adm2481 Analog Devices, Inc., adm2481 Datasheet - Page 16

• Manufacturer Part Number: adm2481
• Description: Half-duplex, Icoupler Isolated Rs-485 Transceiver Adm2481
• Manufacturer: Analog Devices, Inc.

ADM2481
APPLICATIONS INFORMATION
PRINTED CIRCUIT BOARD (PCB) LAYOUT
The ADM2481 signal isolated RS-485 transceiver requires no
external interface circuitry for the logic interfaces. Power supply
bypassing is required at the input and output supply pins (see
Figure 29).
Bypass capacitors are most conveniently connected between
Pin 1 and Pin 2 for V
V
The total lead length between both ends of the capacitor and
the input power supply pin must not exceed 20 mm.
DD2
. The capacitor value must be between 0.01 μF and 0.1 μF.
GND
GND
GND
V
RxD
TxD
Figure 29. Recommended Printed Circuit Board Layout
DD1
RE
DE
1
1
1
DD1
NC = NO CONNECT
and between Pin 15 and Pin 16 for
ADM2481
TRANSFORMER
DRIVER
V
CC
V
GND
NC
B
A
NC
GND
GND
DD2
V
V
GND
V
Figure 30. Isolated Power Supply Circuit
2
2
2
CC
DD1
CC
ADM2481
ISOLATION
1
BARRIER
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SD103C
SD103C
GND
V
DD2
2
+
22µF
In applications involving high common-mode transients, take
care to ensure that board coupling across the isolation barrier
is minimized. Furthermore, the board layout must be designed
such that any coupling that does occur equally affects all pins
on a given component side.
Failure to ensure this can cause voltage differentials between
pins that exceed the absolute maximum ratings of the device,
thereby leading to latch-up or permanent damage.
ISOLATED POWER SUPPLY CIRCUIT
The ADM2481 requires isolated power capable of 5 V at
100 mA to be supplied between the V
no suitable integrated power supply is available, a discrete
circuit, such as the one in Figure 30, can be used. A center-
tapped transformer provides electrical isolation. The primary
winding is excited with a pair of square waveforms that are 180°
out of phase with each other. A pair of Schottky diodes and a
smoothing capacitor are used to create a rectified signal from
the secondary winding. The
provides a regulated power supply to the bus-side circuitry of
the ADM2481.
IN
SD
ERR
NR
ADP3330
GND
OUT
5V
+
10µF
ADP3330
DD2
linear voltage regulator
and GND
2
pins. If