Elmos chipset implements automotive start-stop function

May 03, 2011 // By Christoph Hammerschmidt
A chipset from semiconductor manufacturer Elmos AG helps automotive electronics designers to easily implement an automatic start-stop function for vehicles. With Elmos chips E981.01 and E910.28, the voltage supply of the automotive on-board system can be maintained when car and engine stop in front of a red light or while passengers are getting in or out. This not only saves fuel but also improves the CO2 balance of the vehicles.

Used together, the multiphase boost converter (E981.01) and the synchronous buck converter (E910.28) reach a very high efficiency level. The operation of the boost converter is started as soon as the engine is running and the generator is supplying power. Due to the possible high output current of the multiphase boost converter, an energy storage device such as a supercap is charged within just a few seconds and provides an intermediate circuit voltage of 24 to 48V. during normal engine operation, the buck converters are bypassed and thus out of operation. When the engine stops and the on-board voltage drops to the level of the battery voltage, the bypass is removed and the functional units receive their supply voltage from the buck converters that receive their input voltage out of the energy storage.

The boost converter (E981.01) works with up to 9 phases and is able, together with suitable external components (storage choke, N-channel MOSFET's, diodes), to supply several hundred watts at an efficiency rate of 96% without difficulty. By applying the multiphase principle, a very high switching frequency of up to 4.5 MHz is achieved. In addition, the overlapping of the single phases leads to an improvement of electromagnetic compatibility (EMC). Moreover, system costs can be reduced further by the use of simple external components for additional filtering.

Due to synchronous rectification and the applied PFM control principle, the buck converters (E910.28) are able to compensate very fast load fluctuations at a high overall efficiency rate of up to 95% with high accuracy. The controller components supply extensive diagnostic information and are able to communicate with a microcontroller for the control of energy distribution.

Samples and demo boards are available for both automotive-qualified components.

For more information, visit www.elmos.de.