adm2486 Analog Devices, Inc., adm2486 Datasheet - Page 14

• Manufacturer Part Number: adm2486
• Description: High Speed, Half-duplex Icoupler Isolated Rs-485 Transceiver
• Manufacturer: Analog Devices, Inc.

ADM2486
CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
In the ADM2486, 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 request-to-send signals,
applied to the TxD and RTS pins, respectively, and referenced to
logic ground (GND
appear at the transceiver section referenced to isolated ground
(GND
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.
TRUTH TABLES
The truth tables in this section use these abbreviations:
Letter
H
I
L
X
Z
NC
RTS
RxD
TxD
RE
Figure 26. ADM2486 Digital Isolation and Transceiver Sections
2
). Similarly, the receiver output, referenced to isolated
DIGITAL ISOLATION
GND
V
ENCODE
ENCODE
DECODE
DD1
1
1
), are coupled across an isolation barrier to
ISOLATION
BARRIER
Description
High level
Indeterminate
Low level
Irrelevant
High impedance (off )
Disconnected
ENCODE
DECODE
DECODE
GND
V
DD2
2
TRANSCEIVER
D
R
Rev. D | Page 14 of 20
DE
A
B
Table 9. Transmitting
Supply Status
V
On
On
On
On
Off
Off
1
Table 10. Receiving
Supply Status
V
On
On
On
On
On
On
Off
Off
1
POWER-UP/POWER-DOWN THRESHOLDS
The power-up/power-down characteristics of the ADM2486 are
in accordance with the supply thresholds shown in Table 11.
Upon power-up, the ADM2486 output signals (A, B, RxD, and
DE) reach their correct state once both supplies have exceeded
their thresholds. Upon power-down, the ADM2486 output
signals retain their correct state until at least one of the supplies
drops below its power-down threshold. When the V
down threshold is crossed, the ADM2486 output signals reach
their unpowered states within 4 μs.
Table 11. Power-Up/Power-Down Thresholds
Supply
V
V
V
V
The PV pin is tied high.
The PV pin is tied high.
DD1
DD1
DD2
DD2
DD1
DD1
V
On
On
On
On
On
Off
On
Off
DD2
V
On
On
On
Off
On
Off
DD2
Transition
Power-up
Power-down
Power-up
Power-down
A − B (V)
>0.2
<−0.2
−0.2 < A − B < 0.2
Inputs open
X
X
X
X
RTS
H
H
L
X
X
X
Inputs
Inputs
TxD
H
L
X
X
X
X
Threshold (V)
2.0
1.0
3.3
2.4
L or NC
L or NC
L or NC
L or NC
H
L or NC
L or NC
L or NC
RE
A
H
L
Z
Z
Z
Z
Outputs
DD1
B
L
H
Z
Z
Z
Z
Output
RxD
H
L
I
H
Z
H
H
L
power-
DE
L
H
H
L
L
L
1
1