参数资料
型号: ADM2485BRWZ-REEL7
厂商: Analog Devices Inc
文件页数: 6/20页
文件大小: 0K
描述: IC TXRX ISOLATED RS-485 16SOIC
产品培训模块: iCoupler Digital Isolater Technology
设计资源: Half-Duplex, Isolated RS-485 Interface (CN0031)
标准包装: 1
系列: *
其它名称: ADM2485BRWZ-REEL7DKR
ADM2485
Rev. A | Page 14 of 20
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
(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.
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.
ISOLATION
BARRIER
VDD2
VDD1
A
B
DE OUT
GND2
GND1
TxD
RTS
RxD
RE
ENCODE
DECODE
ENCODE
D
R
TRANSCEIVER
DIGITAL ISOLATION
D1
D2
OSC
06021-
026
Figure 30. ADM2485 Digital Isolation and Transceiver Sections
TRUTH TABLES
Table 10 and Table 11 use the abbreviations found in Table 9.
Table 9. Truth Table Abbreviations
Letter
Description
H
High level
I
Indeterminate
L
Low level
X
Irrelevant
Z
High impedance (off )
NC
Disconnected
Table 10. Transmitting
Supply Status
Inputs
Outputs
VDD1
VDD2
RTS
TxD
A
B
DE OUT
On
H
L
H
On
H
L
H
On
L
X
Z
L
On
Off
X
Z
L
Off
On
X
Z
L
Off
X
Z
L
Table 11. Receiving
Supply Status
Input
Outputs
VDD1
VDD2
A B
RE
RxD
On
>+0.2 V
L or NC
H
On
<–0.2 V
L or NC
L
On
0.2 V < A B < +0.2 V
L or NC
I
On
Inputs open
L or NC
H
On
X
H
Z
On
Off
X
L or NC
H
Off
On
X
L or NC
H
Off
X
L or NC
L
THERMAL SHUTDOWN
The ADM2485 contains thermal shutdown circuitry that
protects the part from excessive power dissipation during fault
conditions. Shorting the driver outputs to a low impedance
source can result in high driver currents. The thermal sensing
circuitry detects the increase in die temperature under this
condition and disables the driver outputs. This circuitry is
designed to disable the driver outputs when a die temperature
of 150°C is reached. As the device cools, the drivers are re-enabled
at a temperature of 140°C.
RECEIVER FAIL-SAFE INPUTS
The receiver input includes a fail-safe feature that guarantees a
Logic high RxD output when the A and B inputs are floating or
open-circuited.
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