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Compare isolated gate drivers and noise immunity

30th January 2020
Alex Lynn

Isolated gate drivers are used to drive power semiconductors, such as IGBTs and power MOSFETS, in inverters, motor drives, UPS, and EV charger. The gate drivers are used to provide galvanic insulation between the control circuits and the high voltages. Watch the video to learn more about the basics of isolated gate drivers and noise immunity.

Among other things, isolated gate drivers are also used for level shifting to provide high gate voltage and current to switch the IGBT or MOSFET. Here, and in the video below, you can learn about the various uses of isolated gate drivers, as well as a comparison between two different modules. 

With the emergence of wideband gap power semiconductors such as SiC and GaN, power electronics are operating at higher frequencies to increase system efficiency and reduce system size and cost. However, the increase in frequency results in a higher switching noise, commonly known as common mode transient dV/dt. This noise can be coupled to the input and cause wrong output at the power semiconductors.

As well as this, another important specification of the isolated gate driver is its ability to reject high common mode transient. This specification is normally terms as CMR (Common Mode Rejection), or CMTI (Common Mode Transient Immunity), and it is measured in kilovolt per microsecond, or volt per nanosecond. To meet today’s high frequency applications when using silicon carbide or gallium nitride MOSFET, it is recommended to have a CMTI of at least 100kV per microsecond. As the frequency increases, it is expected the CMTI to double, to 200kV per microsecond, in order to reap the benefits of SiC and GaN.

Comparing two isolated gate drivers

Two isolated gate drivers that are recommended for SiC and GaN and have a CMTI of over 100kV per microsecond. They are the isolated driver Si827x series  from Silicon Labs, and optocoupler ACPL-P349 from Broadcom. The Si827x series uses RF to transmit signal across isolation barriers, while the ACPL-P349 uses optical isolation. To find out more about both of these isolation drivers, watch the video below.

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