100V half-bridge drivers for bidirectional 12V to 48V powertrains

November 08, 2018 // By Nick Flaherty
Renesas Electronics has launched a family of automotive-grade 100V, 4A half-bridge N-channel MOSFET drivers.

The ISL784x4 family features three devices: the ISL78424 and ISL78444 with single tri-level PWM input for controlling both gate drivers, and the ISL78434, which has dual independent inputs that separately control the high-side and low-side drivers. The ISL784x4 half-bridge N-MOSFET drivers complement the ISL78224 4-phase bidirectional controller, enabling it to provide up to 3kW of power and greater than 95 percent efficiency in 12V-48V converters used in mild hybrid vehicles. The ISL784x4 drivers are aimed at 12V-24V bidirectional DC/DC converters, as well as other high current buck or boost applications.

The ISL784x4 drivers simplify driving high-current MOSFETs by offering independent sourcing and sinking MOSFET gate drive pins to use external gate resistors to tune the slew rate of the rising and falling DC/DC switch node transitions, thereby reducing electromagnetic interference (EMI). The ISL784x4 also provide adaptive dead-time control to ensure accurate break-before-make switching operations that prevent shoot-through current that would occur if both DC-DC converter switches were allowed to close simultaneously. The ISL78424 and ISL78434’s adaptive dead time function is also able to sense at the gate of the MOSFETs, eliminating potential errors introduced by voltage drops across the external gate resistors controlling the switching node slew rate.

The ISL784x4 drivers suited to high current DC-DC applications such as the 12-48V converter for 48V mild hybrids. They improve efficiency by delivering a gate drive of 3A peak sourcing current and 4A peak sinking current. Strong gate drive allows them to rapidly switch high current MOSFETs with large gate capacitance, which reduces switching losses. The half-bridge MOSFET drivers’ adaptive dead time control minimizes excess dead time to reduce conduction losses and further increase DC-DC conversion efficiency. The ISL784x4 drivers also offer voltage ratings that are ideal for 48V automotive systems with the switching node tolerating 70V DC and up to 86V for infrequent transients. Similarly, the high-side driver’s bootstrap node can tolerate 86V DC and up to 100V during transients.


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