ADM2483BRW Ver la hoja de datos (PDF) - Analog Devices
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ADM2483BRW Datasheet PDF : 20 Pages
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Data Sheet
TRUTH TABLES
The following truth tables use these abbreviations:
Letter
H
L
X
Z
NC
Description
High level
Low level
Irrelevant
High impedance (off)
Disconnected
Table 9. Transmitting
Supply Status
VDD1
VDD2
DE
On
On
H
On
On
H
On
On
L
On
Off
X
Off
On
X
Off
Off
X
Inputs
TxD
H
L
X
X
X
X
Outputs
A
B
H
L
L
H
Z
Z
Z
Z
Z
Z
Z
Z
Table 10. Receiving
Supply Status
Inputs
VDD1 VDD2 A − B (V)
RE
On On >−0.03
L or NC
On On <−0.2
L or NC
−0.2 < A − B <
On On −0.03
L or NC
On On Inputs open L or NC
On On X
H
On Off X
L or NC
Off On X
L or NC
Off Off X
L or NC
Outputs
RxD
H
L
Indeterminate
H
Z
H
H
L
POWER-UP/POWER-DOWN CHARACTERISTICS
The power-up/power-down characteristics of the ADM2483 are
in accordance with the supply thresholds shown in Table 11.
Upon power-up, the ADM2483 output signals (A, B, and RxD)
reach their correct state once both supplies exceed their
thresholds. Upon power-down, the ADM2483 output signals
retain their correct state until at least one of the supplies drops
below its power-down threshold. When the VDD1 power-down
threshold is crossed, the ADM2483 output signals reach their
unpowered states within 4 µs.
Table 11. Power-Up/Power-Down Thresholds
Supply
Transition
Threshold (V)
VDD1
Power-up
2.0
VDD1
Power-down
1.0
VDD2
Power-up
3.3
VDD2
Power-down
2.4
ADM2483
THERMAL SHUTDOWN
The ADM2483 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.
TRUE FAIL-SAFE RECEIVER INPUTS
The receiver inputs have a true fail-safe feature, which ensures
that the receiver output is high when the inputs are open or
shorted. During line-idle conditions, when no driver on the bus
is enabled, the voltage across a terminating resistance at the
receiver input decays to 0 V. With traditional transceivers,
receiver input thresholds specified between −200 mV and
+200 mV mean that external bias resistors are required on the
A and B pins to ensure that the receiver outputs are in a known
state. The true fail-safe receiver input feature eliminates the
need for bias resistors by specifying the receiver input threshold
between −30 mV and −200 mV. The guaranteed negative
threshold means that when the voltage between A and B decays
to 0 V, the receiver output is guaranteed to be high.
MAGNETIC FIELD IMMUNITY
Because iCouplers use a coreless technology, no magnetic
components are present, and the problem of magnetic
saturation of the core material does not exist. Therefore,
iCouplers have essentially infinite dc field immunity. The
analysis that follows defines the conditions under which this
might occur. The ADM2483’s 3 V operating condition is
examined because it represents the most susceptible mode of
operation.
The limitation on the iCoupler’s ac magnetic field immunity is
set by the condition in which the induced error voltage in the
receiving coil (the bottom coil in this case) is made sufficiently
large, either to falsely set or reset the decoder. The voltage
induced across the bottom coil is given by
V
=
− dd
dt
∑ πrn2
;
n=
1, 2, ... , N
where if the pulses at the transformer output are greater than
1.0 V in amplitude:
β = magnetic flux density (gauss)
N = number of turns in receiving coil
rn = radius of nth turn in receiving coil (cm)
The decoder has a sensing threshold of about 0.5 V; therefore,
there is a 0.5 V margin in which induced voltages can be
tolerated.
Rev. C | Page 15 of 20
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