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Feb
05

Doubling key figures-of-merit drives up efficiency in MOSFET-based designs

The low voltage power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is the most widely used semiconductor switch.  When compared with other types of switch including Insulated Gate Bipolar Transistors (IGBT) or thyristors the MOSFET will usually demonstrate better commutation speeds and also better efficiency at low voltages.

When selecting a MOSFET for an application one of the challenges designers face is making an ‘apples to apples’ comparison. One of the key performance criteria for a MOSFET is RDS(ON) - the resistance between the Drain and Source when the device is in an on state. RDS(ON) is the summation of several individual elements and is, therefore, a good overall measure of the performance of the device when in use.

Power MOSFETs for automotive applications include both N-channel and P-channel devices with breakdown voltages ranging from around 40V to 100V. Within this voltage range, trench gate technology offers the best combination of conduction and switching performance. Advancement of trench technology is focused on enabling closer trench spacing which translates into a smaller die area for a given on resistance and voltage rating. Parasitic capacitances are also kept low, and the resulting devices have significantly better figures of merit such as RDS(ON) x A (on resistance x active chip area) and RDS(ON) x Ciss (on resistance x input capacitance).

As an example, the RDS(ON) x A value of a 100V N-channel device fabricated using Toshiba’s latest-generation U-MOS 8 process is approximately half that of a comparable U-MOS 4 device. U-MOS 8 also delivers a 20% reduction in Ciss/A over U-MOS IV. Ciss/A has a major influence on drive losses that have a significant impact on power supply circuits and motor control.

Dynamic performance is also improved. The latest U-MOS 8 devices deliver 50% shorter ringing at turn-off compared to the U-MOS 4 generation. The chart shows the improvement in switching performance achieved with a U-MOS 8 device versus the earlier U-MOS 4 technology and a comparable device from another manufacturer.

You can read more about Toshiba’s high performance U-MOS 8 technology and see how it can help in your next application here: http://toshiba.semicon-storage.com/eu/design-support/innovationcentre/whitepapers/tcm0070_AutomotiveMOSFET.html

 


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