Octal gate driver reduces motor-drive BoM

STMicroelectronics has developed an octal gate driver to reduce the bill of materials cost for automotive motors.

L99MH98 8-channel pre-driver uses a patented approach to build motor drives without sensing resistors, reducing power dissipation and the bill of materials for powered seats, sunroof, window lift, sliding doors, trunks and tailgates.

The L99MH98 can drive four external full bridges, eight half bridges or single high-side/low-side powering mechanisms such as seat-position adjusters, window lifters, sunroofs, pumps, seatbelt pretensioners, and other actuators. The L99MH98 can also drive resistive loads such as heaters, and the internal circuitry contains a charge pump whose output can control a reverse-battery protection MOSFET.

While the drivers can control both logic-level and standard-level MOSFETs, extended gate current capability, programmable up to 120mA, permits driving large numbers of external MOSFETs. Three-stage gate control, which applies the gate signal in three steps, helps to minimize electromagnetic emissions.

The device provides each MOSFET drain-source voltage (VDS) to an analog-digital converter (ADC) with indirect current measurement to replace sensing resistors. This patented technique calculates the drain current in each MOSFET by combining the measured VDS with RDS(on) predicted using sensed temperature.

The system is calibrated at manufacture to find the nominal RDS(on) values, enabling predictions to be made using the MOSFETs’ resistance-versus-temperature curves.

• ST motor drivers for industrial and home appliances
• Multi-channel gate drivers use common pinout

A 24bit serial peripheral interface (SPI) is used for configuring and controlling the eight half-bridges or four H‑bridge. SPI status registers provide high-level diagnostic information such as supply voltage monitoring, the charge pump voltage monitoring, temperature warning and overtemperature shutdown.

A further feature, also patented, is the programmable multi-failsafe function that enhances reliability by turning off bridges individually to protect against faults while allowing unaffected bridges to operate normally. Multi-failsafe detects faults including supply overvoltage, high-side over/undervoltage, thermal warning, charge-pump failure, VDS-monitoring failure, and selectively turns off functions such as diagnostics, watchdog, and charge pump depending on fault type.

The octal gate driver is AEC-Q100 qualified and meets ISO 26262 criteria for functional-safety applications up to safety integrity level (ASIL) B.

The L99MH98 is available now in a VFQFN48L package with wettable flanks and exposed underside cooling pad, the is priced from $2.44 for orders of 1000 pieces.