PRODUCT INNOVATION
Single Component Isolates Data And Power
By David Morrison, Editor, Power Electronics Technology
A
nalog Devices has extended its line of iCoupler
digital isolators by developing three devices
that provide both data and power isolation in a
single eight-pin SOIC package. For applications
that require isolation of both data and power,
and where the isolated power requirement is 50 mW or less,
the new iCouplers can save pc board space and lower design
costs. The iCouplers are designed to replace the combinations
of optocouplers, transformers and supporting components
that are currently used to isolate data and power lines.
For example, in power supply applications that employ secondary-side control, one iCoupler device can
eliminate the need for the additional transformer windings and discrete components that typically provide the
isolated power for startup. The iCoupler devices employ
chipscale microtransformers to obtain galvanic isolation
through inductive coupling. These devices take the place of
optocouplers that are normally used for isolation in signal
paths. According to the vendor, the microtransformers
offer several advantages over optocouplers including the
ability to integrate up to four channels on a single die, better
performance versus price for certain parameters and lower
power consumption.
In each of these new devices, three microtransformers
are fabricated on a single semiconductor die. Two of these
transformers are used for signal isolation, but the third
transformer is the basis for an isolated dc-dc converter that
is implemented on chip. (The company refers to this combination of an isolated dc-dc converter with independent
signal channels as its isoPower technology.)
The dc-dc converter delivers up to 50 mW of isolated,
regulated power at 5 V. Although the device as a whole
specifies operation from a 2.7-V to 5.5-V supply, the dc-dc
converter is enabled at supply voltages above 4.5 V. This converter switches at 300 MHz, which makes it possible to use
the tiny microtransformer. Of course, small size is achieved at
the expense of efficiency, which is only about 15%. However,
the device targets applications where small size and low cost
outweigh the need for efficiency.
Analog Devices cites a design example that originally
used an optocoupler for signal isolation and a 1-W, isolated
dc-dc converter module for powering an interface logic
chip. This design required 12 components, 510 mm2 of
board area, and had a bill-of-materials cost of $6.75. When
the design was changed to use a new iCoupler, component
count dropped to three parts, board area to 60 mm2 and
estimated cost to $2.15.
The three devices built with isoPower are the
ADuM5240,
ADuM5241 and ADuM5242. The prodSecondary
ADuM5242
controller
ucts vary by the directionality of each channel. The
VDD
VISO
ADuM5240 has two signal outputs on the same side as
5V
VDD
the power output. The ADuM5241, which is intended
for bi-directional communications, offers signal chanPWM1
nels in each direction. The ADuM5242 has the two
signal outputs on the same side as the power input,
PWM2
GND V
making it ideal for the power supply applications with
DD
secondary-side control (see the figure).
In terms of the data paths, the ADuM524x isolators
specify operation up to 10 Mbits/s with propagation
Output
delays of < 55 ns and channel-to-channel matching
better than 3 ns. All three ADuM524x devices carry a
2.5-kV isolation rating and will carry regulatory safety
Bus
approvals from the North American and European
agencies upon product release.
The ADuM524x are sampling to lead customers
now, with general sampling scheduled for July 2006.
In power supply applications that employ secondary-side control, the
Each device is priced at $2.95 per unit in 1000-piece
ADuM5242 isolator eliminates the need for the additional transformer windquantities. For more information, see www.analog.
ings and discrete components that typically provide the isolated power
com/icoupler.
PETech
for startup.
Power Electronics Technology March 2006
54
www.powerelectronics.com