Data Sheet
ADuM5401W/ADuM5402W/ADuM5403W
APPLICATIONS INFORMATION
Note that the total lead length between the ends of the low ESR
capacitor and the input power supply pin must not exceed 2 mm.
Installing the bypass capacitor with traces more than 2 mm in
length may result in data corruption. A bypass between Pin 1
and Pin 8 and between Pin 9 and Pin 16 should also be considered
unless both common ground pins are connected together close
to the package.
THEORY OF OPERATION
The dc-to-dc converter section of the ADuM5401W/
ADuM5402W/ADuM5403W works on principles that are
common to most modern power supplies. It is a secondary side
controller architecture with isolated pulse-width modulation
(PWM) feedback. VDD1 power is supplied to an oscillating circuit
that switches current into a chip scale air core transformer.
Power transferred to the secondary side is rectified and regulated
to either 3.3 V or 5 V. The secondary (VISO) side controller
regulates the output by creating a PWM control signal that is
sent to the primary (VDD1) side by a dedicated iCoupler data
channel. The PWM modulates the oscillator circuit to control
the power being sent to the secondary side. Feedback allows for
significantly higher power and efficiency.
BYPASS < 2mm
V
V
DD1
ISO
GND
GND
1
ISO
V
V
V
V
V
V
IA
OA
/V
V
/V
IB OB
OB IB
V
/V
IC OC
/V
OC IC
V
OD
ID
RC
OUT
SEL
GND
GND
1
ISO
The ADuM5401W/ADuM5402W/ADuM5403W implement
undervoltage lockout (UVLO) with hysteresis on the VDD1 power
input. This feature ensures that the converter does not enter
oscillation due to noisy input power or slow power-on ramp rates.
Figure 23. Recommended Printed Circuit Board 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 affects all pins equally on a given component side.
Failure to ensure this can cause voltage differentials between pins,
exceeding the absolute maximum ratings specified in Table 19,
thereby leading to latch-up and/or permanent damage.
In the original ADuM540xW devices, a minimum load current
of 10 mA is recommended to ensure optimum load regulation.
Smaller loads can generate excess noise on chip due to short or
erratic PWM pulses. Excess noise generated in this way can cause
data corruption in some circumstances. This requirement has
been removed in the newer ADuM540xW-1 devices, which are
recommended for new designs.
The ADuM5401W/ADuM5402W/ADuM5403W are power
devices that dissipate about 1 W of power when fully loaded and
running at maximum speed. 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 ground pins. If the
devices are used at high ambient temperatures, provide a thermal
path from the ground pins to the PCB ground plane. The board
layout in Figure 23 shows enlarged pads for Pin 8 and Pin 9. Large
diameter vias should be implemented from the pad to the ground,
and power planes should be used to reduce inductance. Multiple
vias in the thermal pads can significantly reduce temperatures
inside the chip. The dimensions of the expanded pads are left to
the discretion of the designer and the available board space.
PCB LAYOUT
The ADuM5401W/ADuM5402W/ADuM5403W digital isolators
with 0.5 W isoPower integrated dc-to-dc converters require no
external interface circuitry for the logic interfaces. Power supply
bypassing is required at the input and output supply pins (see
Figure 23). Note that a low ESR bypass capacitor is required
between Pin 1 and Pin 2 as well as between Pin 15 and Pin 16,
as close to the chip pads as possible.
The power supply section of the ADuM5401W/ADuM5402W/
ADuM5403W uses a 180 MHz oscillator frequency to efficiently
pass power through its chip scale transformers. In addition,
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; ripple
suppression and proper regulation require a large value capacitor.
These are most conveniently connected between Pin 1 and Pin 2
for VDD1 and between Pin 15 and Pin 16 for VISO. To suppress
noise and reduce ripple, a parallel combination of at least two
capacitors is required. The recommended capacitor values are
0.1 µF and 10 µF for VDD1 and VISO. A 10 nF capacitor should
be used for optimum EMI emissions performance. The smaller
capacitors must have a low ESR; for example, use of an NPO
ceramic capacitor is advised.
THERMAL ANALYSIS
The ADuM5401W/ADuM5402W/ADuM5403W parts consist
of four internal die attached to a split lead frame with two die
attach paddles. For the purposes of thermal analysis, the die is
treated as a thermal unit, with the highest junction temperature
reflected in the θJA value from Table 14. The value of θJA is based
on measurements taken with the parts mounted on a JEDEC
standard, 4-layer board with fine width traces and still air. Under
normal operating conditions, the ADuM5401W/ADuM5402W/
ADuM5403W devices operate at full load across the full temper-
ature range without derating the output current. However,
following the recommendations in the PCB Layout section
decreases thermal resistance to the PCB, allowing increased
thermal margins in high ambient temperatures.
Rev. D | Page 19 of 24
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