ADM2484E
APPLICATIONS INFORMATION
ISOLATED POWER SUPPLY CIRCUIT
PC BOARD LAYOUT
The ADM2484E requires isolated power capable of 3.3 k at up
to approximately 71 mA (this current is dependent on the data
rate and termination resistors used) to be supplied between the
kDD2 and the GND2 pins. A transformer driver circuit with a
center tapped transformer and LDO can be used to generate the
isolated 1 k supply, as shown in Figure 28. The center tapped
transformer provides electrical isolation of the 1 k power
supply. The primary winding of the transformer is excited with
a pair of square waveforms that are ±80° out of phase with each
other. A pair of Schottꢀy diodes and a smoothing capacitor are
used to create a rectified signal from the secondary winding.
The ADP3330 linear voltage regulator provides a regulated
power supply to the bus-side circuitry (kDD2) of the ADM2484E.
ISOLATION
The ADM2484E isolated RS-481 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 conveniently connected between Pin ±
and Pin 2 for kDD± and between Pin ±1 and Pin ±6 for kDD2
.
Best practice suggests the following:
•
•
A capacitor value between 0.0± ꢁF and 0.± ꢁF.
A total lead length between both ends of the capacitor and
the input power supply pin that does not exceed 20 mm.
Unless the ground pair on each pacꢀage side is connected
close to the pacꢀage, consider bypassing between Pin ± and
Pin 8 and between Pin 9 and Pin ±6.
•
V
V
GND
A
DD1
GND
DD2
V
CC
BARRIER
1
2
RxD
RE
SD103C
5V
B
ADM2484E
IN
OUT
+
DE
Z
+
22µF
SD
ERR
NR
TRANSFORMER
DRIVER
10µF
V
ADP3330
TxD
NC
Y
NC
GND
CC
GND
1
2
78253
GND
SD103C
DD2
NC = NO CONNECT
V
CC
Figure 29. Recommended PCB Layout
In applications involving high common-mode transients, ensure
that board coupling across the isolation barrier is minimized.
Furthermore, design the board layout so that any coupling that
does occur equally affects all pins on a given component side.
Failure to ensure this could cause voltage differentials between pins
exceeding the absolute maximum ratings of the device, thereby
leading to latch-up or permanent damage.
V
V
DD1
ADM2484E
GND
GND
2
1
Figure 28. Isolated Power Supply Circuit
Rev. 0 | Page 14 of 16
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