Data Sheet
ADuM5401/ADuM5402/ADuM5403/ADuM5404
APPLICATIONS INFORMATION
BYPASS < 2mm
The dc-to-dc converter section of the ADuM5401/ADuM5402/
ADuM5403/ADuM5404 works on principles that are common to
most switching power supplies. It has 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.
V
V
ISO
DD1
GND
GND
ISO
1
V
V
V
/V
V
V
V
V
V
/V
IA OA
OA IA
/V
/V
IB OB
OB IB
/V
/V
IC OC
OC IC
V
OD
ID
RC
OUT
SEL
GND
GND
ISO
1
Figure 25. 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 affects all pins equally on a given component side.
Failure to ensure this can cause voltage differentials between
pins exceeding the absolute maximum ratings for the device
as specified in Table 19, thereby leading to latch-up and/or
permanent damage.
The ADuM5401/ADuM5402/ADuM5403/ADuM5404 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.
The ADuM5401/ADuM5402/ADuM5403/ADuM5404 are power
devices that dissipate approximately 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 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 25 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 should be implemented from the pad to the ground
plane to significantly reduce the temperature inside the chip.
The dimensions of the expanded pads are at the discretion of
the designer and depend on the available board space.
PCB LAYOUT
The ADuM5401/ADuM5402/ADuM5403/ADuM5404 digital
isolators with 0.5 W isoPower integrated dc-to-dc converter
require no external interface circuitry for the logic interfaces.
Power supply bypassing is required at the input and output
supply pins (see Figure 25). Note that low ESR bypass capacitors
are required between Pin 1 and Pin 2 and between Pin 15 and
Pin 16, as close to the chip pads as possible.
The power supply section of the ADuM5401/ADuM5402/
ADuM5403/ADuM5404 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;
ripple suppression and proper regulation require a large value
capacitor. These are most conveniently connected between Pin 1
THERMAL ANALYSIS
The ADuM5401/ADuM5402/ADuM5403/ADuM5404 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 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 ADuM5401/ADuM5402/ADuM5403/
ADuM5404 devices operate at full load across the full temperature
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.
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. The smaller
capacitor must have a low ESR; for example, use of a ceramic
capacitor is advised.
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. Consider bypassing between Pin 1 and
Pin 8 and between Pin 9 and Pin 16 unless both common ground
pins are connected together close to the package.
Rev. C | Page 21 of 28
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