ADM2482E/ADM2487E
Rev. A | Page 16 of 20
APPLICATIONS INFORMATION
PRINTED CIRCUIT BOARD LAYOUT
The isolated RS-485 transceiver of the ADM2482E/ADM2487E
requires no external interface circuitry for the logic interfaces.
Power supply bypassing is required at the input and output supply
Bypass capacitors are most conveniently connected between
Pin 3 and Pin 4 for VDD1 and between Pin 15 and Pin 16 for
VDD2. The capacitor value must be between 0.01 μF and 0.1 μF.
The total lead length between both ends of the capacitor and
the input power supply pin must not exceed 20 mm.
Bypassing Pin 9 and Pin 16 is also recommended unless the
ground pair on each package side is connected close to the
package.
D1
D2
GND1
VDD1
VDD2
GND2
A
B
RxD
RE
DE
Z
Y
NC
TxD
GND2
NC = NO CONNECT
07
379
-02
5
ADM2482E
OR
ADM2487E
TOP VIEW
(Not to Scale)
Figure 33. Recommended Printed Circuit Board Layout
In applications involving high common-mode transients, care
must be taken 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 exceeding the absolute maximum ratings of the device,
thereby leading to latch-up or permanent damage.
TRANSFORMER SUPPLIERS
The transformer primarily used with the ADM2482E/ADM2487E
must be a center-tapped transformer winding. The turns ratio
of the transformer must be set to provide the minimum required
output voltage at the maximum anticipated load with the mini-
mum input voltage.
Table 13 shows ADM2482E/ADM2487E
transformer suppliers.
Table 13. Transformer Supplies
Manufacturer
Primary Voltage 3.3 V
Primary Voltage 5 V
Coilcraft
DA2303-AL
GA3157
Murata
782482/33VC
782482/53VC
ISOLATED POWER SUPPLY CIRCUIT
The ADM2482E/ADM2487E integrate a transformer driver
that, when used with an external transformer and linear voltage
regulator (LDO), generates an isolated 3.3 V power supply to be
supplied between VDD2 and GND2, as shown in Figure 34. Pin D1 and Pin D2 of the ADM2482E/ADM2487E drive a
center-tapped Transformer T1. A pair of Schottky diodes and a
smoothing capacitor are used to create a rectified signal from the
secondary winding. The
ADP3330 LDO provides a regulated
3.3 V power supply to the ADM2482E/ADM2487E bus side
circuitry (VDD2).
When the ADM2482E/ADM2487E are powered by 3.3 V on the
logic side, a step-up transformer is required to compensate for
the forward voltage drop of the Schottky diodes and the voltage
drop across the regulator. The transformer turns ratio should be
chosen to ensure just enough headroom for the
ADP3330 LDO
to output a regulated 3.3 V output under all operating conditions.
If the ADM2482E/ADM2487E are powered by 5 V on the logic
side, then a step-down transformer should be used. For optimum
efficiency, the transformer turns ratio should be chosen to ensure
just enough headroom for the
ADP3330 LDO to output a regulated
3.3 V output under all operating conditions.
07
37
9-
0
26
ADM2482E/
ADM2487E
ISOLATION
BARRIER
1N5817
T1
22F
VCC
10F
MLC
VDD1
VDD2
D1
D2
GND1
GND2
100nF
ISOLATED 3.3V
100nF
10F
GND
3.3V
IN
OUT
ADP3330
SD
ERR
NR
Figure 34. Applications Diagram