Power supply for infotainment equipment in car start-stop systems (I)

Background information:

Automakers continue to market start-stop systems that help save fuel. As the name implies, the start-stop system shuts down the engine when the vehicle is stopped (rather than letting the engine idle) and quickly restarts the engine when the driver needs to leave. If you are constantly walking and stopping while driving, the start-stop system can prevent the engine from idling for a long time to reduce exhaust emissions and save fuel. The principle is simple. For example, if you stop by waiting for a red light or train to stop, you don't need to keep the engine running; if the engine is not running, you won't waste any energy. As a result, fuel consumption can be as high as 8% in urban traffic environments compared to cars that do not have such a start-stop system.

The automatic start-stop function does not affect the comfort and safety of driving, as it will not be activated until the engine reaches an ideal operating temperature. This principle also applies to situations where the air conditioner has not adjusted the car to the desired temperature, the battery is not fully charged, or the driver has turned the steering wheel.

The automatic start-stop function is coordinated by a central control unit that monitors the data of all relevant sensors, including the starter motor and the alternator. The control unit also automatically restarts the engine for comfort or safety. For example, if the vehicle starts to travel, the amount of battery charge drops to a level that is too low, or condensation water forms on the windshield. In addition, most systems are able to distinguish between short pauses and end of journeys. If the driver's seat belt is loose, or the door or trunk is open, the system will not restart the engine. If necessary, you can completely undo the automatic start and stop function by pressing a button (at least now).

However, when the engine is restarted and an infotainment system is turned on or there is another electronic device that requires more than 5V, the 12V battery may drop below 5V, causing such a system reset. Some navigation and infotainment systems operate with a 5V or higher input voltage. If the input voltage drops below 5V during engine restart, these systems will reset when the DC/DC converter can only step down the input voltage. Obviously, in the process of listening to music or using the navigation system, it is unacceptable for the user to reset these systems when the car is restarted.

solution:

Analog Devices recently introduced a three-output DC/DC controller, the Power by Linear LTC7815, which combines a step-up controller and two step-down controllers in a single package. The high efficiency synchronous boost converter powers two downstream synchronous buck converters to avoid output voltage drop when the vehicle battery voltage drops, which is a very useful feature in automotive start-stop systems. In addition, when the input voltage provided by the car battery is higher than its set boost output voltage, the step-up controller operates at 100% duty cycle, but only transmits the input voltage directly to the buck converter, thereby maximizing Ground reduces power loss.