ADM2484E
CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
TRUTH TABLES
The truth tables in this section use the abbreviations shown
in Table 9.
In the ADM2484E, electrical isolation is implemented on the
logic side of the interface. Therefore, the part has two main
sections: a digital isolation section and a transceiver section
(see Figure 21). The driver input signal, which is applied to the
TxD pin and referenced to the logic ground (GND±), is coupled
across an isolation barrier to appear at the transceiver section
referenced to the isolated ground (GND2). Similarly, the
receiver input, which is referenced to the isolated ground in the
transceiver section, is coupled across the isolation barrier to
appear at the RxD pin referenced to the logic ground.
Table 9. Truth Table Abbreviations
Letter
Description
H
L
High level
Low level
I
X
Z
Indeterminate
Irrelevant
High impedance (off)
Disconnected
NC
iCoupler Technology
Table 10. Transmitting
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
TxD
Outputs
VDD1
On
On
On
On
Off
Off
VDD2
On
On
On
Off
On
Off
DE
H
H
L
X
L
Y
H
L
Z
Z
Z
Z
Z
L
H
L
X
X
X
X
H
Z
Z
Z
Z
Positive and negative logic transitions at the input cause narrow
(~± ns) pulses to be sent to the decoder via the transformer. The
decoder is bistable and is, therefore, set or reset by the pulses,
indicating input logic transitions. In the absence of logic
transitions at the input for more than ~± 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 1 μs, then the input side is
assumed to be unpowered or nonfunctional, in which case the
output is forced to a default state (see Table ±0).
X
Table 11. Receiving
Supply Status
Inputs
Output
RE
RxD
H
L
VDD1
On
On
On
On
On
On
Off
VDD2
On
On
On
On
On
Off
Off
A − B (V)
> −0.03
< −0.2
L or NC
L or NC
L or NC
L or NC
H
−0.2 < A − B < −0.03
I
Inputs open
H
Z
X
X
X
V
V
DD1
DD2
H
L
L or NC
L or NC
ISOLATION
BARRIER
ENCODE
ENCODE
DECODE
DECODE
DECODE
ENCODE
DE
Y
Z
D
TxD
A
B
R
RxD
RE
DIGITAL ISOLATION
TRANSCEIVER
GND
GND
2
1
Figure 25. Digital Isolation and Transceiver Sections
Rev. 0 | Page 12 of 16
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