Datasheet

Data Sheet ADM3053
Rev. E | Page 15 of 18
APPLICATIONS INFORMATION
PCB LAYOUT
The ADM3053 signal and power isolated CAN transceiver contains
an isoPower integrated dc-to-dc converter, requiring no external
interface circuitry for the logic interfaces. Power supply bypassing
is required at the input and output supply pins (see Figure 28).
The power supply section of the ADM3053 uses a 180 MHz
oscillator frequency to pass power efficiently through its chip-
scale transformers. In addition, the normal operation of the
data section of the iCoupler introduces switching transients on
the power supply pins.
Bypass capacitors are required for several operating frequencies.
Noise suppression requires a low inductance, high frequency
capacitor, whereas ripple suppression and proper regulation
require a large value capacitor. These capacitors are connected
between GND1 and Pin 6 (V
IO
) for V
IO
. It is recommended that
a combination of 100 nF and 10 nF be placed as shown in Figure 28
(C6 and C4). It is recommended that a combination of two
capacitors, with values of 100 nF and 10 µF, are placed between
Pin 8 (V
CC
) and Pin 9 (GND1) for V
CC
as shown in Figure 28 (C2
and C1). The V
ISOIN
and V
ISOOUT
capacitors are connected between
Pin 11 (GND2) and Pin 12 (V
ISOOUT
) with recommended values
of 100 nF and 10 µF as shown in Figure 28 (C5 and C8). Two
capacitors are recommended to be fitted Pin 19 (V
ISOIN
) and Pin 20
(GND2) with values of 100nF and 10nF as shown in Figure 28
(C9 and C7). The best practice recommended is to use a very low
inductance ceramic capacitor, or its equivalent, for the smaller
value. The total lead length between both ends of the capacitor
and the input power supply pin must not exceed 10 mm.
The ADM3053 features an internal split paddle, lead frame on the
bus side. For the best noise suppression, filter both the GND2
pins (Pin 11 and Pin13) and V
ISOOUT
signals of the integrated dc-
to-dc converter for high frequency currents. Use surface-mount
ferrite beads in series with the signals before routing back to the
device. See Figure 28 for the recommended PCB layout.
The impedance of the ferrite bead is chosen to be about 2 kΩ
between the 100 MHz and 1 GHz frequency range, to reduce
the emissions at the 180 MHz primary switching frequency and
the 360 MHz secondary side rectifying frequency and
harmonics.
09293-028
GND1
1
NC
2
GND1
3
RxD
4
GND2
20
V
ISOIN
19
R
S
18
CANH
17
TxD
5
GND2
16
V
IO
6
CANL
15
GND1
7
V
REF
14
V
CC
8
GND2
13
GND1
9
V
ISOOUT
12
GND1
10
GND2
11
ADM3053
0.01µF 0.1µF
0.1µF
10µF
0.1µF 0.01µF
10µF 0.1µF
FERRITES
Figure 28. 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 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 for the device, thereby
leading to latch-up and/or permanent damage.
The ADM3053 dissipates approximately 650 mW of power when
fully loaded. Because it is not possible to apply a heat sink to an
isolation device, the devices primarily depend on heat dissipation
into the PCB through the GND pins. If the devices are used at
high ambient temperatures, provide a thermal path from the GND
pins to the PCB ground plane. The board layout in Figure 28 shows
enlarged pads for Pin 1, Pin 3, Pin 9, Pin 10, Pin 11, Pin 14, Pin 16,
and Pin 20. Implement multiple vias from the pad to the ground
plane to reduce the temperature inside the chip significantly. The
dimensions of the expanded pads are at the discretion of the
designer and dependent on the available board space.
EMI CONSIDERATIONS
The dc-to-dc converter section of the ADM3053 must, of necessity,
operate at very high frequency to allow efficient power transfer
through the small transformers. This creates high frequency
currents that can propagate in circuit board ground and power
planes, causing edge and dipole radiation. Grounded enclosures
are recommended for applications that use these devices. If
grounded enclosures are not possible, good RF design practices
must be followed in the layout of the PCB. See the AN-0971
Application Note, Recommendations for Control of Radiated
Emissions with isoPower Devices, for more information.