Six-phase bidirectional controller for automotive systems

This design allows engineers to support the rapid adoption of 48V hybrid powertrains that provide improved emissions and better fuel economy for internal combustion engine/electric mild hybrids.

By 2020, automotive 48V systems will help reduce CO₂ emissions by up to 15%, improve fuel consumption, capture energy typically lost while braking, and provide torque in the low RPM range for start-stop mild hybrids. The 48V power net is needed to manage the next-gen of energy efficient electrical systems that require more power than available with the existing 12V subsystem. To reduce weight, many traditionally mechanical/hydraulic systems such as power steering, roll stabilisation, heating, and air conditioning will be converted to 48V electrical drive. An electric turbocharger will provide on-demand horsepower and torque, enabling the use of smaller more efficient combustion engines without sacrificing drivability. A high power starter/generator will replace the 12V alternator, reducing noise and vibration during engine starting while allowing regenerative braking to recapture up to 4x more of the available kinetic energy. The 12V bus and 12V lead-acid battery will handle the lighter loads, including ignition, interior lighting, navigation and audio systems.

Previously, 48V systems required a DSP with complicated firmware and/or separate buck and boost controllers combined with power stages and complex switching logic. One ISL78226 controller eliminates the complexity associated with previous 48V designs. The controller responds to changing load requirements by automatically adding or dropping phases to maximize system efficiency. It can also manage an abrupt change in power conversion direction. For example, if the 48V starter/generator fails while the vehicle is driving, the ISL78226 DC/DC controller seamlessly reverses power conversion direction so the 12V battery will temporarily supply the 48V subsystems, such as power steering, allowing the vehicle to safely pull over and stop.

The ISL78226 controller also integrates a digital PMBus interface for system control, telemetry and diagnostics that support ISO 26262 functional safety requirements. The controller’s limp-home mode reduces power in the event of a serious fault or failure, allowing the vehicle to be driven home or to a nearby service station for repairs. “The ISL78226’s high integration and innovative features simplify designing a robust 48V/12V power net solution for automakers,” said Philip Chesley, Senior Vice President of Precision Products at Intersil. “Designers don’t have to be digital power experts or assemble multiple buck and boost controllers and the other required circuitry to create a 48V mild hybrid design.”

Key features:

• Six-phase bidirectional synchronous 12-48V controller regulates voltage and current
• Architecture supports up to four ICs in parallel
• Average phase-to-phase current balancing, and average current output with ±1.5% accuracy
• Cycle-by-cycle peak current limiting, negative current limiting, and digitally programmable average current limit
• Analogue/digital control of output voltage
• Selectable phase-dropping and diode emulation for light load efficiency improvement
• Phase dropping enabled with companion ISL78420 FET driver family featuring tri-level input
• Programmable automatic driver bootstrap capacitor refresh pulses
• Supply and clock redundancy for functional safety
• Comprehensive protection with selectable hiccup or latch-off fault responses, and digitally programmable warning and fault thresholds
• Dual-output flyback controller and 200mA adjustable output linear regulator
• AEC-Q100 Grade-1 qualified for operation from -40 to 125°C