The current CO2 debate and the need for higher efficiency has lead to the development of advanced start-stop/idling-stop systems, also called micro hybrid systems. These systems switch off the combustion engine when the vehicle stops at a traffic light or stop sign, thereby reducing fuel consumption and emissions, and restart it as soon as the driver asks for power.
Further fuel savings can be achieved through regenerative braking during deceleration that uses the electric power generate to charge the battery. Both 14 V and 48 V boardnet implementations are possible.
The simplest and least expensive implementation is the belt alternator starter system. In this implementation, the engine is restarted by a belt linking the system to the crankshaft. More advanced systems are crankshaft or integrated starter generator systems, where the electric motor sits directly on the crankshaft.
With our broad automotive product portfolio, NXP can support all types of start-stop system.
Driving diverse loads
The range of load currents in start-stop systems is very extensive. It can vary between a few mA for driving LEDs or LCDs in the instrument cluster, up to more than 200 A for driving the three-phase electric motor or rectification of the generator current. NXP offers discrete solutions such as small-signal MOSFETs, low VCEsat (BISS) transistors, constant current sources (PSSI), high-side loadswitches (PBLS family) and logic devices for small and medium loads such as warning or indicator lamps. As the start-stop system can be switched off by the driver at any time, NXP's broad portfolio of LCD display drivers (PCA85xx) indicate its present state.
The power stage of the starter-alternator utilizes a three-phase MOSFET bridge which can be either used to rectify the generated AC current or to generate a three-phase current in an inverter mode to convert the generator to a starter motor. NXP offers high current Power MOSFET devices based on our advanced TrenchMOS technology in an enhanced D2PAK package with appropriate mechanical and thermal ruggedness for drain-currents far beyond 100 A. And for currents in excess of 300 A, we also offer devices with additional source pins and thickened bond wires in a 7-pin D2PAK.
Systems with a generator output voltage greater than 14 V require a DC:DC step down converter to provide a 14 V voltage supply. Here, the preferred choice is our rugged Power MOSFET family with compact and thermally enhanced Loss Free PAcKages (LFPAK) which allows low inductance board layout and high switching frequencies.
The start-stop module is in intensive dialogue with the engine control, power steering, transmission control and injection control unit. For all required networking protocols, NXP offers standalone LIN, CAN and FlexRay transceivers, with advanced functionality such as failure management and power saving.
We also deliver highly integrated in-vehicle-networking products including system basis chip (SBC) families. The SBCs combine one or several bus transceivers, voltage regulators, I/O pins and the option of a watchdog in a single IC. They offer advanced low power mode control and smart fail-safe behavior. Pin compatible family devices with different transceiver options support scalable platforms by simply changing the chip on the PCB.
Magnetoresistive and temperature sensors
NXP’s MR angular sensors are ideal for capturing wheel speed, pedal position, rotor position and neutral gear position information to derive the proper start-stop strategy. NXPs portfolio ranges from simple MR bridges to temperature compensated devices with signal conditioning and integrated amplifier. Delivering an output signal virtually independent of magnet tolerances, magnet temperature coefficients, magnet-sensor distance and positioning tolerances, MR sensors guarantee reliability and simplify your manufacturing process.
NXP offers a series of ESD protection devices from our PESD family, which are specifically designed to protect automotive networks. For robust reverse polarity protection NXP offers solutions based on either low ohmic power MOSFET devices in advanced TrenchMOS technology or schottky rectifiers in an advanced clip bond technology (PMEG family) in SOD123W and SOD128 packages that enable full performance in a small form factor.
In addition to a complete portfolio of standard logic products with different supply voltage ranges and speed in innovative packages, NXP offers dedicated devices such as low ohmic analog switches, analog and digital multiplexers and I/O expansion devices for cost optimized start-stop solutions.
NXP also offers a wide variety of innovative small-signal discrete products for start stop applications that deliver improved power efficiency, complete system protection and miniaturization and integration to simplify design and reduce costs. Leading the way are our power-efficient low VCEsat (BISS) transistors and low VF (MEGA) Schottky rectifiers.
In case of anticipated low battery performance, NXP offers class D audio amplifier (TDF8597TH) which fully support start/stop systems by operating at battery voltages as low as 6 V.