Some high-power motor-control systems include multiple MOSFETs connected in parallel. Such circuits often call for MOSFETs that have a matched gate-source threshold voltage. Even when a MOSFET’s production facility is very tightly controlled, however, there is inevitably a spread of threshold voltage values across each wafer: any attempt to provide parts with matched threshold voltage values might require special screening and sorting procedures. This in turn will tend to reduce production yield, thus increasing the unit cost of the product.
To address this problem, Nexperia has developed MOSFETs that provide an improved current-sharing capability. When used in parallel configuration, these devices remove the need for matched threshold voltage values.
These are evidence that the parts which support improved current sharing off er important benefits when used in hot-swap linear mode and in motor drives. In fact, even more potential for optimization has been discovered, and new products in the pipeline will implement these additional improvements to bring yet more benefit to these applications.
Encouraging findings have emerged from testing in a parallel motor-drive application: the test compared standard MOSFET designs with the new optimized parts, as shown in Figure 1. The test used three parts each from the 90th percentile, and one from the 10th percentile. The optimized parts achieved close to ideal current-sharing performance, and much better thermal performance than the standard parts, as shown in Figures 2, 3, 4 and 5.
Fig. 1: Parallel motor drive test circuit
The optimizations for improved current sharing complement the superjunction trench technology used in the latest generation of power MOSFETs, which gives outstanding linear-mode performance. This leads to the next innovation in this industry segment.
The 100V, 120A-rated PSMN3R7-100BSE MOSFET from Nexperia is an ideal choice in high-current, battery-powered applications in which the battery voltage must be isolated under certain fault conditions. In this case, the battery-protection MOSFET must sometimes operate in linear mode until the battery voltage is isolated.
Nexperia has developed parts in several package styles which give far superior linear-mode performance, as much as six times better than leading competitors’ products. They also provide high current capability up to 380A. Parts are available to provide the increased spacing required by the UL2595 standard.
Fig. 2: Control (standard parts): Up to 30A current difference during switching
The Nexperia 100V-rated MOSFETs are notable for their low reverse-recovery charge, and provide excellent EMC performance. Other parts under development include 40V, 425A-rated half-bridge and dual MOSFETs supplied in an LFPAK88 package. These parts will be available in several voltage ratings.
Fig. 3: Control (standard parts): Up to 28.7°C difference, and peak of 127°C during switching
Fig. 4: Optimised parts: Up to 4A current difference during switching
Fig. 5: Optimised parts: 11.4°C difference, and peak of 100°C during switching