adm2491e Analog Devices, Inc., adm2491e Datasheet - Page 12

• Manufacturer Part Number: adm2491e
• Description: High Speed, Esd-protected, Half-/full-duplex, Icoupler Isolated Rs-485 Transceiver
• Manufacturer: Analog Devices, Inc.

ADM2491E
CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
In the ADM2491E, 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 25). The driver input signal, which is applied to the
TxD pin and referenced to logic ground (GND
across an isolation barrier to appear at the transceiver section
referenced to isolated ground (GND
input, which is referenced to isolated ground in the transceiver
section, is coupled across the isolation barrier to appear at the
RxD pin referenced to logic ground.
iCoupler Technology
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 decoded into the binary value that was
originally transmitted.
RxD
TxD
DE
RE
Figure 25. ADM2491E Digital Isolation and Transceiver Sections
DIGITAL ISOLATION
GND
V
ENCODE
ENCODE
DECODE
DD1
1
ISOLATION
BARRIER
ENCODE
DECODE
DECODE
2
). Similarly, the receiver
GND
V
DD2
TRANSCEIVER
2
1
D
), is coupled
R
Y
Z
A
B
Rev. 0 | Page 12 of 16
TRUTH TABLES
The truth tables in this section use the abbreviations shown in
Table 9.
Table 9. Truth Table Abbreviations
Letter
H
L
I
X
Z
NC
Table 10. Transmitting
Table 11. Receiving
V
On
On
On
On
On
On
Off
V
On
On
On
On
Off
Off
Supply Status
DD1
DD1
Supply Status
V
On
On
On
On
On
Off
Off
DD2
V
On
On
On
Off
On
Off
DD2
Description
High level
Low level
Indeterminate
Irrelevant
High impedance (off )
Disconnected
A − B (V)
>0.2
<−0.2
−0.2 < A − B < +0.2
Inputs open
X
X
X
DE
H
H
L
X
L
X
Inputs
Inputs
TxD
H
L
X
X
L
X
RE
L or NC
L or NC
L or NC
L or NC
H
L or NC
L or NC
Y
H
L
Z
Z
Z
Z
Outputs
Output
RxD
H
L
I
H
Z
H
L
Z
L
H
Z
Z
Z
Z