Three-phase MOSFET Driver can replace Relays and Discrete Drivers

Designed to replace mechanical relays and discrete driver circuits the new A6861, from Allegro MicroSystems Europe, is a 3-phase N-channel power MOSFET driver IC with built-in isolation. It is designed to meet Automotive Safety Integrity Level (ASIL) requirements in applications such as electronic power steering, electric braking, and three-phase relay drivers. The new device, part of Allegro's A²-SIL family, is designed to replace mechanical relays and discrete driver circuits in safety-critical automotive applications where motor isolation is an essential requirement.

“This product range is designed with industry-leading, innovative features to help customers to achieve ASIL-D certification with the highest ASIL rating possible”, said Steve Lutz, Allegro’s Director, Strategic Marketing – Motors and Interface products: “Our A6861 three-phase isolation driver is intended to replace a relay-driven motor disconnect in automotive safety-critical systems, and can also provide the drive for reverse battery protection and battery isolation.”

The A6861 has three independent floating gate drive outputs to maintain the power MOSFETs in the ‘on’ or ‘off’ state over the full supply range in the presence of high phase-voltage slew rates. With the addition of a few external components, it can also isolate the load when high load currents are present.

An integrated charge pump regulator provides the above battery supply voltage necessary to maintain the power MOSFETs in the ‘on’ state continuously when the phase voltage is equal to the battery voltage. The charge pump will maintain sufficient gate drive (above 7.5V) for battery voltages down to 4.5V with 100kOhm gate-source resistors.

The three gate drives can be independently controlled by a logic level control input. In typical applications the MOSFETs will be switched on within 8μs and will switch off within 1μs. An under-voltage monitor checks that the pumped supply voltage is high enough to ensure that the MOSFETs are maintained in a safe conducting state. The A6861KLPTR-T is available in a 16-lead TSSOP package (suffix LP) with an exposed pad for enhanced thermal performance.