Intelligent power devices for automotive motor and heater controls

Renesas has announced availability of six new intelligent power devices (IPDs) for automotive motor and heater control applications. The devices provide an extremely reliable, high-performance solution compared with mechanical relays that switch the current flow on and off in electronic control units (ECUs). An IPD is a power IC device that integrates in a single package control circuits that implement protection functions and self-diagnostic functions, in addition to power MOSFET (metal–oxide–semiconductor field-effect transistor) switching element(s). The IPDs are compact, lightweight, power efficient, and not subject to the contact wear and tear that affects mechanical relays, enabling highly reliable systems with self-protection functions. Previously, most ECUs used relays as the switching elements in their drive circuits, with the average automobile using around 100 relays. The transition from mechanical relays to semiconductor switching began in applications like lighting control, and the trend is expanding to other automotive systems, such as motor and heater control, driving demand for highly reliable and high-performance semiconductor switching devices. Recently, stricter environmental regulations in Japan and other countries have spurred accelerated efforts to improve fuel efficiency. This has heightened the need to address demands for reduced vehicle weight, more compact and lighter ECU, and low power consumption. However, creating lightweight vehicles has been made difficult as routing of the wire harness is determined and the configuration location is being restricted due to the mechanical relay maintenance in the relay box -or referred as junction box- that is responsible for power distribution within the vehicle, and in which many of the mechanical relays are housed. This has led to the growing demand to free placement constrains in the relay box and to allow greater flexibility of the wire harness routing by configuring the relay box with a semiconductor switch with self-protection function. However, conventional semiconductor switches have been unsuitable for handling large currency, which has impeded efforts to develop semiconductor-based replay boxes previously. Therefore, it is difficult to deal with high current loads when using conventional semiconductor switches. For many years, Renesas has delivered IPDs for automotive body applications that contribute to the compactness / lightweight, higher performance and reduced power consumption of ECUs. Renesas has leveraged its long-time experience and expertise to deliver the new IPDs achieving low on-resistance and high breakdown tolerance that support large current applications, says the company. Three key features : 1 - Low on-resistance for reduced loss and high reliability for an expanded range of large-current applications Previously, switching in large-current applications was handled using mechanical relays or multiple semiconductor switches connected in parallel. The new IPDs combine Renesas’ low-loss technology and a new fabrication process with a cell size of 2µm to achieve an on-resistance of 1.6mohm (RAJ280002, typical value when Tch = 25C). This also enables adoption in high current applications, and it further allows the new devices to replace conventional mechanical relays and provides a reduced mounting area, contributing to smaller and more lightweight ECUs. As solid state devices, the IPDs deliver extremely high reliability and performance levels, operating at up to 100 million switching cycles with no degradation, which is significantly higher than the approximate 10 million cycles expected from a typical mechanical relay. 2 - Guaranteed on-resistance characteristics at low power supply voltages and built-in diagnostic functions An earlier Renesas device, the µPD166033, would transition to the off state when the power supply voltage dropped to 4.5V as a protection function to prevent malfunctions. The new IPDs incorporate enhancements that provide support for continued operation when the voltage obtained from the battery drops temporarily, such as during starter motor cranking. The guaranteed on-resistance characteristics at a power supply voltage of 3.2V allow the IPDs to be used in applications where starter motor cranking might otherwise be an issue, such as cases where the driver turns off the engine at stoplights to prevent the engine from idling. The IPDs also feature built-in diagnostic functions and proportional load sensing. This allows for clearly defined fault signals that flag the system / controller when an abnormal load condition is detected. Since the analog current sense feedback is available, no additional load current sense elements are required. 3 - Excellent breakdown tolerance, contributing to smaller and less costly ECUs In applications that use inductive loads (L loads) such as motors and solenoids, it is possible that counter-electromotive force from the energy that has accumulated in the L load when the device transitions from the on state to the off state could damage or destroy the device. The RAJ280002 of the new devices increases the ability to withstand this energy (active clamp tolerance (EAS)) from the 260 millijoule (mJ) of comparable earlier Renesas devices to 1,700mJ. This expands the range of large-current applications for which the new IPDs can be used. In some applications it may be possible to eliminate the need for flywheel (regenerative) diodes as external protection elements, thereby contributing to more compact ECUs and reduced overall system cost. Samples of the new IPDs are available now. Mass production is scheduled to begin in January 2017 and is expected to reach cumulating 850,000 units per month by January 2018, says the company.