A micro hybrid example
As a real-world example, for the battery switch, the International Rectifier
surface mount MOSFET AUIRF1324S-7P
delivers maximum on-state resistance Rds(on)(max) as low as 1 mΩ and output current up to 240A. (For through hole packaging, IR has AUIRF1324L in conventional TO-262 with 1.65 mΩ Rds(on)(max). Maximum Rds(on) can be reduced by around 20% by introducing the new WideLead TO-262 package product AUIRF1324WL
Wider lead packages mean more areas fit the internal wire bonds at the MOSFET source terminal. The combined effect of both lower Rds(on) and improved wire bonding inside the package results in an approximately 30% increase in the maximum drain current rating. All MOSFETs in 24V 1324 family are suitable candidates for battery switch applications. IR also has 40V automotive grade MOSFETs with Rds(on) as low as 1.25 mΩ suited for DC-DC converter applications.
The automotive grade high-side MOSFET driver AUIR3240S
is specifically designed to drive the battery power switch for start-stop applications, as shown in Figure 4, below. The AUIR3240S is a highly integrated boost converter designed specifically for the start-stop system halting the engine when a vehicle is stopped in traffic. This system requires a “board net stabilizer” using a power switch that disconnects the starter and main battery from the auxiliary electrical systems during engine start. The AUIR3240S is capable of driving several MOSFETs in parallel to achieve very low Rds(on) with current consumption below 50µA. This new device provides 15V on the output with a wide input voltage (4-36V). The AUIR3240S also features diagnostic on the output current and a thermal sensor interface for a robust design.
Figure 4: The dual-battery system can use the highly-integrated AUIR3240S power switch high-side MOSFET driver.
The promising future of a micro hybrid start-stop system is driven by many factors—how to reduce the cranking voltage drop, how to integrate more electronics into the starter, and the evolution of new battery technologies. Given the great potential of the micro hybrid system, the power electronics vendors and car makers have the components to find positive answers.
Masashi Sekine is an application engineer and Jifeng Qin a product manager in the Automotive Product Business Unit of International Rectifier.
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