integration making it compatible with not only their SiC MOSFETs but also those from a wide range of manufacturers. The device includes many basic functions common to general purpose gate drivers, but also features the specialized requirements necessary for designing a reliable SiC MOSFET gate drive circuit using minimal external components. For example, the NCP51705MNTXG incorporates a DESAT function that can be implemented using just two external components. DESAT is a form of overcurrent protection for IGBTs and MOSFETs to monitor a fault whereby V DS can rise at maximum I D . This can affect efficiency and, in a worst-case scenario, possibly damage the MOSFET. Figure 4 shows how the NCP51750MNTXG monitors V DS of the MOSFET (Q1) via the DESAT pin through R1 and D1. The NCP51705MNTXG gate driver also features programmable UVLO. This is an important feature when driving SiC MOSFETs because the switching component’s output should be disabled until VDD is above a known threshold. Allowing the driver to switch the MOSFET at low VDD can damage the device. The NCP51705MNTXG’s programmable UVLO not only protects the load but verifies to the controller that the applied VDD is
Figure 5: The UVLO turn−on threshold for the NCP51705MNTXG SiC MOSFET is set by the UVSET resistor, R UVSET , which is chosen according to a desired UVLO turn−on voltage, V ON . (Image source: ON Semiconductor)
HV gate drivers is on the LV side, any isolation must allow for the passage of digital signals from the microprocessor to the gate drivers. ON Semiconductor also offers a component for this function, the NCID9211R2, a high- speed, dual-channel, bidirectional ceramic digital isolator. The NCID9211R2 is a galvanically isolated, full-duplex digital isolator that allows digital signals to pass between systems without conducting ground loops or hazardous voltages. The device features a maximum working
above the turn−on threshold. The UVLO turn−on threshold is set with a single resistor between UVSET and SGND (Figure 5).
Digital isolation for traction inverters
To complete a traction inverter design, the engineer must ensure that the LV side of the vehicle’s electronics are isolated from the high voltages and currents passing through the inverter (Figure 2 above). However, because the microprocessor controlling the
we get technical
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