Datasheet

Data Sheet ADuM5000
Rev. B | Page 11 of 16
APPLICATIONS INFORMATION
The dc-to-dc converter section of the ADuM5000 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. V
DD1
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 (V
ISO
)
side controller regulates the output by creating a PWM control
signal that is sent to the primary (V
DD1
) 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.
The ADuM5000 provides a regulation control output (RC
OUT
)
signal that can be connected to other isoPower devices. This feature
allows a single regulator to control multiple power modules without
contention. When auxiliary power modules are present, the V
ISO
pins can be connected together to work as a single supply. Because
there is only one feedback control path, the supplies work together
seamlessly. The ADuM5000 can be a source of regulation control,
as well as being controlled by another isoPower device.
There is an undervoltage lockout (UVLO) with hysteresis in the
V
DD1
input protection circuit. When the input voltage rises above
the UVLO threshold, the dc-to-dc converter becomes active.
The input voltage must be decreased below the turn-on threshold
by the hysteresis value to disable the converter. This feature has
many benefits in the power-up sequence of the converter, such
as ensuring that the system supply rises to a minimum level
before the ADuM5000 demands current. It also prevents any
voltage drop due to converter current from turning the supply
off and possibly oscillating.
PCB LAYOUT
The ADuM5000 digital isolator is a 0.5 W isoPower integrated
dc-to-dc converter that requires no external interface circuitry
for the logic interfaces. Power supply bypassing is required at
the input and output supply pins (see Figure 14).
The power supply section of the ADuM5000 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 most conveniently connected between Pin 1 and
Pin 2 for V
DD1
, and between Pin 15 and Pin 16 for V
ISO
.
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. Best practice recommends using 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 should not exceed
10 mm. 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.
V
DD1
GND
1
NC
RC
IN
V
ISO
GND
ISO
NC
NC
NC
V
SEL
RC
OUT
RC
SEL
V
DD1
V
ISO
GND
1
GND
ISO
07539-011
Figure 14. 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 10, thereby leading to latch-up and/or
permanent damage.
The ADuM5000 is a power device that dissipates approximately
1 W of power when fully loaded. Because it is not possible to apply
a heat sink to an isolation device, the device primarily depends
on heat dissipation into the PCB through the GND pins. If the
device is used at high ambient temperatures, provide a thermal
path from the GND pins to the PCB ground plane. The board
layout in Figure 14 shows enlarged pads for Pin 2 and Pin 8
(GND
1
) and for Pin 9 and Pin 15 (GND
ISO
). Implement multiple
vias 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.
START-UP BEHAVIOR
The ADuM5000 does not contain a soft start circuit. Take the
start-up current and voltage behavior into account when designing
with this device.
When power is applied to V
DD1
, the input switching circuit begins
to operate and draw current when the UVLO minimum voltage
is reached. The switching circuit drives the maximum available
power to the output until it reaches the regulation voltage where
PWM control begins. The amount of current and time this
takes depends on the load and the V
DD1
slew rate.