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Automotive MCU system power supplies for idling-stop systems

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By eeNews Europe

A startup sequence setting function is included that can adapt to a variety of MCU specifications and requirements. With the continuing trend towards platform unification (standardisation) in the automotive sector comes a push to promote the use of common parts worldwide. This is expected to increase demand for versatile products that can suit a variety of requirements and support microcontrollers of all types – as well as high-performance devices and solutions optimised for customized dedicated power supplies and specific applications.

In addition, the need to minimize fuel consumption has led to the adoption of systems that stop the engine during idling and other brief stops in order to prevent wasteful fuel consumption. However, this requires countermeasures to prevent MCU malfunction due to battery voltage fluctuations caused by cranking after the engine starts up again.


Rohm has a versatile, standardised power supply IC capable of providing stable voltage after idling stop operation. The BD39001EKV-C uses a 0.35-µm BiCDMOS power processes and takes advantage of Rohm’s analog design expertise to achieve a breakdown voltage of 40V with an ultra-low drive voltage of 4V, providing a wide input voltage range

To ensure compatibility with idling stop systems, rohm adopted a boost-buck automatic switching control method that provides stable voltage (5V) to the MCU, even when the battery voltage fluctuates (below 5V), while increasing power conversion efficiency by 5%. Besides providing continuous, stable power supply for I/O (5V LDO) and the MCU core (3.3V DC/DC) based on a variable primary power supply, a number of surveillance functions are built in, including a window watchdog timer that monitors MCU operation, improving reliability.


The design automatically switches between boost and buck circuits to provide continuous voltage to the MCU including when battery voltage drops (below 5V) when the engine starts after idling stop operation. At the same time, power conversion efficiency during cranking is improved by 5% (conditions: Vin=4V, Vout=5V, Iout=2A, Fosc=350 kHz). The startup sequence can be freely set by connecting a capacitor to the EN terminal, enabling support for a variety of microcontrollers and contributing to the common use of peripheral products and platforms. Watchdog timers monitor the MCU signal and conduct reset and restart operations under initial conditions when abnormalities are detected. The BD39001EKV-C integrates a high-performance window watchdog timer that not only monitors the MCU signal, but also detects frequency variations, contributing to greater reliability.

Rohm Semiconductor; www.rohm.com/eu


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