In half-bridges, high-voltage level shifters or digital isolators must be used to provide isolation for signal paths between the high-side device and control circuit. Using an isolator is optional for the low-side device. However, using and isolator equalizes the propagation delays between the high-side and low-side signal paths, and provides the ability to use different grounds for the GaN device and the controller. If an isolator is not used on the low-side device, the control ground and the power ground must be connected at the device and nowhere else on the board. For more information, see Layout Guidelines. With fast-switching devices, common ground inductance can easily cause noise issues without the use of an isolator.

Choosing a digital isolator for level-shifting is important for improvement of noise immunity. As GaN device can easily create high dv/dt, > 50 V/ns, in hard-switching applications, TI highly recommends to use isolators with high common-mode transient immunity (CMTI). Isolators with low CMTI can easily generate false signals, which could cause shoot-through. Additionally, TI strongly encourages to select isolators which are not edge-triggered. In an edge-triggered isolator, a high dv/dt event can cause the isolator to flip states and cause circuit malfunction.

Generally, ON/OFF keyed isolators are preferred, such as the TI ISO77xxF series, as a high CMTI event would only cause a very short false pulse, a few nanoseconds, which can be filtered out. To filter these false pulses, TI recommends a low pass filter, like 1 kΩ and 22 pF R-C filter, to be placed at the driver input.