Bodo´s Power Systems
®
July 2020 www.bodospower.com86
CONTENT
Fortunately, where this situation was once little short of dire, recent
developments in integrated circuit design, system integration and
packaging are serving to lighten the power designer’s load. In fact, it
is now possible to consistently deliver high-quality designs that pass
the strict limits of CISPR 25 Class 5 or EN 55025, while simultane-
ously reducing overall solution size and managing thermal dissipation.
Allegro MicroSystems’ ClearPower module family of products, which
adopt a ‘system in a package’ approach, provide the answer that
designers have been seeking for some time. ClearPower modules
house all the principal elements of a high-performance switching
power supply or LED driver within a compact package, signicantly
easing the task of designing complete power solutions.
An example of a recently developed ClearPower module is Allegro’s
APM80900 (Figure 1), which is intended for LED lighting applications.
A power inductor, critical bypass capacitors and an advanced switch-
ing regulator IC are co-packaged within an envelope that measures
just 4 × 6 × 2 mm, while routable substrate technology is employed
to connect the various sub-components together, and to the outside
world.
By co-locating these critical power stage components within close
connes, the high current switching paths that promote EMI are
reduced by a factor of 10. Additionally, through direct integration and
innovative IC design, overall size can be up to 70% less compared
with conventional solutions.
Allegro MicroSystems’ ClearPower modules feature an MIS (molded
interconnect substrate) routable lead-frame package with the look and
feel of a conventional QFN solution. Combining this technology in an
industry-standard QFN footprint with wettable anks ensures reliable
operation at the harshest of automotive operating temperatures.
While the task of developing a viable power solution that will pass
EMI limits has become far easier with power modules, achieving high
performance demands a holistic approach to the design of the module
itself. This undertaking involves combining IC design, packaging
technology and passive component integration to achieve the desired
EMI, thermal performance and size.
POWER MODULES
ClearPower Modules Tackle
Designers’ Toughest Challenges
There are fundamental truths that every system designer must face when it comes to power
electronics. First, most projects will need multiple rounds of design, simulation, and trial
to pass strict limits on EMI (electromagnetic interference). Second, there is the issue that
introducing EMI components will reduce system efficiency and add to cost and solution
size. This latter point is particularly pertinent as there is often very little board space
reserved for the power solution, so the option of using large, proven solutions is no longer
valid. Finally, the thermal environment will generally be worse than anticipated.
By John Bazinet, Director of Engineering,
Regulator and Lighting Products, Allegro MicroSystems
and Ben West, Applications Engineering Section Lead,
Regulator and Lighting Products, Allegro MicroSystems
Figure 1: The APM80900 is a 40 V, 1.5 A synchronous buck LED
driver ClearPower module by Allegro MicroSystems
www.bodospower.com July 2020 Bodo´s Power Systems
®
87
CONTENT
Specialised packaging and chip design techniques allow ClearPower
modules to achieve excellent thermal dissipation characteristics. This
factor is critical as both the IC and inductor are heat sources, and
are encased within the same compact package. Notably, deploy-
ing multilayer routable packaging technology within the ClearPower
module, which is not possible with conventional single-layer lead-
frames, permits the creation of connections and component spacing
that maximises thermal dissipation. The routable inner layer(s) of
the module package is used to make contact with the IC and pas-
sive components, while the module’s heat-generating areas (power
switches and inductor) are connected through vias, providing an
efcient way to channel heat from the package interior to its large,
exposed power pads.
Flip-chip IC technology is often used to lower the resistance and
inductance associated with bond wires. Just one ip-chip connection
(referred to as a bump) has an inductance around 20 times less than
a conventional bond wire. As a result, multiple bumps can be used to
connect to each high-power node, producing a total inductance that is
immeasurably small. Flip-chip bumps also lower any high-frequency
ringing that leads to EMI and, in comparison with conventionally
bonded products, serve to decrease power dissipation.
In addition to these advanced packaging techniques, ClearPower
module-based regulators (including the AMP80900) use many of
the same techniques as conventional switching regulators to further
reduce EMI. One method is spread spectrum modulation, which
slightly modulates the converter's switching frequency. Here, energy
is spread out over a broader frequency span to reduce noise energy
peaks. Another effective method of reducing EMI is by reducing
switch turn-on losses. ClearPower modules are uniquely designed
and congured to minimise such losses.
Once a power supply design has gone through its initial stages, EMI
is evaluated in a special testing laboratory, often leading to late nights,
stressed engineering managers and inconvenient late-stage design
modications. As EMI laboratory time is typically charged by the hour,
it is incumbent upon the design team to reach a viable EMI solution
quickly. This demand leads to any number of non-ideal solutions be-
ing employed to quell EMI, including metal shields, passive snubbers
and common mode input chokes. These additional passives add cost,
increase overall size and reduce system efciency, leading to higher
heat dissipation.
The promise of ClearPower modules is that there is no longer any
need for these somewhat desperate measures. Today, a CISPR 25
Class 5 compliant solution can be delivered with far less effort. To
prove this point, a like-for-like comparison between a module solution
and conventional counterpart is shown in Figure 2. Both designs em-
ploy identical input lters and switch at 2.5 MHz. Note that the module
design is typically very close to the noise oor of the measurement
system and exhibits considerably less noise than the conventional
design.
Alongside EMI concerns, reducing the power solution envelope and
prole on the board is an ongoing challenge. While every type of elec-
tronic component requires a power supply to perform its function, this
notion often occurs late in the process and receives little attention.
Treating the power supply as an afterthought means an optimum de-
sign will not be achieved, promoting many system problems. Allegro’s
ClearPower modules are viable solutions that improve performance
and simplify design. Moreover, by reducing external components,
integrating magnetics and using bespoke power packaging designed
to withstand the harshest automotive operating temperature range,
ClearPower modules can reduce overall solution size by up to 70%,
as outlined in Figure 3.
Ultimately, EMI mitigation is an increasing challenge as more systems
become connected wirelessly or are integrated into smaller spaces
where there is a higher potential to interfere with other devices. Clear-
Power modules from Allegro MicroSystems offer a fast, effective and
reliable solution for solving these difcult EMI challenges. In addition,
ClearPower modules reduce R&D time and cost, and simplify the bill
of materials, while the PCB area required for the power solution is
signicantly reduced, leaving space for more value-added functions.
In short, power modules are becoming increasingly mainstream and
compare favorably in the overall cost-benet calculations of system
developers.
www.allegromicro.com
POWER MODULES
Figure 2: Comparing the radiated EMI of Allegro MicroSystems’ Clear-
Power APM80900 module with a conventional solution
Figure 3: Board space comparison between Allegro MicroSystems’
ClearPower APM80900 module and a conventional solution