Electronics in Motion and Conversion July 2012 - Bodo's Power

POWER MODULES
Figure 1: Ultra-Miniature μIPM
The family comprises a series of fully integrated three-phase or single-phase
half-bridge motor control circuits (Figure 2) with DC current
ratings from 2A to 4A and voltage ratings of 250V or 500V. Features
such as an open-source topology for leg-shunt current sensing help
to further simplify motor control designs (common source options are
also available) while optimized dV/dt characteristics minimize losses
and the need for EMI trade-offs. The devices also incorporate propagation
delay matching circuitry, ensuring that the response at the output
to a signal at the input requires approximately the same time
turn-on and turn-off time durations for both the low-side and the highside
channels.
Figure 2: μIPM Internal Schematics
Despite their current and voltage ratings and high levels of integrated
functionality, each of the new devices is supplied in a miniature
‘QFN-like’ package, which until now has been more commonly associated
with lower voltage parts. Indeed, with dimensions of just 12mm
x 12mm x 0.9mm the new devices are the smallest IPMs currently on
the market and can help designers to achieve space savings of up to
60% compared to alternative devices. And this is all without compromising
isolation safety requirements – the μIPMs meet the creepage
distance requirements of the UL standards.
Figure 3: PQFN Design uses PCB as Heatsink
Among the factors that have led to these significant space savings is
the approach taken to device cooling. In particular, unlike the poor
die-to-PCB heat dissipation characteristics of gull-wing lead and DIP
packages, the μIPMs achieve high die-to-PCB heat dissipation,
allowing them to actively use the PCB as a heatsink. This is a similar
approach that point-of-load (PoL) or VRM QFN-based packages use.
As Figure 3 shows, the power semiconductors (500V FredFETs) and
the HVIC die are bonded to the lead-frame, which is exposed and
then soldered to the PCB.
This solution to effective heat dissipation means that the approach
taken to PCB design and layout (in terms of, for example, PCB copper
thickness or the deployment of copper wires/jumpers on thermally
conductive traces) can be used to ‘tune’ thermal performance. As a
result, under the same application and load conditions the new μIPM
devices can be used to deliver improved current capabilities and load
efficiencies than IPM solutions housed in more traditional packages
at the same ambient temperature.
Alternatively, they can be used to achieve ‘cooler running’, placing
less stress on the device, leading to longer term reliability – a particularly
important issue for designers of fans and circulation pumps that
are expected to deliver maintenance-free operation for many years.
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