DirectFET®2 Power MOSFETs Meet AEC-Q101
Over the last two decades, Power MOSFETs have evolved as a necessary power-handling component in virtually all automobiles. To be eligible for use in automotive electronic systems, these power MOSFETs must usually meet the AEC-Q101 standard.
International Rectifier's new DirectFET®2 power MOSFETs are AEC-Q101 qualified and suit the growing needs of electric motors, solenoids, and fuel injectors. These new power MOSFETs have low on-resistance, 40- and 100-V maximum operating voltages, and the ability to tolerate high-voltage transients — such as load dump — that can occur in automotive electrical systems.
Initially, conventional packages such as the TO-220, TO-247, DPak, and D2Pak did the heavy lifting, while SO-8s handled lower-power applications. The new MOSFETs from International Rectifier feature an updated version of the DirectFET package that was first introduced in 2002. For the DirectFET2 MOSFETs, the original package (Fig. 1) has been redesigned specifically for the automotive environment. The first two parts are AUIRF7665S2 and AUIRF7739L2. Table 1 lists the important features of these two parts.
Both MOSFETs are AEC-Q101-qualified, and feature an environmentally friendly, Pb-free and RoHS-compliant bill of materials. They are part of IR's automotive quality initiative targeting zero defects. The DirectFET2 MOSFETs offer overall system-level size and cost reductions, along with improved performance and efficiency compared to traditional standard plastic-packaged components.
The new DirectFET2 devices may be optimized by application for next-generation vehicle platforms for ultra-low on-state resistance, RDS(ON), total gate charge, QG, or logic-level operation to deliver dramatically improved performance and efficiency, and reduce system size and part count.
TAKING A CLOSER LOOK
Offered in the new large can (L) package, the AUIRF7739L2 is said to deliver the industry's lowest RDS(on) — 0.7 mΩ (typical) at 40 V for a given PCB area. Moreover, the large can features a 60% smaller footprint and 85% lower profile than a traditional D2PAK.
The device offers good power density and efficiency, suiting it for driving heavy loads. Typical applications include motor drives and dc-dc converters.
The AUIRF7665S2 small can (S) device is optimized for very low gate charge and exhibits extremely low parasitics to enable fast and efficient switching performance. The DirectFET2 MOSFETs suit automotive switching applications, including the output stage of Class D digital audio amps as well as dc-dc converters and fuel-injection systems.
MOISTURE SENSITIVITY LEVELS
An important feature of these new MOSFETs is their Moisture Sensitivity Level, or MSL. This relates to the packaging and handling precautions for semiconductors and is an electronic standard for the time the device can be exposed to ambient room conditions of approximately 30°C/60%RH.
This is important because thin fine-pitch devices could be damaged during SMT reflow, when moisture trapped inside the component expands. Trapped moisture can damage a semiconductor. In extreme cases, cracks will extend to the component surface.
According to IPC/JEDEC's J-STD-20 Moisture/Reflow Sensitivity Classification for Plastic Integrated Circuit (IC) SMTs, there are eight levels of moisture sensitivity. The original DirectFET was rated at MSL 3, which allowed 168 hours of moisture testing. DirectFET2 is rated MSL 1, which allows an unlimited time for the moisture test.
NEW APPLICATIONS
Today, there are new applications and power MOSFETs continue to grab them. This includes electric power steering (EPS) and micro-hybrid vehicles, and chassis, drive-train, and power-train systems. Besides meeting the AEC Q101 standard, they must meet the cost constraints imposed by automotive manufacturers.
EPS SYSTEMS
For EPS, an electric motor driven by power MOSFETs provides steering assist to the driver of a vehicle. A typical system employs sensors to detect the motion and torque of the steering column, and a computer module controls system performance. Software allows varying amounts of assistance to be applied, depending on driving conditions.
Electric systems have a fuel-efficiency advantage over conventional hydraulic power steering. The electrical approach eliminates the need for a constantly running belt-driven hydraulic pump, whether assistance is required or not.
Another major advantage is the elimination of a belt-driven engine accessory, and several high-pressure hydraulic hoses between the hydraulic pump, mounted on the engine, and the steering gear, mounted on the chassis. This simplifies manufacturing and maintenance.
MICRO-HYBRID SYSTEMS
A micro-hybrid system performs a stop-start function that is completely transparent to the driver. During idling operations, like waiting for a traffic light, the engine is turned off. Then, the engine restarts very quickly and silently when the driver takes their foot off the brake.
This technique cuts fuel consumption and gas emissions at standstill. Tests have shown that this can cut fuel consumption about 6%.
Power MOSFETs have played a major role in making automotive systems more reliable. Among the traditional mechanical components that have been eliminated are shafts, pumps, hoses, fluids, coolers, etc., which reduces the weight of the vehicle and improves fuel efficiency.
Safety improvement is another feature of electronic controls that provide more automated functions that cannot be achieved by mechanical techniques. Compared with mechanical systems, the electronics trend also allows easier modification or upgrade of automotive systems.
PRECONDITIONING REQUIREMENTS
MSL-1 preconditioning is required for SMT-capable devices that are put on Temperature Cycling, H3TRB, IOL, and Autoclave tests. If straight-leaded devices (such as I-PAK or TO-262) are used, the devices are required to undergo the preconditioning with a third reflow exposure in lieu of the surface-mounting step.
PASS/FAIL CRITERIA
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Electrical parameters must not exceed the data-sheet limits.
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Electrical parameters must remain within ±20% of the initial reading of each test (with the exception of leakage limits — which are not to exceed 10 times of the initial value for moisture tests and five times the initial value for all other tests).
