Datasheet

ADM2482E/ADM2487E
Rev. A | Page 14 of 20
CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION TRUTH TABLES
The truth tables in this section use the abbreviations found in
Table 10.
In the ADM2482E/ADM2487E, electrical isolation is imple-
mented on the logic side of the interface. Therefore, the part
has two main sections: a digital isolation section and a transceiver
section (see Figure 30). Driver input and data enable applied to
the TxD and DE pins, respectively, and referenced to logic ground
(GND
1
) are coupled across an isolation barrier to appear at the
transceiver section referenced to isolated ground (GND
2
). Simi-
larly, the receiver output, referenced to isolated ground in the
transceiver section, is coupled across the isolation barrier to
appear at the RxD pin referenced to logic ground.
Table 10. Truth Table Abbreviations
Letter Description
H High level
I Indeterminate
L Low level
X Irrelevant
Z High impedance (off)
NC Disconnected
Table 11. Transmitting
iCoupler Technology
The digital signals transmit across the isolation barrier using
iCoupler technology. This technique uses chip scale transformer
windings to couple the digital signals magnetically from one
side of the barrier to the other. Digital inputs are encoded into
waveforms that are capable of exciting the primary transformer
winding. At the secondary winding, the induced waveforms are
decoded into the binary value that was originally transmitted.
Supply Status Inputs Outputs
V
DD1
V
DD2
DE TxD Y Z
On On H H H L
On On H L L H
On On L X Z Z
On Off X X Z Z
Off On L X Z Z
Off Off X
Positive and negative logic transitions at the input cause narrow
pulses (~1 ns) to be sent to the decoder, via the transformer.
The decoder is bistable and is, therefore, either set or reset by
the pulses, indicating input logic transitions. In the absence of
logic transitions at the input for more than ~1 μs, a periodic set
of refresh pulses indicative of the correct input state are sent to
ensure dc correctness at the output. If the decoder receives no
internal pulses for more than about 5 μs, then the input side is
assumed to be unpowered or nonfunctional, in which case the
output is forced to a default state (see Tabl e 10).
X Z Z
Table 12. Receiving
Supply Status Inputs Outputs
V
DD1
V
DD2
RE
A − B RxD
On On >−0.03 V L or NC H
On On <−0.2 V L or NC L
On On −0.2 V < A − B < −0.03 V L or NC I
On On Inputs open L or NC H
On On X H Z
On Off
V
DD1
GND
1
GND
2
V
DD2
D1 D2
OSC
ENCODE DECODE
ENCODE
DECODE
ENCODE DECODE
DIGITAL ISOLATION TRANSCEIVER
D
R
DE
TxD
RxD
RE
ISOLATION
BARRIER
Y
Z
A
B
07379-022
X L or NC H
Off Off L or NC X L
Figure 30. ADM2482E/ADM2487E Digital Isolation and Transceiver Sections