Isolate GaN gate driver needs no high-side bootstrap

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Isolate GaN gate driver needs no high-side bootstrap

Posted Date: 2024-01-16

Allegro AHV85111 isolated gate driver block

Instead, a dc-dc converter within AHV85111 produces secondary-side dc power rails – one positive and one negative – to provide gate drive power from a 12V supply (10.8 – 13.2V) on the primary side.

A single internal isolation transformer transfers dd-dc power as well as the PWM waveform from primary to secondary sides.

The isolated secondary supply is nominally +6V and -6V with respect to GaN transistor’s source connection. A feedback pin is provided to allow the positive voltage to regulated, while the negative rail will be an unregulated but related voltage – see the data sheet.

Total parasitic capacitance between the primary-side and isolated-side is typically <1pF.

This constant supply for the output driver, “allows the driving of a floating switch in any location in a switching power topology”, said Allegro, including holding the driven device on continuously.

With caveats, a small amount of dc-dc converter output power is also available to supply external circuits.

From input to driven gate, propagation delay (up or down) is typically 50ns (100ns max) with 2Ω gate resistors, and, with 0Ω resistors, rise-time is 9ns while fall time is 7ns (both 20-80% both 15ns max).

Minimum or or off time is 100ns.

High-side drive is up to 2A, and pull-down is up to 4A.

CMTI (common-mode transient immunity) is >100V/ns and the device is approved to 5kVrms (UL 1577) and transients up to 8kV

Creepage and clearance are 8.4mm, and it can work with 1kVpeak or 700Vrms continuously across its 200μm barrier.

“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.

Features include under-voltage lock-out on primary and secondary bias rails, internal pull-downs on input pin and positive output pin, and over-temperature shut-down – die operating temperature is -40 to +125°C.

Applications are foreseen in electric vehicle power-trains, electric vehicle on-board chargers, solar micro-inverters and data centre PSUs.

The AHV85111 product page can be found here, and clicking here will cause the datasheet to download from Allegro’s website.

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