Revolutionary GaN Gate Driver Eliminates High-Side Bootstrap Requirement

Allegro MicroSystems has developed a groundbreaking isolated gate driver IC for GaN power transistors that eliminates the need for high-side bootstrapping and a secondary side drive supply voltage. The AHV85111, a dc-dc converter, generates secondary-side dc power rails - one positive and one negative - to provide gate drive power from a 12V supply on the primary side.

A single internal isolation transformer transfers dc-dc power and the PWM waveform from the primary to the secondary side. The isolated secondary supply is nominally +6V and -6V with respect to the GaN transistor's source connection. A feedback pin is included to regulate the positive voltage, while the negative rail remains unregulated but related.

The total parasitic capacitance between the primary-side and isolated-side is typically less than 1pF. This constant supply for the output driver allows for the driving of a floating switch in any location in a switching power topology, including holding the driven device on continuously, according to Allegro.

Additionally, a small amount of dc-dc converter output power can be used to supply external circuits, with some limitations. The propagation delay from input to driven gate is typically 50ns (100ns max) with 2Ω gate resistors. With 0Ω resistors, the rise-time is 9ns and the fall time is 7ns (both 20-80%, with a maximum of 15ns).

The high-side drive can handle up to 2A, while the pull-down is up to 4A. The device has a common-mode transient immunity (CMTI) of over 100V/ns and is approved for 5kVrms (UL 1577) and transients up to 8kV. It also offers a creepage and clearance of 8.4mm and can work with 1kVpeak or 700Vrms continuously across its 200μm barrier.

"The high CMTI combined with isolated outputs for both bias power and drive make it ideal in applications requiring isolation, level-shifting, or ground separation for noise immunity," said Allegro. The AHV85111 is equipped with features such as under-voltage lock-out on primary and secondary bias rails, internal pull-downs on the input pin and positive output pin, and over-temperature shut-down. The die operating temperature ranges from -40 to +125°C.

Potential applications for the AHV85111 include electric vehicle power-trains, electric vehicle on-board chargers, solar micro-inverters, and data center PSUs. For more information, visit the AHV85111 product page or download the datasheet from Allegro's website.