement that the induced voltage is, at most, 50% of the
0.5 V margin at the decoder, a maximum allowable magnetic
field can be determined using Figure 22.
n
is the radius of the n
V
=
⎛ −
⎜
⎝
dt
dβ
⎞
⎟
⎠
∑
π
r
n
2
th
;
n
turn in the receiving coil (cm).
=
, 1
, 2
K
,
N
Rev. A | Page 13 of 16
For example, at a magnetic field frequency of 1 MHz, the
maximum allowable magnetic field of 0.2 kgauss induces a
voltage of 0.25 V at the receiving coil. This is about 50% of the
sensing threshold and does not cause a faulty output transition.
Similarly, if such an event occurs during a transmitted pulse and
is the worst-case polarity, it reduces the received pulse from
>1.0 V to 0.75 V, still well above the 0.5 V sensing threshold
of the decoder.
Figure 23 shows the magnetic flux density values in terms of
more familiar quantities, such as maximum allowable current
flow at given distances away from the ADM2490E transformers.
With combinations of strong magnetic field and high frequency,
any loops formed by PCB traces can induce error voltages large
enough to trigger the thresholds of succeeding circuitry. Care
should be taken in the layout of such traces to avoid this
possibility.
0.001
1000
Figure 22. Maximum Allowable External Magnetic Flux Density
0.01
0.01
100
100
0.1
0.1
10
10
1
1
1k
1k
DISTANCE = 5mm
Figure 23. Maximum Allowable Current for
Various Current-to-ADM2490E Spacings
DISTANCE = 100mm
10k
10k
MAGNETIC FIELD FREQUENCY (Hz)
MAGNETIC FIELD FREQUENCY (Hz)
100k
100k
DISTANCE = 1m
1M
1M
10M
10M
ADM2490E
100M
100M