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Managing power for automotive mechatronic control modules

12 Dec 2013  | Fritz Burkhardt

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In many applications, the microcontroller cannot be disconnected from the supply. External hardware signals (contacts or sensors) have to be polled periodically and CAN messages have to be sent in order to satisfy the network management requirements.

In such configurations, the ECUs operate in energy saving standby modes while the system microcontroller is still supplied but operating in a low-current mode.

Besides that, the controller needs to keep the operating system in the RAM memory to ensure the necessary reaction times.

To support this concept the regulator supplying the microcontroller must be capable to run also in a low quiescent current mode while being able to provide sufficient peak current immediately upon wake-up of the module.

Consider such a device that you could use in mechatronic modules like power windows, sun roof modules and other LIN slave applications in the car body domain. It includes the power management functions, a LIN transceiver and a variety of auxiliary features embedded in a comprehensive fail-safe concept (figure 2).

L99PM60J block diagram.

Figure 2: The block diagram of a power management system IC. The example IC above is STMicroelectronics' L99PM60J.

Low quiescent current
The power management concept of such a device enables a system design with low quiescent current consumption since the required functionality is integrated in one IC. In the example above, the sleep mode offers a typical quiescent current consumption of 7µA. In this mode the regulator is turned off, that is, the microcontroller is not supplied but the LIN interface detects wake-up conditions via the bus. Use cases may include a "deep sleep" state when the car is parked and the module is woken up by the LIN master ECU.

In other use cases, it may not be possible to turn off the microcontroller supply voltage for the reasons mentioned due to contact monitoring, periodic network messages, etc. Our device should provide a dedicated low power mode allowing supply to the microcontroller while minimising the system quiescent current.

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