adm2485 Analog Devices, Inc., adm2485 Datasheet - Page 14

• Manufacturer Part Number: adm2485
• Description: High Speed Isolated Rs-485 Transceiver With Integrated Transformer Driver
• Manufacturer: Analog Devices, Inc.

ADM2485
CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
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 30). Driver input and data enable, applied to the
TxD and RTS pins, respectively, and referenced to logic ground
(GND
transceiver section referenced to isolated ground (GND
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.
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 then decoded into the binary value that
was originally transmitted.
RTS
RxD
TxD
RE
Figure 30. ADM2485 Digital Isolation and Transceiver Sections
1
), are coupled across an isolation barrier to appear at the
V
DD1
DIGITAL ISOLATION
D1
GND
OSC
ENCODE
ENCODE
DECODE
D2
1
ISOLATION
BARRIER
DECODE
DECODE
ENCODE
GND
V
DD2
2
TRANSCEIVER
D
R
2
).
A
B
DE OUT
Rev. 0 | Page 14 of 20
TRUTH TABLES
The truth tables in this section use the abbreviations found in
Table 9.
Table 9. Truth Table Abbreviations
Letter
H
I
L
X
Z
NC
Table 10. Transmitting
V
On
On
On
On
Off
Off
Table 11. Receiving
V
On
On
On
On
On
On
Off
Off
Supply Status
DD1
DD1
Supply Status
V
On
On
On
On
On
Off
On
Off
V
On
On
On
Off
On
Off
DD2
DD2
Input
A – B
>+0.2 V
<–0.2 V
–0.2 V < A – B < +0.2 V
Inputs open
X
X
X
X
Description
High level
Indeterminate
Low level
Irrelevant
High impedance (off )
Disconnected
RTS
X
X
X
H
H
L
Inputs
TxD
H
L
X
X
X
X
A
Z
H
L
Z
Z
Z
B
L
H
Z
Z
Z
Z
L or NC
L or NC
L or NC
L or NC
H
L or NC
L or NC
L or NC
RE
Outputs
Outputs
DE OUT
H
H
L
L
L
L
RxD
H
L
I
H
Z
H
H
L