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Posted on 02 April 2019

State-of-the-Art Intelligent Power Modules for Appliance Motor Drives

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The latest report into the World Market for Major Home Appliances, by IHS, predicts the industry will spend $3.8 billion on semiconductors by 2017, as new generations of products become more sophisticated and feature-rich.

By Alberto Guerra, International Rectifier Corporation

The fastest growing sector will be power semiconductors including Intelligent Power Modules (IPMs) used in electronic motor controls, which are needed to meet the eco-design targets now effective in various territories worldwide.

IR’s iMotion™ integrated design platform is currently one of the most successful portfolios for electronic motor control, and has enabled the Major Home Appliance (MHA) industry to deliver energy-saving products within tight cost and time-to-market constraints. Bringing together all the digital, analogue and power devices required, as well as motor-control algorithms, development software and design tools, iMotion enables a complete motor drive comprising the IPM and a digital control IC with a small number of external components to turn a motor for evaluation within days instead of weeks. Today, however, changing design priorities and new energy-saving standards are driving demands for enhancements such as smaller size, lower cost and greater scalability.

IPMs for energy saving EC Fan and Compressor Solutions

The key to reducing system cost is generally to increase semiconductor integration while also reducing IC size to benefit from smaller PCB dimensions and easier mechanical design. The arrival of IR’s latest μIPM™ family enables smaller and more competitively priced applications such as heating and ventilation fans or water-circulation pumps up to 200W meeting the most recent energy standards.

The modules are packaged as Power QFN (PQFN) devices, making them the industry’s first fully integrated inverters to utilise the PCB as a heatsink. Drawing on the principles of point-of-load and VRM modules, adapted for high-voltage applications, these modules are up to 60% smaller than existing 3-phase motor-control power ICs. Inside the module, 500V FredFet power switches and the High-Voltage IC (HVIC) die are bonded to an exposed lead-frame, which is soldered to the PCB. Various 3-phase and single-phase (half-bridge) configurations are available, within extremely small package dimensions, as shown in figure 1.

μIPM 2-phase and 3-phase modules in PQFN packages

Figure 2 shows the driver for a 60W condenser fan used in a 2.2kW air-conditioning split system. By providing a complete 500V 3-phase inverter system in one single 12mm x 12mm QFN package, μIPM enables a heatsink-free design and helps reduce component count from 91 to 31 components. PCB cost/area is 43% lower, while assembly and test cycle times are shorter and test coverage is increased.

Designing with μIPM allows engineers to realise extremely compact motor drivers

In order to address higher-power applications in the MHA segment, the μIPM family has expanded with new 7mm x 8mm x 0.9mm and 8mm x 9mm x 0.9mm modules in half-bridge configuration with voltage ratings up to 40V and current rating increased to 10A for the 500V version and up to 30A for the 40V version. This splitting of the integrated 3-phase inverter into three individual half-bridges delivers several benefits, most importantly by distributing the power dissipation across a larger PCB area to improve thermal performance.

Designing with μIPM QFN

The tiny dimensions of the μIPM QFN IC, and the use of the PCB as a primary channel for dissipating power, call for a different approach to some aspects of motor-drive design, in order to maximise performance.

In general, IPM current capability depends on the DC-bus voltage, the ambient temperature, and the switching frequency. As each of these parameters are increased, so too are losses, the complexity of the modulation scheme (from 3-Phase to 2-Phase), dV/dt of phase voltage, and critical FET characteristics such as RDSON and IREC.

For a surface-mount μIPM driver, the current capability also depends on the PCB design; specifically the copper thickness, copper pad areas, number of layers and ultimately the maximum allowable PCB temperature. In practice, the maximum junction temperature of the power semiconductors is less critical than the maximum PCB temperature. Increasing the copper thickness reduces the overall junction-to-ambient thermal resistance thereby also reducing PCB temperature and hence enabling higher current capability.

Effect of copper thickness on thermal performance

Figure 3 illustrates the effects of PCB-copper thickness and heat spreader area on the current capability of a 300W compressor drive with an inverter stage comprising three IRSM807-105MH half-bridge modules. Output current capability increases with higher ΔTCA and also increases when a 2-phase modulation versus a 3-phase modulation scheme is used. Similarly, reducing switching losses by lowering the switching frequency enables higher output current. Adding a top-mounted heat-spreader can further reduce the temperature. By using a set of μIPM half-bridge modules, the overall compressor-driver board dimensions were reduced by 40% to 10cm x 7.7cm.

In addition to revealing the μIPM PQFN family, IR has also extended its dual-inline (DiP μIPM) family for the vast number of applications based on more traditional design and assembly technologies. Designed for use with a heatsink, the DiP μIPM family allows designers to create several products supporting different power output by adjusting heatsink rating. Featuring the same chipset of the μIPM surface-mount family in a DIP26/SOP26 package, these DIP μIPMs give designers freedom to choose the optimum solution for each application.

Like the PQFN family, the DiP μIPMs are available with a choice of power stages built around IR’s 500V or 250V trench FREDFET MOSFET. In addition, a version using 600V Trench IGBT and Pt diode targets higher power requirements up to 250W. Built-in bootstrap functionality and integrated temperature feedback via NTC, which allows for full protection redundancy, are common to all versions.

IPMs for Main Driver Applications

For higher-current applications such as the main drivers of washing machines and air-conditioning systems, IR’s System-in-Package SiP IRAM Gen2 IGBT-based IPMs introduce enhancements that meet appliance-market demands for higher efficiency and wider operating temperature ranges. The new design features an exposed (yet fully isolated) substrate with superior dielectric transition temperature, which permits operating case temperature of up to 140°C. New copper heat-spreaders for both the trench IGBT and FRED freewheeling diode improve junction-to-case thermal resistance by up to 30%. Transient thermal impedance is also greatly reduced, which increases reliability during overload conditions.

The combination of thermal-mechanical improvements, optimised Trench IGBTs, and advanced HVIC three-phase gate driver has yielded a 20% increase in current-handling capability and a 33% increase in maximum case operating temperature. Devices with current rating of up to 20A are available. On the other hand, retaining identical mechanical dimensions and pin-to-pin compatibility allows designers to upgrade established motor-drive designs relatively easily for use in higher performing products that require increased motor current.

The motor-driver board shown in figure 4 has been upgraded from 700W to cover up to 850W motor specification without any fundamental redesign and by maintaining similar heatsink dimensions, so delivering economic advantages and faster time-to-market.

Appliance control board upgraded to 850W using SiP IRAM Gen2 IPM

Cost-Optimised Modules

The market is also demanding more cost-optimised IPMs for lower power opportunities. IR’s new DiP-IRAM platform addresses this demand by packaging the power semiconductors and HVIC in a lead frame based, fully transfer molded Dual-Inline Package (DIP) meeting the industry-standard 24mm x 38mm form factor. This enables a lower-cost solution, compared to the SiP-IRAM Gen2 substrate-based system-in-package, and requires only a few external components to cover current ratings from 6A to 15A.

Conclusion

IR’s iMotion integrated design platform has enabled designers to realise energy-efficient appliance and industrial motor drives at affordable prices. The latest iMotion IPMs deliver all-round performance improvements and extra package choices that simplify upgrading of existing designs.

 

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