Power Electronics

MOSFETs Boost Threshold Voltage Yet Maintain Low On-Resistance

Siliconix has introduced a series of n-channel MOSFETs that combine a high 3.4-V threshold voltage (VTH) with on-resistance (RDS(ON)) as low as 2.7 mΩ. Available in 40-V and 60-V versions, the 10 MOSFETs are intended for use in high-temperature, high-current applications with inductive loads in the automotive, industrial and fixed telecom industries. Some of the specific uses include high-side switches, motor drives and 12-V board nets.

The 10 new models numbers and their key specifications are listed in the table below. Many of the devices in this MOSFET family carry a maximum junction temperature rating of 175°C as opposed to the more common 150°C rating.

When MOSFETs operate in high-temperature, high-current environments, they can turn on spontaneously if their threshold voltage, impacted by heat, starts to approach 0 V. Until now, this posed a dilemma for designers. One solution was the addition of a negative voltage driver to the circuit, but the drawbacks were increased circuit size, cost and complexity. Another solution is to use a device with a high threshold voltage, but the effect in this case is an undesirable increase in on-resistance.

To illustrate this effect, consider two n-channel MOSFETs that are manufactured in the same process, have the same die size, and are housed in the same package. One MOSFET is a logic-level device with a VTH of 2 V. This device specifies a maximum R DS(ON) of 2.3 mΩ. In the other device, VTH is 3 V and maximum RDS(ON) is 2.8 mΩ. Siliconix’s new power MOSFET family provides a solution to this dilemma with high-density silicon technology that allows the same device to deliver both low on-resistance and a high threshold voltage. This combination prevents the problem of spontaneous turn-on at elevated temperatures.

The key to raising VTH while lowering RDS(ON) is an underlying advance in MOSFET process technology that boosts cell density from 45 million cells to 178 million cells. Such increases in cell density are typically used to lower RDS(ON) in a given sized die, or to achieve the same RDS(ON) in a smaller die.

Device Number Package Breakdown Voltage (V) On-resistance @
10-V gate drive (mΩ)
D2PAK(TO-263) 40 2.7
DPAK(T0-252) 40 5.3
SUD50N04-06H DPAK (TO-252) 40 6.0
SUD50N04-09H DPAK (TO-252) 40 9.0
Si7444DP PowerPAK SO-8 40 6.1
Si7962DP PowerPAK SO-8 40 17.0
SUM110N06-3m9H D2PAK (TO-263) 60 3.9
SUD50N06-08H DPAK (TO-252) 60 7.8
Si7452DP PowerPAK SO-8 60 8.3
Si7964DP PowerPAK SO-8 60 23.0

Table. Specifications for N-channel MOSFETs with 3.4-V threshold voltage.

However, with these new MOSFETs, Siliconix used its process improvement to offset the expected increase in RDS(ON) that naturally occurs when VTH is raised. Although, these MOSFETs are not the first devices manufactured in Siliconix’s 178-million-cell process, they are the first to tradeoff on-resistance and threshold voltage so that the devices are optimized for automotive and other high-temperature applications. Furthermore, the new process more than compensates for the expected increase in RDS(ON) at the higher VTH it actually allows for some additional reduction in on resistance. Nevertheless, that reduction in RDS(ON) is less than it would be if VTH was maintained at the original value.

Samples and production quantities of the MOSFETs are available now. In 100,000-piece quantities, prices start at $1.35 per piece.

For more information, visit www.vishay.com/mosfets/.

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