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12V automotive alternator regulator has LIN interface

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By Christoph Hammerschmidt

The L9918 regulator includes a MOSFET to supply excitation current to the alternator and a free-wheeling diode to dissipate rotor current when excitation is off. Regulated operation with load response control (LRC) and return LRC ensures a constant on-board voltage even when the vehicle’s total power demand changes continuously.

The exciter MOSFET can supply up to 13 A to the winding. This value is higher than typical alternative regulators, improving response to fluctuations in power demand. Thanks to the use of the latest process technology, the MOSFET also has an outstandingly low RDS(on) value, which lowers power dissipation and improves efficiency.

Thanks to its integrated non-volatile memory, the L9918 allows customer programming of the voltage setpoint or alternator characteristics, for example. The device can be used with alternators that have up to nine pole pairs. It thus offers more flexibility than other controllers and is suitable for a wide range of charging applications.

The L9918 also has an integrated LIN bus interface and can therefore be connected to the electrical or electronic infrastructure of the respective vehicle, enabling management via an external control unit (ECU). The ECU can not only specify settings such as the target voltage, but also read out status and diagnostic information.

The safety and failsafe features of the L9918 include self-start activation by a phase signal, whereby the target voltage is maintained autonomously if the connection to the LIN bus should be interrupted for any reason. Once communication is re-established, the controller passes control back to the ECU. Current limiting and overcurrent and overheat protection are also integrated, as is temperature compensation that automatically adjusts the setpoint voltage when the system temperature changes.

The L9918 not only meets VDA (German Association of the Automotive Industry) specifications for LIN alternator controllers, but is AEC-Q100 qualified, ISO-26262 compliant and ASIL-B ready for use in functional safety systems.

The L9918, production of which has already begun, is currently sampling for major customers worldwide. Available as a bare die or in a pentwatt inline package (TO220-5), the device can be ordered at prices starting at $6.12 (from 1,000 units).

www.st.com/auto-alter-reg-l9918


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