IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, TIE-11-1768, 2012 1 HV-CMOS Design and Characterization of a Smart Rotor Coil Driver for Automotive Alternators S. Saponara, Member, IEEE, G. Pasetti, F. Tinfena, L. Fanucci, Member, IEEE, P. D'Abramo Abstract 1 —The work presents a single-chip integrated Rotor Coil Driver (RCD) that can be used in automotive alternators. It integrates the power switch with the control circuitry and the diagnostics; with respect to the state of the art new functionalities are integrated such as full reverse polarity protection and programmable output slope control against in-rush currents and current spike transients. The paper will discuss the driver IC design from the choice of the architecture to the real silicon implementation. The proposed innovative RCD has been implemented in a 0.35 µm HV-CMOS technology and has been embedded in a mechatronic brush-holder regulator system-on- chip for an automotive alternator. The simulation results and experimental measurements prove the effectiveness of the proposed RCD facing the harshest automotive conditions. Index Terms - High Voltage (HV) Integrated Circuits (ICs); Alternator Regulator; Smart Driver ICs; Automotive Electronics I. INTRODUCTION The continuous evolution of microelectronic circuits for harsh environments [1-4], integrating on the same chip HV devices for power management or actuator driving and low-power circuits for signal processing and communication [5-8], allows improving the performance of automotive mechatronic systems for safety, driver assistance, vehicle dynamic control, engine and power transmission management [9-13]. The research on vehicle electronic control units (ECU) is mainly focused on the reduction of fuel consumption, which requires improving the efficiency of all car's subsystems. A major contribution is related to the alternator, which transforms the mechanical power, picked up on the engine, in electrical power delivered to the battery and to the electrical loads of the car [13-19]. The alternator power machine consists of the rotor and stator coils, that generate an alternating voltage, and the rectifier diode bridge, whose output is the DC voltage for battery and loads, see Fig. 1. The rotor coil, belt driven by the pulley and rotating with the engine, generates a magnetic field that is induced in the three phase stator. Regulated alternators operate modulating the field current in the rotor coil, EXC output in Fig. 1, to Manuscript received October 26, 2011; accepted for publication March 19, 2012. Copyright © 2009 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to pubs-permissions@ieee.org S. Saponara, L. Fanucci are with Dip. Ingegneria dell'Informazione, Università di Pisa, via G. Caruso 16, 56122, Pisa, Italy, tel/fax: +39 0502217602/522; e-mail: s.saponara@iet.unipi.it G. Pasetti, F, Tinfena and P. D'abramo are with Austriamicrosystems AG, via Giuntini 13, I-56023 Navacchio, Italy. This work has been partially supported by the EU 7th FP under grant agreement n°216436 (project ATHENIS). maintain an ad hoc voltage at the output of the rectifier bridge, V BAT in Fig. 1. New mixed-signal architectures for the regulator IC of next generation vehicles have been recently proposed in [19-21]. They feature a power excitation block, driving the rotor coil, interfaced to a low-power processing core including: i) a phase block, measuring the amplitude and frequency of two stator phases (PH1, PH2 in Fig. 1), ii) a battery block, measuring the status of the battery voltage at node V BAT , iii) an I/O communication block providing a digital serial interface to a master ECU, iv) a digital control core implementing the closed loop regulation algorithm. The design of the rotor coil current driver (RCD) poses several challenges still to be overcome in state of the art. The RCD for next vehicle generation should not be a simple PWM (Pulse Width Modulation) power switch, but programmable output current slope control functionalities are required against in- rush currents and current spike transients. This way electromagnetic interference and compatibility (EMI/EMC) issues are reduced and the device reliability is increased. Protection and monitoring circuitry should be integrated in the smart driver; the former to face over-current or open/short- circuit or reverse voltage polarity conditions, while the latter is needed for a continuous control of the load response. The RCD block shall be directly interfaced to the digital core of the voltage regulator IC, which receives from the RCD the information on the rotor coil current and, after measuring battery voltage and stator phases, sends to the RCD proper driving commands according to a closed loop control algorithm. More in details, the digital core sends to the RCD the order to increase or decrease the rotor coil current changing the duty cycle of a PWM excitation signal having a fixed frequency of some hundreds of Hz. Fig.1. Regulated alternator block diagram. The alternator, which is mounted close to the engine, has to work in one of the most critical and harsh environment that can be found in a car [1,14,18-20]. The RCD shall sustain temperature levels typically closed to 100 °C, but peaks up to 180 °C can be reached. The alternator mechanical moving parts easily generate electrostatic charge, so the RCD must manage very high ESD (Electro-Static Discharge) level, up to