ADuM5200/ADuM5201/ADuM5202
APPLICATIONS INFORMATION
The dc-to-dc converter section of the ADuM520x works on
principles that are common to most 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.
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. Consider bypassing between
Pin 1 and Pin 8 and between Pin 9 and Pin 16 unless both of the
common ground pins are connected together close to the
package.
BYPASS < 2mm
V
V
DD1
ISO
GND
/V
GND
1
ISO
V
V
V
/V
IA OA
OA IA
V
/V
IB OB
/V
OB IB
RC
NC
IN
The ADuM520x implements 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.
RC
V
V
SEL
SEL
/NC
E2
V
/NC
E1
GND
GND
ISO
1
Figure 21. Recommended PCB Layout
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
this way can cause data corruption in some circumstances.
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 differential voltages
between pins exceeding the absolute maximum ratings for the
device (specified in Table 8) thereby leading to latch-up and/or
permanent damage.
The ADuM520x can accept an external regulation control signal
(RCIN) that can be connected to other isoPower devices. This
allows a single regulator to control multiple power modules
without contention. When accepting control from a master
power module, the VISO pins can be connected together adding
their power. Because there is only one feedback control path, the
supplies work together seamlessly. The ADuM520x can only
regulate itself or accept regulation (slave device) from another
device in this product line; it cannot provide a regulation signal
to other devices.
The ADuM520x is a power device that dissipates 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 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 21
shows enlarged pads for Pin 2, Pin 8, Pin 9, and Pin 15. 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 ADuM520x 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 21). 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.
EMI CONSIDERATIONS
The dc-to-dc converter section of the ADuM520x components
must operate at a 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 emissions and dipole radiation
between the primary and secondary ground planes. Grounded
enclosures are recommended for applications that use these
devices. If grounded enclosures are not possible, follow good RF
design practices in layout of the PCB. See www.analog.com for the
most current PCB layout recommendations specifically for the
ADuM520x.
The power supply section of the ADuM520x 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 induc-
tance, high frequency capacitor, whereas 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
.
The smaller capacitor must have a low ESR; for example, use of a
ceramic capacitor is advised.
Rev. 0 | Page 18 of 24
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