boost | PartQuest™ Explore

For vehicles with Start-Stop capability, the engine (ICE) is turned off during idle periods, for the purpose of fuel economy. But low-voltage nuisance drop-out of key electronic functions must be avoided during engine re-start. The NCV8876 is designed specifically for this purpose. It uses current-mode control, with many integrated functions to reduce the complexity of the external boost circuit.

Simulation results show the output to the load during battery drop-out and recovery. Note that in this application, the output voltage (dark blue waveform) is maintained above 6.4V during the drop-out transient, and regulates at 6.8V during sustained low voltage (4V) battery operation (orange waveform).

This circuit also demonstrates the value of soft-saturation inductor components from Coilcraft:

http://www.coilcraft.com/pdfs/Doc1140_Beyond_the_data_sheet_Part1.pdf

The load current for the XAL4030-332 inductor in this application is 4A during nominal 12V operation. But during boost operation, the current reaches 6.6A peak (light blue waveform). This could saturate a typical inductor if it were sized for the nominal load, resulting in a collapse of the effective inductance. But notice that the actual instantaneous inductance (green waveform) only drops to 2.2uH, for this nominal 3.3uH part. This relatively small percentage drop in inductance can easily be accommodated by the converter design.

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