ADM2485
Preliminary Technical Data
CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
TRUTH TABLES
In the ADM2485, 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 26). Driver input and data enable, applied to the
TxD and RTS pins, respectively, and referenced to logic ground
(GND1), are coupled across an isolation barrier to appear at the
transceiver section referenced to isolated ground (GND2).
Similarly, 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.
The truth tables in this section use these abbreviations:
Letter
Description
High level
Indeterminate
Low level
H
I
L
X
Z
NC
Irrelevant
High impedance (off)
Disconnected
Table 6. Transmitting
Supply Status
Inputs
Output
iCoupler Technology
VDD1
On
On
On
On
Off
Off
VDD2
On
On
On
Off
On
Off
RTS
H
H
L
X
TxD
H
L
X
X
A
H
L
B
L
DE OUT
H
H
L
L
L
The digital signals are transmitted 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 then decoded into the binary value that
was originally transmitted.
H
Z
Z
Z
Z
Z
Z
Z
Z
X
X
X
X
L
Table 7. Receiving
VDD1
VDD2
Supply Status
Inputs
Output
ISOLATION
BARRIER
VDD1
VDD2
A−B (V)
RxD
RE
A
B
On
On
On
On
On
On
Off
Off
On
On
On
On
On
Off
On
Off
>0.2
<−0.2
L or NC
L or NC
H
L
I
H
Z
H
H
L
TxD
RTS
D
DECODE
DECODE
ENCODE
ENCODE
ENCODE
DECODE
−0.2 < A − B < 0.2 L or NC
Inputs open
X
X
X
X
DE OUT
L or NC
H
L or NC
L or NC
L or NC
RxD
RE
R
DIGITAL ISOLATION
GND1
TRANSCEIVER
GND2
Figure 26. ADM2485 Digital Isolation and Transceiver Sections
Rev. PrK | Page 12 of 15
ADI [ ADI ]
